Heat Losses in Switchgear 2

[KenAlmon]

Does anyone have rules of thumb or can they point me to any references on heat losses in switchgear?

I have a room with a variety of electrical equipment: 4.16 kV drives, 600 V drives, 600 V and 4.16 kV switchgear, as well as dry type transformers.

For the transformers, it is fairly common to use a figure such as 2% losses to size for the AC requirements.

Any comments?

TIA
Ken

 

[jraef]

Switchgear itself is designed to NOT have heat losses if at all possible since heat losses mean resistance which means poor connections or exceeded capacity. Overall losses will vary depending on the number of transformers and other sensing devices, plus the loading of the switchgear and bus resistance so I doubt that there is a "rule of thumb" that would be meaningful. I would be surprised however if it was over 1% aggregate. Losses through Vacuum Contactors for instance are shown as 0.03% (99.97% efficient)

Drives are another story all together. Any decent drive manufacturer should be able to tell you the desgned heat losses at variuos load points in the speed curve. They need that info in order to design their own internal cooling systems. A worst case scenario (assuming new or nearly new drive designs) would be 5% losses at full speed, and as much as 10% losses at 1/2 speed. This is typically true for MV and LV drives. Some (if not most) would be better than that. Drive manufacturers will often list that info as "system efficiency".

If your motors are in the same environment, keep in mind that motors on VFDs run hotter than normal as well. If you look for a "Throughput Efficincy" rating of the drive and motor as a system, the losses are all heat as far as the building AC is concerned. Subvert the dominant paradigm... Think first, then act!

 

[dpc]

From GE MCC data:

250 watts per foot of MCC lineup is reasonable assumption.

If you need more detailed info:

For circuit breaker starters with control power transformers:

Size 1 - 27 watts
Size 2 - 57 watts
Size 3 - 130 watts
Size 4 - 200 watts
Size 5 - 300 watts
Size 6 - 650 watts

For feeders and mains:

50 A - 15 watts
225 A - 40 watts
600 A - 80 watts
1200 A - 150 watts

From Cutler Hammer Consulting Application Guide:

15 kV and 5 kV switchgear:

1200A breaker - 600 watts
2000A breaker - 1400 watts
3000A breaker - 2000 watts

Medium-voltage motor starters:

400A - 600 Watts
800A - 1000 watts

Low voltage switchgear

800A breaker - 400 watts
1600A breaker - 1000 watts
2000A breaker - 1500 watts

225A Panelboard (42 circuit) - 300 watts

This data is based on full load, so normally you will have some fraction of this.

Hope this helps.

 

[busbar]

Possible supporting info at:

http://www.copper.org/pub_list/energy-efficiency.html