POWER AVAILABILITY
CONTINUOUS POWER-TIE CONFIGURATION
USER MANUAL
Series 610
Multi-Module UPS
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TABLE OF CONTENTS
SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
System Flexibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Inter-System Isolation and Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Control System Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Operational Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5.1 Operational Choices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5.2 Momentary Tie Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5.3 Continuous Tie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5.4 Tie System Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5.5 Modes of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
OPERATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Continuous Power-Tie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Separating Tied Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Load Transfers Between UPS Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Combined Loads on One System from Continuous Tie Operation . . . . . . . . . . . . . . . . . . . . 14
Combined Loads on One System to Continuous Tie Operation. . . . . . . . . . . . . . . . . . . . . . . 14
Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Improper User Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Tie Circuit Breaker or Logic Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.8.1 What Happens If a Failure Occurs During a Power Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.8.2 What Happens If a Logic Failure Occurs During Power Transfer . . . . . . . . . . . . . . . . . . . . . 19
2.8.3 Hardware Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Recommendations - Tie Circuit Breaker Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.5
CONTROL PANEL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Mimic Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Load Transfer Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Continuous Tie Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Control Inhibits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Manual Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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OPERATING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Initial System Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Basic Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.1 Momentary Tie - Load Transfers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.2 Normal Transfer Operation Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.3 Maintenance Procedures - Isolating Each UPS System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.4 Isolating a UPS System for Maintenance - Combined Loads Operation. . . . . . . . . . . . . . . . . 26
4.2.5 Transfer of Load Between Two Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.7 Maintenance Procedures - Maintaining Power-Tie Components . . . . . . . . . . . . . . . . . . . . . . 27
4.2.8 Maintenance Procedures - Tie Control Logic Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.9 Abnormal Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.10 Trouble Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.11 Continuous Tie-Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.12 Isolation for Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.13 Operation Scenarios/Transfer Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
FIGURES
Basic Dual-Bus Power-Tie one-line diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Power-Tie systems - fault isolation issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Power-Tie systems - control interface diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Power-Tie system one-line diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Control panel layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power-Tie system - fault isolation issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Power-Tie systems - fault tolerance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Power-Tie system one-line diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
From start-up to normal operation, loads to be split between two distribution feeders . . . . . . . 33
Figure 10 From combined loads operation to loads split between two feeders . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 11 From continuous tied systems to loads split between two systems . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 12 Transfer both load feeders to one UPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 13 Both feeders on one system to normal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 14 Transfer 100% load on one system to 100% load on a second system (a two-step operation) . . . 34
Figure 15 Normal split load operations to Continuous Tie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 16 Continuous Tie to normal split load operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 17 Continuous Tie to load on one system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 18 Load on one system to Continuous Tie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 19 One system in bypass to both feeders combined on remaining operational system . . . . . . . . . . 36
Figure 20 One system in bypass to Continuous Tie operation (Option 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 21 One system in bypass to Continuous Tie operation (Option 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
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System Description
1.0 SYSTEM DESCRIPTION
1.1
Function
The Liebert Continuous Power-Tie™ system provides the capability to momentarily or continuously
manually initiated, uninterrupted transfers of a critical load bus between the two UPS Systems.
This topology permits one UPS and its associated distribution system to be shut down for mainte-
nance while the load continues to be supplied by another UPS, without the necessity of transferring
the load to bypass during shutdown or restart of the UPS being maintained.
1.2
System Flexibility
In the unlikely event that one or both UPS systems have only partial available capacity (e.g., loss of
one or more modules in an otherwise functional system), this partial capacity system can be continu-
ously tied to a second full (or partial) capacity system, powering simultaneously the now-tied two crit-
ical buses.
This results in a single, fully redundant UPS system powering two different distribution strings
through a single UPS critical bus.
When the off-line (whether for maintenance or repair) modules are brought on-line again, the two
UPS critical buses are again separated without the need to transfer to the bypass source. For continu-
ous-tied systems, module kVA and kW ratings must be identical.
1.3
Inter-System Isolation and Reliability
For multiple UPS installations at a single site, best total system reliability is achieved when system-
to-system independence is maximized. However, to transfer loads or parallel critical buses between
multiple UPS systems, a certain amount of cross-connected system-to-system power and signal con-
Proper implementation of power conductor runs and circuit breaker placement will minimize the risk
that a catastrophic critical bus fault (e.g., a dropped wrench) on one system will cause a failure in a
second system.
Liebert has minimized the risk of system-to-system electrical noise susceptibility and faults in sys-
tem-to-system copper wire control circuitry through the use of fiber-optic technology as well as trans-
former and impedance isolation techniques in critical control circuits.
The possibility of signal and ground loops through control interconnections has been eliminated by
isolating all control signals between each UPS system and the Tie Controls (See Figure 3). For exam-
ple, a water leak over one UPS could effectively short all the control conductors together, causing a
catastrophic fault in one system. Through the noted isolation techniques, this fault will not be propa-
gated through intersystem (e.g., load sharing control conductors) control wiring to the second system.
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System Description
1.4
Control System Features
A key control feature necessary for successful momentary or continuous tie operation of two UPSs is
the dynamic load current sharing function.
A key design requirement for maximizing multiple system reliability and inverter availability in tied
configurations is assuring maximum system independence under the normal, separated operating
conditions.
Liebert has incorporated a number of unique solutions in your Power-Tie System to accomplish these
high availability/high reliability performance goals:
Digital Controls
Digital Controls provide more precise control than analog techniques. They permit the direct use of
fiber-optics for the most critical inter-system control functions without the need for the additional
complexity of A/D and D/A converters. Digital Controls are very reliable—implemented using inter-
nally redundant ASICs (application specific integrated circuits) with millions of field-proven trouble-
free operating hours—and provide rock-solid UPS load sharing and synchronization control under
dynamic load conditions.
Digital Phase Lock of Uninterruptible Power Module (UPM) Inverters
Parallel module inverters are all tightly phase-locked together by redundant digital oscillators. No
master oscillator is required. This feature, coupled with closely matched module output impedances,
provides the primary module-to-module load sharing function to approximately ±10%. This degree of
load sharing is good enough, under emergency conditions, to provide acceptable operation for system
load sharing and transfer operations.
System Output Voltage Control
A separate, independent and isolated system control function for output voltage which also makes a
secondary contribution to the load share function of an additional ±3%.
Module Load Sharing
An additional, separate, independent secondary control function contributes another ±3% of inter-
module load sharing.
These three independent control functions are additive in contribution to the module load share
function, and provide an additional level of redundancy to this function without simply duplicating a
circuit.
In combination, these three control functions provide module load sharing to better than ±5%. The
system will continue to operate acceptably well with the loss of one or more of these control functions.
The loss of which will be annunciated through the diagnostic system.
In a tied system configuration these critical functions, coupled with the Tie Control Unit, provide the
degree of load share control required, while maintaining system-to-system independence and
isolation.
1.5
Operational Description
1.5.1 Operational Choices
Momentary Tie provides intersystem transfer capability without bypass required, permitting on-line
maintenance of the unloaded UPS and distribution system.
Continuous Tie permits tying the available modules in both systems together to act as a single multi-
module system, in the unlikely event that multiple module failures have reduced the capacity of the
UPS system(s).
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System Description
1.5.2 Momentary Tie Operation
Momentary Tie operation provides manually initiated, uninterrupted transfers of a critical load bus
between two otherwise independent multi-module UPS systems. This topology permits individual
UPS shutdown for maintenance while its load continues to be supplied by another UPS without the
necessity of transferring the load to bypass during shutdown or restart of the UPS being maintained.
A major goal in the design of Momentary Tie Operation was to provide the same high reliability asso-
ciated with a standard parallel redundant system while providing more system flexibility for mainte-
nance purposes.
