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Overvoltage Operating Limits

Overvoltage Operating Limits

Overvoltage Operating Limits

(OP)
As per CAN-3-C235-83 "Preferred Voltage Levels For AC Systems 0 to 50,000V" For a system nominal of 600VAC, the over-voltage limits are:

Normal Operating Limit: 625V or 104.2% nominal
Extreme Operating Limit: 635V or 105.8% nominal

On a black start condition (with transoformer tap inevitably set to -5% due to bad undervoltage condition), the over-voltage at the 600V bus when the incomer breaker is closed (with all 600V circuit breakers OFF, no motor running) is 105.77% nominal.

I am thinking of making conditions to ensure that all 600V feeder circuit breakers feeding non-motor loads (i.e. transformers) should be closed. This will operate some downstream loads as soon as the incomer breaker is closed and develop a voltage drop. However, is this feasible in real operation?

If the over-voltage fall below the extreme operating limit, does this mean that this is tolerable and a planned corrective action should be taken (see section 2.2.b of the standars). I think this will have similar ANSI counterpart.

I am a little confuse of the condition and in need of experienced technical person's opinion.

  
 

RE: Overvoltage Operating Limits

(OP)
Can I safely assume that here in Canada, all utilization equipment are designed to continuously withstand the overvoltage limit specified under the Extreme Operating Conditions?

RE: Overvoltage Operating Limits

To answer your question, look at the Extreme Operating Conditions as defined in the STd:
Extreme Operating Conditions.  Where voltages lie outside the indicated limits for normal operating conditions but within the indicated limits for extreme operating conditions improvement or corrective action should be taken on a planned and programmed basis but not necessarily on an emergency basis.  

So according to the std, withstand continuously: no
On a black start: yes since the system will adjust and transformer will change tap rapidly enough. No need for improvement or corrective action since it is already there.

Corrective action will be required if after black start the tap does not adjust and voltage remains too high (seen that!)

Hope this helps

 

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