protect undervoltage release unit

Kataeb · Jan 28, 2009

Dear Sirs,
We have the following item on our machine:
Circuit breaker, 4-pole, Irated 1000A, Ioverload 400-1000A + undervoltage release, Siemens, 3VL77 10-1BE46-2JA0

The undervoltage release was damaged and we had to replace it. We suspect that this is caused by the plant power supply which is frequently shut off and on.
We are trying to find a way to protect the undervoltage release unit, like by installing a varistor or an RC element.

We are considering the use of one of the following:
Varistor: 3TX7 402-3L , 3RT19 16-1BF00 , 3RT19 26-1BF00, 3TX7 402-3L , 3TX7 462-3L
RC element: 3TX7 402-3V , 3RT19 16-1CF00 , 3RT19 26-1CF00 , 3RT19 36-1CF00 , 3RT19 56-1CF00

What do you recommend?
How can we protect the undervoltage release unit?

Thank you for your help...

BobB · Jan 28, 2009

Never seen that problem before - a bit strange.
Schneider, Legrand etc etc make surge protection devices that may help but also may not. You really need to calculate out the potential and sixe a protection device to suit the application.

Kataeb · Jan 29, 2009

this undervoltage release has the following specs:
operating voltage 400 vac
power consumption 1.8 VA
maximum opening time 50 ms
what is the appropriate hardware to use for protection of this coil from voltage fluctuations?

thank you

leitmotif · Jan 29, 2009

Kataeb said:
this undervoltage release has the following specs:
operating voltage 400 vac
power consumption 1.8 VA
maximum opening time 50 ms
what is the appropriate hardware to use for protection of this coil from voltage fluctuations? thank you

What is the system voltage?
What is the rated voltage of the unit?
Does its rated voltage exceed the system line voltage.

Is the operating voltage you quote the trip setpoint
OR is it the line voltage the unit is rated at?

If it is rated at only 400 V and you install it on 480 it is nearly a sure bet you will burn the coil out.

Dan Bentler

Kataeb · Jan 30, 2009

the system line voltage is 3 x 380 vac + neutral 50 hz
the rated voltage of the unit is 380 to 415 vac

this unit trips (release) the circuit breaker at a voltage 0.35 to 0.7 x Us
it picks up the circuit breaker (can be closed) at 0.85 to 1.1 x Us
in our case Us should be = 400 vac

Gil47 · Jan 30, 2009

My guess would be, and its only a guess, is that you had a trip on your power supply and when the voltage came back on, one of the leads to the coil was down to earth, whilst the other was onto a live supply, this would give you about 220 volts on the coil not the 300 + volts needed for the 400 volt coils pole faces to pull together, but enough to make the coil burn out because it could not generate enough magnetic force to close the pole faces.

My solution would be to fit a phase failure phase reversal relay to detect that all 3 phases are present and correct

leitmotif · Jan 30, 2009

one more thought
What does this circuit breaker protect ie is it connected to alternator or a motor??

What are you connecting the undervolt coil to ? In other words what voltage is it sensing?

Dan Bentler

Kataeb · Jan 30, 2009

dear Gil47,
you mean by "pole faces" the ones inside the circuit breaker whose role is to supply our machine with rated current 1000 A? note that the undervoltage does not turn the circuit breaker on. it only releases the cb if the main supply drops too low. we turn the cb on manually by pulling its handle.
we have already installed a phase (+neutral) failure relay which cuts off the supply to the undervoltage coil in case of any power problem (low voltage, missing phase or neutral).

dear Dan,
the circuit breaker supplies (3x380vac+neutral 50hz) a big machine (upto 1000A) which includes many motors + drives + heaters + plc + modules... it is directly connected to copper busbars (3phases+neutral).
the undervoltage release is connected to 2 live incoming phases (380vac) through fuses (1A) & phase failure relay contact & emergency button contacts.

note that our customer installed a very big ups power supply to feed all his machines due to the frequent power shut down in our country. could this ups supplying damaging voltages to the undervoltage?

Gil47 · Jan 30, 2009

Kataeb said:
dear Gil47,
you mean by "pole faces" the ones inside the circuit breaker whose role is to supply our machine with rated current 1000 A? note that the undervoltage does not turn the circuit breaker on. it only releases the cb if the main supply drops too low. we turn the cb on manually by pulling its handle.
we have already installed a phase (+neutral) failure relay which cuts off the supply to the undervoltage coil in case of any power problem (low voltage, missing phase or neutral).

