Electric heaters in Switchgears/MCCs

[CuriousElectron]

Greetings,
What is the purpose of having electric heaters in switchgears/MCC if these are located indoors with a functioning HVAC system which maintains a temperature setpoint above dew point in the building? I understand the circuit breakers/surge arrestor need to be protected against moisture ingress. Are the internal heaters function as a backup to the plant AHU?
Thanks,
EE

 

[itsmoked]

They do sound unneeded in this case if the room temp is kept reasonable. They could stand in during an A/C issue. They should probably be changed to being thermostatically controlled if they aren't already.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

If they are anti condensation heaters they should never be controlled by a thermostat.
Condensation may occur at any temperature.
Anti condensation heaters are typically connected at one half the rated voltage and develop 1/4 rated wattage.
They are left energized, 24/7, year round.
We used them on our generators in Central America.
If the a;arm went off indicating a heater failure the plant would phone me immediately.
I would be on the next available flight to the island.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Good point Bill..

Keith Cress
kcress -

http://www.flaminsystems.com

 

[CuriousElectron]

Thanks for the replies.
I understand in tropical countries where the humidity is high year round, you'd want to run the heater to keep the generator windings warm.
In location where the humidity is low year round, I think the thermostatically controlled heaters would be used against swings in temperature and to keep the air temp. above the dew point.
Am I going in the right direction with my reasoning?

Thanks,
EE

 

[FreddyNurk]

CuriousElectron, with the sites that I used to deal with, we had locations with varying levels of humidity, from near coastal locations in tropical areas with higher levels of relative humidity, through to arid locations with larger ambient temperature swings and much lower relative humidity.
We didn't bother with control for the drier sites, rather the heaters were turned on at all times with the exception of when the relevant set was running.
Thermostat control to manage temperature is easier, managing the changing dew point, which itself is based on changing factors, is much harder, as waross also pointed out.

All the above considerations though, are for generators. I've not seen them installed in MCC cubicles, I have seen them installed in control panels that aren't sited within climate controlled buildings. When in panels I've seen thermostat controls used to prevent overly high internal cabinet temperatures.

EDMS Australia

 

[waross]

I have seen both types of heater in the same enclosure.
This was the control cabinet associated with a large circuit breaker in a substation.
The breaker was outdoors.
The thermostatically controlled heater ensured that the mechanical linkages would not malfunction during extreme cold weather.
The smaller anti-condensation heater was energized 24/7, year round.
The location was one of the driest locations in Canada.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

In my previous job I ran into a situation where a relay failed due to moisture in the relay case. Happened to be a frequency relay and when it failed it tripped all the feeders on UF. Went to see the conditions.

Walk-in switchgear. Always on section heaters and a thermostatically controller aisle way heater. The aisle way heater was directly opposite the failed relay. By the time I got there they had discovered that the section heater in that section had failed. The front of the relay was warm, the rear was much cooler. It was the Pacific Northwest, lots of winter humidity. Had a miniature weather system in the relay case. Had rain in the relay that didn’t exist outside the relay.

 

[che12345]

Dear Mr. CuriousElectron

Q. "...What is the purpose of having electric heaters in switchgears/MCC if these are located indoors with a functioning HVAC system which maintains a temperature setpoint above dew point in the building? ..."
A. It depends on the climatical condition where the MCC is located. Panel heaters are "frequently" specified in tender documents, for the following reasons:
a) when the MCC is in (operation), the i2 R heat lose is usually sufficient to keep the MCC [heated up and kept dry]. Heaters if installed shall be controlled by thermostat,
b) when the MCC is (down for (maintenance) [over nigh] and with A/C on; condensation may happen over the cooled surfaces in the morning hours. Attention: the thermostatic controlled heater may need to be supplied from a separate source, if the whole MCC is isolated from up-stream,
c) when A/C is [down] and (MCC is on light load), condensation may happen in the early morning hours; the thermostatic controlled heater would keep the MCC heated and dry.
Che Kuan Yau (Singapore)