Zero Current on phase 3 of Merlin Gerin Masterpact circuit breaker

[albarkani]

Dear Guys,
I have Merlin Gerin Masterpact NW 2500A circuit breaker and the trip uint is micrologic 2.0A

THE PROBLEM IS THAT:
WHEN WE CLOSE THE CB ON THE GENERATOR IT GIVE US ZERO CURRENT ON PHASE 3 ??

any suggestion??

 

[Zogzog]

Hmm, have you tested the breaker yet? These new plastic breakers that all the OEM's are making these days seem to be failing more often than the good old AKR's, RL's, K-Lines, and DB's did. Lots of recalls and very difficult to work on if something like this happens.

If you are not familiar with these breakers you should call a testing company or breaker shop to look at it for you.

Did you check the voltages on the line side of tis breaker? Load side?

 

[Zogzog]

There was a recall on this breaker, problems with the finger clusters falling off, which could cause your problem.

http://www.vikingelectric.com/Customers/Safety_Recall/MasterPact_NW_Resolution022508.pdf

 

[waross]

I have only had two circuit breaker failures in the first week of service of a new generator. Both the same brand breakers. It has left me a little prejudiced and I will change out a certain brand breaker at the drop of an electron. BTW both failures were broken parts that I attributed to poor or faulty material quality.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Zogzog]

"I have only had two circuit breaker failures in the first week of service of a new generator. Both the same brand breakers. It has left me a little prejudiced and I will change out a certain brand breaker at the drop of an electron. BTW both failures were broken parts that I attributed to poor or faulty material quality"

Bill,

Can we assume that this post is relevant to this thread?

 

[waross]

If MG is the abbreviation for Motor-Generator, these may have been MG² breakers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

albarkani:

Your information is not adequate. When you say zero current, is that the reading on its LCD display reads zero even when there is actual current in the conductor? or there is no voltage on line side of the breaker meaning the contacts are not closing?

What tests were done on the breaker? What are the current in other two phases?

 

[YuriSarcas]

What do the other two phases read? Is this a new breaker or has it been in service for a while? Has it been tested by a valid testing agency? Are you getting trips? How is the voltage?

I have seen these trip units do funky things but they are rather easy to change out.

As for the fingers falling off I had a tech experience this. The fingers grounded out when they racked it back it and the fault went all the way back to the utility. I am not sure why none of the protection relays did not trip. When you rack these breakers out verify that the fingers are good and in line before you rack it back in.

 

[alehman]

The finger issue was also discussed in thread238-211745. It is probably unrelated to the OP's question.

 

[albarkani]

Dear all
Here is some information it may help you to comment

We are working on power plant and the generators are connected in parallel to the transformers.

However before close the C.B from the generator side the voltage is stable (equal 450 on each line)

after closing the breaker the voltage become equal on line 1 and 2 and more on line 3 (475)

Keep in mind if the genset operate in ISO mode, the breaker trip due to high ac voltage
In other words, the current on line 1 and 2 goes to the max value and force the breaker and genset to trip.


I have done the following test.

Current measurement :
On 20 % of load on the Genset it give me 650 Amp on line 1 and 2 and zero on line 3

The breaker is provided with LCD also and it shows the same reading as per Genset PCC LCD.

Note that i checked the current flow on the L.V cable of line 3 with the power analysis meter and there is no current flow on line 3 at all.

 

[rbulsara]

Probably the bad breaker but you need to acetain that first. Have a testing co. check out the breaker and its contacts per NETA- ATS specs. Meanwhile, I still have some questions:

1. Is this load only fed from this generator? Meaning there is no utility source or a tranfer switch in between the gen and the load?

2. Has this gen/breaker ever worked corretcly?

3. Verify that the breaker phase 3 contacts are closing. First with denergized conditon. If found OK in denenrgized condition, open all the breaker/switches and then after closing the gen breaker see that you still get the voltage on load terminal of the breaker.

4. If above test prove good breaker then there is something else wrong with load circuits. If not replace the breaker. Have the new breaker thoroughly tested by a testing co.

 

[albarkani]

Dear rbulsara,
Regarding your questions:

1. this genset is connected in parrallel with 2 other gensets as per attached file (layout). meaning:

a. each 3 generators are connected togather to one transformer

b. each 2 transformers connected to gather to one switchgear

c. each switch gear is connected to the main bas bar (13.8 KV)


2. yes, this breaker worked corretcly almost for one year.

3. the breaker phase 3 contacts are closing with denergized condition, but its diff to find out if there is voltage after closing the genrator C.B because the bus bar is live from the transformer coming from the main bas bar.

but with dead bus bar, after closing the breaker (energize single transoformer)the generator RPM move to 1950 infact the actual RPM is 1800 and the voltage is not stable. this is maybe because the T.F is not energized correctly as the current is zero on line 3.

regards.

 

[rbulsara]

Aha, it's amazing how much details are unveiled when asked questions!!

The real and best advice is you need to engage some experience professional electrical engineer, starting with one who put this system togehther, to look into the issue. It appears that it is not the breaker. But you still need to remove the breaker and have it tested.

You can exchange a few ideas here but, it is not wise to troubleshoot this type of issue with free advice from strangers.

Having said that, I am still curious:

1. What happens to the amps and volt readings of other two generators? or to the other two gens?

2. What happens when you lockout this generator and let the other two energizes the transformer?

 

[DanDel]

If there's any chance that the Square D finger-cluster issue is involved, you must verify that the switchboard buses are completey de-energized before racking out the suspect C/B, since those loose/broken finger clusters may fall and short out something.

 

[albarkani]

rbulsara,

the other 2 genset are working normal without any problem. and nothing happen when we lockout this generator means every thing is working well with ot without this genset the problem is only involved with one genset thats all

 

[rbulsara]

albarkani:

OK that narrows it down to the breaker and the generator.

Check the breaker first, you may want to take it out and check it and get it tested. Since it is straight forward and will affirm or rule out the breaker as a cause. dandel's advice is also good when racking out the breaker.

If breaker is found ok, then you need to focus on the generator...load test, windings, AVR,..lots of variables there.

 

[ScottyUK]

AVR and field can pretty much be ruled out if two phases are carrying current and the third isn't. Stator winding maybe, or a bad cable connection. Could be a problem at the star point too. Ten minutes with a couple of spanners, a milliohmmeter and a Megger should give you a fair idea about the stator winding condition.

I am puzzled by the comment "the generator RPM move to 1950 infact the actual RPM is 1800". Are you saying the machine is rotating at 1950 rpm while the breaker is closed and the unit is supposedly synchronised to the bus?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[waross]

1> No current on one phase but we don't know if the breaker is closed.
> RPM indication jumps 150 RPM when the breaker is closed.
> Voltage is unstable.
Do you have a synchroscope? If the Tachometer is in error, the synchroscope will be spinning at 150 RPM before closing. A jump in any reading when the breaker is closed is usually not a good sign. If you do not see any current while the voltage is changing, you probably have an open circuit, either in the breaker or the generator.
With all these funny readings, you should take this machine out of service and follow Scotty's last suggestions.
Or, wait a few days and it may take itself out of service!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[albarkani]

thank you very much to all of you.

the problem has been solved by chaning new breaker, this issue was due to loose contact on phase 3 on the breaker it self.

regards.

 

[rbulsara]

albakrani:

Great! and thank you for posting the feedback. It's always good to hear a happy ending.

Rafiq.