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Just out of curiosity... did you check the resistance between the different motor windings and find them equal/close? Not incredibly "scientific", but at least might help explain an unbalanced leg.

Originally Posted by BLohman

Okay... once I got my mind out of the gutter... I've seen "competent" guys megger stuff w/o lifting the motor lead off the starter. Which is fine unless you have a soft start/vfd. You might have taken some damage during the megger process if the leads were still made up (which may have added another problem). As for the moisture... if you do dry/clean the components and that appears to correct the problem, then maybe consider installing a heater in the enclosure to control that moisture?

Megger was done by taking off all leads. First megger was on the studs connected to the motor only. Since this could be a fault in the studs or the motor, we dismantled the studs to the motor. Motor megger was fine.

Okay... once I got my mind out of the gutter... I've seen "competent" guys megger stuff w/o lifting the motor lead off the starter. Which is fine unless you have a soft start/vfd. You might have taken some damage during the megger process if the leads were still made up (which may have added another problem). As for the moisture... if you do dry/clean the components and that appears to correct the problem, then maybe consider installing a heater in the enclosure to control that moisture?

Dear All.

The problem was finally solved. To conclude (hopefully it helps others in the future)
1) Chiller had intermittent tripping - it could run for days and suddenly trip with error " Solid State Starter fault" at the LCD panel of the chiller - this is basically a feedback from the Trane Starter Card which detects the SSS starter electronic module (another electronic card) is not sending back an "OK" signal to allow start of the chiller. The SSS Control card had no specific error at this stage except warnings on voltage imbalance.
2) Trips became more frequent and eventually SCR error was observed at the SSS control card.
3) Decision made to check the motor winding and studs. One paid of Studs which are connected to the motor winding was found to have insulation problems after megger test. To confirm if it was the studs or the winding itself, the motor assembly was removed - the check proved that the studs were bad and (luckily) the winding were OK.
3) Although only 2 studs were confirmed to be faulty - we replaced all 6
4) SCR fault still appeared in the SSS Control Card
5) Techs suggested possible faulty control card but could not confirm - this was based on visual inspection where capacitors in the card were damaged. New Card was ordered. New Card was installed but the fault on the SCR appeared intermittently. The damaged card was sent for a "check-up" and damaged components was replaced.
6) All SCRs was replaced although the resistance test indicated they were OK. SCRs are hard to test and best to test when it is running - not possible in this case due to the fact the chiller could not start.
7) With all replaced, another round of testing and the error was a digital input. This was traced to the temperature sensor attached to the heat sink of the SSS. All contacts were cleaned and re-connected.
8) Chiller started and is in operation for the last 2 weeks.
9) The damaged SSS Control Card which was repaired is also working fine!

This was an problem that started from possible surges in power supply and components were affected.
A quick solution would have been to just replace the entire SSS - it was a choice and possibly the original SCRs are fine but we did not want to take any more chances.
A surge suppressor device is now sourced to avoid re- occurrence.


Special thanks to Screwit - exceptional individual who took the extra effort to help. Could not have solved the problem without his support. Invaluable advice that I used to direct the techs working on the chiller!

Benshaw - excellent service and quick communication

Thanks to all others who took the trouble to reply and provide advice

Hvac_MY,

Thanks for the excellent feedback, it is appreciated by all who contribute to this site.

Thats is a lot of components to fail at once, if there are issues with the voltage supply it may pay to investigate surge suppression for the mains voltage supply as this will also assist with chiller up-time.

Originally Posted by Screwit

RTHD CHHC compressor uses ceramic motor terminal insulators, if the ceramic is cracked moisture will enter (motor teminal is exposed to suction temperature which is below due point) causing a low insulation reading.

Good job identifying the correct fault - have seen motors condemmed by those with less experience due to motor terminal issues.

HVAC_MY you have the information I sent you to test the Silicone Controlled Rectifiers

Thanks for the info. It was most helpful. I will take pictures of the system and the replaced parts once the system is up and running!

Originally Posted by Healey Nut

So now were all totally confused is it the motor the starter the SCRs the insulators ??

Sorry guys - i type fast and miss out the finer words - it should be the motor studs - the culprit because it all started from there..but there were a lot of surge issues from the utility in the recent months. I cannot confirm if the surges damaged some components over time.

