ABB REG670 - Function Block

• Unbalanced loads
• Line to line faults
• Line to earth faults
• Broken conductors
• Malfunction of one or more poles of a circuit breaker or a disconnector
NS2PTOC can also be used as a backup protection, that is, to protect the generator in
case line protections or circuit breakers fail to clear unbalanced system faults.
To provide an effective protection for the generator for external unbalanced
conditions, NS2PTOC is able to directly measure the negative sequence current.
NS2PTOC also has a time delay characteristic which matches the heating
characteristic of the generator
2
2
I t K=
as defined in standard IEEE C50.13.
where:
I
2
is negative sequence current expressed in per unit of the rated
generator current
t is operating time in seconds
K is a constant which depends of the generators size and design
NS2PTOC has a wide range of K settings and the sensitivity and capability of
detecting and tripping for negative sequence currents down to the continuous
capability of a generator.
In order to match the heating characteristics of the generator a reset time parameter can
be set.
A separate definite time delayed output is available as an alarm feature to warn the
operator of a potentially dangerous situation.
8.12.3 Function block
NS2PTOC
I3P*
BL OCK
BL KST1
BL KST2
BL KTR
TRIP
TR1
TR2
S TART
ST1
ST2
ALARM
NSCURR
IEC08000359.vsdx
IEC08000359-1-EN V3 EN
Figure 201: NS2PTOC function block
Section 8 1MRK502052-UEN B
Current protection
436
Technical manual