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Thermal Capacity Reset Method
It is not possible to reset (to empty) the thermal capacity.
Reset, of "Thermal Level 2", is prevented until
"Thermal Capacity "cools down" bellow 50%. Therefore, even for
a “Key Holder” reset of Thermal Level 2 trip is not possible for a cooling down period of time.
Emergency Restart
If one of the Discrete inputs A,B,C or D is configured as an Emergency Restart input and if this input
(Emergency Restart Switch) is closed, then the Thermal Capacity automatically resets to 0 every time the motor
is stopped. It is done to allow immediate restarting even if motor is hot. Closing the Emergency Restart switch
while motor is already stopped causes also an immediate reset of the thermal capacity. As long as motor is
running, the Emergency Restart switch has no effect. Therefore the MPS3000 can still trip for Thermal Level 2
even if the Emergency Restart switch is closed.
Note: If an Emergency Restart input is used, RTD Bias should be set to OFF to ensure resetting of the Thermal
capacity while motor is stopped.
Warning: Use only for emergency case. Open switch immediately after Emergency is ended.
Unbalance Level 1 (Unbalance Level 1)
Current unbalance is the Ratio between motor’s Negative Sequence current to its Positive Sequence current.
Unbalance = I
N
/ I
P
(Limited to: Unbalance <= 100%)
If Motor average RMS current is less than the rated Motor FLC, then the Unbalance value is decreased by the
factor Iavg / FLC, where Iavg is the RMS average of the three phase currents.
Unbalance = (I
N
/ I
P) * (
Iavg / FLC)
This method prevents nuisance alarming at low currents. The MPS3000 initiates an alarm, UNBALANCE MIN T
seconds after the actual unbalance value increases above 50% of Unbalance Level 2 setting.
Auto reset, when Enabled, occurs when the actual unbalance decreases to below 50% of "Unbalance Level 2"
setting, or when motor stops or trips.
Unbalance Level 2 (Unbalance Level 2)
Unbalance Level 2 setting, determines the minimum value of actual unbalance for Unbalance level 2 fault.
If the actual unbalance exceeds Unbalance Level 2 setting, a time delay is initiated. The time delay is related to
Unbal. Max. Time parameter, and to the inverse of the square of the actual unbalance (smaller delay for larger
unbalance). Minimum value of the time delay is UNBALANCE MIN T seconds.
Auto reset, when enabled, occurs when the actual unbalance decreases to below Unbal. Level 2 setting, or
when motor stops or trips. See next figure to select the required trip time for any unbalance value.
Note:
Mains phase sequence (positive or negative) is used while calculating positive and negative sequence currents.
Mains phase sequence is determined, using to the mains (three phase) voltages.
If the MAINS (all three phases) is not connected to the MPS3000, positive MAINS sequence is assumed. If
currents negative sequence is present, Unbalance Trip (if enabled) as well as wrong K factor (Unbalance Bias
for Thermal Overload) influence is expected.
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