5–64
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Note
The
GROUND FAULT ALARM PICKUP
and
GROUND FAULT TRIP PICKUP
settings are entered in
units of ‘
×
CT’ if the Ground CT is programmed as 1 A or 5 A Secondary or in units of ‘A’ is
the Ground CT is programmed as “50:0.025”.
The Ground Fault element functions as follows. Once the ground current magnitude
exceeds the Pickup Level ×
GROUND CT PRIMARY
(see 5.3.1: Current Sensing on page –17)
for the time specified by the delay, a trip and/or alarm will occur. There is also a backup trip
feature that can be enabled. If the
GROUND FAULT TRIP BACKUP
is “On”, and a Ground Fault
trip has initiated, a second trip will occur if the ground current persists longer than the
GROUND FAULT TRIP BACKUP DELAY
. It is intended that this second trip be assigned to
2 Auxiliary or 3 Auxiliary, which would be dedicated as an upstream breaker trip relay. The
GROUND FAULT TRIP BACKUP DELAY
must be set to a time longer than the breaker clearing
time. Whenever the output relay assigned to the backup trip operates, it will stay latched
regardless of how the trip relay is configured for the Ground Fault element.
Note
Care must be taken when turning On this feature. If the interrupting device (contactor or
circuit breaker) is not rated to break ground fault current (low resistance or solidly
grounded systems), the feature should be disabled. Alternately, the feature may be
assigned to an auxiliary relay and connected such that it trips an upstream device that is
capable of breaking the fault current.
Various situations (e.g. contactor bounce) may cause transient ground currents during
motor starting that may exceed the Ground Fault pickup levels for a very short period of
time. The Ground Fault time delays are adjustable in 10 ms increments. The delay can be
fine tuned to an application such that it still responds very fast, but rides through normal
operational disturbances. Normally, the Ground Fault time delays are set as quick as
possible, that is, 0 ms. Time may have to be increased if nuisance tripping occurs.
Special care must be taken when the ground input is wired to the phase CTs in a residual
connection. When a motor starts, the starting current (typically 6 × FLA for an induction
motor) has an asymmetrical component. This asymmetrical current may cause one phase
to see as much as 1.6 times the normal RMS starting current. This momentary DC
component will cause each of the phase CTs to react differently and the net current into
the ground input of the 469 will not be negligible. A 20 ms block of the ground fault
elements when the motor starts enables the 469 to ride through this momentary ground
current signal.
The overreach filter removed the DC component from the asymmetrical current present at
the moment a fault occurs. This results in no overreach whatsoever, however, the response
time slows slightly (10 to 15 ms) but times still remain within specifications.
5.7.7
Phase Differential
PATH: SETTINGS
ZV
S6 CURRENT ELEM.
ZV
PHASE DIFFERENTIAL
MESSAGE
GROUND FAULT TRIP
BACKUP DELAY: 200
Range: 10 to 2000 ms in steps of 10
PHASE
[
PHASE DIFFEREN-
TIAL
Range: Off, Latched, Unlatched
Summary of Contents for 469
Page 62: ...2 16 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL CHAPTER 2 INTRODUCTION ...
Page 90: ...3 28 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL CHAPTER 3 INSTALLATION ...
Page 292: ...6 42 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL CHAPTER 6 ACTUAL VALUES ...
Page 313: ...A APPENDIX 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL A 7 HGF5C 808841A1 HGF8 808842A1 ...
Page 315: ...A APPENDIX 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL A 9 808712A1 CDR ...
Page 320: ...A 14 469 MOTOR MANAGEMENT RELAY INSTRUCTION MANUAL A APPENDIX ...