On the display
The control center displays the message VSD - MOTOR CURRENT IMBALANCE. The manuals print the display text in this single form. The message is listed among the safety shutdown messages of the unit.
What it means
This safety shutdown responds to an unbalance among the currents of the three phase compressor motor. One manual gives the meaning as motor phase current imbalance above 30%. The other manual gives it as a current imbalance value greater than 32 amps. That value is found by comparing every phase of motor current with the average current of the three phases. The check is held off until the chiller has been running for at least 45 seconds and the average motor current of the three phases is greater than 80% of the programmed 100% Full Load Amps of the chiller. Detection takes place in the Variable Speed Drive, which advises the OptiView Control Center Microboard of the unbalance condition via serial communications.
Why it appears
- The imbalance among the three phase compressor motor currents exceeded 30% without interruption for 45 seconds.
- The current imbalance value, obtained by comparing every phase with the three-phase average, stayed greater than 32 amps for 45 seconds.
Setpoints and thresholds
- Trip limit in percent: motor phase current imbalance above 30%.
- Trip limit in amps: current imbalance value greater than 32 amps.
- Trip duration: the imbalance must be present continuously for 45 seconds.
- Arming: the check of the imbalance starts only once the chiller has run for at least 45 seconds.
- Load condition: the average motor current of the three phases must be greater than 80% of the programmed 100% Full Load Amps of the chiller.
- Average: the average of the three phases is the sum of the three phase currents divided by 3.
- Example from the manuals: three motor current RMS values of 200, 225 and 240 amps give an average of 233 amps, and an imbalance of 33 amps maintained for 45 seconds generates the shutdown.
Reset and restart
Both manuals give the same action for this shutdown: The chiller can be started after the CLEAR faults button is pressed.
Questions engineers ask
What does VSD - MOTOR CURRENT IMBALANCE mean on a YORK YMC2?
It is a safety shutdown for an unbalance among the currents of the three phase compressor motor. The manuals state the limit as motor phase current imbalance above 30% and, in the second manual, as a current imbalance value greater than 32 amps, in each case for 45 seconds.
How is a YORK YMC2 restarted after a VSD - MOTOR CURRENT IMBALANCE shutdown?
Both manuals give the same action: the chiller can be started after the CLEAR FAULTS button is pressed.
When does the YMC2 begin checking motor current imbalance?
The check waits until the chiller has run for at least 45 seconds and the average motor current of the three phases is greater than 80% of the programmed 100% Full Load Amps of the chiller.
What imbalance value trips the VSD - MOTOR CURRENT IMBALANCE shutdown?
An imbalance value greater than 32 amps for 45 seconds, found by comparing every phase of motor current with the average of the three phases. In the manuals' example, an imbalance of 33 amps held for 45 seconds generates the shutdown.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YMC2; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YMC2 messages: fault codes · YORK YMC2 documentation · YORK manuals