The key to maximizing reliability of this configuration is to maintain as much independence as possi-
ble between systems, and retain the same basic concepts in transfer philosophy that have served so
well in current standard Series 610 UPS systems (as well as previous Series 500 designs).
The only time intersystem controls are active is during the actual operation of transferring loads back
and forth between the UPS systems, a period of a few cycles. At all other times, the UPS systems are
operating independently.
Following are two main functions associated with the Momentary Tie:
• Intersystem synchronizing
• Intersystem transfer control and switchgear
Intersystem Synchronizing
Synchronization between UPS systems is accomplished by momentarily synchronizing one UPS out-
put (the system accepting the load) to the same sync source the other system is using. The internal
clock frequency reference will be used if the Bypass Source is not available as a frequency reference.
When sync signal coincidence is achieved the module sync buses will be tied to lock the modules of
both systems in tight synchronization. The associated Tie Control Unit does not perform the sync
function, but instead simply supplies each UPS with a sync reference signal, depending on which
direction the transfer is going to go. Synchronization of each UPS will automatically revert to its
internal bypass sync at the conclusion of the transfer sequence.
Momentary Tie Transfer Controls
The transfer control operates the Tie Breaker and System Isolation Breakers in a sequential make-
before-break manner to permit the uninterrupted transfer of a critical load between two UPS sys-
tems.
The breakers are operated such that there is an approximate 5 cycle overlap time when the two UPS
systems are paralleled prior to one or the other UPS being isolated by its associated Isolation
Breaker. Or, the systems are separated via the Tie Breaker opening when returning a load to its nor-
mal position).
Should one system transfer to bypass due to overloads or faults, this function can be used to transfer
the critical load bus to the second on-line system. The second system is able to pick up the load from
the first system’s bypass without having to bypass the second system.
This transfer operation is identical to the normal internal transfer from UPS to bypass and return, an
operational sequence that is a reliability cornerstone of the Liebert UPS. The difference in this tie
function is that the Isolation and Tie breakers replace the functions otherwise performed by the Sys-
tem Bypass Breaker (SBB) and UPS Output Breaker (UOB) devices.
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System Description
The Tie Control Unit also contains interlock and monitoring circuitry necessary to assure successful
transfers of load between UPS systems. These consist of the following:
1. Sync Verification circuitry, similar to the circuitry employed in each UPS, provides the sync check
function in two independent modes:
a. Phase Difference detection for ±3 degrees.
Phase Difference inhibits a transfer if limits are exceeded.
b. Voltage Difference detection for ±3%.
Voltage Differential inhibits transfers if limits are exceeded (if phase error is greater than ±3
degrees, the Voltage Difference will also exceed ±5%), making the differential voltage detec-
tion a redundant phase detector.
2. Load Verification circuitry prohibits transfer if the resulting total system load will exceed the
capacity of one UPS System (the system which will assume all the critical load once the transfer is
complete).
1.5.3 Continuous Tie
The Liebert Continuous Tie system is a topology that extends the concept of a manually initiated
momentary tie of UPS critical load buses by providing the capability to continuously parallel the out-
put buses of two otherwise independent UPS Systems.
All the performance features of a momentary tie system are available in the continuous tie system. In
the unlikely event that one UPS system or both UPS systems have only partial available capacity
(e.g., loss of one or more modules in an otherwise functional system), this partial capacity system can
be continuously tied to a second full (or partial) capacity system, powering simultaneously the now-
tied two critical buses.
This results in a single, fully redundant UPS system powering two different distribution strings
through a single UPS critical output bus. When the off-line (whether for maintenance or repair) mod-
ules are brought on-line again, the two UPS critical buses are again separated, all in a make-before-
break manner, and without the need to transfer to bypass sources. For continuous-tied systems, mod-
ule kVA/kW ratings must be identical.
There are two main control functions associated with the Continuous Tie:
• Intersystem synchronizing and load sharing;
• Intersystem transfer/parallel control and switch gear.
Intersystem Sync and Power Sharing
Synchronization between the UPS systems is accomplished in a two step process:
First, a line sync source is chosen. This will be the bypass power source of the UPS system that is the
manually selected preferred bypass source. Generally, if one system is to be shut down for mainte-
nance after the two systems and loads are paralleled, the preferred bypass source is the system
remaining on line during the maintenance activities. Both systems are synchronized to the preferred
bypass.
Second, once both UPSs are in sync with one bypass, inter-module sync is enabled. This is a digital
sync bus that holds all modules of both systems in phase-lock operation, with or without a bypass ref-
erence. This ensures that the individual modules of both systems are tightly controlled to enable par-
alleling.
Load sharing between UPS systems is accomplished by interconnecting the load sharing circuitry—
the combination of the System Output Voltage Adjustment Control plus the Module Load Sharing
Control—of the two systems when the tie breaker between the systems is closed. This operation is
analogous to bringing a module on-line in a multi-module system
The voltage synchronizing and load sharing loops also back up each other. Together, they hold module
load sharing to within ±5% of load current. Should one or the other loop be inoperative, load sharing
can still be maintained within acceptable limits.
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System Description
Synchronizing activity takes place automatically once the preferred source is chosen and a manually
initiated “SYNCHRONIZE SYSTEMS” signal is given. Visual indicators show that the systems are
synchronizing and when the systems are ready for the manually initiated, automatically controlled
paralleling sequence.
Continuous Tie/Transfer/Parallel Control
The transfer load and tie controls operate the tie breakers between systems in a sequential manner to
allow paralleling and make-before-break transfer of loads. Once the synchronizing sequence is com-
plete, visual indicators show parallel operation is permitted. The operator initiates the closing of the
tie breaker. Once initiated, the tie command is executed when conditions of sync and voltage match-
ing are verified prior to tie execution. In essence, the tie breaker closes and two UPS systems are par-
alleled.
With the two systems operating in parallel, only one bypass circuit is active. Should something occur
that requires the UPS to automatically transfer to bypass, then all the load will be supplied through
the static switch and bypass circuit breaker of the system that was selected as the preferred source.
When the two systems are paralleled, it is possible to isolate and then shut down one system entirely
for maintenance. The system to be shut down must be the one that is not the designated preferred
source. Shutdown is accomplished by first opening the System Isolation Breaker of the selected sys-
tem. Once this action is taken, all the load remains on the preferred system.
The three load sharing control circuits between systems are disconnected with the opening of the Sys-
tem Isolation Breaker. At this time, sync control of the off-line system will be returned to its own local
bypass source, and the system can be operated in its normal manner for testing and maintenance.
Restart of the systems under maintenance is accomplished in the normal manner. Once the system
has been brought on-line, the resync to the on-line system can be initiated. The sequence from this
point is similar to the sequence that paralleled the two systems initially. As soon as the OK TO TIE
SYSTEMS indication is given the System Isolation Breaker can be closed, once again paralleling the
two systems and enabling the load-sharing loops between the two.
Taking the systems out of parallel operation is manually initiated. The tie breaker automatically
opens separating the loads onto their respective UPS systems. The intersystem power sharing is dis-
abled and the sync circuits revert to independent operation.
1.5.4 Tie System Components
A Liebert Power-Tie Uninterruptible Power System consists of the following basic components:
1. Two complete, independent UPSs with individual load buses, each with the capability to source
the combined critical load of the two load buses. Each of the two UPSs may be a single-module
system (SMS) or a multi-module system (MMS).
2. Two discrete system input sources, each with the capacity to source the combined critical load.
The two input sources need only be acceptable with regard to frequency and voltage. The two
sources do not require an in-phase relationship, although under this circumstance, a “V Lockout”
alarm will be indicated until the “Sync Systems” button is pushed. Then the “V Lockout” should
clear.
