Frequency; Underfrequency 1 (2) - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

5 SETPOINTS
The 745 can be used as the primary detecting relay in automatic load shedding schemes based on underfre-
quency. This need arises if, during a system disturbance, an area becomes electrically isolated from the main
system and suffers generation deficiency due to loss of either transmission or generation facilities. If reserve
generation is not available in the area, conditions of low system frequency occur that may lead to a complete
collapse. The 745 provides a means of automatically disconnecting sufficient load to restore an acceptable bal-
ance between load and generation.
The 745 uses both frequency and frequency rate-of-change as the basis for its operating criteria. These values
are measured based on the voltage input or, if voltage is disabled, the Winding 1 phase A current input. The
relay has two underfrequency and four rate-of-change levels. Thus, four or more separate blocks of load can
be shed, according to the severity of the disturbance.
In addition to these elements, the 745 has an overfrequency element. A significant overfrequency condition,
likely caused by a breaker opening and disconnecting load from a particular generation location, can be
detected and used to quickly ramp the turbine speed back to normal. If this is not done, the overspeed can lead
to a turbine trip, which would then subsequently require a turbine start up before restoring the system. If the
turbine speed can be controlled successfully, system restoration can be much quicker. The overfrequency ele-
ment of the 745 can be used for this purpose at a generating location.
WE STRONGLY RECOMMEND THE USE OF EITHER THE VOLTAGE OR CURRENT OR BOTH
SIGNAL FOR SUPERVISION. IF NO SUPERVISING CONDITIONS ARE ENABLED, THE ELE-
MENT COULD PRODUCE UNDESIRABLE OPERATION!
NOTE
S FREQUENCY
S [ENTER] for more
a) UNDERFREQUENCY 1 (2)
S UNDERFREQUENCY 1
S [ENTER] for more
UNDERFREQUENCY 1
FUNCTION: Disabled
UNDERFREQUENCY 1
TARGET: Self-reset
CURRENT SENSING:
Enabled
MINIMUM OPERATING
CURRENT: 0.20 x CT
MINIMUM OPERATING
VOLTAGE: 0.50 x VT
UNDERFREQUENCY 1
PICKUP: 59.00 Hz
GE Power Management
This message indicates the start of the FREQUENCY section. To continue
these setpoints press
EN TE R
This message indicates the start of the UNDERFREQUENCY section. To
continue these setpoints press
Range: Disabled / Enabled
Range: Self-reset / Latched / None
Select None to inhibit the display of the target message when the element
operates. Thus an element whose "target type" is None never disables the
LED self-test feature since it cannot generate a displayable target message.
Range: Disabled / Enabled
Range: 0.20 to 1.00 (steps of 0.01)
Enter the minimum value of winding 1 phase A current (in units of relay
nominal current) required to allow the underfrequency element to operate.
Range: 0.10 to 0.99 (steps of 0.01)
Enter the minimum value of voltage (in units of relay nominal voltage)
required to allow the underfrequency element to operate.
Range: 45.00 to 59.99 (steps of 0.01)
Enter the frequency (in Hz) below which the Underfrequency 1 element will
pickup and start the delay timer.
745 Transformer Management Relay
5.6 S4 ELEMENTS

5.6.11 FREQUENCY

or press to go to the next section.
M E SSA G E
or press
E N TE R
M E SSA G E
5
for the next section.
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