Ampcontrol Pty Ltd
– ABN 28 000 915 542
IPM V2 USER MANUAL
IPM2B003 Revision 15
– MAY/18
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 37 of 83
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7.1 Overload Protection
The motor overload function is based on a thermal model of the motor. The three phase currents are
squared to provide the I
2
R heating input to the motor model. The selected „Stopped Cooling Ratio‟
determines the cooling output for the model.
The state of the thermal model is shown by the „Thermal Accumulator‟, which can be viewed on the
'Current/Volts Information' level on the display. The thermal accumulator represents the motor
temperature. When the accumulator reaches 100%, a Motor Overload Trip occurs.
The full load current is selected via the „100% Current‟ setting (Level 6, Screen 2) and can be set
between 0.5125A and 640A in 448 steps. See the Appendix section of this manual for the respective Full
Load Current Selection tables for a 100:1 CT or 1000:1 CT.
The trip time is selected via the „O/L Trp t @ 6x‟ setting (Level 6, Screen 6). It is a function of the current
and the selected trip time curve. Refer to APPENDIX 6: Drawings for details of the motor overload and
short circuit trip times.
The fifteen (15) motor overload curves allow trip settings from 3 to 40 seconds at six (6) times FLC and
are shown for both cold and hot conditions. The hot curve corresponds to the trip time after the motor
has been running at the selected full load current indefinitely.
The trip time can be calculated as follows:
Where:
C = Curve Selected
I = Current (FLC = 1)
A% = Initial Thermal Accumulator Value
NOTE
For Cold Start A = 0% and on Hot Start, A = 89%.
The motor manufacturer's data should always be consulted to select the appropriate settings for the
motor being protected. Typically, the capacity of a cold motor is given at six times its rated current.
The IPM Relay's trip curves can then be used to select the trip time curve, which best suits the motors
overload capacity.
The motor overload trip latches once the thermal accumulator reaches 100% and can only be reset once
the thermal accumulator falls below a pre-set value. The pre-set
value is selected via the „O/L Rst Level‟
setting (Level 6, Screen 8) and can be set to 30%, 40%, 50%, 60%, 70%, 80%, 90%, A-30%, A-40%, A-
50%, A-60%, A-70%, A-80%, A-90%. The
“A-“settings automatically reset a motor overload trip once the
thermal accumulator falls below the set value. Otherwise the trip has to be reset manually by pressing
the keypad „RESET‟ button or activating the „RESET‟ digital input once the thermal accumulator has
fallen below the set value.
An emergency restart on a hot motor can be achieved by zeroing the thermal accumulator
memory. This is done by closing the Lock input and Reset key/digital input simultaneously for
1.5 seconds
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