3. Two discrete bypass sources, each with the capacity to source the combined critical load. The two
bypass sources need only be acceptable with regard to voltage and frequency, such as the utility or
an emergency generator, and are not required to be in-phase. However, if make-before-break
downstream load switching equipment, such as automatic transfer switches, static transfer
switches (STS) or dual input power distribution units, is intended to be used, having the two
bypass sources in sync is preferable.
4. One system isolation and tie switchboard containing system isolation breakers and tie breaker(s).
5. Tie Control Unit, wall or floor mounted or installed in the tie switchboard.
6. Optional maintenance bypass breakers and test load distribution.
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System Description
1.5.5 Modes of Operation
The Power-Tie Uninterruptible Power System is designed to operate in the following modes:
1. Normal - Each load bus is fed from its respective UPS and the tie breaker is open. Each inverter
is synchronized to its respective bypass source. Each load is supplied by its inverter(s), with its
bypass available as an alternate source.
2. Momentary Tie - The load bus and the two UPSs are momentarily paralleled through the tie
breaker. Both UPSs are on-line, and the bypass source of one UPS will be selected as the primary
sync source. When one UPS drops off-line, then operation reverts to the Combined Loads Mode
below.
3. Combined Loads - Both loads are running on one UPS through the tie breaker. The combined
loads are supplied by the selected UPS’s inverter(s), with that UPS’s bypass available as the
alternate and sync source. This mode is typically used for servicing a UPS system, including its
bypass and bypass transfer controls, without placing that UPS’s load on bypass.
4. Continuous Tie - The load bus and the available modules from the two UPS are continuously
paralleled through the tie breaker. Both UPSs are on-line, and one UPS’s bypass source will be
selected as the alternate bypass and sync source. Although not normally done from this
operational mode, one of the two UPSs could be shut down and isolated at this point as well.
5. System Isolation - A selected load bus which has had all load removed (via shutdown, external
maintenance bypass or downstream critical load switchover devices—dual input PDU, STS or
ATS) may be isolated from one or both UPSs for maintenance.
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Operation Description
2.0 OPERATION DESCRIPTION
There are two types of operations which can be performed with the Liebert Continuous Power-Tie
System.
• Create a continuous tie between the critical buses of two UPS systems
• Transfer of a critical load between two UPS systems
2.1
Continuous Power-Tie
The following sequence of operations describe the actions to take to continuously tie two UPS systems
Selecting a Line Sync Source
From the Continuous Power-Tie Control Panel, select SYS1 or SYS2 using the PRIMARY BYPASS
SELECT switch.
Should a fault occur with the UPS systems in parallel, the chosen line sync source becomes the bypass
source for the critical loads.
Synchronizing the UPS Systems
From the Continuous Power-Tie Control panel, press the SYNCHRONIZE SYSTEMS button. The
Power-Tie logic checks for proper state indications from the UPS systems and the circuit breakers.
The SYNCHRONIZE SYSTEMS button light turns on to indicate the UPS systems have begun syn-
chronizing to the selected primary bypass.
The PRIMARY BYPASS light from the selected UPS system (UPS System 1 or UPS System 2) turns
on to identify the primary bypass.
With the line sync controls tied, the continuous Power-Tie logic checks the inter-module sync signals
for coincidence. The Power-Tie logic ties the inter-module sync signals when coincidence occurs.
This redundant digital sync bus holds all modules in sync, with or without a bypass reference. Using
the redundant digital sync makes certain the individual modules of both systems are tightly con-
trolled to enable the parallel operation of the UPS systems.
The SYNCHRONIZING light on the Control Status panel turns on (and stays on) during synchroniza-
tion.
Checking for Phase, Voltage, and Capacity
The Power-Tie logic checks these UPS system parameters, phase, voltage, and capacity, to determine
if they are within their proper limits. The OK TO TIE SYSTEMS light (from the CONTINUOUS TIE
CONTROL section of the control panel) turns on when these parameters are within their proper lim-
its.
OK to Tie UPS Systems
After the OK TO TIE SYSTEMS light turns on, press the PUSH TO TIE SYSTEMS AFTER OK but-
ton, on the CONTINUOUS TIE CONTROL panel. The TIE CB (tie circuit breaker) light turns on,
indicating the breaker has closed.
Both of the SYSTEMS TIED lights (on the LOAD 1 and LOAD 2 panels) turn on to indicate the tied
UPS system status.
NOTE
Systems may be paralleled with the UPS systems initially separate or if both loads are initially
on one UPS system while the other was being serviced.
With the two UPS systems in parallel, the voltage synchronization and power sharing loops become
tied. Together, these controls hold the module load sharing to within ±5% of load current. Should one
or the other control be inoperative, the Power-Tie logic can still maintain load sharing within accept-
able limits.
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Operation Description
2.2
Separating Tied Systems
The following sequence of operations describes the actions taken to separate two tied UPS systems.
Synchronize Systems
From the CONTINUOUS TIE CONTROL section, press the SYNCHRONIZE SYSTEMS button. The
button’s light turns off to provide a visual indication of the operator’s intention to separate the sys-
tems. The SYNCHRONIZE SYSTEMS button toggles between indicating the intention to parallel or
separate the two UPS systems.
Verifying Capacity
The Power-Tie logic checks the UPS systems and their loads to verify both systems have sufficient
capacity to maintain their loads once the systems are separated. If both UPS systems have sufficient
capacity, the OK TO OPEN TIE light turns on in the TIE CONTROLS section of the control panel.
OK to Open Tie
After the OK TO OPEN TIE light turns on, press the PUSH TO OPEN TIE AFTER OK button. The
tie breaker trips to separate the two UPS systems. Both systems automatically resynchronize to their
own bypass source; and all control loops between the systems separate.
2.3
Load Transfers Between UPS Systems
Functionally, load transfers are a continuous tie operation followed by an immediate selective separa-
tion of the systems. The following sequence of operations describes the actions taken to transfer a load
between UPS systems.
Selecting a System for Transfer
Select the system you want to receive the load, system 1 or system 2. Press the TRANSFER LOAD TO
button (for system 1 or system 2) on the LOAD TRANSFER CONTROL section of the control panel.
The system 1 or system 2 light turns on to indicate your selection.
You can cancel your selection by pressing the system button again. The button toggles between select
and deselect.
Synchronizing to the Bypass Source
The two UPS systems synchronize to the proper bypass source to perform the selected transfer. With
the line sync controls tied, the Continuous Power-Tie logic checks the inter-module sync signals for
coincidence. The Power-Tie logic ties the inter-module sync signals when coincidence occurs.
The SYNCHRONIZING light in the CONTROL STATUS section of the MIMIC panel turns on to let
the operator know synchronization is still in progress.
Checking for Phase, Voltage, and Capacity
The Power-Tie logic checks these UPS system parameters, phase, voltage, and capacity, to determine
when they have reached their proper limits. The OK TO TRANSFER LOAD (#) TO SYSTEM (#) indi-
cator turns on in the LOAD TRANSFER CONTROL section of the control panel on when these
parameters reach their proper limits.
Transferring the Load
After the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light turns on, press the PUSH TO TRANS-
FER AFTER OK button.
The Power-Tie logic operates the proper circuit breakers in a make-before-break manner to transfer
the load.
Once the transfer starts, the TRANSFERRING light in the CONTROL STATUS section of the MIMIC
panel turns on indicating a transfer in progress. With the two UPS systems in parallel, the voltage
synchronization and power sharing loops become tied.
Transfer Complete
When transfer is complete, both systems automatically resynchronize to their own bypass source; and
all control loops between the systems separate.
