Negative-Sequence Time Overcurrent Protection For Machines Ns2Ptoc; Identification; Functionality - ABB REG650 Technical Manual

1MRK 502 048-UEN A
8.9
8.9.1
8.9.2
Technical manual
Function Range or value
Critical impulse time, 10 ms typically at 2 to 0 x U
undervoltage
Impulse margin time, 15 ms typically
undervoltage
Operate value, (2-200)% of UBase
overvoltage
Timers (0.000-60.000) s
Negative-sequence time overcurrent protection for
machines NS2PTOC

Identification

Function description
Negative sequence time overcurrent
protection for machines

Functionality

Negative-sequence time overcurrent protection for machines NS2PTOC is intended
primarily for the protection of generators against possible overheating of the rotor
caused by negative sequence current in the stator current.
The negative sequence currents in a generator may, among others, be caused by:
• 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
where:
I
2
t
set
IEC 61850 IEC 60617
identification identification
NS2PTOC
2
=
I t K
as defined in standard IEEE C50.13.
2
is negative sequence current expressed in per unit of the rated
generator current
is operating time in seconds
Section 8
Current protection
Accuracy
-
-
± 0.5% of U at U<U
r r
± 0.5% of U at U>U
r
± 0.5% ± 25 ms
ANSI/IEEE C37.2
device number
2I2> 46I2
243