These general guidelines will help you complete the installation of an efficient and reliable genset.
Engine-generator sets now have countless applications, often with multiple uses within the same facility. Most engine-generator systems provide for human safety and protection of property. Typical applications include apartment and office buildings, hotels and motels, places of assembly, and government facilities. Hospitals and nursing homes have special needs vital to life, and these emergency power systems reflect these requirements.
Other applications include highly dependable back-up power for computer installations, communications networks, and modern research and development laboratories, each of which call for multiple engine-generator sets incorporating a wide variety of support equipment and systems.
Also, an increasing number of facilities use on-site power to reduce operating costs. This is accomplished through peak-shaving, which calls for the application of generator power to selected loads that are shed from the normal utility supply. This results in lower demand for power from the utility by cutting power peaks during selected 15- or 30-min intervals. Where appropriate, this can save significant amounts of money.
Cogeneration, another energy-saving, cost-cutting technique, utilizes waste heat from one or more engine-generator sets to perform useful functions. When such energy-conservation installations are implemented, grants or rebates that can amount to hundreds of thousands of dollars may be available from the local utility or governmental body. As a result, not only are energy costs reduced, but also capital costs are frequently slashed, permitting a fast payback of the initial capital investment.
What to check
NEC. Applicable Code rules, which serve as excellent guidelines for effective design, selection, and installation, vary with the purpose of the system under consideration.
Be sure to review in detail Art. 445, Generators; Art. 517, Health Care Facilities; Art. 695, Fire Pumps; Art. 700, Emergency Systems; Art. 701, Legally Required Standby Systems; Art. 702, Optional Standby Systems; and Art. 705, Interconnected Electric Power Production sources.
Specifications. Prior to starting an installation, be sure that all specifications are in order. Important installation considerations include:
* Type of generator;
* RPM, frequency;
* Location, enclosures;
* Kilowatt rating, efficiency;
* Number of phases, power factor;
* Controls, related switchgear;
* Transfer switching; and
* Duty, starting conditions, etc.
Important operating parameters
Installation procedures for large auxiliary-power units (1000kW to 2000kW) are usually more costly because of requirements for foundations, vibration damping, sound reduction, water cooling, exhaust stacks, and starting equipment. In addition, special considerations are usually required for use in ambient temperatures below 40 [degrees] F.
Mounting. A genset must be mounted on a substantial and level base. This foundation serves three important functions: It supports the weight of the engine-generator set; it maintains correct alignment between engine and generator; and it isolates any vibration produced. You should also evaluate the weight-bearing ability and characteristics of the surface (soil, steel-work, etc.) where the unit is to be installed so that the most appropriate foundation is provided.
The foundation may be a large concrete mass or simply a fabricated steel base, depending upon the size of the genset and the type of soil or supporting material. Proper preparation includes excavation, setting of forms, reinforcing of structural steel where the unit is installed on an upper floor, vibration isolation, anchor-bolt positioning, and shimming and grouting.
Vibration. Smaller gensets have rubber vibration isolators located between the engine and generator assemblies and the skid. Additional isolation usually is not required.
Several types of manufactured vibration isolating devices are available and are effective in reducing vibration transmission when installed between the genset and the supporting foundation or floor slab. Steel spring vibration isolators are normally provided on engine-generator sets rated from about 150kW up. These can reduce up to 98% of the vibration produced. When additional vibration reduction is required, heavy-duty isolators and/or specially designed structural components can be provided, such as "floating" floors or foundations that rest on rubberized "hockey-puck" isolators.
Cooling. Reliable operation of an engine-generator set is dependent upon adequate Ventilation and cooling. Be sure openings are provided and located so that cool clean air can be brought in, force through the engine cooling system, and directed out without recirculating. Also note that an adequate volume of air, based on the genset size, is required. For example, a 350kW unit may require as much as 33,000 cfm of air when running.
In most instances, an engine-mounted radiator and fan provide genset cooling. If fan noise is excessive for a nearby area, a remote fan and radiator can be used. However, the farther away a remote radiator and fan are located, the higher the installation and maintenance costs. In addition, be sure to allow a minimum of 3 ft around the genset for service (as required by the NEC) and to assure free flow of cooling air.
