CYG PRS-7367 User Manual

Protection Functions
80 PRS-7367
and underground cables.
The operation of 46D is based on the ratio of positive and negative sequence currents. This gives
better sensitivity and stability compared to plain negative sequence current protection since the
calculated ratio of positive and negative sequence currents is relatively constant during load
variations.
3.9.4 46D Settings
Table 3.9-3 46D settings
No.
Name
Values(Range)
Unit
Step
Default
Description
1
46D_Ratio_I2/I1
10~100
%
0.01
20%
Current ratio setting I2 /
I1
2
46D_Op_T
0.1 -30.00
s
0.001
0.1
Operate time delay
3
46D_Ena
0~1
-
1
0
Operation
Disable/Enable
4
46D_Reset_T
0.0- 60.000
s
0.001
0.2
Reset time delay
5
46D_Min_PhCur_St
r
0.04In~20In
A
0.01In
20In
Minimum starting phase
current
3.10 Negative sequence current protection 46N
3.10.1 46N Overview
This relay provides one stage of negative sequence overcurrent protection.
The application of negative sequence overcurrent protection has a special significance to motors.
Unbalanced loads create counter-rotating fields in three-phase induction motors, which act on the
rotor at double frequency. Eddy currents are induced on the rotor surface, which causes local
overheating in rotor end zones and the slot wedges. This especially goes for motors which are
tripped via vacuum contactors with fuses connected in series. With single phasing due to
operation of a fuse, the motor only generates small and pulsing torques such that it soon is the
normally strained assuming that the torque required by the machine remains unchanged. In
addition, the unbalanced supply voltage introduces the risk of thermal overload. Due to the small
negative sequence reactance even small voltage asymmetries lead to large negative sequence
currents.
3.10.1.1 Function Block
The function block of the protection is as below.

CYG PRS-7367 Specifications

General

Brand	CYG
Model	PRS-7367
Category	Control Unit
Language	English