Smart AC Power Circuit Breaker with Web Control?

FM does it with frequency!
User avatar
jthorusen
Posts: 85
Joined: Sun Sep 02, 2018 4:35 am
Contact:

Re: Smart AC Power Circuit Breaker with Web Control?

Post by jthorusen »

Three comments:

The Collins 831G had phase loss relays in the interlock string. We had one of these go intermittent due to dirty contacts and had nuisance trips of the transmitter, but never lost the plate supply breaker. It was the devil to find. I'm surprised that the phase loss sense system wasn't fast enough to protect the transmitter.... after all, that's what it was designed to do.

Motor operated circuit breakers are found in UHF TV transmitters employing IOT's (Inductive Output Tubes). The crowbar circuit which protects the IOT throws a dead short on the beam supply via a hydrogen thyratron. This trips the 3-phase breaker for the beam supply located (in the case of the Harris Sigma) in the transmitter line control cabinet, which is a motorized breaker. Since the transmitter logic is designed to recover the transmitter from a crowbar event, it resets the breaker and tries to bring the beam supply up again. Three crowbar events in rapid succession will convince the logic to give up and you have to go work on the transmitter... but if the reset works, everything continues on. There were transient crowbar events every once in a while, not repeated, and with no obvious cause. Just part of doing business with 35 KV.

As far as the Internet Of Things (the pirate of the abbreviation for the tube) is concerned, I already pointed out in an earlier post that anything that you can reset by remote control, a hacker can turn off.

Regards,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

User avatar
jthorusen
Posts: 85
Joined: Sun Sep 02, 2018 4:35 am
Contact:

Re: Smart AC Power Circuit Breaker with Web Control?

Post by jthorusen »

A little more thought about Bob's post....

It finally occurred to me that he was talking about the actual control signal to the SCR gating circuitry. That, of course, could be a problem, as there was no actual phase loss and therefore the phase loss system wouldn't detect it.

It confused me because the 831G that we had did not have those relays in it. I guess they were added later as an after-thought to correct a problem with the 831. Something that we noted was that small power line transients or other noise would occasionally trigger the SCR's in the old Collins. One could stand in front of the transmitter when it was switched off via the plate off button and watch the plate volts meter give little occasional "ticks" upward. Noise transients would trigger the SCR's from time to time and you could actually see the power supply develop a small voltage spike. The transmitter was switched "OFF" only by removing the gating signal from the SCR's via the gating logic board. Apparently, its noise immunity left something to be desired. I'm guessing the relays Bob mentioned were added later in an attempt to address this problem. One of our other engineers maintained that that transmitter wasn't really "OFF" unless one manually opened the breaker. :D

Regards,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

kcbooboo
Posts: 610
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Smart AC Power Circuit Breaker with Web Control?

Post by kcbooboo »

The phase loss relay would have detected an incoming phase loss and dumped the transmitter. This was an internal phase loss of the power feeding the SCR controller's three small transformers. I know a lot of engineering went into the SCR control circuit between the Collins and Continental versions, including relocating the SCR control boards from somewhere in the rear of the middle bay to the logic chassis in the front of the middle bay.

Part of the SCR controller test procedure involves pulling two of the three control boards, finding one that works, and sliding it into each of the three slots to verify the SCRs work. The TX will come up on one phase at vastly reduced power, but if you try to get it to run on two phases, it will dump the plate breaker. In our case, that was the effect when the relay broke one of the phase power signals to the controller chassis. A lot of other parts were replaced before the relay issue was found by tapping it during operation, which involved running with lots of panels open and interlocks blocked.

So in this situation, a remotely resettable plate breaker would have been desirable since these were nuisance trips, but they were happening for a valid reason that just took months to find.

Bob M.

NECRAT
Site Admin
Posts: 3204
Joined: Sat Nov 17, 2007 9:13 pm
Location: Taunton, MA
Contact:

Re: Smart AC Power Circuit Breaker with Web Control?

Post by NECRAT »

jthorusen wrote:
Thu Jan 09, 2020 12:29 am
Three comments:

Motor operated circuit breakers are found in UHF TV transmitters employing IOT's (Inductive Output Tubes). The crowbar circuit which protects the IOT throws a dead short on the beam supply via a hydrogen thyratron. This trips the 3-phase breaker for the beam supply located (in the case of the Harris Sigma) in the transmitter line control cabinet, which is a motorized breaker. Since the transmitter logic is designed to recover the transmitter from a crowbar event, it resets the breaker and tries to bring the beam supply up again. Three crowbar events in rapid succession will convince the logic to give up and you have to go work on the transmitter... but if the reset works, everything continues on. There were transient crowbar events every once in a while, not repeated, and with no obvious cause. Just part of doing business with 35 KV.
In the Comark Rig, this was in the left hand side of the PA cabinet. The first generation of the IOX and DCX series rigs had undersized breakers, and the breaker would physically break on a shunt trip from the Crowbar supply. They offered an upgrade, but expect almost six hours to complete the upgrade with your using the entire dictionary of profanity by the time it's done. Like in the movie A Christmas Story, a cloud laced of profanity still hangs over Rehoboth, Massachusetts to this day from said upgrade....
Mike Fitzpatrick
Broadcast Engineer/Tower Photographer
Boston area.
https://www.necrat.us, https://www.scan-ne.net/

"If you don’t think you’re good, nobody else will" - Tom Laun (RIP)."

Post Reply