6/18/2009 10:00 AM
For truly large backup power or to power a system for many hours or days, a generator is required. We could spend the next week covering aspects of generators, but if you take away anything from this series of articles on backup power, remember this: Designing and installing a backup power system is best left to the experts.
Sure, you’ll need to know some basics, system designs, trade-offs and principles. But when it comes to mounting that behemoth and connecting the system to your power grid, get some help. Let’s begin our discussion on generators with some basic terminology.
When I was an active amateur radio operator, one goal was to somehow obtain a MARS generator. MARS stands for Military Affiliate Radio System. Basically a MARS station was some guy or group that managed to parlay ex-armed forces equipment, which they used to build a ham radio club. I was always jealous.
However, I had a neighbor who was successful in getting a MARS generator, and he installed it on a skid inside his garage. When fired up, I’ll bet that old generator violated every noise and environmental pollution regulation in existence. So much for military surplus.
What I’m getting at here is when planning a backup power system, don’t go for cheap. There may be old generators available for sale, but you don’t want them. With increased regulations on noise and pollution, you don’t want to spend $25,000 only to find that the generator violates some regulation. Besides, the entire goal of backup power is for it to be a reliable source of power. Old equipment often equates to unreliable equipment.
Reliability is everything
Let’s first establish the need for dependability. Based on data centers, the need for generators to provide 100 percent, five or more nines predictability has become paramount. New generators are designed from the get-go to be reliable. And, they are designed to be monitored and operated by less technical personnel.
A television station may have someone on staff who could “kick start” an uncooperative generator, but modern data and computer centers do not. Those guys know nothing about circuits carrying more than 5V — but that’s not meant to be demeaning. See my first paragraph. Even so, would your local IT geek know how to determine when a generator’s oil pressure was too high? Could she manually operate the automatic transfer switch (ATS), assuming she even knew where it was located? Next time your CFO tells you to “Let the IT people handle it,” refer her to my blog post on using nonexperts to build your backup power system.
A typical backup power configuration and management control system is shown in Figure 1 to the right. While your installation will differ, the basic components will be similar. So, let’s move on and look at some of the issues that need careful consideration before you buy that backup plant.
Step one: Select a fuel
Today’s gensets are typically diesel, natural-gas, Liquid Petroleum (LP) or gasoline-powered. For any facility-sized generator, a gas-powered version may be your least desirable solution. Why? I thought you’d never ask.
Do you have any gas engines at home? What is the recommended winter maintenance? I’ll bet the manufacturer says to either run the engine until it’s totally out of fuel, or that you add a fuel stabilizer (heat is one product) for wintering. In addition, what happens to stored gasoline? First, it evaporates. Second, it collects water. Third, it solidifies. None of this is good for an engine that must be reliable and start in a matter of seconds.
Actually, the selection of the type of fuel to power your generator depends on several factors, including environmental regulations and, well, that about covers it. Many, if not most, of your decisions when it comes to installing genset are controlled by regulations, not technology.
For instance, storing gasoline underground poses a significant hazard to ground water. While you may be able to get a permit to install an underground fuel tank, you will also likely to be required to install an EPA-approved leakage detection system. In addition, should anyone in 50 miles complain about tainted water, be sure you know the phone number of your company’s attorney. For these and many more reasons, today’s generators are often powered by LP or natural gas, both of which don’t suffer the problems from inground storage systems.
Step two: Noise, emissions and exhaust
My story about the MARS generator is an indication of how important nonelectrical issues may be to your selection of a generator. Almost any HVAC guy could build the ductwork to vent a generator. However, whether or not the result would meet environmental and regulatory issues is something else.
Many of the regulations you’ll face are local. One significant requirement will be noise pollution. Typically, there are three levels of permitted noise levels, and you have to certify the installed system will meet the one for which you have a permit. Again, rely on your vendor for this information and assurance.
Step three: Cooling and air
Other key factors that must be considered include air intake and cooling needs. Generators require a lot of air and produce a lot of heat. The site installation must fully accommodate both of these factors.
Air filtering performance must be monitored as the generator will perform a safety shutoff if inadequate cooling or insufficient clean air is available.
If you’d like to know more about generators and their installation and maintenance, the Electrical Generating Systems Association (EGSA) is a wealth of information. You can even become EGSA-certified in the installation, maintenance and repair of generators and on-site power systems. Check out their Web site if you’re interested in the program, or in case you need help in learning more about gensets.
Step four: Generator mechanicals
I once knew of a TV station that installed a generator next to its studio, thinking there would be no significant issues. However, all heck broke loose when the production director discovered he couldn’t record in the studio because of the vibration caused by the generator’s operation. Of course, this issue didn’t reveal itself until a new show was in the production schedule and the generator fired up to perform its weekly maintenance test. I think the CE retired as a career grade school teacher.
In addition to the previous requirements, generators need lubrication, which means lots of filtered oil. Also required is filtered air and fuel. All these mechanical systems require maintenance. Fuel and oil must be properly filtered and stored. Reserves must be maintained — and checked. On large systems, dual oil paths will be provided for both so maintenance can be performed while the system is operating. All this sounds simple until someone forgets and the generator fails to perform when needed.
The bottom line is that regular generator maintenance may be left to an outside firm. The technology may seem simple, but never forget, the idea is that it must run when required. No ifs, ands or buts ...
A genset is worthless unless it is running. That’s where the starter motor comes in. Once triggered, this small motor spins the combustion engine until it starts. Hopefully that will happen rapidly. Any facility UPS equipment will be operating because the main AC power has failed, and there is only a brief time before their batteries will die. The generator must get up to speed, switch to online operation and assume the load quickly. This often takes 10-15 seconds. Unless the generator gets online before the UPS batteries run down, the entire backup system will have failed. So much for protection.
Unfortunately, as any engineer of experience may confess, that startup period may be far longer. The key is to be sure that the generator starts promptly. That predictability is wholly based on proper maintenance.
Starter batteries must be trickle charged by an external circuit. If the generator is located in a cold climate, block and battery heaters also may be needed. Keep in mind that batteries are rated in Cold Cranking Amperes (CCA). That’s how many amps the battery can produce for 30 seconds at 0 degrees F. If a battery is called upon to crank a baulking generator at even colder temperatures, the battery may die quickly, perhaps before the generator can start. The No. 1 cause for a backup generator not producing power when required is that it won’t start. Duh!
Generators need to be regularly maintained and tested. The failure to perform either task virtually guarantees that when you need it most, the generator won’t work. Remind yourself of that former CE who ended up being a grade school teacher.
In the next column, we’ll discuss the workhorse part of the generator — the alternator and key sizing factors when combined with facility-sized UPS systems. The final part of the article will look at how kinetic energy systems (flywheels) can be used to produce power to bridge that breath-holding time gap between when the generator is asked to start — and it finally does.
Fundamental principles of generators for information technology
Essential standby generator system requirements for next-generation data centers
UPS and generators together — the only true 24/7 power solution