The Broadcast Bridge recently had the opportunity to ask GatesAir Television Transmission product manager Martyn Horspool about transmitter power protection systems. When installing transmitters, Horspool suggests engineers consider these points.

Q: What do transmitters need, spike protection, surge protection, power conditioning or full UPS?

Today's transmitters comprise complex electronic circuitry, which includes sensitive items within the exciter and control circuitry. Modern transmitters contain microprocessors, FPGA’s (Field Programmable Gate Arrays) and other low-level logic devices which may be very sensitive to noise, voltage transients (spikes) and voltage variations. Also, the power supplies used in transmitters are generally of the high-efficiency switch mode type that although rugged and well protected, may sometimes need additional protection. The requirement for protection is very site specific and can vary from case-to-case.

Typically a UPS for the entire transmitter site is only purchased by stations wishing to avoid off air situations due to brief power interruptions. A diesel generator can be used to provide long-term power. However, because these items are quite costly, they are typically limited to use at sites owned by large stations in key markets.

Q: What are the risks with raw power?

“Raw power” is defined as a power source that includes zero surge protection or voltage regulation. There are risks associated with using raw power at a transmitter facility. High voltages may cause damage to sensitive electronics, not only in the exciter and transmitter but also in microwave equipment, tower light controllers and other equipment at the transmitter site. Low voltages may cause equipment to perform outside of its specifications, or even shut down.

Q: What exactly are we trying to protect the transmitter and associated electronics from?

The main protection required at the transmitter plant will be for transient overvoltage events, which are usually very short “spikes” or transients in voltage that are riding on the AC waveform.

Q: Where are risks higher, in the city or out in cow pastures?

This is a bit hard to answer as there are certainly sites in a city where there is potential for large transient spikes to enter the AC power service to a building, including the transmitter site. It depends a lot on the AC power service, location of transformers, overhead power wiring that is exposed to lightning and also the amount of isolation from power surges due to load switching in the area. In the countryside there is a greater risk, due to the usually longer power distribution network (distance from the power source) and usually greater opportunity for lightning to be a factor.

Q: What are the important differences between spike protection, surge protection, and power conditioning? Are there other alternatives worth considering?

There are many words that describe various types of AC power line protection:

• In my opinion, spike protection and surge protection are the same thing. Spikes, or surges on the AC power line describe short term events that represent a transient overvoltage condition. Usually the duration is measured in nanoseconds to milliseconds and the overvoltage (or “spike”) may be from hundreds of volts to thousands of volts. I use the term transient protection to describe the type of device that protects against this. This type of device may be termed a “Transient” protector, or even a “TVSS” (Transient Voltage Surge Suppressor).
• Power conditioning is an ill-defined term that may include transient protection, filtering to reduce noise on the line and voltage regulation to stabilize the AC line voltage to an acceptable range. I  would not use this term, as requirements for transient protection, filtering and voltage regulation may be different.

You will need a bigger power strip

Q: What, other than voltage and current capabilities, what might be the difference between what a transmitter plant needs and an inexpensive power strip I can buy at the local hardware store?

Just the size and the ratings. A single phase power strip with built-in transient protection is useful for protecting a PC, or other electronics but it isn’t big enough to protect a transmitter.

Q: What is the best choice for TV transmitter plants, likely to include a STL or satellite receiver link, an exciter/modulator, and an internet connection, router, and other small electronics?

The answer depends upon the site specifics and location as well as the quality of the power source and the geographic region. The very best solution for a transmitter site will be a large, high-quality transient protection device at the main AC power panel complemented with additional smaller transient devices downstream. These power strips should be located close to smaller sensitive equipment which may include exciters, satellite receiver, computers and other control systems.

Q: Is 50/60Hz frequency regulation an important issue?

No, this is not an issue. Modern transmitters will make all specifications with an AC frequency range of 47Hz to 63Hz. The frequency of the AC mains power is extremely stable in the USA and most other countries. The expected frequency range is typically within +/- 0.5Hz of 60Hz for the USA and usually it is well within 0.1Hz.

Q: What should I look for in surge protection?

The best transient surge protectors clamp the maximum voltages to an acceptable level that will protect downstream equipment. Because lightning can produce huge transients that could easily destroy electronic equipment, transient protection can make a huge difference in the reliability of such equipment. 

