GE 750, Instruction Manual

Page: 277 / 504

GE Power Management 750/760 Feeder Management Relay 14-
21
14 S7 CONTROL 14.7 TRANSFER
14
Line Voltage Undervoltage (27-3) (Incomers 1 and 2 only)
This element is used as an input to transfer scheme logic in this application, and therefore the function setpoint
must be set to
Control . An Undervoltage 3 operation is used to signal relay 2 to block transfer initiation from
that relay, because source 1 is experiencing low voltage. Also, 27-3 is enabled by instantaneous overcurrent to
block transfer initiation. This ensures that if a fault on the load side of bus 1 causes a dip below the undervolt-
age pickup setting, transfer will not be initiated until the voltage has risen above the voltage setting for the inter-
val established by the
TRANSFER DELAY THIS SOURCE
setpoint. The pickup setting of 27-3 should be below the
minimum expected normal (low) voltage, usually around 0.9 Pick Up voltage. A Definite Time curve with the
delay set to zero provides instantaneous operation. The minimum operating voltage must be set to zero.
Line Voltage Undervoltage (27-4) (Incomers 1 and 2 only)
This element is used as an input to transfer scheme logic in this application, and therefore the function setpoint
should be set to
Control . An Undervoltage 4 operation is used to initiate a transfer on loss-of-source. Typical
settings have a pickup about 0.7 to 0.8 of Pick Up voltage, a curve setting selected as ‘Inverse Time’, and a
delay setting to provide operation in 0.7 to 1.4 seconds at 0 volts. 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 setpoint
DEAD
SOURCE PERMISSIVE
be set to 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-synchronism’ elements
are blocked while a transfer is in progress. The synchrocheck function can be selected as either
Control or
Alarm . It is imperative that setpoint
DEAD SOURCE PERMISSIVE
be set to 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.
The
DEAD BUS MAXIMUM VOLTAGE
and
DEAD LINE MAXIMUM VOLTAGE
setpoints establish the level of decayed volt-
age above which transfers are inhibited. A normal setting for this element is about 0.25 Pick Up of nominal volt-
age. Because the 750/760 measures a single phase-phase voltage, these values should be multiplied by 1 /
√
3
to cover the case of a phase-ground fault on a measured phase reducing that phase voltage but leaving the
other two phases at a higher voltage. If experience shows this setting causes a delay of transfer presenting
problems, it is occasionally raised to a maximum of 0.40 Pick Up. The user establishes all other setpoints for
this element.
14.7.4 LOGIC INPUTS FOR INCOMER #1, #2, & BUS TIE RELAYS
The programming of the required logic inputs is as follows. Note that the input number matches the wiring
shown on the DC schematics. It is not necessary that the specific inputs are programmed as shown, but field
connections must match the logic functions.
If logic inputs identified as optional on the schematics and the following table are not required, they
can be programmed to perform other functions. The Message Mode may be programmed to
Disabled
or Self Reset .
NOTE