One of the morriss Crane in a factory was retrofitted last year by a contractor. But since then it is been used very rarely.
Last month this crane failed four times in the span of 15 Days.
All the four times problem was in its Incoming section of rectifier and precharge circuit.
Inverter section never went faulty. All the failures were only in Long Travel drive. L.T drive is used to drive four motors parallel.
Replacing the defective cards Drive was repaired every time. But reason for the failure was untraceable. The input contactor found short few times. And was replaced.
The fourth failure was with Damaged Precharge resistor as well as the welded input Contactor.
Interaction with customer has enabled us to think more, following points were enlightened.
- Last time input contactor of L.T drive founds chattering during the operation and was been replaced .
- All the drives were used to trip on under voltage fault.
- The current collector leads were found damaged last time ,two out of eight were wearied off, and never been aligned properly since beginning. They had caused direct short circuit many times.
- During one of the operation the swing drive had misbehaved and people escaped narrowly.
- The crane is operated on radio remote control, which is locally made. Without any CE or UL ratings. Operation frequency for it is 440MhZ.
We strongly suspect on the operation and installation of this radio receiver. This is mounted just near to L.T panel. And have used many interlock for operation. Mains contactor was also enabled through Radio remote.
Hence we suggest to by pass this radio remote temporarily. And simultaneously replaced the Breaking Module.
Since then the drive is working very fine. Trials were taken continuously for 1 week And drive never tripped with Under voltage fault.
As it was hard to believe for people that radio remote can produce this type of damage to drive, as they had multiple reasons in favor of it. Everyone was suspecting the replaced Breaking Module.
The breaking Module (50Kw and 40Amp max) is tested separately and found perfectly ok.
I have read somewhere that range of RFI generated by drive is around 7 MHz. And Radio remote is working on 443Mhz.Again it is difficult for me to explain how can these create damage to inverter.
Do any one have some inputs for me.