# Cutler Hammer Easy Start Soft Start for Motors (Trouble)



## KevinKM (Oct 8, 2012)

Got a call from an operator today that a motor has stopped worked tried resetting and motor will not restart. Get there to check it out find that the soft start logix indicates a phase unbalance. I check out the connections and fuses on the CT all seems well. This part of the plant we actually generate our own power for so we have a good bit of monitoring and control for our generators. Power factor is .84 and voltage is maintaining about 480 to 482 at the max as well, frequency is 59.95 to 60 HZ. Nothing out of the ordinary. There are two identical motors with the same exact buckets as the one I am having trouble with and both are running fine. Reset the board and put the motor on. Stick around and check things for about ten minutes all is well. Thirty Minutes later get a call motor is down again. Return and same indication as before. tried to find something after about thirty minutes and no results. I am not too familiar with these electronics and I hate to blame it on the electronics, but tomorrow going to do some checks on the SCR's in the logix. Hate to blame the controls, but I have two that are exact same settings and are running fine. Any suggestions or comments? Thanks for the help in advance.


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## nolabama (Oct 3, 2007)

Swap buckets and see if it follows the bucket


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## JRaef (Mar 23, 2009)

KevinKM said:


> Got a call from an operator today that a motor has stopped worked tried resetting and motor will not restart. Get there to check it out find that the soft start logix indicates a phase unbalance. I check out the connections and fuses on the CT all seems well. This part of the plant we actually generate our own power for so we have a good bit of monitoring and control for our generators. Power factor is .84 and voltage is maintaining about 480 to 482 at the max as well, frequency is 59.95 to 60 HZ. Nothing out of the ordinary. There are two identical motors with the same exact buckets as the one I am having trouble with and both are running fine. Reset the board and put the motor on. Stick around and check things for about ten minutes all is well. Thirty Minutes later get a call motor is down again. Return and same indication as before. tried to find something after about thirty minutes and no results. I am not too familiar with these electronics and I hate to blame it on the electronics, but tomorrow going to do some checks on the SCR's in the logix. Hate to blame the controls, but I have two that are exact same settings and are running fine. Any suggestions or comments? Thanks for the help in advance.


First off: You said "check out the connections *and fuses on the CT* all seems well." That has me worried, you should NEVER have fuses on a CT circuit, but maybe you meant CT as in something other than Current Transformer? If you meant Control (Power) Transformer, then OK. 

Those are old Westinghouse soft starters, the name later changed to C-H because the C-H soft starter at that time was worse junk, so when they bought Westinghouse they scrapped their old soft starter line. I serviced them for a while and on those it was either the Current Sensing circuit, or it was the SCR Gate circuit if you got that Current Unbalance light. First off use a clamp-on and see if the current really is unbalanced. If it is, then you can eliminate the Current Sensing circuit and move on to the Gate Circuit. If the current is relatively balanced (or you have a Bypass Contactor), then it is something in the Current Sensing circuit.

If it is the Current Sensing circuit (because the current really is balanced, but the PC board THINKS it is not), then you have to check the connections really thoroughly. Look at the CT (Current Transformers, the black donut looking things) circuits, make sure they are all good, especially where the CT leads plug into the PC board. There are some cheap little Amphenol connectors on there and if they get dirty or loose, you lose the connection from one of the CTs and the board thinks there is no current on one phase. If those are all OK, then it is either a bad CT (unlikely) or a problem on the PC board. If you have a spare board, swap it out, it's not worth the trouble to try to fix it yourself. If you don't have a spare, good luck. The Easy Start has been obsolete for a while now, I think they quit selling them in around 1998 or so. I'm not sure if C-H still supports it. But you can probably still get it repaired by someone like Electrical South. If you don't have a spare and can't wait for it to get repaired, it's time to junk it and buy something newer, then keep the rest of that one as spares for the others.

