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By Michael Fluegeman
March 2014 -
Power & Communication Article Use Policy
The stakes are quite high when it comes to optional or life-safety emergency standby power systems. Failure to start or failure to run can have enormous consequences. Regular testing, maintenance, exercising, and inspection can help keep standby generators ready to perform when needed.
For optional standby generators (not required by life-safety code), critical loads supported by the generator system typically include data center and call center equipment such as UPS systems, cooling, phone systems, and desktop equipment (computers, etc.).
For emergency standby generators (required by life-safety code), critical loads supported by the generator system typically include emergency lighting, fire alarm systems, fire pumps, and elevators. Life-safety generators are also sometimes used to additionally support optional loads, such as data centers; however, in this case the life-safety loads take precedence over the optional loads.
Good design, quality equipment, trained operating personnel, commissioning, regular inspections and exercising, preventative maintenance, trained service support, and performance testing are all key to reliable performance.
It is important to understand the difference between continuous onsite power generation (prime power), long-term power backup systems (standby generators, almost always diesel-fired), and short-term power backup systems (uninterruptible power systems, or UPS).
Prime power generation includes natural gas-fired turbines and micro-turbine generators, fuel cells, solar, and wind-generated power. Prime power generation is designed to run continuously or at least for many hundreds of hours per year as required by demand or energy economics. To improve prime power economics, engines can operate from alternative fuels (methane, bio-diesel) and heat byproducts can be re-used for other purposes (combined heat/power or co-generation). It is almost never economical to use diesel-fired generators for prime power generation, and in many areas this is prohibited by air quality regulations. When operating critical equipment from onsite-generated prime power, utility power can normally be used as a long-term backup power source. Prime power sources do not normally make good standby backup power sources; prime power sources can take many minutes to start up and often require steady base loads for stable operation.
Backup power system main components can include the engine, fuel storage, fuel delivery, speed governor, voltage regulator, engine exhaust and filter, engine cooling, alternator, circuit breaker(s), engine cranking batteries, battery charger, block heater, paralleling switchgear, load prioritizing and shedding controls, distribution switchboard, automatic and manual transfer switches (ATS, MTS), and local and remote monitoring. Improper operation, lax maintenance, or random failures in any of these components can result in failure of the backup power system to perform when it is needed.
Long-term power backup systems are normally off and in a standby state, waiting for a command to start and provide power for minutes, hours, or days (depending on available fuel and re-fueling capability) during a failure of prime power (typically the power utility). Backup generators are almost always diesel-fired, for quick starting, acceptance of large load blocks, and for effective speed/frequency/voltage regulation with load changes. Backup generators cannot replace UPS systems, however, because they simply cannot start fast enough to maintain adequate voltage continuity for IT equipment.
UPS systems, even though they may run continuously, are intended only to provide short-term power backup, in the matter of seconds or minutes, most often using batteries for energy storage. UPS systems take care of the majority of prime power bumps and failures, which are typically less than a minute in duration. However, UPS systems are not normally suitable for heavy block loads common with HVAC equipment, fire pumps, etc. UPS systems cannot be used for long-term power backup because supported loads are normally limited to IT equipment, and the scale of required stored energy in the form of batteries for UPS systems for long operation escalates exponentially compared to that of diesel fuel for generators. One barrel of diesel fuel is equivalent in power storage energy to a large room full of batteries.
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