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Operation Description
2.4
2.5
Combined Loads on One System from Continuous Tie Operation
To combine two loads onto one system, perform a LOAD TRANSFER BETWEEN UPS SYSTEMS
tain both loads using the TRANSFER LOAD TO buttons. The operator can then proceed with the rest
Combined Loads on One System to Continuous Tie Operation
To create a continuous tie from combined loads on one UPS system, perform a CONTINUOUS TIE
The Power-Tie logic selects the proper circuit breaker to operate. Once the tie operation begins, the
two UPS systems synchronize to the selected primary bypass source.
The Power-Tie logic:
• Checks the system configuration
• Verifies synchronization
• Verifies system voltages are within limit
• Verifies both the on-line UPS systems have sufficient capacity to maintain the combined loads
before allowing the systems to tie
2.6
Design Criteria
The ultimate power goal in the design of the Liebert Continuous Tie System is to provide maximum
UPS availability and maintainability without compromising the inherent reliability of the UPS sys-
tems. We have designed the Continuous Power-Tie system to minimize or eliminate possible failure
modes and their effect on the system.
Isolation and Fault Tolerance
Signal isolation prevents an internal failure from propagating between systems. By using fiber-optics,
optical isolators, and isolation amplifiers, we isolate all control signals between each UPS system and
the Power-Tie Controls.
To parallel systems requires some amount of intersystem information. The controls have been
designed to be as fault tolerant as possible.
We use a parallel module sync bus means because the system will still function if a 60Hz clock in an
individual module fails. The parallel module sync bus eliminates the need for a system master oscilla-
tor function.
In tied systems we use a parallel module sync and fiber-optics. Fiber optics transport the digital mod-
ule sync signals between systems to maintain isolation. We use fiber optics for these signals since
they are the most critical intersystem signals in parallel systems.
Load Share Signal
The Load Share signal is sent between UPS systems when they are in parallel. Isolation amplifiers
isolate the Load Share signal levels between the systems. The load sharing loop and the voltage con-
trol improves the module load sharing capability of the modules to within ±5% of module load.
Because a Continuous Tie system uses modules of the same kVA/kW rating, the modules have some
inherent capability to share loads due to their similar output impedance. Load Share signals are not
as critical as module sync signals.
System Voltage Control Signal
The System Voltage Control signal is sent between UPS systems when they are in parallel. Isolation
amplifiers isolate the System Voltage Control signal levels between the two systems. The System
Voltage Control signal helps to maintain load sharing by giving all the modules a common reference
signal for output voltage. The System Voltage Control signal is not a critical signal. Loss of the Sys-
tem Voltage Control signal should only cause a minor degrade in module sharing capability, if at all.
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Operation Description
Line Sync Signal
The Line Sync signal is sent between UPS systems when they are in parallel. Isolation amplifiers iso-
late the Line Sync signal levels between the two systems. The Line Sync signal synchronizes the UPS
systems to the Primary Bypass line. By maintaining sync with the Primary Bypass, uninterrupted
transfers to the Primary Bypass can be made, if a fault occurs while the systems are in parallel.
All status signals sent between the UPS system and the Tie Controls are isolated through optical cou-
plers. In addition, all these status signals have impedance protection between the signal wire connec-
tions and the system power supplies and ground.
The Tie Control’s power supply can use either UPS system’s output as its source and the Tie Control
power supply employs transformer isolation.
All necessary voltage sensing occurs at the tie cabinet and employs fuse, transformer and/or imped-
ance protection.
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Operation Description
2.7
Improper User Operation
tor use does not directly cause a loss of critical bus functions. Additional security functions, such as
removable key switches, are available as system options.
Transfer Operation
Transfer functions require two push-button operations. Pushing any single button at random, does
not put the system at risk. The Power-Tie system has redundant status sensors and monitors them
for proper operation.
The operator should use good judgement when operating the Tie Control. The Tie Control cannot pre-
vent an operator from tying to a source that subsequently goes bad.
For example, assume one UPS has gone to bypass. You want to bring the bypass feeder onto the sec-
ond system. The second system must momentarily tie to the first system’s bypass source. If a bypass
fault occurs in the first system during the tie operation, both load feeders could fault. To prevent this
type of fault, put the first system’s bypass source on a standby engine generator.
Tie Operation
The tie process only requires selection of the desired Primary Bypass Source (which may be left in a
default desired position) and the sequential pushing of two buttons. The Power-Tie logic takes care of
synchronizing to the select Primary Bypass Source, checking that the systems are in an acceptable
configuration, verifying that electrical parameters are within tolerance, and verifying sufficient com-
bined systems capacity.
The sequential operation serves both to eliminate accidental operation and allows the operator an
opportunity to cancel an undesired action. Before a transfer or tie operation can be performed the
Power-Tie control turns on an OK indicator.
The OK indicator clearly describes the action which will occur.
If the action indicated is not the desired action, the operator simply presses the button he used to ini-
tiate the original operation and the operation is canceled. Directions on how to use the “Push Again to
Cancel” feature are posted on the Power-Tie control panel, next to each applicable push button.
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Operation Description
2.8
Tie Circuit Breaker or Logic Faults
The Continuous Power-Tie system has been designed to anticipate circuit breaker and logic faults.
Should a circuit breaker or logic fault occur, the Power-Tie system maintains the critical bus function
under fault conditions
2.8.1 What Happens If a Failure Occurs During a Power Transfer
During normal operation, the Power-Tie logic maintains system isolation. Upon power transfer initia-
tion, the Power-Tie logic checks the circuit breaker (CB) positions. The Power-Tie logic inhibits the
power transfer if the circuit breaker positions are incorrect.
For Continuous Tie, if all circuit breakers are in their correct positions, then all circuit breakers
momentarily remain closed, tying both systems together. The power transfer sequence stops. The
static bypass becomes the backup.
If the operator selects momentary Power-Tie, the isolation circuit breaker opens. If this circuit
breaker fails to open, the system returns to its initial configuration, maintaining the critical bus.
2.8.2 What Happens If a Logic Failure Occurs During Power Transfer
If a failure occurs before the power transfer, the Power-Tie logic inhibits the power transfer operation.
If a failure during the power transfer, one of the following occurs:
• If the failure occurs before overlap period has timed out, the Power-Tie logic returns the system to
its initial configuration.
• If failure occurs after overlap period has expired (e.g., the isolating breaker has already been com-
manded to trip), the Power-Tie logic completes the transfer.
• If the power transfer does not complete (e.g., the isolating breaker fails to trip within an accept-
able time period), the Power-Tie logic returns the system to its initial configuration.
• If the failure occurs after the transfer has occurred, the static bypass becomes the backup.
2.8.3 Hardware Failures
Improper operation of the Power-Tie are caused primarily by tie circuit breaker failures. The
Power-Tie logic monitors the “Close” and “Open” sent to the circuit breakers. If the breaker command
is not completed by the breaker within an acceptable time period, the Power-Tie logic takes corrective
action. The Power-Tie implements corrective action based on the operation being performed and the
current system configuration.
The Power-Tie logic takes protective action if a fault occurs on a UPS system during a load transfer or
while the UPS systems are in continuous parallel operation. The Power-Tie logic takes action based
on the current system configuration and the active operation to minimize the affects of the fault.
The Power-Tie controls add additional protection to the individual UPS systems. And, the protective
controls of the individual UPS become an integral part of the overall fault protection scheme used by
the Power-Tie controls.
2.9
Recommendations - Tie Circuit Breaker Selection
Consider using non-automatic circuit breakers for continuous Power-Tie applications. The circuit
breaker function should not be the primary fault limiting function. Using non-automatic circuit
breakers eliminates a primary circuit breaker failure mode, the trip unit components within the cir-
cuit breaker.
