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Motors tripped by under voltage in Siemens simocode
2

Motors tripped by under voltage in Siemens simocode

Motors tripped by under voltage in Siemens simocode

(OP)
Hi
We are a power plant exporting to the utility grid. Since our power plant start operation, we had several power plant trips due to motor tripping by under voltage in Siemens Simocode. We contacted Siemens. They requested to lower the settings. But still same problem. After a discrimination study, the settings are now 160V 25.5s on some motors. Previously it was 176 V 4 s. A few days back we had a power plant trip due to under voltage following a capacitor explosion.

The motors may trip following a fault on the utility network whenever there is a voltage drop.

As a test can we disable this UV protection in the simocode? Is there a risk that the motors may burn?

Has any one encountered same problem with UV in Siemens Simocode.

Typical motor ratings are 110 kW, 132kW, 350 kW, 400 kW. Voltage 690 Vac

Thanks

RE: Motors tripped by under voltage in Siemens simocode

If the power contactor is AC powered, there is no need to program motor UV trip separately in Simocode. It can be disabled. The reason is that in case of genuine undervoltage or loss of supply, the contactor will also drop anyway. This is presuming the same AC supply that is powering motor is also powering the Contactor coil (which is the case normally).
Is there voltage dip ride-through function available in Simocode? This is also bundled with Auto restart function in some devices.
If available, it is prudent to enable the function to ride-through large voltage dips or short time loss of power (not exceeding a second or two in duration). This function is helpful in improving the power plant reliability. However, this function shall be restricted to critical motors only.

RE: Motors tripped by under voltage in Siemens simocode

(OP)
All motor control voltage is supplied by UPS to avoid voltage fluctuation stopping the motors.

RE: Motors tripped by under voltage in Siemens simocode

> the settings are now 160V 25.5s on some motors. Previously it was 176 V 4 s.

> Typical motor ratings are 110 kW, 132kW, 350 kW, 400 kW. Voltage 690 Vac

The settings seem to represent pretty dramatic sustained drops to me. 176 would be 25% voltage (or maybe sqrt3 higher if 176 represents a line to neutral voltage). For four seconds... I don't think there's any question we want the motor to trip in that scenario (at least until the voltage comes back) is there?

> As a test can we disable this UV protection in the simocode? Is there a risk that the motors may burn?

I'd say yes there is a risk you'll damage the motors. The motors may drop to a low speed with lowered air cooling flow but higher than full load current ... for how long I don't know (>25 seconds?!?)... and after that if still connected they're subject to another start when the voltage rises.


=====================================
(2B)+(2B)' ?

RE: Motors tripped by under voltage in Siemens simocode

176 V line to line or phase voltage is very low for 690 V motors to operate. +/- 10% voltage variation is the design / standards limit to prevent motor burnout. Solve the root cause of the voltage sags. Many versions of voltage stabilizers are available in the market.

Muthu
www.edison.co.in

RE: Motors tripped by under voltage in Siemens simocode

I agree with Muthu Sir. Voltage dropping to < 176V for 4s is serious in itself and any further increase is not going to help.
I think the sequence of events leading to motor trip could have been as below:
1) Initially, voltage dip is caused by fault elsewhere in the system.
2) The faulty feeder is isolated by the respective feeder protection.
3) Now, there is no fault in the system and all the motors are trying to pull up to rated speed and in the process, draw currents close to respective motor starting currents.
4) Such large currents flowing in the system prevent voltage from recovering.
5) UV protection operates to isolate the motors.
From what I think, the issue is not UV protection settings. Rather,
1) the system is not strong enough to be able to take starting current of those large motors simultaneously
2) The protection system is not isolating the faulty feeder quick enough for the motors to reaccelerate without voltage issues.
You may like to review and do needful.

RE: Motors tripped by under voltage in Siemens simocode

How weak is your power system? That capacitor failure should have caused the capacitor fuses to blow within a cycle, so even if there was a voltage dip for a cycle the motors should ride through that just fine.

RE: Motors tripped by under voltage in Siemens simocode

(OP)
Can the issue be in the way the under voltage protection in the simocode operates?
We had several power plant trips due voltage relay in four panels after network disturbance. Finally we had to bypass the voltage relays. Since then the motors have operated well without any failure.

Voltage relays are Schneider RM4TR32.





Disturbance on utility network usually are unbalance, may be on 1 phase only.

RE: Motors tripped by under voltage in Siemens simocode

Can you share .sdp configuration from Simocode devise which trips by UV protection? It will better for understanding what happened.

RE: Motors tripped by under voltage in Siemens simocode

"Can the issue be in the way the under voltage protection in the simocode operates?" - I don't have much idea about Simocode specifically. But, I have seen some voltage relays whose technical literature clearly states - in case aux voltage going <65% of rated, the output contacts change their status instantly which means the delay whatever is set for the UV protection will not be effective.
You can test the Simocode as well as other relays with a small set up in your workshop / laboratory, I suppose!

RE: Motors tripped by under voltage in Siemens simocode

You have it set up as "Application (Control Function): Soft Starter"
Is this being used on a Soft Starter then? That could be the problem right there. If you are having a power glitch, that may be making your Soft Starter reset and start ramping again, which means the Simocode is responding to the artificially lowered voltage coming from the Soft Starter. Does the Soft Starter not have it's own motor protection functions built-in?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Motors tripped by under voltage in Siemens simocode

(OP)
All 4 motors are controlled by a soft starter and a bypass contactor. The soft starter has motor protections.

RE: Motors tripped by under voltage in Siemens simocode

So you have one soft starter running four motors downstream of it, then the Simonides are being used to protect each individual motor?

If so, I would either disable the UV protection in the Simocode and let the Soft Starter handle that. If you are uncomfortable with that, at least put the trip delay out to be longer than the ramp time. UV protection for a motor does not need to be very fast.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Motors tripped by under voltage in Siemens simocode

(OP)
No each motor has its soft starter and simocode

RE: Motors tripped by under voltage in Siemens simocode

Well, I still would set the UV trip delay to exceed the ramp time.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Motors tripped by under voltage in Siemens simocode

(OP)
Hi

We would like to know if we can disable the under voltage protection in Siemens Simocode for the following motors?

132 kW 690 Vac
350 kW 690 Vac
400 kW 690 Vac

We are a power plant exporting to the utility grid. We had many power plant trips in the past due to under voltage in simocode after a network disturbance.

We have UV protection on our export line and on our alternator.
We estimate that the voltage will not drop below the actual setting of the simocode. Either the line or the alternator will trip first. Can you please confirm if ok?

Please see attached draft of set up.

RE: Motors tripped by under voltage in Siemens simocode

Soooo... the previous conversation didn't happen then?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Motors tripped by under voltage in Siemens simocode

(OP)
It did happen. We want solutions to prevent this from happening again.

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