We’ve a York Centrifugal Chiller installed at our site with the following specs
Series YT Codepak
Unit Model YTH3J3E35COG
Capacity 500 Tons
Compressor Model YDTL.126
Starter SSS 26L-50A
There was a leak in the purge system and we recently had the refrigerant refilled. The chiller was out of service for a good 2 months or so. Before the leak, the chiller was running perfectly fine. After the refill, ‘High Line Voltage’ indication started coming, all the voltages were checked and were found to be within acceptable ranges.
During the course of troubleshoot, Trigger Board (031-00925-003) was changed, then the logic card (031-00936-004) and finally the Micro Board (031-01065-001). After replacement of Micro Board, the indication disappeared and York Chiller was turned on. It completed its start sequence properly but after approximately five minutes of running, “Coast Shutdown” indication appeared meaning the York Chiller is shutting down, while the chiller was still running. Chiller was not accepting any command; therefore it was turned off from the circuit breaker. After checking all the jumpers on the micro card the breaker was switched on again and the motor started without any start command effectively bypassing the soft starter. The breaker was immediately turned off. The SCRs were checked and were found shorted. (Three shorted, one on each phase).
All six SCRs and the Trigger Board (031-00925-003) were replaced. The circuit breaker was switched on; this time around the motor didn’t start automatically without the command. The start command was given and after the sequence initiation it the chiller started and tripped immediately. Our supply scheme is such that the chiller is supplied to by a 400V 3Ph feeder which in turn is supplied to by an 11kV distribution grid. When the chiller tripped, the 11kV circuit breaker tripped as well clearly indicating that a significant amount of inrush current went through (we didn’t have any measurement on the current available at that point). For reference, the normal startup current of this motor is around 2400 Amperes and the FLA is 515 Amperes. When we inspected the SCR’s, two of them on a particular phase were found to be shorted.
The faulty SCR’s were replaced, motor was meggered and was found ok. Furthermore, the motor was decoupled from the compressor and tested and was found to be working perfectly fine.
During the decouple we found that the coupling on the compressor side had been damaged with the four of the six bolts completely sheared off. When the compressor was checked, it was found to be rotating perfectly fine (with hands).
The coupling was replaced and the chiller was started again with absolutely no problems.
My question here is that what could have possibly caused the coupling damage and bolt shearing since the compressor and the motor are perfectly fine?
I’ll be posting the pictures of the damaged coupling.