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Control Panel Description
3.0 CONTROL PANEL DESCRIPTION
3.1
Mimic Panel
The Mimic panel consists of the following:
• UPS SYSTEM 1 - PRIMARY BYPASS
• UPS SYSTEM 2 - PRlMARY BYPASS
• UPS SYSTEM 1 - ON BYPASS
• UPS SYSTEM 2 - ON BYPASS
• LOAD 1 CIRCUIT BREAKER
• LOAD 2 CIRCUIT BREAKER
• TIE CIRCUIT BREAKER
• LOAD 1 - NORMAL
• LOAD 1 - ON SYSTEM 2
• LOAD 1 - SYSTEMS TIED
• LOAD 1 - OFF
• LOAD 2 - NORMAL
• LOAD 2 - ON SYSTEM 1
• LOAD 2 - SYSTEMS TIED
• LOAD 2 - OFF
• CONTROL STATUS - SYNCHRONIZING
• CONTROL STATUS - TRANSFERRING
UPS System 1 - Primary Bypass
This light turns on when UPS System 1 is the selected Primary Bypass. When lit, the light indicates
the UPS Modules of both UPS systems are synchronizing to the bypass of UPS System 1, when sys-
tems are tied or in the process of transferring load.
UPS System 2 - Primary Bypass
This light turns on when UPS System 2 is the selected Primary Bypass. When lit, the light indicates
that the UPS Modules of both UPS systems are synchronizing to the bypass of UPS System 2, when
systems are tied or in the process of transferring load.
UPS System 1 - On Bypass
This light turns on when UPS System 1 is on Bypass.
UPS System 2 - On Bypass
This light turns on when UPS System 2 is on bypass.
Load 1 Circuit Breaker
These two lights indicate the OPEN (Red light) or CLOSED (Green light) state of the Load 1 circuit
breaker.
Load 2 Circuit Breaker
These two lights indicate the OPEN (Red light) or CLOSED (Green light) state of the Load 2 circuit
breaker.
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Control Panel Description
Tie Circuit Breaker
These two lights indicate the OPEN (Red light) or CLOSED (Green light) state of the Tie circuit
breaker.
Load 1 - Normal
This light indicates that Load 1 is being supplied by UPS System 1. Load 1 supplied by UPS system 1
represents the normal operating mode.
Load 1 - On System 2
This light indicates that Load 1 is being supplied by UPS System 2 through the Tie circuit breaker.
Load 1 - Systems Tied
This light indicates that Load 1 is being supplied by both UPS Systems which share the combined
loads.
Load 1 - Off
This light indicates that Load 1 is isolated from both UPS Systems.
Load 2 - Normal
This light indicates that Load 2 is being supplied by UPS System 2. Load 2 supplied by UPS system 2
represents the normal operating mode
Load 2 - On System 1
This light indicates that Load 2 is being supplied by UPS System 1 through the Tie circuit breaker.
Load 2 - Systems Tied
This light indicates that Load 2 is being supplied by both UPS Systems which share the combined
loads.
Load 2 - Off
This light indicates that Load 2 is isolated from both UPS Systems.
Control Status - Synchronizing
This light indicates that the UPS Systems are currently synchronizing to the selected bypass line.
Control Status - Transferring
This light indicates that the controls are transferring a load from one system to the other system.
3.2
Load Transfer Controls
This section of the control panel gives indications and allows control of load transfers between the
UPS Systems.
OK to Transfer Load 1 to System 1
This light indicates that it is safe to transfer Load 1 from UPS System 2 to UPS System 1. The trans-
fer occurs when the PUSH TO TRANSFER AFTER OK button is pressed, but only if this light is on.
OK to Transfer Load 1 to System 2
This light indicates that it is safe to transfer Load 1 from UPS System 1 to UPS System 2. The trans-
fer occurs when the PUSH TO TRANSFER AFTER OK button is pressed, but only if this light is on.
OK to Transfer Load 2 to System 1
This light indicates that it is safe to transfer Load 2 from UPS System 2 to UPS System 1. The trans-
fer occurs when the PUSH TO TRANSFER AFTER OK button is pressed, but only if this light is on.
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Control Panel Description
OK to Transfer Load 2 to System 2
This light indicates that it is safe to transfer Load 2 from UPS System 1 to UPS System 2. The trans-
fer occurs when the PUSH TO TRANSFER AFTER OK button is pressed, but only if this light is on.
Transfer Control Disabled
This light indicates that load transfers are not allowed because the systems are currently being put in
parallel operation.
Transfer Function Available
The Transfer Function Available lights indicate the transfer options the operator has available based
on the current system configuration.
Transfer Function Available - OK to Transfer Load 1 to System 1
This light indicates that the systems are in a configuration where a transfer of load 1 from UPS Sys-
tem 2 to UPS System 1 can be attempted.
Transfer Function Available - OK to Transfer Load 1 to System 2
This light indicates that the systems are in a configuration where a transfer of load 1 from the UPS
System 1 to UPS System 2 can be attempted.
Transfer Function Available - OK to Transfer Load 2 to System 1
This light indicates that the systems are in a configuration where a transfer of load 2 from UPS Sys-
tem 2 to UPS System 1 can be attempted.
Transfer Function Available - OK to Transfer Load 2 to System 1
This light indicates that the systems are in a configuration where a transfer of load 2 from UPS Sys-
tem 1 to UPS System 2 can be attempted.
Transfer Load To - System 1
When this button is pressed, it initiates a sequence to allow a load transfer to UPS System 1. The
transfer to be performed is automatically determined by the current state of the Tie and Load circuit
breakers. The button turns on indicating that the sequence is armed. When the control logic deter-
mines all conditions for a safe transfer have been met, it turns on the appropriate OK TO TRANSFER
light.
Transfer Load To - System 2
When this button is pressed it initiates a sequence to allow a load transfer to UPS System 2. The
transfer to be performed is automatically determined by the current state of the Tie and Load circuit
breakers. The button turns on indicating that the sequence is armed. When the control logic deter-
mines that all conditions for a safe transfer have been met, it turns on the appropriate OK TO
TRANSFER light.
Push to Transfer After OK
This button starts the transfer after the OK TO TRANSFER light turns on.
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Control Panel Description
3.3
Continuous Tie Control
This section of the control panel provides indicators and controls for the control of tied systems
functions.
OK to Tie Systems
This light indicates that it is safe to tie UPS Systems 1 and 2 together. The systems are tied after the
PUSH TO TIE SYSTEMS AFTER OK button is pressed, but only if this light is on.
OK to Open Tie
This light indicates that it is safe to separate UPS Systems 1 and 2. The Tie circuit breaker opens
after the PUSH TO OPEN TIE AFTER OK button is pressed, but only if this light is on.
Tie Control Disabled
This light indicates that the tie controls are disabled because the systems are transferring a load.
Primary Bypass Select
This switch is used to select which systems bypass to synchronize with when a tie sequence is initi-
ated. It is also the bypass source the Loads will be transferred to should a fault occur while the sys-
tems are in parallel operation.
Synchronize Systems
This button is used to begin and end a tied systems operation. When the SYNCHRONIZE SYSTEMS
BUTTON is first pressed, the button will light on indicating, that tied systems operation is desired.
The systems synchronize to the bypass source selected by the PRIMARY BYPASS SELECT switch.
Once the systems are synchronized and all other conditions to safely tie the systems have been met
the OK TO TIE SYSTEMS light turns on.
