This contactor was used to replace the Furnas contactor installed as original equipment when the transmitter was manufactured in 1986. Furnas is no longer in business, thus the ABB A145-30 was substituted. It was purchased directly from Broadcast Electronics for an FM35A transmitter:
It was installed about 18 months ago and has been in nearly continuous use since. The broken white plastic housing surrounds the contactor coil and is responsible for pushing and holding down the contact fingers.
Looks like the coil is running too hot and damaging the plastic. This resulted in a failure of the contactor to make and no high voltage to the transmitter PA. Obviously a problem. I spoke to BE about this and they did not have a good answer. Actually, what they said was “That contactor is rated for 220 amps,” which is true enough. The only thing that I can think of is the coil is rated for 208 volts and the transmitter is connected to a 240-volt delta service.
A new contactor was ordered and installed yesterday.
I will investigate the coil voltages further, but for now, the 27-year-old transmitter remains on the air.
If one considers paradise an FM35A. Going through another iteration of blown transmitter fuses for WEBE, Bridgeport, CT. Yesterday, I spent the afternoon examining the transmitter and found several interesting things:
Fresh arc tracks on the PA cavity and PA loading capacitor
The shoes and bars in the high-voltage contactor were severely pitted
One of the mains phases (middle) in the high voltage supply appears to be heating up, likely due to a loose connection.
I checked and re-tightened all of the mains connections. Apparently, this is an old problem, as the Allen screw was tight. Interestingly, the fuse that was blown was on the red phase, which is different from what it was last time.
I spent the afternoon filing and sanding off the arc track marks in the PA cavity. It is very important to file flat all sharp points that were the result of arcing. Any sharp points will induce corona. I also filed down all of the contacts in a high voltage contactor, which took a fair amount of time. These are soft copper shoes and bars that had so much pitting and carbon I wonder how they didn’t catch on fire. I filed them flat. We were back on the 35A transmitter at full power by 4:30 pm.
If this happens again, I will bring my megger out and check the insulation on the wire between the disconnect switch and the HV power supply.
When I left the site at 5:30, I felt like we did some good work.