switchgear heaters
switchgear heaters
(OP)
Hello,
When preparing a spec for switchgear when and where do you require stripheaters; and how do you size them?
Regards,
TULUM
When preparing a spec for switchgear when and where do you require stripheaters; and how do you size them?
Regards,
TULUM






RE: switchgear heaters
Energized, loaded, switchgear wil typically keep itself warm enough to avoid problems.
If you have switchgear that is de-energized or unloaded at night in an unheated area then consider strip heaters. They just have to keep the internal parts a few degrees above the dew point.
Usually mounted on stand-off brackes fairly low so as to cause convection ait currents and spread the heat around.
yours
RE: switchgear heaters
We used to require the use of strip heaters rated at 240V but applied and sized to operate at 120V just to reduce odds of burnout (or burn up!).
RE: switchgear heaters
Any ideas on what type of equipment needs them? IE I never see them in drives or starters (600V), but they seem to come standard (for us anyways) in switchgear (5kv and up)?
Is it just to protect insulators from tracking or all types equipment?
Rgards,
TULUM
RE: switchgear heaters
The breaker might sit in the closed position for 10 years straight, so you want to make sure it doesn't end up stuck there when you need to trip it.
RE: switchgear heaters
yours
RE: switchgear heaters
One manufacturer provided a thermostat in the same high voltage cabinet with the heater and left it in the off position. Nothing in the instruction manual mentioned the need to even open this compartment prior to energization. The problem was discovered some time later when the breaker doors were blown open. Our spec now calls for thermostats to be located in the low voltage compartment.
RE: switchgear heaters
Your observation on drives and starters is acurate, but not because they don't need them, in fact the opposite is true. Anything with capacitors needs to be protected from freezing at least, and anything with PC boards is subject to tracking and shorting on the boards from moisture. It's unfortunate that not enough people take this seriously, but it's a fact nonetheless. People look at these expensive enclosure heaters and decide it isn't worth it, when in reality it can be done very inexpensively. I always use a simple little thermostat set to 40 deg. F feeding a strip heater stood off the inner panel with a few washers. That has never failed me on soft starters, drives and PLCs in outdoor and moisture laden areas. I know others who put in light bulbs as a heat source, although I don't recommend it because of how fragile the bulb is, but it does work in a pinch.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: switchgear heaters
RE: switchgear heaters
So if I should use them... any ideas on how to properly size them? The strip heaters we use on the 5kV-15kV gear are pretty simple caloritec ss type strip heaters. The heaters are sized to 300W no matter what size of enclosure... a little excessive I would think (100W-150W seems more resonable depending?).
I guess the question is... if I know the compartment size is there a simple calculation to determine the size?
Regards,
TULUM
RE: switchgear heaters
Equipment that is energized and then turned off sucks up water as it cools.
RE: switchgear heaters
Another point, I'm not a big fan of thermostats. The cause of condensation in apparatus is often the air temperature rising and the relative humidity and the dew point rising with it, until the dew point is above the temperature of the slower heating metal mass. Our Generators are in an ambient temperature that much of the year ranges from the high 70s to the low or mid 90s. Condensation is more of a threat as the temperature rises than when it is falling. When the temperature is falling, the temperature of the metal mass is typically above the ambient temperature and so above the dew point. Condensation ocurrs at or below the dew point.
Put some warm metal in a cool moist environment and it doesn't attract condensation. Put a piece of cool metal in a warm moist environment and it immediately attracts condensation. Start to heat a thick piece of steel with a torch and it will sometimes condense moisture out of the flame. You have cool metal and very hot and moderately moist flame. Once the metal is heated above the effective dew point of the flame the condensation on the surface of the metal ceases.
You are not trying to dry the air, you are using the air to heat, via convection, the mass of metal. It doesn't have to be hot, just above the expected dew point.
Lose the thermostats, size the heaters as tulum suggests, and if you wish turn them off with a relay when the equipment is energised and producing enough internal heat to protect itself. Sizing; for a generator the heaters that I see are sized about 1 to 3 watts per KVA. 50 watts for a 50 KVA set does the job. When you get up to 3 watts per KVA I believe that it's a case of the nearest readily available size rather than a need for that much heat.
respectfully
RE: switchgear heaters
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RE: switchgear heaters
RE: switchgear heaters
Jraef is right about keeping drives above freezing. Electrolytic capacitors have water in them!
Starting batteries may also need a heater. Below about 40 or 45 dergrees Fahrenheit the electrical resistance of water based electrolyes increases dramatically partly because water molecules start clumping together which is how the idea of liquid crystals got started.
If you are in an arctic climate sulfur hexafluoride swutchgear also needs heaters to keep up the SF6 vapor pressure.
If ammonia gas or other corrosive gas is present then you would need to purge and pressurize the switchgear from say a regenerative blower that is across the street or other source of uncontaminated air. In this case you would need to dehumidify the air so that you are not introducing MORE moisture.
RE: switchgear heaters
One more quick one. I am in the process of installing a type ss strip heater in a exisiting 5kV contactor compartment. I am told that all strip heater wires need to be run in a separate emt (or equivalent) - it is metal enclosed so there is 5kv at the back of the compartment...
Is this neccesary? There are control wires in the vicinity of where I am going to run the heater wires and they are just tie wrapped to the enclosure - no emt?
I am in Canada..
Regards,
TULUM
RE: switchgear heaters
Since heat rises the optimal location for the heater is at the bottom of the compartment. There should be minimal penetration into the high voltage compartment. I don't see what the conduit would buy you. Make sure you use heater wire. Regular wire tends to get crispy close to the heater.
RE: switchgear heaters
RE: switchgear heaters
Can you reference a standard? I believe most of our switchgear comes without any barrier. And wires must exit the conduit before connecting to heater terminals.
RE: switchgear heaters
If I want to put a local/remote switch for the space heater power for (a) local when energized and (b) remote when deenergized is it advisable to break both the line and the neutral?
Typically, you would not break a neutral and the line in a control circuit, however, on this piece of mobile equipment, the remote will be a hubbel 120vac plug and the local is a on-board lighting panel.
I am not sure if I should just break the lines and let the remote neutral and local neutral be common, or break both and keep both neutrals separate? I would run a ground too...
seems trivial...but my pee size brain does not see an advantage to either...
Regards,
TULUM
RE: switchgear heaters
Rather than trying to make it safe under all conditions, consider a second strip heater energized by the 120 volt plug.
Two strip heaters and two completely seperate supply systems with no interconnection.
respectfully