In very humid conditions 6.6kV motor terminal boxes have flashed over. I have witnessed more than one litre water removed from one such terminal box. Does any one have similar experience? What are the practices to avoid such situations - especially in coastal regions? Is is improper to use HV motors instead of 440V types?

 

Responding to kulkarni nandu’s 13-Aug (12:30) query; humid conditions are expected. While termination quality is certainly suspect, there could be a more insidious cause. Please answer the following:

1) Is the feeder cable 1x3/c or 3x1/c?
2) Is the cable shielded?
3) What is (are) conductor size(s)?
4) What is (are) motor size(s)?
5) What are environmental conditions?
6) Is system neutral earthed? If so, what method?

Regards, Phil Corso, PE ([email protected])

 

Always take IR and PI values of the drive on opportunity. Make sure you have space heaters installed and same are in good working condition. You might want to alter the settings a bit to fine tune the system to your advantage. Use good quality packings to deter moist air to come in, but that is a tricky thing to do. If your junction box is in any case exchanging air with atmosphere, provide a small drain hole to drain any condensate... Make sure it doesn't fall on any other live part.

Hope it helps.

 

In order to have condensation, there must be humidity AND cold temperature--sufficient cold temperature to cause the humidity to condense.

So, why is ambient air permitted to enter 6.6 kV motor terminal enclosures (i.e, why aren't the enclosures properly sealed (they are usually NEMA 4 enclosures if they are outside--or should be)) and most large motor terminal enclosures if not NEMA 4 type enclosures have covers which are bolted in place with some type of gasket around the edges. That's first: How is the humid air entering the enclosure?

Even conduit penetrations into the motor terminal enclosures should be sealed.

Second: How is the enclosure so cold that it's causing the humidity to condense? Air conditioning in humid environments is provided primarily as humidity control, not to make the space so cold one could store meat there indefinitely. If the temperature during the day is so cold that at night humidity condenses, or when the outside door is open that humidity immediately condenses on metal cabinets and walls, then it's too bloody cold! By recirculating the air in the compartment over the evaporator coils, the moisture in the air should be condensed by the evaporator coils and removed through the condensate drain from the air conditioner.

So, find out how humid air is getting into what should be "sealed" (weather-tight, not necessarily waterproof), AND resolve the condition that's allowing the moisture to condense and you should have no more arc lighting problems.