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Harris FM 3.5K TX Issue!

J

jorr

Hello Everyone,

With all the knowledge available here, I am hoping someone has run into this before and can point me in the right direction.

I have a Harris FM 3.5K FM transmitter that does not like the facility main Kohler generator. Whenever the main generator kicks on the unit will throw its main breaker (panel, none on unit itself). Our Harris 2.5k backup transmitter hums along just fine on utility, generator, backup generator, etc. We are the only one experiencing issues with this. Several other transmitters (BE, Harris HD, Continental, Harris TV, our other Harris, etc) all work just fine. Therefore, I am not seeing it be an issue with line frequency. Also, the unit is single phase, so no phase to phase issues. We get the occasional screen / afc overload, but nothing that ever takes us off the air, except when the generator kicks on.

I also want to note that the main breaker is warmer than any other in the box. I suspected there the mains line was to small, so I had it replaced with a lager wire. We also had an issue in the past where over a period of several months the breaker would trip, then trip again in less and less time intervals. The breaker was replaced and the issue went away. That occurred 2 years ago, and 3 months ago. The breaker is a 60amp (If I remember correctly) 220v double pole breaker. Off the top of my head, I believe I measured the transmitter using 48 amps.

Thanks in advance!

Jeff
 
I have not had this type of problem but from the sounds of it I would check all AC connections inside the transmitter and all the AC connections from the breaker box.

I have had the problem with the screen overload when on generator power - since the transmitter uses the screen supply to control power output and generators typically have better line voltage than the power company the transmitter will come on at a much higher % power output.

If that is the case with yours - is it possible that this is causing your problem?

I know it sounds wild but you might try dropping the screens until you have about 80% output and then see what happens when the generator comes on - it might give a clue.

We just had to do major repairs to a 3.5K and one thing that we found was that the nuts on the plate transformer/choke were slightly loose - this could be causing an arc that could be tripping the breaker.

Good luck and I hope this helps.
 
Clarify for me, it trips when the power swaps from main to genset, or when there is no power, and then the genset comes on? If it has a fairly efficient plate transformer and you swap to genset out of phase, and the transfer switch has no 'delay on neutral' or in phase controls, it will trip the breaker. If the breaker trips when the electricity fails and then the generator comes on, it's something else... overpower being a prime suspect as Sparks says.
 
a '60-amp' breaker is only good for 48 amps (80%) 'continuous load'

the fact that the problem went away and then came back with increasing frequency (no pun) after replacement, plus your observation that the breaker 'is warmer than any other in the box' confirms that your breaker is running right at the edge of its rating

IF the transmitter has internal fuses on the incoming line, pull in whatever size wire is needed for an 80-amp breaker (# 2, I think) and use an 80-amp in the panel
 
I have a Nautel 5 kW FM that the generator did not like. When the generator took the load, there was a loud hum from the transmitter cabinet, the fluorescent lights went way bright and all the fuses blew in the equipment in the STL rack. I measured the voltage from the generator and it was over 320 volts (supposed to be 240) when the transmitter was connected. A call to Nautel resulted in disconnecting some capacitors that are placed across the incoming line for power factor correction (apparently a Canadian requirement). The voltage regulator in the generator did not like those capacitors if its frequency was off a bit.
 
I ran into this twice with a HT-5 and each time replacing the breaker solved the problem for about 5 years. The station had a cheap GE panel with inexpensive breakers and I just chalked it up to the breakers failing.

I used to have a similar problem with nuisence breaker trips with both a Harris FM-10H3 at one station and a FM-10k at another. In in one case the breaker was bad and in the other the breaker was undersized (the station had gone from 7.2kw to 10kw at some point in the past and no one had bothered to up the ampacity. Luckily the wire to the tx was sized for 10kw so it was a simple matter to replace the breaker.

I know of several engineers who solve this problem by upping the breaker size to say 80A and then using a 60A fused disconnect to feed the problematic tx. Fuses can be much more forgiving and I think Harris even specifies a certain type fuse for that transmitter. The handle on the disconnect also serves as a easily identifiable way to shut off the transmitter in a hurry.
 
Keep in mind that the thing that makes a properly operating circuit breaker trip is heat. When you draw too much current through the breaker, the heat caused by the overload forces the breaker to trip. The fact that it is already hot when the generator kicks on makes it something less than a 60 amp breaker.

They should NOT be hot under normal circumstances. You are probably using a residential panel instad of a commercial panel, and they just aren't designed for the 24x7 load you are putting on it. Then when the generator kicks on, the surge current from the startup is enough to kick it off.

I had a station that did the same thing, for the same reason. A residential panel is so much cheaper than a commercial panel, that many owners will opt for that, especially if they plan to build it then sell it. Because it works for a few years.

In my case, it was a 100 amp breaker for a Harris HT-10. It eventually started burning up the connections inside the panel, where the breakers plugged in.

A good electrician and $3500 and my problems went away.
 
Before you go crazy solving this put a wattmeter on it. Do the wattmeter and the indirect method meet? How has your tube life been?

The 3.5k will do 8 kw and Harris sold this box with a different meter and label as their 7.5k.

Retapping the plate transformer for more plate voltage goes most of the way with the stock solid state ipa. Easy 7kw no external modification.

Then if it is operating normally change to a 100 amp breaker (with appropriately size wiring) or turn the power down.

Let us know what you find...or not?
 
I had suggested an increase in the size of the breaker. I will have to double check to see if that had been done (or if it was replaced with like). I know the 2.5K has a fuse on each leg of the mains. The 3.5k has circuit breakers for each sub-component.

The tube is a little over a year old (operating wonderfully). About two months ago, I did the normal tear down/clean/checkup on the unit. Everything appeared fine. As far as the electric service goes, the entire building is done commercial (no residential equipment). Actually, the TV station owner does not allow me to do any electric work there, my client had to have an electrician come in to replace the breaker.

As far as temp with the fuse/breaker... Another station here was blowing fuses often on their kW Harris rig. When they used a laser thermometer only the fuses were hot. Simply adding a blower to the fused disconnect solved their problem. They have not blown a fuse in (10?) years!

Thank you all for the great suggestions and observations!! As soon as I can either get the site owner to allow us to load the generator overnight, or a car hits a pole nearby (more often than one might think...) I will check all the various point you folks have mentioned. I will post back with what I find.
 
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