Help with 15KV Switchgear

[Chad12]

Hello all, I have a question regarding 15KV metal-clad switchgear. The facility I am at this week is using ABB 15KV switchgear and supplying it with a nominal voltage of 16,600 volts. I cannot find anything in IEEE that addresses justification for using this voltage on 15KV gear. Any help would be appreciated!

Thanks,

Chad

Chad Snyder
Director of Operations
American Power Technology

http://www.ampowertech.com

 

[Jereb]

Could it be to up the secondary of a transformer somewhere perhaps? Just thinking outloud.

 

[norcalnewb]

Check with ABB, but I bet the site is exceeding the rated maximum voltage on the switchgear. I used to work for one of ABB's competitors, and the max voltage on their 15 kV gear was 15.5 kV. This meant you were not to exceed 15.5 kV even with allowable utility swings. It sounds like this gear really should be 27 kV class, and running the gear at 16.6 kV could lead to pre-mature insulation failure.

Jim

 

[oldfieldguy]

How long has this been going on? I've seen some really strange readings in new gear that was improperly commissioned.

How do you KNOW the voltage is that high? Can you see that voltage indication at multiple locations? If this is feeding a downstream device, does that device have its own voltage indication? Does that voltage corroborate this reading?

If you're reading a digital meter, make sure that it is programmed correctly. If it's analog, make sure the meter is scaled correctly. Measure the secondary voltage on the potential transformer circuit and compare it with the KNOWN PT ratio.

Absent all that, a direct reading of voltage with a high voltage tester is called for.

The voltage you're reading is above the manufacturer maximum for the equipment. Liability and reliability issues abound.

old field guy

 

[dpc]

If built to ANSI C39 specs, maximum rated voltage for 15 kV class swgr is, I believe, 15 kV (at 3300 feet altitude, max.) However, 27 kV gear is also available. The withstand voltage test for 15 kV gear is 36 kV, IIRC.

I'd check the equipment nameplates, and verify the actual operating voltage as already suggested.



"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[stevenal]

Perhaps your gear has a voltage range (k) factor that is greater than 1.0. New gear is all 1.0, and the factor has been removed from the IEEE standards. Older gear built to the old standards with a >1 k factor could be operated above the voltage rating with a reduction in interrupting capacity. See IEEE Std C37.010-1979 or earlier.

 

[Zogzog]

Hey schmedley, 16.6 is > 15

 

[racobb]

Stevenal,

I am familiar with the k factor idea with the old breakers, but was not aware that it could apply to switchgear insulation as well. In an attempt to be lazy and not consult the standards, is this also applicable to the switchgear?

Thanks,
Alan

Alan

 

[jraef]

16.6kV conforms to no standard that I know of, so most likely this is on some sort of custom equipment associated with a transformer, maybe feeding a power supply or arc furnace, something like that. My guess then would be that the OEM of that equipment may have modified the 15kV gear to handle the additional voltage level, or tested it for the application. If you are concerned, a thorough investigation is warranted.


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[Kiribanda]

Chad12,

If the name plate indicates that your swgr is 15 kV rated,then it is based on the standard voltage levels given in ANSI C84.1.Per C84.1,the extreme Utilization voltage should be 14.52 kV,so that the swgr still gives satisfactory performance.

Per swgr standard C37.20.2 the rated maximum voltage should be 15 kV. Also if there are CBs attached to the swgr then their rated maximum voltage should also to be 15 kV (with or without K factor)per ANSIC37.06.

Since you cannot "MEASURE" the "NOMINAL" system voltage,on what grounds would you say that your nominal system voltage is 16,600?So you need to investigate how much is your nominal system voltage at your installation.

Stevenal/racobb,
K factor is relevant to CBs only(old constant MVA concept).Eventhough,the K>1,the rated maximum voltage for the CB should be 15 kV. But depending on the K value,the CB can operate down to a lower voltage (maximum rated voltage/K) with a higher SC interrupting rating (rated SC current x K).

 

[racobb]

Thanks, I think I have seen it as high as 15.5 kV max. but the constant MVA concept would obviously be at a lower voltage. Did not think it would apply to switchgear insulation.

Alan

 

[stevenal]

Sorry, I was attempting to go by flawed memory. After consulting legacy standards, it seems the k factor is used to adjust the interrupting capacity upward at voltages less than the normal range. The maximum voltage is the maximum. Too confusing, I see why it was changed.