Control Relay overheat

[Tamer Mansour]

I have an issue with medium voltage switch gear "schneider ", the control relays always overheated at coil measured by infra camera 80 °c , 110 VDC , and the actual VDC supplied is 122 VDC , but Relay withstand 125 VDC , I don't know the reason .

 

[davidbeach]

Are you continuously holding a coil energized that was intended for intermittent duty?

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[TugboatEng]

Is 80 °C overheated? That seems to be a low temperature in my experience.

 

[waross]

176 degrees Fahrenheit a low temperature?
Okay.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

The standard rating for electromagnetic equipment in air is 40°C rise over an ambient of 40°C. DC solenoids experience a non-variable power requirement (always max) and do suffer from a lack of fan cooling. Unless oversized one should expect an 80°C coil temp and much higher as well depending on insulation rating. AC could run cooler but DC coils typically operate near max temp if run continuously.

 

[waross]

+40C = 104F Ambient.
The Weather Network is forecasting a maximum high of +28C in Cairo the coming week.
Tamer Mansour, what is your ambient temperature, and how hot is it inside your relay cabinet.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

Maybe you could give the part number of the relay?

 

[TugboatEng]

For clarification, I am speaking of the coil on the relay, not the entire relay assembly.

 

[che12345]

"...I have an issue with medium voltage switch gear "schneider ", the control relays always overheated at coil measured by infra camera 80 °c , 110 VDC , and the actual VDC supplied is 122 VDC , but Relay withstand 125 VDC ..."
I have the following opinion for your consideration.
1. No matter what the temperature inside the relay cabinet is, the coil temperature 80 [sup]o[/sup] C is acceptable.
2. Note: Temperature measurement using infra-red camera is always very tricky, affected very much by the emissivity setting and on which spot measurement is taken. You can easily check with a spirit (NOT mercury) thermometer or by coil copper resistance.
3. As pointed out by Mr. davidbeach, some ac/dc relays are intended for momentary say < 1s energization. Some dc relays insert series resistor in the coil circuit after energization when the magnetic iron core gap is closed/contact is closed.
4. SI unit for temperature measurement is [sup]o[/sup] C.
Che Kuan Yau (Singapore)

 

[RRaghunath]

Tamer Mansour, Control relay coils are not continuously energised. One of the contacts of the coil that is being energised is supposed to cut off the power to that coil as soon as the status is changed. The changed contact status is maintained by a latch until the other coil picks up. The two coils are called pick up and reset coils.
Hence, the coil temperature you mentioned is surprising.

R Raghunath