ABB Relion REG670, Applications Manual

Page: 397 / 780

• Line to earth faults
• Double line to earth faults
• Line to line faults
• Open conductors, includes
•
Broken line conductors
• Malfunction of one pole of a circuit breaker
.
9.12.3 Setting guidelines
When inverse time overcurrent characteristic is selected, the operate
time of the stage will be the sum of the inverse time delay and the set
definite time delay. Thus, if only the inverse time delay is required, it
is important to set the definite time delay for that stage to zero.
9.12.3.1 Operate time characteristic
Negative sequence time overcurrent protection for machines NS2PTOC provides two
operating time delay characteristics for step 1 and 2:
• Definite time delay characteristic
• Inverse time delay characteristic
The desired operate time delay characteristic is selected by setting CurveType1 as
follows:
• CurveType1 = Definite
• CurveType1 = Inverse
Definite time delay
[1]
is independent of the magnitude of the negative sequence
current once the start value is exceeded, while inverse time delay characteristic do
depend on the magnitude of the negative sequence current.
This means that inverse time delay is long for a small overcurrent and becomes
progressively shorter as the magnitude of the negative sequence current increases.
Inverse time delay characteristic of the NS2PTOC function is represented in the
equation
2
2
I t K
=
, where the K1 setting is adjustable over the range of 1 – 99 seconds.
A typical inverse time overcurrent curve is shown in Figure 202 .
[1] The definite time delay is described by the setting t1, which is the time between activation of start and trip outputs.
1MRK 502 071-UEN -
Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 391
Application manual