NO, the pole faces I was refering to were the ones on the coil itself.
Most under voltage trips that I know of, are powered all the time that it is OK for you to manually close the breaker.
The under voltage coil opens on low voltage and closes again when there is enough voltage, what I was meaning was that it thinks there is enough voltage for the coil to close, but can't manage it, say at more than 220 volts, but it is expecting 380 volts, even though you have not yet gone to the breaker to manually turn it on.

leitmotif · Jan 30, 2009

Kataeb said:
dear Gil47,
you mean by "pole faces" the ones inside the circuit breaker whose role is to supply our machine with rated current 1000 A? note that the undervoltage does not turn the circuit breaker on. it only releases the cb if the main supply drops too low. we turn the cb on manually by pulling its handle.
we have already installed a phase (+neutral) failure relay which cuts off the supply to the undervoltage coil in case of any power problem (low voltage, missing phase or neutral).

dear Dan,
the circuit breaker supplies (3x380vac+neutral 50hz) a big machine (upto 1000A) which includes many motors + drives + heaters + plc + modules... it is directly connected to copper busbars (3phases+neutral).
the undervoltage release is connected to 2 live incoming phases (380vac) through fuses (1A) & phase failure relay contact & emergency button contacts.

note that our customer installed a very big ups power supply to feed all his machines due to the frequent power shut down in our country. could this ups supplying damaging voltages to the undervoltage?

Ahhh now we are getting somewhere.
1. Plant power is 50 Hz 380 volt 3 phase with neutral
2 circuit breaker is used to feed a distribuition panel
3. Distribution panel feeds motors and VFD drives
4. Circuit breaker is a manual shut and open
5. Circuit breaker has shunt trip
6. Shunt trip controlled by the undervoltage protection
and a phase loss sensor
7. Power to the whole setup is backed up with UPS

To confirm PROBLEM the coil on undervoltage is burning out- how many times has this happened?

What is ******t temperature and what is temperature in the breaker enclosure?
Is the undervoltage possibly designed for 60 Hz

Could a high ******t temp and a reduced inductance (60 Hz component on 50Hz line) be causing the coil to overheat??
******t = A M B I E N T
Think I would be talking with Siemens about this.

IDEA TO CONSIDER
Since a phase sensing relay is installed and it has the ability to do undervoltage why not take out the other undervoltage unit and rely on the phase loss unit?

Dan Bentler

Kataeb · Feb 2, 2009

Check my reply below:
NO, the pole faces I was refering to were the ones on the coil itself.
Most under voltage trips that I know of, are powered all the time that it is OK for you to manually close the breaker.
The under voltage coil opens on low voltage and closes again when there is enough voltage, what I was meaning was that it thinks there is enough voltage for the coil to close, but can't manage it, say at more than 220 volts, but it is expecting 380 volts, even though you have not yet gone to the breaker to manually turn it on.
The undervoltage release does not have the capability to turn the cb off. It only trips it in case of low voltage. So I think this case is not happening.
………………………………………………………………………………………………
Ahhh now we are getting somewhere.
1. Plant power is 50 Hz 380 volt 3 phase with neutral
2 circuit breaker is used to feed a distribuition panel
3. Distribution panel feeds motors and VFD drives
4. Circuit breaker is a manual shut and open
5. Circuit breaker has shunt trip
6. Shunt trip controlled by the undervoltage protection
and a phase loss sensor
7. Power to the whole setup is backed up with UPS

To confirm PROBLEM the coil on undervoltage is burning out- how many times has this happened?
One time.

What is ******t temperature and what is temperature in the breaker enclosure?
The ******t temperature is 25 degrees celsius, and the enclosure could reach 35 degrees.

Is the undervoltage possibly designed for 60 Hz
Could a high ******t temp and a reduced inductance (60 Hz component on 50Hz line) be causing the coil to overheat??
******t = A M B I E N T
We always us 50 hz hardware. But I will double check it with Siemens.

Think I would be talking with Siemens about this.
I contacted them but did not get a useful response.

IDEA TO CONSIDER
Since a phase sensing relay is installed and it has the ability to do undervoltage why not take out the other undervoltage unit and rely on the phase loss unit?
Because we want to shut power off all the enclosure in case of phase loss. The undervoltage release controlled by the contact of the phase loss relay will do this. It is working on other machines without problems till now.

I am considering the installation of a varistor or an RC element in parallel with the coil to protect it from voltage surges… what do you think?

Vic · Feb 2, 2009

How long is the coil energized?

Is it possible the power is remaining on the trip coil after the breaker has tripped?

Most breaker trip coils are designed for very short operation - the coil energizes, the breaker trips and the power is removed from the coil. Is it possible that the UPS is supplying power which will keep the trip coil energized?

Kataeb · Feb 2, 2009

The coil is energized through a phase loss relay contact and an emergency button contact in series. So it will remain energized as long as these two are on. It is not supposed to cause a problem because the undervoltage coil has the only task of tripping the cb and not to turn it on. i think Siemens have taken into consideration the issue of having this unit powered most of the time.

Gil47 · Feb 2, 2009

By reading your description in your last post, we are dealing with a shunt trip coil, they are designed to give a fast action time during a trip, but the down side of that is they are only able to be powered for a short period before burning out.
You need to treat them like a 230 volt coil that has got 380 volts applied for a short time they will operate quick, and if left powered up will burn out quick.

I think Vic has probably summed up your issue.

Kataeb · Feb 2, 2009

similar coils are installed on other machines in our plant. they have been operating for more then 6 months without problems. the rated voltage of this coil is 400 vac (and can accept 415 vac).
what do you think about installing a varistor or an RC element in parallel with the coil to protect it from voltage surges?

protect undervoltage release unit

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