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measuring 460 volt phase balance

measuring 460 volt phase balance

measuring 460 volt phase balance

(OP)
I asked that a customer measure voltage and amps for each phase.  A reply came back that it is "too dangerous."  I do not have any plant control layout yet, but I think it is common to have current sensors on the lower voltage side of some transformers for general control room monitoring.  I was thinking if all 3 phases have such measurement points, I could encourage them to get amp readings there.

Any words of advice?

thanks,

Dan T

RE: measuring 460 volt phase balance

I do not believe it is common to have sensors at the transformers. Also unless the customer is or has qualified electricians with proper instruments and training, it can be "too dangerous" to mess around with 480V. And he does not feel comfortable doing it, it IS dangerous.

 

Rafiq Bulsara
http://www.srengineersct.com

RE: measuring 460 volt phase balance

It's normal to have metering CTs and VTs at the switchgear for a transformer incomer. That would be a reasonably safe place to make the measurements. Any reason why those CTs can't be used?

If it's a new installation you might also have the option to pull information from an electronic tripping unit if the incomer is an ACB. Not an option with fuses though!
  

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

RE: measuring 460 volt phase balance

At our plant, it would be easier to get those type measurements for higher voltage motors (4kv, 13.2kv) then for low voltage (460vac) motors.

For the higher voltage motors the bus has PT's where we can monitor voltage, and opening the load center cubicle door provides easy access to the CT secondary signals at input to the relays.  

For the lower voltage motors, there is no CT or PT so we have to find some place to clamp on to  480vac cable... either in the energized MCC/Load center or in an energized motor term box.  None of these is to be taken lightly.  
 

=====================================
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RE: measuring 460 volt phase balance

What kind of facility is this? I can't imagine running a plant with no one qualified to take measurements.

RE: measuring 460 volt phase balance

(OP)
1800 MW coal fired power plant

Certainly I am not privy to with much detail, but comments similar to Thedroids have been repeated by others having far more direct relevant experience than I.  Like, Those qualified and certified and otherwise allowed if not encouraged to play with Medium voltage (4160) are reportedly on-staff and in-house at all times.

Qualified doesn't get too far unaccompanied by willing, and Q and W sometimes aren't even in the same room, especially when the request comes in 4th hand.  

RE: measuring 460 volt phase balance

The plant may be limited by the arc-flash hazard at the location where you want readings.  In many facilities in the US, if the calculated exposure is over 40 cal/cm2, they simply are not going to take the risk.  

As far a qualifed and willing - a foreman once told me - "we've got old electricians and bold electricians.  But we do not have any old bold electricians."

 

David Castor
www.cvoes.com

RE: measuring 460 volt phase balance

I think DPC hit it on the nose. A new OSHA law officially went into effect I believe last year. If this is a power plant, I'm sure there is a good chance the available fault currents may be large, and can produce exposure levels beyond what they can protect the employees. If that's the case, even qualified electricans, are simply "not allowed" to attempt it.

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