Press the PUSH TO TIE SYSTEMS AFTER OK button to close the appropriate circuit breaker to put
the systems in parallel. To separate tied systems press this button again. The light turns off indicat-
ing the tied condition is no longer desired.
If it is safe to separate the systems the OK TO OPEN TIE light turns on. Press the PUSH TO OPEN
TIE AFTER OK button to open the Tie breaker. Both UPS systems will resume independent opera-
tion.
Push to Tie Systems After OK
Once the OK TO TIE SYSTEMS turns on, pressing this button closes the appropriate circuit breaker
to tie the systems.
Push to Open Tie After OK
Once an OK TO OPEN TIE turns on, pressing this button opens the Tie circuit breaker to separate
the systems.
3.4
Control Inhibits
This section of the control panel provides alarm indicators which prevent transfers and parallel oper-
ation of the UPS systems.
Phase Lockout
This light indicates the systems are not synchronized. It is a waveform-based redundant check of syn-
chronization. The primary sync indicator is based on UPS module sync bus coincidence.
This light normally turns on while the systems are synchronizing prior to a Tie or Transfer operation.
If the light does not turn off, contact Liebert Global Services for assistance.
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Control Panel Description
Voltage Lockout
This light indicates the system voltages are too far apart to allow safe transfers and parallel operation
of the UPS systems. To correct this condition, adjust the UPS system voltage to proper levels.
If both system voltages are adjusted correctly, and the PHASE LOCKOUT alarm is not present, then
check the voltage detection circuitry. Contact Liebert Global Services for assistance.
Load Lockout
This light indicates insufficient UPS capacity to perform the selected operation. The control logic
intelligently checks the UPS systems and the Loads based on the specific operation in progress.
Verify UPS capacity and shed load as necessary until UPS capacity is not being exceeded. If UPS
capacity is sufficient, then check the load/capacity detection circuitry. Contact Liebert Global Services
for assistance.
Logic Failure
This light indicates that a logic failure has occurred. No Tie operations are allowed while this condi-
tion exists.
Check all tie control logic functions to determine the source of the fault. Contact Liebert Global Ser-
vices for assistance.
Lamp Test
This button is pressed to check all indicators on the MIMIC and CONTROL PANEL.
3.5
Manual Controls
These controls are located on a panel behind the Control Panel door. They are provided to assist in
initial system start-up and provide emergency manual breaker trip capability. During normal opera-
tions they should not need to be used.
Close Load 1
This button closes the Load 1 circuit breaker during start-up. It only functions if the Tie breaker is
open.
Close Load 2
This button closes the Load 2 circuit breaker during start-up. It only functions if the Tie breaker is
open.
Trip Load 1
This button is used to manually trip the Load 1 circuit breaker and is provided for emergency pur-
poses.
The light on this push button will go out when load is being supplied through the breaker. Pressing
this button when the light is out will result in loss of power to an on-line load.
Trip Load 2
This button is used to manually trip the Load 2 circuit breaker and is provided for emergency pur-
poses.
The light on this push button will go out when load is being supplied through the breaker. Pressing
this button when the light is out will result in loss of power to an on-line load.
Trip Tie
This button is used to manually trip the Tie circuit breaker and is provided for emergency purposes.
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Operating Instructions
4.0 OPERATING INSTRUCTIONS
4.1
Initial System Start-Up
All load circuit breakers and tie circuit breakers are initially open.
1. Press the CLOSE LOAD 1 button located on the panel behind the Control door. The Load 1
breaker should close when the button is pressed.
2. Press the CLOSE LOAD 2 button located behind the Control door. The Load 2 breaker should
close when the button is pushed.
NOTE
The operation can be performed with the UPS on bypass or inverter output. The Power-Tie
logic confirms that the Tie breaker is open to prevent inadvertently putting the systems in
parallel.
3. Once one or both UPS systems are on-line, a transfer of either critical load between systems or a
continuous tie operation can be performed subject to conditions outlined in 1.0 - System
4.2
Basic Operation
4.2.1 Momentary Tie - Load Transfers
A momentary tie operation is used to transfer a critical load from a UPS system, which requires isola-
tion for maintenance, to another UPS system without placing the critical load on utility bypass.
The isolated UPS system can be serviced while the critical load remains protected by a fully func-
tional UPS system. Once service is complete, perform another Momentary tie operation to return the
critical load to its normal UPS system. This can be done without placing the critical load on utility
bypass.
4.2.2 Normal Transfer Operation Configurations
Transfers of a critical load between systems can be performed from several initial system configura-
tions. The guiding criteria for permitting transfers is that the critical load must remain on UPS
inverter output.
Transfers to a UPS system operating on its bypass source cannot be initiated due to logic lockouts.
However, a critical load initially on a UPS system’s bypass source can be transferred to the other UPS
system operating on inverter output.
In addition to checking system configurations, the Power-Tie logic uses three independent criteria for
verifying synchronization. The Power-Tie logic verifies system voltages are within proper limits. And
the Power-Tie logic verifies the UPS system which will accept the additional load has sufficient UPS
capacity.
The logic intelligently determines which system to synchronize with, which UPS system capacity to
check, and which load(s) to check, based on which system the operator selects to transfer load. The
Power-Tie logic “knows” the present system configuration.
The Power-Tie logic automatically returns both UPS systems to independent operation by resynchro-
nizing them to their own bypass source and separating all control loops between the systems when
the transfer is complete.
4.2.3 Maintenance Procedures - Isolating Each UPS System
Power-Tie system capabilities permit each UPS system to be completely isolated for service while its
load continues to be powered and protected by the other UPS system. In addition, since all controls of
each system are electrically isolated from the other system, any operation or fault on the system being
serviced does not affect the system supplying the combined loads.
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Operating Instructions
4.2.4 Isolating a UPS System for Maintenance - Combined Loads Operation
Both Load circuit breakers are initially closed and the Tie circuit breaker initially open. The Tie cir-
cuit breaker is closed if the UPS systems are currently in parallel operation.
1. Select the UPS system that will carry both loads by pressing the appropriate SYSTEM button in
the LOAD TRANSFER CONTROL section of the control panel. If System 2 is to be isolated then
the press the SYSTEM 1 button. Load 2 will be transferred to System 1.
2. Wait for the OK TO TRANSFER LOAD light to turn on. If System 2 is to be isolated then the OK
TO TRANSFER LOAD 2 TO SYSTEM 1 light should turn on when it is safe to perform the
transfer.
3. Once the OK indication is received, press the PUSH TO TRANSFER AFTER OK button and the
transfer wilt be performed. If System 2 is to be isolated then the Tie breaker will close. Then, the
Load 2 circuit breaker opens after the overlap period times out.
4. The isolated UPS system (System 2) can now be safely serviced.
4.2.5 Transfer of Load Between Two Systems
This procedure may be performed from three initial states:
• Tie circuit breaker is open and both load circuit breakers are closed.
• Both loads are on System 1.
• Both loads are on System 2. The UPS system losing the load may be on UPS or Bypass. The
UPS system accepting the load must be on UPS.
1. Select the UPS system to carry the transfer load. Press the TRANSFER LOAD TO SYSTEM (#)
button. If you want to transfer Load 2 to System 1, press the “SYSTEM 1” button. Both systems
synchronize to the bypass of the system receiving the additional load.
The SYNCHRONIZING light in the CONTROL STATUS section of the mimic turns on while the
systems are synchronizing. The light turns off when the sync lines (bypass and oscillator) are in
the proper state.
At this point the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light should turn on if there are
no inhibits. If Load 2 can be transferred to System 1, the OK TO TRANSFER LOAD 2 TO SYS-
TEM 1 light turns on.
NOTE
When a transfer sequence is initiated, the Tie controls are locked out and the TIE CONTROL
DISABLED light turns on.