If it was not the Current Sensing circuit (because the current really is unbalanced), then eliminate all the obvious stuff first, like bad motor connections, breaker connections, stuff like that. After that, THEN do the SCR checks. If the SCR itself is bad, the current imbalance would happen immediately on start-up and you would also get a Shorted SCR indicator. But if the Gate cathode is bad or going bad, then that's how you could get a failure after it's been running a while. Here is the test procedure for the gate circuits on the SCRs themselves:


*Open or Shorted Gate 
*- Remove the 3
gate plugs, J-101, J-201, J-301, from the
logic board. The ohmmeter
measurements should be made between
pins 1 to 4 and pins 3 to 6 of each plug.
The typical ohmic value should be
between 5 and 200 ohms. If readings of
near zero ohms, or near infinity, are​measured, replace the SCR.

If the SCRs check out OK, again, it's the PC board and not worth trying to find the internal problem to fix. See above. 
​


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## micromind (Aug 11, 2007)

I would add, if you're doing anything with CTs, make absolutely sure that both the secondary leads are connected to a load or shorted any time there's current in the primary. 

To operate a CT with current in the primary (no matter how little), and the secondary circuit open will almost always destroy the CT.


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## KevinKM (Oct 8, 2012)

JRaef said:


> First off: You said "check out the connections *and fuses on the CT* all seems well." That has me worried, you should NEVER have fuses on a CT circuit, but maybe you meant CT as in something other than Current Transformer? If you meant Control (Power) Transformer, then OK.
> 
> Those are old Westinghouse soft starters, the name later changed to C-H because the C-H soft starter at that time was worse junk, so when they bought Westinghouse they scrapped their old soft starter line. I serviced them for a while and on those it was either the Current Sensing circuit, or it was the SCR Gate circuit if you got that Current Unbalance light. First off use a clamp-on and see if the current really is unbalanced. If it is, then you can eliminate the Current Sensing circuit and move on to the Gate Circuit. If the current is relatively balanced (or you have a Bypass Contactor), then it is something in the Current Sensing circuit.
> 
> ...


Did check the amps and voltage across all phases after powering back up and running the second time. Also had someone monitor voltage and current ont he bus for an imbalance and there was none. I was thinking of this, let me know what you think. The logix is powered on by the main breaker. If I turn the breaker on and no start in the motor just have the board powered up and wait and see if it trips out on a balance failure. After that checking all connections and then on to the SCR itself. Thanks,


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## JRaef (Mar 23, 2009)

KevinKM said:


> Did check the amps and voltage across all phases after powering back up and running the second time. Also had someone monitor voltage and current ont he bus for an imbalance and there was none. I was thinking of this, let me know what you think. The logix is powered on by the main breaker. If I turn the breaker on and no start in the motor just have the board powered up and wait and see if it trips out on a balance failure. After that checking all connections and then on to the SCR itself. Thanks,


If you just power it up and do not give a Start command, you will not likely get the imbalance light. What that circuit is doing is looking at the vector sum of the three phase currents through the CTs, which should come out to Zero. If it is anything other than Zero, or actually more than about 30% of the unit rating off of Zero, then it trips on imbalance. With no current going through it, the vector sum of Zero is Zero. 

If you have 2 shorted SCRs in separate phases, you would have current flow through those two phases through the motor winding even without a Start command, so that would trigger the imbalance circuit. But it would trigger the Shorted SCR protection first and it would happen immediately, not 10 minutes later. After a soft starter is done ramping, it has no idea if an SCR is shorted or not.

If as you say, the current measurements while running were balanced, then it's likely a problem in that sensing circuit and given that it happened after running a while, I'd say it's either in that CT connection or in the A/D converter on the PC board. With the power off, pull those CT connectors off inspect them closely for corrosion or wear from vibration, any black marks indicate the circuit was going open and arcing. Try cleaning them up, and at the very least, plug and unplug them a dozen times or so to try to improve the connection. If that doesn't help it, then the next likely thing is one of the A/D converters on the board. When they over heat, they tend to go high, meaning the PC board will think you have something like 10,000A on one phase, an obvious imbalance! But those are nearly impossible to replace in the field unless you can recognize them on the PCB and have some mad soldering skills. Then when you are done, that may not have been the problem! The board really needs a thorough diagnostic by someone with access to all of the component specs, that's what people like Electrical South do.


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