GE D90 Plus - Overfrequency

CHAPTER 7: PROTECTION CONTROL ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 363
Block
Range: any FlexLogic operand or shared operand
Default: OFF
Assertion of the operand assigned to this setting blocks operation of the underfrequency
element.
Events
Range: Enabled, Disabled
Default: Disabled
This setting enables and disables the logging of underfrequency events in the sequence
of events recorder.
The figure shows the logic for the underfrequency function.
Figure 304: Underfrequency logic
Overfrequency
There are two identical overfrequency elements.
A frequency calculation for a given source is made on the input of a voltage or current
channel, depending on which is available. The channels are searched for the signal input in
the following order:
1. Voltage channel A
2. Auxiliary voltage channel
3. Current channel A
4. Ground current channel
The first available signal is used for frequency calculation.
The steady-state frequency of a power system is an indicator of the existing balance
between the generated power and the load. Whenever this balance is disrupted through
the disconnection of significant load or the isolation of a part of the system that has a
surplus of generation, the effect is an increase in frequency. If the control systems of the
generators do not respond fast enough, to quickly ramp the turbine speed back to normal,
the overspeed can lead to the turbine trip. The overfrequency element can be used to
control the turbine frequency ramp down at a generating location. This element can also
be used for feeder reclosing as part of the after load shedding restoration.
Select the Settings > Protection > Control > Overfrequency menu to open the
overfrequency settings window.
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