Function Block - ABB RED615 Technical Manual

1YHT530004D05 D
4.6.2.2
4.6.2.3
4.6.2.4
615 series
Technical Manual

Function block

GUID-1B46D13E-4F26-4CFA-9655-E979E0E05D67 V2 EN
Figure 262: Function block
Functionality
The load shedding and restoration function LSHDPFRQ is capable of performing
load shedding based on underfrequency and the rate of change of the frequency.
The load that is shed during the frequency disturbance can be restored once the
frequency has stabilized to the normal level.
The measured system frequency is compared to the set value to detect the
underfrequency condition. The measured rate of change of frequency (df/dt) is
compared to the set value to detect a high frequency reduction rate. The
combination of the detected underfrequency and the high df/dt is used for the
activation of the load shedding. There is a definite time delay between the detection
of the underfrequency and high df/dt and the activation of LSHDPFRQ. This time
delay can be set and it is used to prevent unwanted load-shedding actions when the
system frequency recovers to the normal level.
Throughout this document, "high df/dt" is used to mean "a high rate
of change of the frequency in negative direction."
Once the frequency has stabilized, LSHDPFRQ can restore the load that is shed
during the frequency disturbance. The restoration is possible manually or
automatically.
The function contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.
Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of the load shedding and restoration function can be described using
a module diagram. All the modules are explained in the next sections.
Section 4
Protection functions
503