Can't explain sporadic reduction in output power through 175A Shunt Breaker. 2

[Bowin db]

THANK you all for the kind replies. I am adding some additional information.

The sequence of power is as follows: City voltage 208-220v - 175A breaker - 175A shunt breaker (this is a breaker that has a secondary emergency feature called a shunt, ( I believe they are 120V normally open, when triggered they close the circuit sending 120V to the breaker and tripping it thereby killing the power to the motor. Next in line is the Isolation Transformer which cleans ( makes it that there are not high and low fluctuations to ) the current before it enters the main Control Unit. The control unit regulates the 220v motor (which was running but not in a consistent manner )

The Incoming volts from City 217,218,216 through Shunt Breaker (meaning tested each leg to neutral on the Load Side reading 123v, 94v, 216v Shouldn't it be the same voltage on either side of the breaker (high and low side) of the breaker? 2 of the 3 legs were losing voltage with no apparent load, though the load side of the breaker was still connected to the transformer and the shunt was still connected to the 110v supply.


This resulted in a blown transformer (where the coils on one of the 3 windings sparked and bulged out). Perhaps the Shunt (for some reason)was sending just enough to almost trip the breaker which reflected on the lower voltage reading on the load side.

Any comments would be greatly appreciated. The video would not upload so I attached Pics.

Here is a short video:

https://www.dropbox.com/t/u8NCiZrmc4BHrCPF

Thank you Bow

 

[FacEngrPE]

This is what I would expect if one of the three poles of the breaker is making very poor contact. Any downstream motor that does not have loss of phase protection is at risk of letting the smoke out.

 

[pwrengrds]

Would have been nice to see voltage across the poles instead of between them but, yes, it's a bad breaker, have very high impedance A phase contacts.
David

 

[che12345]

Dear Mr. Bowin db (Electrical)(OP)23 May 22 19:
"...The #1. Shunt Breaker Incoming #2. volts from City 217,218,216 through Shunt Breaker #3. to results on the Load Side 123, 94, 216? . Shouldn't it be the same voltage high and low side of the breaker? ......#4. This resulted in a blown transformer (I think) or perhaps the Shunt (for some reason)was sending just enough to almost trip the breaker...".
#1. what do you mean "shunt breaker incoming" What is the significance of the word "shunt"?
#2. What is the City supply declared voltage at the location? Is 217,218,216 V taken between line-to-line or line-to-neutral?
#3. With load, the breaker line side voltage may be say 2-3 V > load side Note: This reading is measured across the same line . Compare the three readings, they should not deviate generally > 5% . Attention: Check whether the current is balance.
#4. What do you mean by : " the shunt was sending ...."? See above #1.
Presumption: It is likely that the breaker is faulty.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr. Bowin db (Electrical)(OP)23 May 22 19:53
".... additional information....City voltage 208-220v - 175A breaker #1. - 175A shunt breaker (this is a breaker that has a secondary emergency feature called a shunt, ( I believe they are 120V normally open, when triggered they close the circuit sending 120V to the breaker and tripping it thereby killing the power to the motor. #2. Next in line is the Isolation Transformer which cleans ( makes it that there are not high and low fluctuations to ) the current before it enters the main Control Unit. The control unit regulates the 220v motor (which was running but not in a consistent manner )..."
#3. "...The Incoming volts from City 217,218,216 through Shunt Breaker (meaning tested each leg to neutral on the Load Side reading 123v, 94v, 216v Shouldn't it be the same voltage on either side...."
#1. It is confusing to name it " shunt breaker". It is a ( breaker ) instilled with a [shunt release], with coil rated 120V.
#2. Again confusion. " Isolation Transformer which cleans ...." It could be an (isolating transformer), instead of a costly/confiscated ; [regulating transformer] which cleans....
#3. If your City (3-phase) [always between line-to-line] declared voltage is 208-220v, then your measure voltage [between line to neutral] at the line side 217,218,216V and at load side are incorrect. See my earlier post #3.
Che Kuan Yau (Singapore)

 

[JezNZ]

Is this a new installation?

If so, what commissioning checks were performed? Was contact resistance measured?


If no to either, under isolation conditions use a microOhmeter (colloq. aka Ductor) to measure across each pole of the breaker.

Expect to see high contact resistance on one phase pole. If so, consider faulty and replace.

Otherwise, consider were torque settings correct on all terminations?

 

[jraef]

Stop focusing on the shunt, that has nothing to do with reducing voltage through a breaker. A shunt trip on a breaker simply activates the trip mechanism from an external signal at whatever the voltage rating of the shunt coil.

The simplest explanation would be bad / burned contacts in the breaker. It happens, especially if a breaker is opened under load a lot. That might be a side effect of there being a shunt trip in the breaker actually, depending on how it is used. I’ve seen people use a shunt trip in an Emergency Stop scenario, which is technically OK, but then operators get lazy and just hit the E-Stop every time they want to shut down. Do that 4 or 5 times per shift and the contacts on that breaker will burn. Breakers are NOT designed to be contactors!


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