By Don Markley
Editor’s note: Maintaining power to a facility is job one for any engineer. For the next few columns, we will learn from Broadcast Engineering’s former expert on power and RF systems, Don Markley. While his dedication to teach others was timeless, Don left us Oct. 22, 2009.
There is an old joke that has been floating around the industry for years. It claims that a station chief tested the standby power plant every week for years by starting it and running it for a short time. When the day came that the power actually failed for the first time, he couldn't get the generator online; it seems that the starter button was worn out.
That doesn't mean you should stop doing maintenance. In truth, the entire primary power system needs ongoing service. The time involved and frequency of the work may be different than for the RF or video systems, but it's an absolute must.
Primary power system
The primary power system includes at least four smaller systems in a modern television transmitting facility. The main disconnecting switch enables the delivery of primary power to the entire plant. That switch may also contain fuses or a circuit breaker in accordance with the system design. The design should include a short circuit analysis by a professional engineer. In the simplest terms, the short circuit test determines the maximum current that would flow if the power mains were shorted after the main disconnect. The switch, fuses or circuit breaker must then be designed to actually break the circuit if a short occurs.
The maintenance on this part of the system is relatively minor. It's necessary to keep the inside of the box clean and rodent-free. In addition, thermal imaging should be done at least every two years to check for hot connectors or failing components. Use appropriate protective clothing and devices when opening this unit to comply with OSHA requirements. Again, calculations are needed to determine the extent of such protection.
The next system in line is the transfer switch between the commercial mains and the auxiliary power plant. Maintenance includes occasional activating, which could occur when the entire auxiliary plant is exercised. Without other indication of failure, keep everything clean. Again, thermal imaging on a periodic basis will show overheating contacts of components.
Start the standby generator itself periodically. Operate it under load until the engine and generator reach normal operating temperatures. The frequency of such testing is as recommended by the individual manufacturer. In addition to running the unit, check the vital liquids. That includes the lubricating oil and coolant. The manufacturer will specify the actual coolant to be used. Tap water is never recommended. The coolant will normally contain additives to prevent rust and corrosion.
The fuel system varies from plain old gasoline to diesel, propane and natural gas. Generally, the type used is selected at the time of the original installation. Conversion between some fuels is possible by the manufacturer or dealer but not for such a change as from gas to diesel. Propane and natural gas only require minimal servicing. Gasoline works well if the system is regularly operated. Problems can occur when the gas isn't moved through the lines. If it's allowed to sit there, gasoline will cause residue to accumulate inside the lines and, if used, the carburetor. Diesel fuel tends to allow microbes to grow in the tank until they totally plug up the fuel system. This can be avoided by using one of the common additives available from your local part store or truck stop. The use of such protection in diesel fuel is almost mandatory in both the storage and the day operating tank.
The uninterruptible power supply (UPS) units filter and regulate the primary power. In case of failure of the main power source, they maintain the needed power output until the generator is online and capable of accepting the load. To keep everything going during that gap, they use either batteries or a flywheel and generator.
If batteries are used, the obvious maintenance includes cleaning off all corrosion from the posts and connectors. If the batteries are not the sealed type, the liquid levels must be maintained and the charge confirmed. There is no excuse that will placate the front office if the system won't function because you allowed the batteries to die. The charging circuits must be checked regularly as well as the battery charger on the standby power plant.
Some new UPS systems use a high-speed flywheel with a generator to supply the interim power. The flywheels operate in a sealed environment, which is often pressurized with a suitable gas. There isn't a lot to do on the flywheels other than to follow the manufacturer's direction for returning it to the factory upon failure. Although high-tech, the new designs of these units are physically small, quiet and highly reliable.
So, what should you do to check and maintain power systems? Cleanliness is important inside the various cabinets. You'd be amazed how much damage mouse or rat occupancy causes.
Thermal imaging of all parts of the system should be done on a periodic basis to catch failing components before they cause off-the-air time. Check the standby power plant as recommended by the manufacturer. The entire system should be tested on a periodic basis. At least once or twice a year, shut down the primary power by opening the main disconnect. If all goes as planned, you shouldn't notice anything wrong in the equipment. I recommend performing this test during the wee hours just in case something doesn't go well. The idea of trying to explain what happened to management when the station went down during high paying time is simply unthinkable.
Keeping the standby and primary power systems in good condition is relatively simple. Maintaining these systems is straightforward and doesn't require much time. If incorporated into a regular maintenance schedule along with that for the rest of the transmitting equipment, everything can be done in a few hours per month. However, no maintenance will likely cause a lot of hours to be blown, as well as a possible job, if the system doesn't provide the necessary functions to keep the stations on the air during power failures.
Acknowledgement: This article originally appeared in the Sept. 2008 edition of Broadcast Engineering magazine.