Pictures of a backup power systems replacement evolution at one of our clients. The old generator was a Katolight 45FGH4, circa 1990. The new generator is a Cummins Power GGHE-1503557 60 KW 3 phase. Unfortunately, when the Katolight generator was moved from the previous studio location in 1998, it was never installed correctly. The 500 gallon propane tank was undersized, the gas tubing was undersized, etc. We fixed those items, but the damage was done. After running too lean under load a few times, the head gasket blew and there is oil in the antifreeze and antifreeze in the oil. It is a Ford straight six engine, and sure, we could rebuild it, but why bother. This is a major group of stations in a very lucrative market, it makes much more sense to replace the entire unit.
In addition to the head gasket problem, the load on the generator has increased. Since the old generator was installed in 1998, two more stations have been added to this facility. That means another air studio, another production studio, more computers, servers, air conditioning etc. Thus, the new generator is rated for 60 KW.
After the GENSET is placed, connections for remote start, battery charger, block heater and AC power output are made. We were able to reuse the existing conduit and cable, thankfully the electricians used 3/0 AWG cable for the AC power connections to the transfer switch.
It appears that they have dropped the Onan name, but not the color, completely.
Radio facilities, particularly mountain top transmitter sites, are prone to power transients. The causes can be varied, but most often, lightning is the culprit. Long power transmission lines to the site are vulnerable to direct strikes and EMF induced spikes from nearby strikes. Other issues, such as switching transients, load fluctuations, and malfunctioning equipment can lead “clear weather” outages. Of course, the best way to deal with such things is prevention.
Power line surge suppressors have been around for quite some time. They usually take the form of a MOV (Metal Oxide Varistor) connected between the hot leg and neutral or ground. There are a few differences in designs, however. Typically, most facilities employ a parallel surge suppressor. That normally take to form of an enclosure hung next to the main power panel with a group of MOV modules in it. The MOVs are feed from a circuit breaker in the panel. Like this:
This is an LEA three phase 208 volt shunt surge suppression unit, which has MOVs between all phases to ground and each other. That is connected in parallel to the electrical service with the circuit breaker disconnect. These function well enough, provided there is a good bit of series inductance before the unit and also, preferably after. The series inductance can come from many sources, including long secondary leads from the utility company transformer or electrical conductors enclosed in metal conduit, particularly rigid (verses EMT, or FMC) metal conduit. The inductance adds a bit of resistance to the transient voltages, which come in higher than 50 or 60 Hz AC waveform.
A better method of transient protection is the Series Surge Suppressor. These units are installed in line with the incoming service and include an inductor to add the required series resistance coupled with MOVs and capacitors. Most series surge suppressor also filter out harmonics and RF by design, something desirable particularly at a transmitter site. Series surge suppressors look like this:
This is a LEA three phase 240 volt unit. As in the other example, all phases have MOVs to neutral and each other. There are MOVs and capacitors on the line and load side of this unit (line side is the bottom of the inductor). A basic schematic looks like this:
A few things to note; MOVs have a short circuit failure mode and must be fused to protect the incoming line from shorts to ground. MOVs also deteriorate with age, the more they fire, the lower the breakdown voltage becomes. Eventually, the will begin to conduct current at all times and heat up, thus they should also be thermally fused. MOVs that are not properly protected from over current or over temperature conditions have the alarming capacity to explode and/or catch on fire. From experience, this is something to be avoided. Matched MOVs can be paralleled to increase current handling capacity.
The inductor is in the 100 µH range, which adds almost no inductive reactance at 60 Hz. However, it becomes more resistive as the frequency goes up. Most transients, especially lightning, happen at many times the 60 Hz fundamental frequency used in power distribution (50 Hz elsewhere unless airborne, then it may be 400 Hz).
Capacitors are in the 1-10 mF range and rated for 1 KV or greater as a safety factor. The net effect of adding capacitance is to create a low pass filter. Hypothetically speaking, of course, playing around with the capacitance values may net a better lowpass filter. For example, at 100 uH and 5 mF, the cutoff frequency is 225 Hz, or below the fourth harmonic. Care must be taken not to affect or distort the 60 Hz wave form or all sorts of bad things will happen, especially to switching power supplies.
These units also need have a bypass method installed. If one of the MOV modules needs to be replaced, power to the unit has to be secured. This can be done by connecting it to the AC mains before any generator transfer switch. That way, the main power can be secured and the site can run on generator power while the maintenance on the surge suppression unit is taking place.
Power loss is a critical failure, thus much money is spent to prevent or mitigate commercial power interruptions in broadcast facilities. Backup generators and Uninterruptible Power Supplies (UPS) are the first line of defense against commercial power interruptions. It is prudent to research products and check reliability and interoperability when specifying and installing these systems. However, even the best mechanical and electrical systems will fail, often at the worst possible time. The UPS has a startling tendency to shut down, often at the worst possible moment, due to some internal control circuit or something similar. This can happen when commercial power is being supplied without interruption. The net result is some critical piece of equipment is now dark and the station is off the air.
There is a solution: The Eaton EATS EPDU TPC 2234-A Automatic Transfer Switch.
With this unit, the primary plug is connected to the output of the UPS, the secondary plug is connected to the commercial power source. If the UPS fails, the load is automatically transferred to the commercial power. Typically, the commercial power is also backup up with a generator. The secondary plug can also be connected to a second UPS. In theory, having two UPSs connected in parallel via an Automatic Transfer Switch would increase the Mean Time Between Failure (MTBF) by 50%.
The Eaton products come with a variety of options, including basic network monitoring, advanced network monitoring, switching and management. Those features are available via Ethernet or serial data port.
Multiple layers of redundancy is the best method to avoid those late night, weekend or holiday phone calls.