2. After the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light turns on, press the PUSH TO
TRANSFER AFTER OK button to transfer the load. The proper circuit breaker closes and, after a
delay, the proper isolating circuit breaker opens.
White the systems are tied the Load Sharing and Voltage Adjust Controls will also be tied
between the systems. The LOAD TRANSFERRING light turns on to tell the operator that a
transfer is in progress.
Once transfer is complete, the systems return to their own internal sync, the current share and
voltage adjust controls separate, the TRANSFERRING and TIE CONTROL DISABLED lights
turn off. The SYSTEM (#) push-button light turns off and the NORMAL status light turns on.
All load transfers follow this same procedure. The logic knows whether Load 2 is to be transferred
from System 2 to System 1 or Load 1 is being returned to System 1. The SYSTEM 1 button is
pressed for both operations because the systems’ initial configuration make only one choice
possible.
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Operating Instructions
4.2.6 Returning an Isolated System to Normal Operation - End Combined Loads Operation
One Load circuit breaker and the Tie circuit breaker are closed. The Load circuit breaker of the iso-
lated system which was being serviced will be opened.
1. Select the UPS system to accept the load. Press the TRANSFER LOAD TO SYSTEM (#). If
System 2 had been isolated then press the SYSTEM 2 button. Load 2 will be returned to System 2.
2. Wait for the OK TO TRANSFER LOAD light to turn on. If System 2 was isolated then the OK TO
TRANSFER LOAD 2 TO SYSTEM 2 light should turn on when it is safe to perform the transfer.
3. After the OK TO TRANSFER LOAD 2 TO SYSTEM 2 light turns on, press the PUSH TO
TRANSFER AFTER OK button. The transfer will be performed. If System 2 was isolated then the
Load 2 breaker will close and the Tie circuit breaker opens after the overlap period times out.
4. Both UPS systems will now be supplying their normal Load and operating independent of each
other.
4.2.7 Maintenance Procedures - Maintaining Power-Tie Components
late the UPS’s load circuit breaker and the associated downstream feeders for service.
By using downstream switchover devices for the individual critical loads, such as ATSs or dual input
PDUs, the load feeder components to be maintained are de-energized. All critical load operations are
transferred to the feeder which will power the combined loads.
There are three approaches to maintaining the Tie circuit breaker and its associated circuit compo-
nents depending on the convenience and isolation desired.
1. Single fixed-mount Tie circuit breaker
Complete UPS system and critical loads must be placed on a reliable maintenance bypass source
(e.g., standby engine-generator) to de-energize the Tie circuit breaker.
Using appropriate safety equipment and procedures, the Tie circuit breaker can be serviced while
one or both systems remain energized (depending on isolation breaker usage).
2. Single drawout Tie circuit breaker
Drawout mechanism permits servicing the Tie circuit breaker and associated circuitry while the
Power-Tie system is in its normal mode of operation.
To de-energize the drawout carriage plug-in stubs and buswork, however, one feeder at a time
must be isolated for service. Refer to 4.2.3 - Maintenance Procedures - Isolating Each UPS
Using appropriate safety equipment and procedures, these components can be serviced while one
or both systems remain energized (depending on isolation breaker usage).
3. Two Tie circuit breakers in series—Fixed-mount or Drawout
By using two Tie circuit breakers in series, each circuit breaker and its associated buswork can be
conveniently and completely de-energized for service. Refer to 4.2.3 - Maintenance Procedures
Using appropriate safety equipment and procedures, these components can be serviced while one
of the two systems remains energized.
4.2.8 Maintenance Procedures - Tie Control Logic Components
Unless the controls are in a continuous parallel mode or currently in the process of transferring a
load, it is possible to service the Tie controls by taking a few precautions. Since all control signals are
isolated, they can be safely de-energized for maintenance without affecting the UPS systems.
27
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Operating Instructions
4.2.9 Abnormal Operations
Improper Transfer
Transfers can not be performed unless the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light turns
on. This makes it difficult to begin an improper transfer.
The source feeding the UPS modules does not matter because the UPS inverter output is isolated
from the rectifier.
The logic permits transfers to and from a UPS system with the UPS modules running on Utility, Bat-
tery, or Engine-generator so long as the system accepting the load is running on inverter output.
Synchronization is verified by forcing the system to meet three independent criteria. First, all on-line
module oscillators must be synchronized. Second, the voltage zero crossings must be within tolerance.
Third, the instantaneous voltage differential between UPS system voltages must be within tolerance.
But, regardless of synchronization status, a critical load will not be allowed to transfer to a system
running on its bypass source. Transfers from a bypass source to a system on UPS is permitted.
Circuit Breaker Failure
If a “Close” or “Open” command to a circuit breaker fails to return a confirmation of completion within
an acceptable time period the Power-Tie logic initiates corrective actions based on the system’s initial
state and current state.
Loss of Tie Controls
Since UPS system independence has been stressed throughout the design of this Power-Tie configura-
tion, complete loss of Tie Controls will not affect either UPS system operating in any Momentary Tie
(Combined Loads Mode) configuration.
4.2.10 Trouble Recovery
While failures are extremely unlikely, the Power-Tie system has been designed to restart from any
description of the operating modes.
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Operating Instructions
4.2.11 Continuous Tie-Systems
A UPS system that has lost one or more modules can be taken off-line for service. The UPS system
with partial capacity can be continuously tied to the other UPS system (also full or partial capacity)
and the critical loads of both systems are protected by the single, fully redundant UPS. When service
is complete the UPS module(s) can be brought on-line again and the system separated, without plac-
ing a critical load on the Bypass source.
Normal Operating Configuration
Initially both load isolation breakers are closed. The Tie breaker is open. Both UPS systems are on
Once the Tie operation is initiated the systems synchronize to the selected Primary Bypass source.
The Power-Tie logic checks the system configurations, verifies synchronization, verifies system volt-
ages are within proper limits, and verifies that the on-line UPS modules of both system have suffi-
cient capacity to maintain the combined loads before allowing the systems to be tied.
Tying the UPS Systems - Continuous Parallel Operations
Both load isolation circuit breakers will be initially closed and the Tie circuit breaker initially open.
The Tie circuit breaker is closed if the systems are in a combined loads mode. Both UPS systems will
be on inverter output.
1. Select the Primary Bypass source for the combined systems with the PRIMARY BYPASS
SELECT switch in the CONTINUOUS TIE CONTROL section of the control panel. If System 1
will be the Primary Bypass then the switch should be in the SYS1 position.
2. Press the SYNCHRONIZE SYSTEMS button in the CONTINUOUS TIE CONTROL section of the
control panel. The push button turns on.
3. Wait for the OK TO TIE SYSTEMS light to turn on.
4. After the OK TO TIE SYSTEMS light turns on, press the PUSH TO TIE SYSTEMS AFTER OK
button. The Tie breaker will close to put the systems in parallel operation.
5. Both systems will share both critical load feeders.
Returning Parallel Systems to Normal Operation - End Continuous Tie
Both Load circuit breakers and the Tie circuit breaker will be initially closed.
1. Press the SYNCHRONIZE SYSTEMS button. The light turns off.
2. Wait for the OK TO OPEN TIE light to turn on.
3. Once the OK TO OPEN TIE light turns on, press the PUSH TO OPEN TIE AFTER OK button.
The Tie circuit breaker opens, separating the systems.
4. Both UPS systems will supply their normal load feeders and operate independent of each other.
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Operating Instructions
Maintenance Procedures - Tie Control Logic and Power Components
late the UPS’s load circuit breaker and the associated downstream feeders for service.
