THE DANGERS OF REDUNDANT POWER SUPPLIES
Part 2 – Distributed Generation Technology
Part one of this topiccovered tenant redundant power supplies and how electricity comes into a building and is distributed to the tenants. This article begins a discussion of how an entire commercial building can meet some or even all of its power demand in the event it is removed from the local electrical grid. This issue must be understood by first responders,since it may impact their operations and their safety.
The August 2003 blackout in the Northeast cost businesses millions of dollars in lost revenue and underscored the need to avoid reliance on the local utility company as a consistently dependable power source. When New York City went dark, several buildings stayed lit. What did these buildings possess that others did not?
The answer is building redundant power sources. The high-profile tenants who occupy space in these properties cannot afford to be without power and sustain substantial losses. Tenants such as banking, trading, law and insurance firms require uninterruptible power supplies to continue doing business when power from the grid is lost. They also cannot lose their electronic security measures. Thus, the idea of distributed generation (DG) was proven to be a valid, viable concept.
What is “distributed generation”? It is the generation of electricity by a sufficiently large electrical generating system as to allow interconnection near the point of service at distribution voltages, including points on the customer side of the meter. A distributed generating system may be operated in parallel or independent of the electric power system. It may be fueled by many sources, including but not limited to, renewable energy sources.
Cogeneration
Cogeneration is defined as the simultaneous production of electricity and either steam or high-temperature water that is used for a beneficial purpose. Cogeneration is also sometimes referred to as “combined heat and power” (CHP). Sometimes, the heat product is ultimately used as an energy source to produce air conditioning through the use of an absorption chiller. The simplest uses for waste heat are domestic hot water, winter heat and summer air conditioning. Server farms and high-density data centers are ideal candidates for cogeneration since their electrical demands are high and constant, and the heat load from the equipment requires that the space be air conditioned 24/7. While cogeneration can be feasible in a wide variety of applications up to a 25,000 kilowatt commercial installation, they all need a well-matched (and stable) electric demand and a requirement for the heat product. Making optimum use of the waste heat product can raise total fuel efficiency from less than 30% as much as 85%, far better than the 50% or less efficiency delivered by the local electric utility. That’s right; approximately half of the electricity created at power plants never makes it to the customers’ wall outlets, due to losses at the plant and in the distribution network.
Reciprocating Engine/ Internal Combustion Generators
The true definition of an emergency generator according to the U.S. Environmental Protection Agency (EPA) is, “a generator whose sole function is to provide backup power when electric power from the local utility is interrupted.” An “engine-generator” is the combination of an electrical generator and an engine mounted together to form a single piece of equipment. This combination is also called an “engine-generator set” or a “genset.”
In many contexts, the engine is taken for granted and the combined unit is simply called a “generator.” In addition to the engine and generator, engine-generators generally include a fuel tank (for dieselpowered units), an engine-speed regulator and a generator-voltage regulator. Many units are equipped with a battery and electric starter.
Standby power generating units often include an automatic starting system and a transfer switch to disconnect the load from the utility power source and connect it to the generator. Standby generators are permanently installed and kept ready to supply power to critical loads during termporary interruptions of the utility power supply. They can provide emergency power to an individual tenant (single or multiple units, depending on power demands) or they can be arranged in series to provide power to meet all base building power demands and beyond.
These units can be found anywhere in a given building (including even in tenant spaces with attached “day tanks”), but usually are found in the basement or at ground level, on the roof or on mechanical decks within the tower. They can also be located in or on top of adjacent parking garages. Day tanks provide fuel to meet the immediate demands of a generator; longer-duration operations dictate larger storage tanks in the basement, usually in 5,000- to 10,000-gallon capacities. If a set is located on the roof, expect to see a fuel riser running up through the core of the building. We pre-planned one high-rise that had 180,000 gallons of diesel fuel in the basement in 18 holding tanks, each containing 10,000 gallons.
