Siemens RCCB trips even while inductive motor is off

[NicElectrician]

Good day everyone

This is my first thread here, and I'm writing because I have a problem which I'm not sure how to solve. Since its company money, I just want to make sure that the conclusion to the problem is correct.

We have an autoclave that works at 121 celsius to sterilize with steam. Its equipped with a vacuum pump of 2 HP which draws around 8.5 A with 208 V. The power comes on direct line (No VFD), through an RCCB 0.1A and 25A power surge.

The RCCB keeps tripping on a specific point of the process and even goes off while the motor is off. We use a normal 4x1.5mm cablet (3power 1ground), no shielding. The insulation is new (we just painted with dialectric paint the stator of the motor, changed bearings and clean it).

Is it parasitic capacitance of the cables?
Is there a leak through the stator?
Or the RCCB is damaged?

If you guys need more information let me know.

Thanks

 

[Megawatt]

Good day everyone

This is my first thread here, and I'm writing because I have a problem which I'm not sure how to solve. Since its company money, I just want to make sure that the conclusion to the problem is correct.

We have an autoclave that works at 121 celsius to sterilize with steam. Its equipped with a vacuum pump of 2 HP which draws around 8.5 A with 208 V. The power comes on direct line (No VFD), through an RCCB 0.1A and 25A power surge.

The RCCB keeps tripping on a specific point of the process and even goes off while the motor is off. We use a normal 4x1.5mm cablet (3power 1ground), no shielding. The insulation is new (we just painted with dialectric paint the stator of the motor, changed bearings and clean it).

Is it parasitic capacitance of the cables?
Is there a leak through the stator?
Or the RCCB is damaged?

If you guys need more information let me know.

Thanks

If I was you I would take a close look at the motor you took apart. Did you have problems before you took the motor apart?

 

[Pete999]

Good day everyone

This is my first thread here, and I'm writing because I have a problem which I'm not sure how to solve. Since its company money, I just want to make sure that the conclusion to the problem is correct.

We have an autoclave that works at 121 celsius to sterilize with steam. Its equipped with a vacuum pump of 2 HP which draws around 8.5 A with 208 V. The power comes on direct line (No VFD), through an RCCB 0.1A and 25A power surge.

The RCCB keeps tripping on a specific point of the process and even goes off while the motor is off. We use a normal 4x1.5mm cablet (3power 1ground), no shielding. The insulation is new (we just painted with dialectric paint the stator of the motor, changed bearings and clean it).

Is it parasitic capacitance of the cables?
Is there a leak through the stator?
Or the RCCB is damaged?

If you guys need more information let me know.

Thanks

Call an Electrician to do some testing of the Motor and the wiring.

 

[marconi]

As Pete999 says do some testing of the motor insulation resistance but from what you described, the RCCB trips even when the motor's DOL contactor/starter is open - yes? That the RCCB does trip when the DOL is open indicates the problem is elsewhere.

Does it always trip at exactly the same point in the cycle? If so what happens at this point of the cycle? Do an IR test on the heating elements and ampclamp the live conductors when they are on and also the earth/cpc to them. It could be these elements are failing/have failed.

Or did you mean that when the contactor/starter opens the RCCB trips?

The other tests to do are to measure with an ampclamp to measure the leakage current in the earth/cpc and the residual current in all three line conductors. For the latter do it to the whole machine and other sub-systems of the machine.

Does the RCCB only supply the autoclave or other circuits as well?

Please post a drawing of the wiring would be very helpful to folk of the EF to 'set the scene' and for them to study - pictures are often helpful too.

Pay particular attention to the possibility of tracking between live conductors and earthed metalwork. Dust, water, cleaning agents, debris can all start off and promote tracking so it would be a good thing to thoroughly inspect and then clean away such dirt and detritus.

What is the earthing system? TT, TNCS, TNS...?

Last for now - are all connections good electrically by being clean and tightly secured? Try the tug and wiggle test on them all. This includes connections before and after the RCCD.

 

[marconi]

PS: The tug and wiggle test (TWT copyright marconi) includes cpc/earth conductors.

 

[Pete999]

PS: The tug and wiggle test (TWT copyright marconi) includes cpc/earth conductors.

Is the TWT explained in GN3? does anyone know lol

 

[NicElectrician]

If I was you I would take a close look at the motor you took apart. Did you have problems before you took the motor apart?

We disassemble the motor because it was giving the trip problem. I read about the winding could be leaking through the housing.

 

[NicElectrician]

I also noticed yesterday that the Test button does not work, does this mean the RCCB got damaged?


As you see in picture 2 with the message POWER FAIL, it means the RCCB went off while the motor was not working. But the DOL stays close, so current can flow.

In picture 1 you can also see when it usually the RCCB goes open.

To clarify at this moment, I don't have a Megger nor the purchase of one will be approved. Is there a way to test insulation without one?