By using downstream switchover devices for the individual critical loads, such as ATSs or dual input
PDUs, the load feeder components to be maintained are de-energized. All critical load operations are
transferred to the feeder which will power the combined loads.
There are three approaches to maintaining the Tie circuit breaker and its associated circuit compo-
nents depending on the convenience and isolation desired.
1. Single fixed-mount Tie circuit breaker
Complete UPS system and critical loads must be placed on a reliable maintenance bypass source
(e.g., standby engine-generator) to de-energize the Tie circuit breaker.
Using appropriate safety equipment and procedures, the Tie circuit breaker can be serviced while
remaining energized.
2. Single drawout Tie circuit breaker
Drawout mechanism permits servicing the Tie circuit breaker and associated circuitry while the
Power-Tie system is in its normal mode of operation.
To de-energize the drawout carriage plug-in stubs and buswork, however, one feeder at a time
must be isolated for service. Refer to 4.2.3 - Maintenance Procedures - Isolating Each UPS
Using appropriate safety equipment and procedures, these components can be serviced while
remaining energized.
3. Two Tie circuit breakers in series - Fixed-Mount or Drawout
By using two Tie circuit breakers in series, each circuit breaker and its associated buswork can be
conveniently and completely de-energized for service. Refer to 4.2.3 - Maintenance Procedures
Unless the controls are in a continuous parallel mode or currently in the process of transferring a
load, it is possible to service the Tie controls by taking a few precautions. Since all control signals are
isolated, they can be safely de-energized for maintenance without affecting the UPS systems.
Abnormal Operations
Improper Transfer
Transfers cannot be performed unless the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light turns
on. This makes it difficult to begin an improper transfer.
The source feeding the UPS modules does not matter because the UPS inverter output is isolated
from the rectifier.
The logic permits transfers to and from a UPS system with the UPS modules running on Utility, Bat-
tery, or Engine-generator so long as the system accepting the load is running on inverter output.
Synchronization is verified by forcing the system to meet three independent criteria. First, all on-line
module oscillators must be synchronized. Second, the voltage zero crossings must be within tolerance.
Third, the instantaneous voltage differential between UPS system voltages must be within tolerance.
But, regardless of synchronization status, a critical load will not be allowed to transfer to a system
running on its bypass source. Transfers from a bypass source to a system on UPS is permitted.
Circuit Breaker Failure
If a “Close” or “Open” command to a circuit breaker fails to return a confirmation of completion within
an acceptable time period the Power-Tie logic initiates corrective actions based on the system’s initial
state and current state.
Loss of Tie Controls
Should a failure occur while the UPS systems are tied, the Loads will be transferred to the selected
Primary Bypass. And, the Load breaker to the other UPS system will be opened to prevent backfeed
from the Primary Bypass. A failure in the Tie controls while the systems are separated has no effect
on either UPS system since all control signals are isolated.
30
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Operating Instructions
Trouble Recovery
While failures are extremely unlikely, this system has been designed to allow restart from any system
tion of the operating modes.
4.2.12 Isolation for Maintenance
Once the critical loads are transferred to the desired UPS, the maintenance bypass circuit breakers
and isolation circuit breakers may be operated. The details of these isolation/maintenance operations
are dependent on the specific arrangement of your switchboards. Typically, to assist maintenance
personnel, maintenance circuit breaker operation is further guided by an electrical or electromechan-
ical interlock system.
For detailed instructions for use of the maintenance bypass switchboard, refer to the Operation and
Maintenance Manual for your Liebert Series 610 UPS.
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Operating Instructions
4.2.13 Operation Scenarios/Transfer Procedures
Refer to the section listed below each figure for the operational procedure to perform the function
indicated.
Figure 9 From start-up to normal operation, loads to be split between two distribution feeders
FROM:
TO:
Initial Conditions Prior to Startup
Normal Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Tie Open
Tie Open
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 10 From combined loads operation to loads split between two feeders
FROM:
TO:
Normal Operation
Combined Loads Operation
System 1
M1
System 2
M2
System 1
M1
System 2
M1
SS1
SS2
M2
M1
SS1
SS2
M2
M2
Tie Closed
Tie Open
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 11 From continuous tied systems to loads split between two systems
FROM:
TO:
Normal Operation
Continuous Tied Systems
System 1
System 2
System 1
M1
System 2
M1
M1
SS1
SS2
M2
M2
M1
SS1
SS2
M2
M2
Continuous Tie
operation for
module out of
service
Tie Closed
Tie Open
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
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Operating Instructions
Figure 12 Transfer both load feeders to one UPS
FROM:
Normal Operation
TO:
Combined Loads Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Momentary Tie
for transfer of
Load 2 to
Tie Open
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
System 1
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 13 Both feeders on one system to normal operation
FROM:
Combined Loads Operation
TO:
Normal Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Tie Closed
Tie Open
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 14 Transfer 100% load on one system to 100% load on a second system (a two-step operation)
FROM:
TO:
Combined Loads Operation on System 1
Combined Loads Operation on System 2
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Momentary Tie for transfer
of Load 2 to System 2,
then Momentary Tie for
transfer of Load 1 to
System 2
Tie Closed
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
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Operating Instructions
Figure 15 Normal split load operations to Continuous Tie
FROM:
Normal Operation
TO:
Continuous Tied Systems
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Continuous Tie
operation for
module out of
service
Tie Open
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 16 Continuous Tie to normal split load operation
FROM:
Continuous Tied Systems
TO:
Normal Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Module
returned
to service
Tie Closed
Tie Open
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 17 Continuous Tie to load on one system
FROM:
Continuous Tied Systems
TO:
Combined Loads Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Module
returned
to service
Tie Closed
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
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Operating Instructions
Figure 18 Load on one system to Continuous Tie
FROM:
Combined Loads Operation
TO:
Continuous Tied Systems
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Momentary Tie
for transfer of
Load 2 to System 1
Tie Closed
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Figure 19 One system in bypass to both feeders combined on remaining operational system
FROM:
TO:
One System in Bypass Mode
Combined Loads Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Momentary Tie
for transfer of
Load 2 to
Tie Open
Tie Closed
Tie
Load 1 Load 2
Tie
Load 1 Load 2
System 1
LEGEND: M = Module
x
SS = Static Bypass Switch
x
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Operating Instructions
Figure 20 One system in bypass to Continuous Tie operation (Option 1)
FROM:
TO:
Restart Bypassed System
One System in Bypass Mode
System 1
M1
System 2
M2
System 1
System 2
Partial
or full
M1
SS1
SS2
M2
M1
M1
SS1
SS2
M2
M2
capacity
Tie Open
Tie Open
Tie
Tie
Load 1 Load 2
Load 1 Load 2
TO:
Continuous Tied Systems
System 1
System 2
M1
M1
SS1
SS2
M2
M2
Tie Closed
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Restart the bypassed system, then use the procedures in Tying the UPS Systems - Continuous
Figure 21 One system in bypass to Continuous Tie operation (Option 2)
FROM:
TO:
One System in Bypass Mode
Combined Loads Operation
System 1
System 2
System 1
System 2
M1
M1
SS1
SS2
M2
M2
M1
M1
SS1
SS2
M2
M2
Momentary Tie
for transfer of
Load 2 to
Tie Open
Tie Closed
Tie
Tie
Load 1 Load 2
Load 1 Load 2
System 1
TO:
Continuous Tied Systems
System 1
System 2
Partial or
full capacity
M1
M1
SS1
SS2
M2
M2
Tie Closed
Tie
Load 1 Load 2
LEGEND: M = Module
x
SS = Static Bypass Switch
x
Combined loads on one system—See 4.2.4 - Isolating a UPS System for Maintenance - Combined
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Operating Instructions
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