Underfrequency Protection; Underfrequency Protection Implementation; Underfrequency Protection Logic; Figure 126: Underfrequency Logic (Single Stage) - GE MiCOM P40 Agile Technical Manual

Chapter 11 - Frequency Protection Functions
3

UNDERFREQUENCY PROTECTION

A reduced system frequency implies that the net load is in excess of the available generation. Such a condition can
arise, when an interconnected system splits, and the load left connected to one of the subsystems is in excess of
the capacity of the generators in that particular subsystem. Industrial plants that are dependent on utilities to
supply part of their loads will experience underfrequency conditions when the incoming lines are lost.
Many types of industrial loads have limited tolerances on the operating frequency and running speeds (e.g.
synchronous motors). Sustained underfrequency has implications on the stability of the system, whereby any
subsequent disturbance may damage equipment and even lead to blackouts. It is therefore essential to provide
protection for underfrequency conditions.
3.1

UNDERFREQUENCY PROTECTION IMPLEMENTATION

The following settings are relevant for underfrequency:
Stg (n) f+t Status: determines whether the stage is underfrequency, overfrequency, or disabled
●
Stg (n) f+t Freq: defines the frequency pickup setting
●
● Stg (n) f+t Time: sets the time delay
Note:
This section refers to advanced frequency protection. The basic frequency protection works in a similar manner, but the
setting names and DDB signal names are different.
3.2

UNDERFREQUENCY PROTECTION LOGIC

Freq
Averaging
Stg 1 f+t Freq
Stage 1
Enabled
Stg 1 f+t Status
Under
Adv Freq Inh
1
Freq Not Found
V<B Status
Enabled
1
UV Block
V00850

Figure 126: Underfrequency logic (single stage)

If the frequency is below the setting and not blocked the DT timer is started. If the frequency cannot be
determined, the function is blocked.
Note:
This section refers to advanced frequency protection. The basic frequency protection works in a similar manner, but the
setting names and DDB signal names are different.
238
DT
&
Note: This diagram does not show all stages . Other stages follow similar principles.
P14x
Stg1 f+t Sta
Stg1 f+t Trp
P14xEd1-TM-EN-1