The standby power plant is expected to stay in its own little room, be ignored and still spring to life to save the day. Sounds like the chief engineer, doesn't it?
In addition, run the plant often enough to use up the full tank of fuel annually.
The subject of lightning protection has been treated before in these pages (some would even say that it has been beaten to death). Therefore, let it be assumed that the tower has been appropriately equipped with funny looking, spiny things; the ground system is appropriately bonded and buried; and all possible precautions have been taken.
And then, there is a blinding flash of light and a very loud bang when lightning hits despite your precautions. For a while, one will usually sit quite still in an effort to perform a quick inventory of one's own vital functions. Once it is realized that no injury has occurred, other than a possible need to change clothes, a few things will start to become apparent. First, there is a funny smell in the air. Hopefully, it will only be ozone and not smoke. The next few realizations come quickly. It is dark, it is very quiet, nothing is running and the production people are asking what happened. They are usually a little slow in noticing things that are subtle, such as lightning. If the chief engineer's job has been done well and the management has permitted reasonable funding, the station will come back to life as the standby generator comes on line.
In fact, today's technology can even eliminate the gap when the station is down waiting for the standby generator. Uninterruptible power systems (UPS) are available to keep the whole plant running for a brief period, even including very large transmitters. UPS equipment doesn't have to keep the whole station running for an extended period. It is only necessary to keep the essential systems running until the standby generator has started and is on line. One or two minutes are more than satisfactory. By then, a modern standby plant is more than ready to accept the full station load until the primary power source is available. Then the UPS can again keep the necessary systems running while the switch is made back to the utility power system. In addition, a UPS will eliminate the glitches that often occur in the building power when switches are made.
Actually, the UPS system doesn't have to be sized to keep everything on line. For example, the building heating and air conditioning systems can wait for the standby plant to come on line. They should, if properly designed, cycle back on line without any difficulty. In a similar fashion, such short-term non-essentials as outside lighting, signs and even the tower lights can wait for the generator. However, as the UPS will probably be added to an existing plant, it may be less expensive to simply buy a larger unit than to rewire the distribution system to bypass smaller non-essential loads.
To be realistic, most stations won't opt for a UPS that is big enough to carry the whole load. Management will probably accept the momentary break in power while the generator comes on line. In that case, it makes a lot of sense to install several smaller UPS systems to keep some systems on line over the break. For example, a small UPS such as is available at any electronics supermarket will work to keep the control circuits and exciter in the transmitter up and running. In these days where the transmitters have multiple computer systems in operation, this can avoid glitches requiring rebooting from occurring. The transmitter will stay ready to come back on line with only the high power systems down. The UPS in the transmitter control and exciter circuits will keep those systems ready to resume operation, but some precautions need to be taken.
In some transmitters, maintaining the control systems with no power to the high voltage or high power circuits can result in a big bang when power returns. For example, step-start circuits may not realize that there has been a break in the power. As a result, high voltage can be applied instantly to amplifiers that have been without filament voltage, magnet currents, etc. That can result in the resumption of power being accompanied by loud and expensive noises and the recognizable odor of burnt carbon. Before a UPS is installed in the control circuits, check with the manufacturer of your transmitter to determine just what systems can be safely included in the standby feed.
In addition to the transmitter exciter and control systems, many of the studio systems can benefit from a UPS. This would include a number of pieces of equipment that are digital and controlled by computers. It isn't really the total loss of power that can cause this equipment to enter La La Land. Most systems will tolerate a clean break in power just as they handle being switched off. While they may require a little time to boot back up, most equipment will return to a reasonable state on the return of clean power. Some equipment will actually return to the exact mode in operation when power failed although many may require that you bring them back from some default mode. The problem is when the power fluctuates as the utility system attempts to recover from its own problems. Everyone has experienced this problem during storms. The electrical power may experience short-term transients as distribution circuit breakers reset after faults or as the power system eliminates feeds to downed power lines. The power may come and go two or three times or drop to a low level during such situations. This introduces some really ugly glitches into system power supplies that operate computer driven controllers. The computers see incoming pulses, albeit from the wrong inputs, that look like more ones and zeros, and attempt to include them in their operation.
The UPS systems will eliminate most if not all of those glitches, even if the final result is that the systems will end up being without power. At least the break will be clean rather than erratic and noisy. Those same glitches can result from the switchover from main to auxiliary power. In this respect, the UPS is used not as much for the standby power aspect as for valuable power conditioning.
One more item in the whole chain should still be considered. The standby power plant is expected to stay in its own little room or enclosure, be ignored almost all of the time and still spring to life to save the day. Sounds like the chief engineer, doesn't it? It will fulfill that role only if it also receives a little tender loving care. Most large plants are diesel powered. Diesel fuel is susceptible to some really nasty critters that love to live in that atmosphere. These can build up to the point where they occupy most of the volume of the fuel tank and have to be physically removed. They can be avoided by adding appropriate fuel additives. These additives can be found at most truck stops. Even better, try visiting a marine supply store. Boaters tend to let their craft sit through the winter without operation. That allows the bacteria to build in the fuel tank and cause great difficulties in the spring. The additives need to be put into the fuel to prevent such growths. They will work after the fact by killing off the intruders, but the result will be continuing problems with fuel filters as dead bacteria plug them. The solution is to prevent the bacteria from forming in the first place. In addition, run the plant often enough to use up the full tank of fuel annually. That not only exercises the plant but keeps reasonably fresh fuel on hand.
The regular exercising of the standby plant serves a number of functions. First, it is good for the engine itself to be operated. Some manufacturers strongly advise that their engines be operated at least once a month and that the operation be long enough to bring all operating temperatures up to normal values. In addition, this will assure that the starting batteries are maintained at full charge. Engine block heaters must be checked to determine that they are operating normally. Nothing will make the chief engineer look more foolish than a trip to the auto supply store for batteries or a can of ether when the generator won't start when needed. The suits in the front office become unhappy when they have authorized big bucks for a standby plant and still find themselves in a dark, cold office with no hot coffee.
Don Markley is president of D.L.Markley and Associates, Peoria, IL.
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