Sometimes there is just no way around it, especially with some modern equipment:
Hard restart, Nautel VS2500 transmitter
This Nautel VS2500 transmitter got all cranky after lightning struck the tower (or nearby) on Friday night. Thunderstorms in February are not unheard of, but they are unusual, at least in the Northeastern United States.
Nautel VS2500 FM transmitter, WBEC-FM, Pittsfield, MA
Anyway, the transmitter would not reset or restart via remote control, therefore, we had to ride the chair lift to the top of the hill and pull the plug to reset its logic and start over again.
Bousquet Ski Area Chair lift
At least the trip up to the transmitter site was scenic. We had to wait a day for the winds to calm down, but all in all, not a terrible day. Did I mention the scenery?
Some people work in offices and make lots of money. Others work outside, oblivious to the world going on around them. A fortunate few, myself included, get to work in many different environments, and appreciate them all.
A week or so ago, at the end of the day, I was carrying my tool bag back to the truck and was surprised to see this view:
View looking west from the WRKI transmitter site, Brookfield, CT
The picture really does not do justice. A much wider view is required to get the full effect. It looked like the sky was on fire, something out of a science fiction movie.
Then again, yesterday, I spent the day in a dank, smelly basement tracing out telephone wires. In the end, it all evens out.
An issue I had to deal with recently; was an unstable generator/UPS relationship. When the generator was running under load, it surged repeatedly causing the UPS to drop out and not recharge. Eventually, the UPS ran out of juice and shut down, killing the power to the Sine Systems remote control and telephone system. Of the two, the remote control was the biggest pain to fix, as it lost its timed commands and would not reduce power at sunset for the associated class D AM station.
What went wrong? This is a chart of typical problems with generators operating UPS loads:
Symptom
Potential Problem
Fail to “lock on” to generator power
Improper generator frequency or voltage Poor generator regulation Unrealistic performance requirements
Instability of generator
Voltage regulator sensitivity Control loop compatibility Filter/control interaction Governor or AVR problem
Generator excitation methods can be the culprit in many of these situations. Generators often use one of three types of excitation for their field coils:
Shunt-excited SCR (silicon-controlled rectifier)
Shunt-excited PWM (pulse width modulation)
PGM (permanent magnet generator)
Of the three, the permanent magnet generator is the most stable since the AVR (automatic voltage regulator) is powered by a separate small generator which is unaffected by the load on the main generator output. SCR and PWM both use the generator output windings, which makes them susceptible to load-inducted voltage distortion brought on by non-linear loads. Therefore, in locations where large UPSs are known to be part of the load, PGM-excited generators are the best choice.
PMG generator diagram
Sometimes, the generator is already in use before the UPS is installed. In that case, there are some remedial steps that can be taken. The speed which the voltage regulator reacts to changes in the load is often the culprit in many of these situations. It may seem counterintuitive, however, the faster the AVR reacts, the more fluctuations there will be in the voltage and frequency. A UPS can operate under a wide range of voltages and frequency, provided they do not rapidly change.
Depending on other loads, it may be necessary to dampen the gain on the AVR to slow it’s reactions down. This will work if there are no large intermittent starting loads on the generator such as air conditioning compressors.
Another method would be to delay the UPS transfer to generator power until after all the other loads have been satisfied. This will ensure that the generator voltage and current fluctuations are damped by the existing load.
The generator’s size needs to account for the equipment attached to the UPS and the battery charging load. With a larger UPS, the battery charging load can be significant. Generators that are improperly sized will not be made to work under any circumstances, hence the “unrealistic performance requirements” noted in the chart above.
You can read the entire Cummins Power white paper on generators powering UPS loads here.
I found this manual from 1946 in the drawer at the WICC transmitter site, which is a sort of time capsule due to its inaccessibility. I figured I would bring it home and scan it, then return it to the file drawer out on the island. Step one is done:
Raytheon RM-10 Monitor Amp
This is a cool little monitor amp, capable of driving line-level or speaker outputs up to about 10 watts or so. It could be used as a front or input stage for a larger audio amp. By the way, 10 watts is a lot more than it seems, if using efficient speakers to convert that power into sound waves. Specs show total harmonic distortion is between 0.6 to 2 percent depending on power and frequency. Lower power output levels net less distortion.
Schematic is pretty simple, a pair of 6L6’s in push-pull for the output. Inverse feedback into the previous stage via the output transformer. Click on image for higher resolution.
