September 2017
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Failed High Voltage Contactor

This contactor was used to replaced 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 purchased from directly from Broadcast Electronics for an FM35A transmitter:

ABB A145-30 contactor

ABB A145-30 contactor

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.

ABB A145-30 contactor coil cover

ABB A145-30 contactor coil cover

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.

Broadcast Electronics FM35A

Broadcast Electronics FM35A

All is not well in paradise

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:

  1. Fresh arc tracks on the PA cavity and PA loading capacitor
  2. The shoes and bars in the high voltage contactor were severely pitted
  3. One of the mains phases (middle) in the high voltage supply appears to be heating up, likely due to a loose connection.
Discolored wire on buss bar

Discolored wire on buss bar

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 where the result of arcing.  Any sharp points will induce corona.  I also filed down all of the contacts in high voltage contactor, which took a fair amount of time. These are soft copper shoes and bars which 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 4:30pm.

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.

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

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