ABB Relion 615 series Applications Manual page 36

Section 3
REM615 variants
30
GUID-47B67152-61E5-4948-9EAC-EDE15641C455 V1 EN
Figure 13: Phase unbalance protection
Two negative-sequence overcurrent stages (MNSPTOC1 and MNSPTOC2) are
offered for phase unbalance protection. These functions are used to protect the
motor against phase unbalance caused by, for example, a broken conductor. Phase
unbalance in network feeding of the motor causes overheating of the motor.
The phase reversal protection (PREVPTOC1) is based on the calculated negative
phase-sequence current. It detects too high NPS current values during motor start
up, caused by incorrectly connected phases, which in turn causes the motor to
rotate in the opposite direction.
The negative-sequence protection and phase reversal protection is blocked if the
current circuit supervision detects failure in current measuring circuit or if the
external information of reverse network rotation is activated by a binary input
(X110:5-6).
The loss of load situation is detected by LFLPTUC1. The loss of load situation can
happen, for example, if there is damaged pump or a broken conveyor.
1MRS756885 A
REM615
Application Manual