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CHAPTER 5: SETPOINTS
PROTECTION ELEMENTS
MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
5–47
NOTE
NOTE: NCV - Nominal Control Voltage - is calculated depending on Aux VT connection:
If Aux VT is set for Direct:
NCV = MNV /
√
3
If Aux VT is set for VabVT, VbcVT, VcaVT, VanVT, VbnVT, VcnVT:
NCV = Aux VT secondary
For additional information, refer to:
Phase undervoltage
Ground fault
protection
When motor stator windings become wet or otherwise suffer insulation deterioration, low
magnitude leakage currents often precede complete failure and resultant destructive fault
currents. Ground fault protection provides early detection of such leakage current,
allowing the motor to be taken offline in time to limit motor damage. However, if a high
magnitude ground fault occurs that is beyond the capability of the contactor to interrupt,
it is desirable to wait for the fuses or an upstream device to provide the interruption.
The ground fault protection will alarm or trip when the ground current magnitude meets or
exceeds the pickup for the specified time, provided that the maximum phase current is less
than 8 × FLA. When used with a core-balance CT, this protection becomes a sensitive
ground fault protection.
A ground fault trip is a serious event, and therefore results in a lockout that can not be
reset until the motor has cooled except with a level 2 or level 3 security login.
NOTE
NOTE:
The ground fault protection pickup setpoints are entered in %FLA if the
Ground CT
setpoint
is selected as "Residual," or in units of primary amps if a 50:0.025 core balance CT is used
and the ground CT is selected as “CBCT 2000:1”.
Various situations (for example, contactor bounce) may cause transient ground currents
during motor starting that exceed the ground fault pickup levels for a very short period of
time. The delay can be fine-tuned to an application so it still responds very quickly, but
rides through normal operational disturbances. Normally, the ground fault time delays are
set as short 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 or DC component. This momentary DC component will cause
each of the phase CTs to react differently, and cause a net current into the ground input of
the relay.
The following setpoints are available for the ground fault protection element.
Ground Trip Level
Range: 10 to 100% FLA in steps of 1%, or OFF, when Ground CT type is set to "Residual"
Range: 0.5 to 15.0 A in steps of 0.1 A, when Ground CT type is set to "CBCT 2000:1"
Default: OFF
This setpoint specifies the ground fault trip pickup level. A value of “OFF” disables the
ground fault trip function.
Ground Trip Delay on Start
Range: 0.0 to 10.0 s in steps of 0.1 s
Default: 0.0 s
This setpoint specifies the time that the motor ground fault current must meet or exceed
pickup to generate a ground fault trip when the motor is in a starting condition.
Ground Trip Delay on Run
Range: 0.0 to 5.0 s in steps of 0.1 s
Default: 0.0 s
This setpoint specifies the time that the motor ground fault current must meet or exceed
pickup to generate a ground fault trip when the motor is in a running condition.
Summary of Contents for Multilin MM300
Page 20: ...1 14 MM300 MOTOR MANAGEMENT SYSTEM INSTRUCTION MANUAL SPECIFICATIONS CHAPTER 1 INTRODUCTION ...
Page 184: ...6 8 MM300 MOTOR MANAGEMENT SYSTEM INSTRUCTION MANUAL COMMANDS CHAPTER 6 DIAGNOSTICS ...
Page 198: ...A 6 MM300 MOTOR MANAGEMENT SYSTEM INSTRUCTION MANUAL REPAIRS CHAPTER A APPENDIX A ...