This is the electrical diagram the currents displayed are not correct. The OLR1 (The RCCB) is as specified in the picture before and that is what goes open.

To answer also megawatt, the motor used to trigger the RCCB a lot more often, after we painted the stator, it only happens randomly and usually at the point in the process where I already specified (Picture above).

As you may notice I am not an electric Engineer but and Industrial Engineer my knowledge is not so advance as you.

Hope the attachments help.

Best regards

 

[marconi]

ONLY DO THIS IF YOU FEEL SAFE TO DO IT AND HAVE SOMEONE IN ATTENDANCE

Do you have a test equipment to measure ac voltage up to say 450V and do you know how to use it safely? If you do could you measure and tell us the following voltages:

L1-L2
L1-L3
L2-L3
L1-N
L2-N
L3-N
N-E
L1-E
L2-E
L3-E

For my EF colleagues this RCCD uses L3 and N for the test function. See page 6/30 of:

https://www.lcautomation.com/wb_documents/siemens/siemens%20circuit%20protection%20-%20rccbs.pdf

My initial thought - test button does not work - > somewhere(upstream?) an N conductor fault/missing/loose/lost? (-> assumes DOL takes(tbc) its coil supply line to line so remains closed and motor will run while 3 lines energised/stops when RCCB trips.)

 

[marconi]

PS: Second thoughts on my initial thoughts OP said DOL remains closed when RCCD trips...

 

[NicElectrician]

PS: Second thoughts on my initial thoughts OP said DOL remains closed when RCCD trips...

As shown in the electric diagram, first comes and MCB of 25A, then the RCCB also of 25A. The only thing that trips is the RCCB. The equipment detects the trip and stops the process. As I previously said It also tripped when the motor was not ON.

My current thought following marconi ideas is to constantly measure earth line from the motor to check if I actually have a leak, if not leak I'll try just to change the RCCB for a new one.

 

[marconi]

Thank you Nicelectrician. Do work safely at all times.

Your measurement readings are very useful to us in helping you. Please be careful to describe the measurement you are taking and the circumstances of it (ie what is or is not on/off, running/stopped). Those voltage and IR measurements I mentioned are typical standard first checks to do so if you can safely do them that would be great.

What is definitely wrong is that the RCCB does not trip when the test button is pressed.

What is the temperature in the electrical cabinet?

There is no harm in doing low voltage insulation resistance(IR) checks using a multimeter set to Ohms of motor winding or heating element to earth and between windings of the motor, but the proper way would be using a proper 250/500V IR tester such as a Megger if you can get or borrow one. Please report any measurements you take. Remember safe isolation before you do any testing and have someone standing by you. Wear electricians rubber gloves near exposed live equipment and remove watches, bracelets, rings, etcetera.

 

[marconi]

I have read again what you said in your #8. You wrote:

This is the electrical diagram the currents displayed are not correct. The OLR1 (The RCCB) is as specified in the picture before and that is what goes open.

I need to check what you mean to say. In #8 you say that the motor's protection Overload Relay OLR1 trips but then you mention and have shown a picture of a different electrical device - a Residual Current Circuit Breaker(RCCB): They are not one and the same device. The RCCB will be before the Miniature Curcuit Breaker MCB1.

If OLR1 trips then the motor has drawn a sustained over current in one or more lines (L1, L2, L3). If the RCCB trips then there is overall an unbalanced/residual current flowing (to earth) across L1, L2, L3 and N through the RCCB. Could you confirm OLR1 trips as well? If it does then there are a number of reasons why this could be happening.

 

[marconi]

Could try to find out and provide a circuit diagram for how the autoclave's computer/controller monitors the incoming power supply to detect a power failure?

 

[Bobster]

Could try to find out and provide a circuit diagram for how the autoclave's computer/controller monitors the incoming power supply to detect a power failure?

Most common way of monitoring a tripped device in these situations is to include an auxiliary volt free contact onto the motor protection circuit breaker, or in this case RCCB.

I'm still trying to understand, which device is actually tripping.

An if the contactor is closed when it does. One post suggests when the motor is running, the other suggests that the contactor is closed even when there isn't power?

He also suggests that OLR1 is an RCCB, if this is the case, it is not offering correct protection to the motor.

I imagine this problem would be rather quickly fixed with a few tests using an insulation tester. OP says there is no funding for this, ask your boss/manager, how much is downtime costing him?

A decent top end insulation tested will be around £400 but can be gotten for <£100. Take a look here, also I believe a forum member discount can be gotten:

Insulation Testers from Megger, Metrel, Kewtech and Martindale

Suppliers of insulation testers from leading manufacturers including Megger, Kewtech, Metrel and Martindale. Our analogue, digital insulation testers and Megohmmeters are great for electricians.

www.test-meter.co.uk