For much of our discussion, we’ll rely on standards established for data centers. One reason is that there exists a large database of information about how to harden these facilities against power outages. Another is that data centers can be deemed to be at least as critical to the public as broadcasters’ signals.
Finally, using data center guidelines as a backdrop provides a uniform standard of measurement of expected performance. The user can determine what tier of performance is needed for any particular facility. Then, the appropriate decisions regarding equipment, predicted downtime and other issues can be made. Let’s get started.
Types of backup power
Auxiliary power systems seem obvious, but upon a closer look there is a plethora of options, technologies and solutions to providing standby, backup, auxiliary — whatever you want to call it — power. The gamut runs from just having separate electrical feeds into a facility to complex double-conversion online power systems. The simplest system can rely on dual electrical feeds to the facility. Switching between the feeds will probably be a manual process. This is an effective and quite cost-efficient solution, albeit with some signifying drawbacks.
This solution is effective if each power feed comes from a different power company power grid. It makes no sense to have dual feeds from two close-by power company substations. Any weather phenomena will likely affect both substations, thereby making it highly likely that both feeds could fail at the same time. So much for “backup.”
One problem with getting a power feed from two widely separated substations is the cost. Unless both feeds just happen to be located close to the station, the cost of installing miles of power line will be substantial — perhaps even cost-prohibitive. To the power company, it’s not just the installation cost it has to recover from the user, it’s also the ongoing maintenance costs. And, such a feed may upset the overall system design, further complicating this solution. Of course, money talks, and if you’ve got the budget, this is an effective and totally maintenance-free solution.
If you can’t get a second feed, or even if you can, what is another solution? The most obvious is a generator. Generators are typically powered by diesel fuel with sufficient capacity to power at least the technical sections of your facility for hours or days.
Generators are complex devices. And, they are typically outside the knowledge range of video engineers. Gone are the days when the transmitter engineer could also be expected to maintain the generators. Today, generator systems are often sized, installed and maintained by outside expertise. Don’t let the fact that you can’t maintain this portion of your plant depress you. Just look upon the generator and backup system as a huge hunk of steel that requires people with knowledge of electrical power, engines and transfer switches — all of which can kill you if not handled properly. Leave this work to the experts!
Also, installing generators at any urban location can create its own set of challenges. Pollution requirements make fuel storage difficult, they are noisy, and they are not particularly “green friendly.” And because diesel generator sets use engines, like any motor, they require maintenance. They have a low MTBF and a high MTTR. Motor-generator sets also take time to begin producing power, as much as 20 or more seconds. In broadcast terms, that can be an eternity.
Finally, with generators there is always the cost trade-off of how much of your facility can you afford to power. Generators are expensive solutions, and you may not be able buy one that can power all the technical areas plus business lighting, offices and visitor spaces.
If that’s the case, then you have to have an expert decide how much power is needed for the critical technical spaces, environmental systems and security. Then those systems have to be rewired to they will be on the generator’s feed. Installing a studio generator is not a DIY project.
We’ll look at generator systems, installations and technology much more closely in a later column.
There are several types of UPS systems, but in general they can be broken down into three types:
• Passive-standby (offline, relay-switched and battery-powered, available in .5kVA to 5kVA sizes)
• Line interactive (provide voltage regulation and filtering, available in .5kVA to 5kVA sizes)
• Double conversion online (capable of 10kVA and more, similar as above except that the primary power path is through an AD/DC and DC/AC converter)
UPS systems are sometimes classified by “level of service.” In general the following characteristics apply. (See Table 1 to the left.) While there are iterations of the above, the table represents the most common configurations and enables easy comparisons. Prices will vary widely, and the key is to make careful comparisons about considered models.
Choosing a UPS solution
If only a small area needs to have auxiliary power, a standby UPS may be a good solution. These systems provide no line voltage regulation. Runtime is limited to internal batteries, which often means three to eight minutes of backup protection. A standby UPS block diagram is shown in Figure 2 to the right.
Online UPS devices seldom produce a "clean" sine wave output. If your application depends on clean power, this is not a good solution. Also, a standby UPS system requires a 3ms-5ms delay between AC and backup power. Often this means a relay, so unless your installation can tolerate a brief power interruption, this may not be the best answer.
A line interactive UPS, shown in Figure 3 to the left, has the dual advantage of providing backup power plus, it continually filters the output AC power. A level 5 UPS provides protection against undervoltage and overvoltage. The result is a primitive form of voltage regulation of "bumping" the AC output voltage up or down as needed. The output waveform is often a pure sine wave, which reduces environmental noise.
Level 5 UPS systems may suffer shorter battery life as they are continually turned on and off by incoming voltage changes (recall the primitive voltage regulation scenario described above).The number of transfers to and from the battery may be 10 times higher than of a level 9 UPS.
A level 9 UPS, shown in Figure 4 to the right, is targeted at the needs of crucial equipment. It provides complete protection against all forms of power failures, irregularities and noise. A common description for a level 9 UPS is “online” or “double conversion.” A level 9 UPS uses an inverter to continuously generate clean, regulated AC power. In addition, a level 9 UPS will meet the requirement of providing clean AC power, a feed with less than 5 percent maximum harmonic noise. This is a criteria for approved computer power systems. If you’ve ever tried to remove the noise that is sometimes generated by a level 3 UPS system, you’ll appreciate this feature.
We’ll begin a detailed examination of UPS technology in the next column.