Update

Originally Posted by milkyway

HVAC certainly seems knowledgable ,. Must be a typo., good job Hvac for the diagnosis

Hi...sorry was busy and away. yes, type - the motor is fine, the stud was the issue. (the first issue of many to come ). I design chilled water system but get very involved in my projects and keep close eye on performance of the system. I am not a maintenance technician and therefore I listen and learn to ensure I make informed decisions. And forums such as this is heaven sent for me because in this part of the world, knowledge is not shared freely! Thanks to the forum I know I am on the right track.


The status as of today:

1) The Control board had damaged capacitors that were replaced. The coils on the card was ok - card tested and is working well
(I purchased a new board but that is now kept as a spare - plus the new boards have a different software version which means I will have to set the parameters which is something I want to avoid at this stage)
2) Replaced all SCRs (since there was a error reading indicating SCR shorted) - 2 SCRs has fluctuating ohm readings but was still within the required spec of 8 to 50 ohm. I was told that SCRs diagnostics is not straightforward. Replaced all SCRs as we cannot afford this issue cropping up again.
3) The started system is OK but there is an external fault which has been traced to the starter module. Removed for checking.

The root cause for the problem is probably a surge or shorted circuit - i.e. capacitors damages , SCRs damaged and now the starter module.

Will update the status.

HVAC certainly seems knowledgable ,. Must be a typo., good job Hvac for the diagnosis

I you follow the entire thread pretty certain it is just a typo

The motor is fine - it was one of the connecting studs. We actually removed the studs and checked the motor. The culprit is the motor stud.
The started is confirmed as the problem - but it could be the card or the SCRs. I have asked supplier to replace the SCRs as well instead of just the cards

We actually removed the studs and checked the motor. The culprit is the motor.
The started is confirmed as the problem - but it could be the card or the SCRs. I have asked supplier to replace the SCRs as well instead of just the cards -

??

Originally Posted by Healey Nut

So now were all totally confused is it the motor the starter the SCRs the insulators ??

i thought i was reading that wrong too!

Originally Posted by HVAC_MY

I can't recall off hand how low it was. The motor is fine - it was one of the connecting studs. We actually removed the studs and checked the motor. The culprit is the motor.
The started is confirmed as the problem - but it could be the card or the SCRs. I have asked supplier to replace the SCRs as well instead of just the cards - as mentioned earlier, everyday the chiller is down, it is profit loss due to the nature of the shared saving contract

So now were all totally confused is it the motor the starter the SCRs the insulators ??

RTHD CHHC compressor uses ceramic motor terminal insulators, if the ceramic is cracked moisture will enter (motor teminal is exposed to suction temperature which is below due point) causing a low insulation reading.

Good job identifying the correct fault - have seen motors condemmed by those with less experience due to motor terminal issues.

HVAC_MY you have the information I sent you to test the Silicone Controlled Rectifiers

Originally Posted by KnewYork

When you say megger readings were low...how low? If you have a motor problem, why are you pointing at the starter?

I can't recall off hand how low it was. The motor is fine - it was one of the connecting studs. We actually removed the studs and checked the motor. The culprit is the motor.
The started is confirmed as the problem - but it could be the card or the SCRs. I have asked supplier to replace the SCRs as well instead of just the cards - as mentioned earlier, everyday the chiller is down, it is profit loss due to the nature of the shared saving contract

Originally Posted by HVAC_MY

Nope. Not the softstarter. There studs connected to the motor - disconnected all wiring to the studs - from softstater , and megged the studs while attached to the motor. One of the studs resistance was very low. Megger was done by the supplier of the chiller.

When you say megger readings were low...how low? If you have a motor problem, why are you pointing at the starter?

Nope. Not the softstarter. There studs connected to the motor - disconnected all wiring to the studs - from softstater , and megged the studs while attached to the motor. One of the studs resistance was very low. Megger was done by the supplier of the chiller.

Originally Posted by HVAC_MY

we megged the studs connected to the motor (before and after) and the motor by itself

Are you saying you megged the soft starter terminals?

Originally Posted by steveoo

When you megged motor did you remove leads from soft start?

Hi

Yes, completely removed all connections including controls etc. we megged the studs connected to the motor (before and after) and the motor by itself

When you megged motor did you remove leads from soft start?