8 replies to this topic

[raj]

i have a Aucom ( NHP) soft starter on a 75 kw motor. when the motor starts , the rotor gives grubbing noise and doesnt move at all. i replaced the starter with a new one and that worked only for a month and i have the same problem again. on d.o.l there isnt any problem at all. any suggestions

[marke]

Hello Raj

Can you please give us more detail. ie model number and a description of load installation etc. Is this unit installed in three wire or six wire connection?
Have you contacted NHP for suport? I assume that you are in Australia.

On first glance, it sounds like the behaviour that you get when one SCR is not being turned ON.
This could be due to a number of factors, but what happened to the last unit? was it returned for service? was there any information on what the problems was?

Please check the control voltage going into the unit. It should either be 240VAC or 415 VAC. What is the actual voltage and what does the voltage do when you try to start? If the control voltage is dropping severely, then it is possible that there may be insufficient energy getting to the firing circuits.

It is also posible that you have a failed pcb which is not controlling one SCR properly.
If the unit is an IMS2, you have three yellow phase indicator LEDs on the left hand side of the panel. These glow at full brightness when the power is ON but the SCRs are not conducting. As the output voltage is increased, the LEDs get dimmer and extinguish at full output. If you watch these LEDs during a start, you can see which phase is not behaving.
You can also exchange the pcb for another one and see if the problem stays or goes away.

Another trick is to replace the motor with three 100 watt 240 volt lamps connected in star across the motor terminals. These will also give you an idea of what is hapeneing with the starter during start. All three lamps should be the same brightness during the start.

Best regards,

[GGOSS]

Hello Raj,

I am in Australia and have always found the support provided by NHP to be pretty good. Have you spoken with the Product Manager?

Regards,
GGOSS

[raj]

Hi Marke thanks for the tips, yes it is an IMS202 model and the one we had before was EMX2 model. It is a 3 wire (Bypass operation), where the bypass contactor comes in after 15s. it has 240V supply for its control operation, but 415 output. the only LED's on it are for start, run, trip and remote. we had 3 diffrent error codes appearing, 4, 7 and 8. the most obvious seemed to be 4, which is phase imbalance but we have found the phase current to be almost the same on d.o.l. we really havent done much voltage test, which i presume would be varying in the start. i havent tried the lamp test yet, which could be good idea. we have spoken to NHP about it and they reckon the starter could be faulty. but i would be really interested in knowing what is actually causing it

[raj]

sorry marke , actually there is three LEDS for each phase as you said, i will try and hook it up next week and give it another go. now would you think that having 415 volts for its control operation would be more stable than 240 V , becos i think its been picked up from one of the phases on the start contactor input.

[raj]

Hello GGOSS,

yes one of our engineers did speak to them and the suspect fault starter, but what would be actual cause of it. we also have recently installed some sinuspenta VFD supplied by NHP and its been a lot of trouble on one application. actually we had the NHP engineers on site to install for the first time. whenever the conveyor is fully loaded and is stopped for some reason, it would start at all. we have played around with few of the parameters but still not very good , as we had to deramp the preceeding conveyor a lot faster when there was a stop. this results in gaps in material and is not very good for quality tracking. we have spoken to NHP and there answer is that it could either be in speed control mode or torque control. speed control is critical to us as there is whole lot of other things synchronised with the conveyor but we also need the starting torque as well. the motor is only 75 KW with nominal current of 130 A but the VFD is capable of supplying 290 Amps for at least 2 minutes in every 20 minutes in need be. any suggestions.

[jraef]

Have you switched this discussion to a VFD now, or are you still referring to the Aucom soft starter? If the 75kW application with the soft starter is still in discussion, it appears more likely from your description of the faults that you have lost a firing circuit for at least one of the SCRs. That would explain the growling noise and the phase imbalance on soft starting only. The reasons for that failure are most likely a manufacturing flaw or excessive heat in the starter cabinet that is causing PC board components to fail. Before you just swap out the board, make sure that you don't have a heat problem.

It might be better and more clear if you start a new thread on the SinusPenta VFD application. It can get confusing to people who read these threads later on for help if you are mixing applications, especially if they happen to be the same size as these two seem to be.

[marke]

Hello Raj

It should not make any difference whether you use 240 volt control or 415 volt control provided that the voltage remains within limits and is correctly connected.

To have two failures, EMX followed by IMS2 so soon after, suggests that there is something common outside of the starters that is causing the problems. I think that I would be verifying the control voltage initially.

Best regards,

[GGOSS]

Hello raj,

I would agree with Marke re 240 / 415VAC control, this should not make a difference. In fact I would suggest 240VAC would be better.

With the EMX and IMS soft starters it is important that the control supply remains within specification. If this reduces by 25 - 30% during motor starting, it is possible that SCR missfiring will occur. This may have something to do with what you are experiencing at the momment.

More details would allow the members of this forum to guide you further.

Regards,
GGOSS