GE Multilin 750/760 Feeder Management Relay 5-109
5 SETPOINTS 5.8 S7 CONTROL
5
Once a condition has caused Relay 1 to initiate a transfer, including the close signal to Relay 3 on the Bus Tie breaker, the
command is maintained until Relay 1 determines that Breaker 1 has opened. When Relay 3 receives the close command
from Relay 1, it is captured and retained until either the Bus Tie breaker closes or the Block Transfer logic input is received.
Relay 3 is inhibited from initiating a close command to Breaker 3 by its synchrocheck element. Synchrocheck provides the
bus decayed (residual) voltage permission-to-close, when the Bus 1 voltage decays to the preset level.
The three breakers are under prevent-parallel checking whenever the transfer scheme is operational. If a third breaker is
closed when the other two breakers are already closed, the scheme will automatically trip the breaker selected by Switch
43/10, ‘Selected To Trip’.
If the transfer scheme is not required, set
TRANSFER FUNCTION to "Disabled". If not disabled, this setpoint assigns the func-
tion of the associated circuit breaker to the relay. This selection programs the relay to use the logic required by each of the
three breakers. Select "Incomer 1" or "Incomer 2" for this setpoint if the relay is associated with the breaker to be used as
Incomer 1 or 2 respectively. Select "Bus Tie" if the relay is associated with the bus tie breaker.
The
TRANSFER DELAY THIS SOURCE time establishes an interval from the reset of an operated instantaneous overcurrent
element on this source, during which the line instantaneous undervoltage element (Device 27-3) is allowed to block a trans-
fer. The
TRANSFER DELAY OTHER SOURCE delay time prevents transfers that could otherwise be caused by a non-simulta-
neous return of source voltages after a loss of both sources. It establishes an interval from the return of the first source to
the return of the second source during which a transfer cannot be initiated.
The BLOCK TRIP ON DOUBLE LOSS setpoint selects the required scheme operation in the event of a simultaneous loss of
both Source 1 and Source 2. If it is desired to have both of the Incomers trip on timed undervoltage when this occurs, select
"Disabled". If it is desired to prevent the Incomers from tripping on timed undervoltage when this occurs, select "Enabled".
With either selection a transfer-initiated close of the bus tie breaker is not allowed.
The settings and functions of other elements associated with the transfer scheme are shown below:
• Output Relays 4-7 Auxiliary (all breakers): These output relays are used to implement the transfer scheme, and
must therefore not be operated by any other feature of the relay. These relays must be programmed to have a non-
operated state of ‘De-energized’ with the output type as ‘Self-reset’. These are the default settings.
• Instantaneous Phase (50P1 or 2) and Neutral (50N-1 or 2) [Incomers 1 and 2 only]: These fault detectors can be
used as an input to transfer scheme logic in this application, and therefore the function setpoint of elements that are
used must be set to Control. These elements block a transfer while a fault, which can cause a severe voltage dip, is
present on the load side of the breaker. This fault should be cleared by time overcurrent protection on the incomer or
an upstream breaker. If Device 50P is set properly, during this event it will allow Device 27-4 to time out before the
inverse time phase overcurrent operates, but still prevent transfer initiation. The 50P element should be set above the
maximum current caused by either the bus motor contribution to an upstream fault, or the maximum current during low
voltage conditions. The 50N element should be set to detect arcing ground faults, but allow permitted unbalances.
• Line Undervoltage 3 (27-3) [Incomers 1 and 2 only]: Since element is used as an input to transfer scheme logic in
this application, set
LINE UNDERVOLTAGE 3 FUNCTION to “Control”. An Undervoltage 3 operation signals Relay 2 to block
transfer initiation from that relay, as Source 1 is experiencing low voltage. Also, Device 27-3 is enabled by instanta-
neous overcurrent to block transfer initiation. This ensures that if a fault on the load side of Bus 1 causes a dip below
the undervoltage pickup setting, transfer will not be initiated until the voltage has risen above the voltage setting for the
interval established by the
TRANSFER DELAY THIS SOURCE setpoint. The Device 27-3 pickup setting should be below the
minimum expected normal (low) voltage, usually around 0.9 of pickup voltage. A Definite Time curve with the delay set
to zero provides instantaneous operation. The minimum operating voltage must be set to zero.
Line Undervoltage 4 (27-4) [Incomers 1 and 2 only]: Since this element is used as a transfer scheme logic input in
this application, set
LINE UNDERVOLTAGE 4 FUNCTION to "Control". An Undervoltage 4 operation initiates a transfer on
loss-of-source. Typical settings have a pickup about 0.7 to 0.8 of pickup voltage, an "Inverse Time" curve setting, and
a delay setting to provide operation in 0.7 to 1.4 seconds at 0 V. The minimum operating voltage must be set to zero.
• Synchrocheck (25) [Incomers 1 and 2 only]: The synchrocheck function can be selected as either Control or Alarm.
It is imperative that the
DEAD SOURCE PERMISSIVE setpoint be "LL&DB" (Live Line and Dead Bus) to allow initial closing
of the incoming breakers. The user establishes all other setpoints for this element.
Synchrocheck (25) [Bus Tie only]: This element is used to provide synchronism check supervision when paralleling
the busses. The Dead Source Permissive portion of this feature is also used to measure the residual voltage on the
bus that has lost source. To ensure that transfers are supervised by the decayed voltage magnitude only, the ‘in-syn-
chronism’ elements are blocked while a transfer is in progress. The synchrocheck function can be selected as either
Control or Alarm. It is imperative that the
DEAD SOURCE PERMISSIVE setpoint be either "DL|DB" (Dead Line or Dead
Bus) or "DLXDB" (Dead Line or Dead Bus, but not both) to allow for transfers to either incomer.
Courtesy of NationalSwitchgear.com
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