Q: At what point does it kick in and pay for itself?

This you will never know. Because you can’t easily measure the reliability of equipment, or determine what caused a failure, it becomes almost impossible to calculate a payback period. However, based on service records kept by us, the evidence points to the value in using high-quality transient protection. Stations that have had failures during a thunderstorm have seen fewer failures after installing good quality protection. While power protection technology does not guarantee that no damage will be caused by a direct lightning hit to the power line, but it can certainly reduce, or eliminate such damage.

Q: What is the cost of saving money?

Let's compare the value of the investments. A transmitter plant can cost between $50k and $1M. The cost of a well-designed surge protection system will cost from $1k to about $10k, depending on the technology used and the level of protection provided. The average price of surge protection devices that we sell with our new transmitters cost around $2k. This seems like a small price to pay for additional protection.

Q: How does its circuitry do the job? Diversion, regulation, regeneration?

The typical surge protector diverts the energy of the transient through a device that can absorb the short duration and high-energy event. Surge protection devices include; MOV’s (Metal Oxide Varistors), SAD’s (Siilcon Avalanche Diodes) and spark gaps. These all start to conduct energy (power) when a threshold voltage is reached. The number and size of devices used in parallel within one surge protection device will determine how effective it will be in protecting against transient events and how much protection is provided. At least one manufacturer uses both MOV and SAD technology together in the same device, to provide an extremely effective solution and very fast conduction turn on time.

Q: What are the significant specs to look for when purchasing?

There are industry standards that all reputable surge protector manufacturers use. These define things such as the test waveforms used, the clamping voltage, “let through” voltage, the speed of the device and the maximum surge current that it can divert (absorb). Some industry standards to look for include:

a) UL 1449 3rd edition, Sept. 2009

b) IEC 60643-1

c) EN 61643-11

d) CAN/CSA-C22.2 No. 8

Some technical specifications that are recommended (for a 208 WYE service):

a) Maximum continuous operating voltage: 275 V AC

b) Response time: ≤ 25 ns

c) UL: type 2

d) Nominal discharge current 20 kA

e) Maximum surge current per Phase 50 kA

f) Short-circuit current rating (SCCR) 50 kA

Installing protection

Q: Any installation tips?

In general, installation should always be per the manufacturer's recommendations. My own thought is to ensure that the device is located as close to the main AC service panel as possible. Always use the shortest most-direct electrical connections and avoid bends in the wiring. Keep the wiring short for all parallel surge protection devices. This will help reduce inductance and resistance, both of which can negatively affect their performance.

Q: Can you review the importance of good grounding practices for transmitter buildings, including around the building and tower.

Perhaps equally important to overall lighting and surge protection is to ensure that the building ground and tower ground are as good as possible. The topic of grounding at a transmitter site can be quite complex and deserves a lot of detail, well beyond the scope of this discussion. Here are some general recommendations:

• Keep grounding leads as short and direct as possible.
• Use large conductors for ground wires; wide, flat copper straps are preferable to round wires.
• Bends in ground wires must have a minimum 20 cm (8 in) radius. Do not bend the conductor into acute angles; any angle formed by the conductor should be no sharper than 90 degrees.
• Use compatible materials when constructing grounds. Any exposure to moisture will result in corrosion between dissimilar metals.
• Keep ground leads separated from other wiring.
• Weld, clamp, or crimp grounding connections. Do not solder ground leads.
• Use single-point grounding. Do not install equipment in the path to ground (i.e., antenna connected at top of cabinet, ground at bottom).
• Bond all main and incidental grounds together. This includes the ac power, telephone, perimeter and tower grounds, water lines and other underground facilities, except gas lines.
• Do not run grounding conductors through metallic conduit unless the conductor is bonded to the conduit at each end.
• Do not run grounding conductors through metallic surfaces or plates unless absolutely necessary. If the surface or plate is grounded, attach the ground conductor on one side and attach a continuing conductor on the other side.
• Do not encircle grounding conductors with metallic clamps or brackets unless they are to provide an electrical connection to the conductor.
• Document the ground system.
• Periodically inspect the ground system.
• Measure and record the soil resistivity and the grounding system resistance for future reference.

Finally, get professional advice when planning or designing the station ground system. It will be money well spent.