Application; Signals - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.2.1.6
4.2.1.7
272
Operating curve type
(18) Inv. Curve B
(19) Inv. Curve C
(20) Programmable

Application

Overvoltage in a network occurs either due to the transient surges on the network or due
to prolonged power frequency overvoltages. Surge arresters are used to protect the
network against the transient overvoltages, but the relay's protection function is used to
protect against power frequency overvoltages.
The power frequency overvoltage may occur in the network due to contingencies such as:
• The defective operation of the automatic voltage regulator when the generator is in
isolated operation.
• Operation under manual control with the voltage regulator out of service. A sudden
variation of load, in particular the reactive power component, gives rise to a
substantial change in voltage because of the inherent large voltage regulation of a
typical alternator.
• Sudden loss of load due to the tripping of outgoing feeders, leaving the generator
isolated or feeding a very small load. This causes a sudden rise in the terminal voltage
due to the trapped field flux and overspeed.
If a load sensitive to overvoltage remains connected, it leads to equipment damage.
It is essential to provide power frequency overvoltage protection, in the form of time
delayed element, either IDMT or DT to prevent equipment damage.

Signals

Table 217: 59 Input signals
Name Type
V_A_AB SIGNAL
V_B_BC SIGNAL
V_C_CA SIGNAL
BLOCK BOOLEAN
Default Description
0 Phase to ground voltage A or phase to phase voltage AB
0 Phase to ground voltage B or phase to phase voltage BC
0 Phase to ground voltage C or phase to phase voltage
CA
0=False Block signal for activating the blocking mode
1MAC504801-IB E
620 series ANSI
Technical Manual