Note of interest about day tanks – The object of a day tank is to provide a “day’s” quantity of fuel that is guaranteed to be clean and dry for the engine. Sometimes, it is used to overcome the problem of excessive suction heads on the engine lift pump. It is important to remember that the clean and dry fuel in the day tank will be exposed to the same conditions that cause the fuel in the main storage tank to become bad. Given enough time, the fuel in the day tank will get to the same condition as the fuel in the main tank. A filter and a water separator are still required on the outlet of the day tank. To provide the desired results, this tank must, in fact, be a “day tank.” That is, the fuel in this tank must remain there for only a short time. All the problems of longterm fuel storage in the main tank will be present in the day tank if fuel remains in it for long periods. Once it ceases to be a “day tank,” it must be treated just like any other tank. Neglected, aged fuel is one of the primary reasons for emergency generator failure.
How Does a Generator Work?
A generator creates an electric current in the conductive wire of its windings. Mechanical energy is manipulated into a rotational force that shoves a magnetic field through a coil of wire and induces a flow of electrons in the wire, converting the mechanical energy into electrical energy. It can do this because electricity and magnetism are two sides of the same coin – the electro-magnetic force. The generator is somewhat analogous to a water pump, which creates a flow of water, but does not create water itself. The most common fuel source is liquid diesel fuel, although natural gas and propane can be used as well. In the majority of high-rise buildings, the typical generator could be expected to be of about 1,000-kilowatt capacity. Sometimes generators are rated in kilovolt amps (KVAs) rather than kilowatts (KWs). The difference between KW and KVA in the simplest of terms is that KW is “true” power, where KVA is “apparent” power, similar to foam in a beer mug for all you firefighters out there. So, a 1,000KW generator would be closely equal to 1,200 KVAs in output.
Generator Compatibility with Uninterruptible Power Supply Systems
A classic operational problem is the starting of other loads on the generator, causing the generator’s output frequency to vary, which then causes the offline or line-interactive uninterruptible power supply (UPS) to cycle on to battery operation. The problem is especially pronounced with natural gas-powered gensets. This repetitive battery cycling can cause the battery to discharge completely, while significantly shortening battery life.
Another potential problem is the generator instability that occurs when the UPS load is transitioned to the generator. The UPS load transfer causes the generator voltage and frequency to sag, causing the UPS to go back to battery operation. Soon thereafter, the UPS senses stable generator output, transfers the load back to the generator, then transfers back to battery operation when generator output dips again.
These problems don’t exist for conventional double-conversion UPSs, which rectify the input supply to DC and can accommodate large swings in supply frequency while continuing to provide regulated, stable AC output frequency without the use of the batteries.
Note: During the 2003 Northeast blackout, data gathered afterwards told a surprising story – approximately 80% of diesel-powered emergency generators failed to come on line or even start, due to gelled (aged) fuel, no fuel or lack of proper maintenance. Another note: In h igh-rise fires, when emergency generators are called on to function when base building power is lost, they fail over half the time. Much of this is due to the generators not being run or tested regularly, or not being run with a load placed on them (such as lights, fans and elevators), which is the environment they will have to operate in when a fire occurs. In other words, do not bank on these working for you when they are needed.
During the Meridian Plaza Fire in Philadelphia in 1991, the generator not only failed to run, but the emergency backup wiring harness in the building core’s vertical chase burned through, causing a complete loss of power to the entire building. The 38-story, 800,000 square-foot office tower has since been demolished.
CURTIS S.D.MASSEY is president of Massey Enterprises Inc., the world’s leading disaster planning firm. Massey Disaster/Pre-Fire Plans protect the vast majority of the tallest and highest-profile buildings in North America. He also teaches an advanced course on High-Rise Fire Department Emergency Operations to major city fire departments throughout the U.S. and Canada. Massey also regularly writes articles regarding “new age” technology that impacts firefighter safety. Special thanks to Capstone Turbine, ONSI Fuel Cells, Wikipedia, Bob Lasseter, Dennis Hughes, Ed Lewis, Bob Kistner, Joe Lechtanski, Steve Boos, Jim Haffey and Jim Jenkins.