ABB REF615 - Negative Sequence Overvoltage Protection NSPTOV

5.5.4 Negative sequence overvoltage protection NSPTOV
5.5.4.1 Identification
Table 72: Function identification
IEC 61850 identification: NSPTOV
IEC 60617 identification: U2>
ANSI/IEEE C37.2 device number: 47O-
5.5.4.2 Functionality
The negative sequence overvoltage protection NSPTOV is used to detect negative
phase sequence overvoltage conditions. NSPTOV is used for protection of machines.
The function starts when the negative phase sequence voltage exceeds the set limit.
NSPTOV operates with the definite time (DT) characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
the definite timer or the function itself, if desired.
5.5.4.3 Application
A continuous or temporary voltage unbalance may appear in the network for various
reasons. Mainly, the voltage unbalance occurs due to broken conductors or
asymmetrical loads and is characterized by the appearance of a negative sequence
component of the voltage. In rotating machines, the voltage unbalance results in a
current unbalance, which heats the rotors of the machines. The rotating machines,
therefore, do not tolerate continuous negative phase sequence voltage higher than
typically 1-2 percent x U
n
.
The negative phase sequence current I
2
, drawn by an asynchronous or a synchronous
machine, is linearly proportional to the negative phase sequence voltage U
2
.
Typically, I
2
is 5...7 times U
2
.
The negative sequence overcurrent NSPTOC blocks are used to accomplish selective
protection against the voltage and current unbalance for each machine separately.
Alternatively, the protection can be implemented with the NSPTOV function,
monitoring the voltage unbalance of the bus bar.
If the machines have unbalance protection of their own, the NSPTOV operation can
be applied as a backup protection or it can be used as an alarm. The latter can be
applied when it is not required to trip loads tolerating voltage unbalance better than
the rotating machines.
If there is a considerable degree of voltage unbalance in the network, the rotating
machines should not be connected to the network at all. This logic can be implemented
by inhibiting the closure of the circuit breaker if the NSPTOV operation has started.
Section 5 1MRS756378 D
Protection functions
170 REF615
Application Manual