Exhaust. Because exhaust fumes are deadly, you should take great care in installing the exhaust system. Exhaust pipes should be wrought iron, cast iron, or steel, and should be free standing, not supported by the engine or muffler. Where exhaust pipes attach to the engine, they must be connected with flexible connectors to minimize vibrations that can cause damage to the exhaust system. The exhaust pipe should terminate outdoors, away from doors, windows, or other building openings.
Never connect the genset exhaust system to an exhaust system serving other equipment.
Generator sets installed outdoors inside weather-protective enclosures should have their exhaust directed so that it will disperse away from buildings and building air intakes.
Noise. Noise from a genset can be a significant problem, depending upon the location and how it affects people in nearby locations. Noise comes from four sources: The engine, generator, cooling fan, and exhaust. Noise from the engine and generator can be reduced by providing baffles, a rigid sealed enclosure, or a rigid sealed enclosure lined with sound absorption material.
The major source of noise is the engine exhaust. Here, it's vital to install the proper muffler in the correct manner. A variety of mufflers is available; in most instances, a critical-grade muffler on the exhaust piping is most effective. However, it's also the most expensive.
The direction of the muffler discharge is an important factor in noise reduction. Pointing the exhaust pipe straight up is the most effective direction, although a rain cap is then required to keep moisture out of the system. Another approach is to point the terminating exhaust pipes away from any nearby buildings or locations to be protected from noise.
When reduction of noise is vital, it's best to bring in an engineer or firm that specializes in sound reduction.
Fig. 1, on page 60, shows important details of a typical diesel engine-generator installation. Generally, it's best to locate the engine-driven generator in a room designed for the purpose. The genset should be installed close to the normal electric service, but in a location where it's warm enough so that the genset will start easily. Locations where ambient temperatures may be unusually high should be avoided because inefficient cooling will result. Most units are designed to operate in ambient temperatures up to 120 [degrees] F, if necessary.
Plan the space carefully. There should be access (doorways or removable walls) for replacing the generator with a minimum of difficulty. Provide adequate lighting, space for batteries, day tank, and other accessories.
If a genset is located at a high altitude, especially over 1000 ft, or exposed to higher-than-rated ambient temperature, it must be derated. Specific derating factors must obtained from the supplier.
When the genset must be located outdoors, you should consider all the elements that could cause problems: Wind, ice, snow, flooding, lightning, fire, earthquake, and vandals. A variety of measures can be taken to minimize these problems. For example, where flooding is a possibility, install the genset on a raised platform or concrete mounting base. In locations where temperatures fall below 50 [degrees] F, special accessories such as an electric water jacket heater or manifold heater will be needed to ensure dependable starting. Use of heaters is also recommended if the genset is installed in a humid location to prevent moisture collection in the generator windings.
Where exposed to excessive sun, an enclosure painted white will help keep ambient temperatures down.
Various fueled gensets
Gasoline. Gasoline engines are normally used in smaller applications, up to about 100kW, so that mounting and installation requirements are usually basic. Air cooling is usually sufficient for these units.
These smaller applications normally call for a comparatively small fuel tank. Thus, ready availability of fuel is important. But remember, gasoline tends to deteriorate over time, so the fuel supply must be replaced on a regular basis. Therefore, be sure to have a means of effective refueling.
Diesel fuel. In many applications, diesel fuel is chosen because it offers easy on-site storage, has fewer problems with long-term storage, is a reduced fire hazard, and allows more operating hours between overhauls. A disadvantage of diesel fuel is its low volatility at low ambient temperatures. This problem is minimized by providing diesels with thermostatically controlled coolant heaters to maintain the water jacket temperature at 90 [degrees] F or higher. Be sure all fuel level gauges, low-level alarms, and other controls are installed for maintenance reliability.
In many applications, regular test running of the diesel engine is recommended and may be required by code or law. Operation of a diesel engine unloaded can result in detrimental internal carbon deposits. This is caused by unburned fuel being carried over into the exhaust system, resulting in a restriction of exhaust that reduces engine power, possibly leading to complete engine failure. Therefore, if at all possible, operate the engine under load (supplying power to its connected load). If this creates a problem, then you should run the genset while supplying a load bank. This solves the engine damage problem, but does not provide for testing of the auxiliary system power conductors, transfer switches, and related components.
Gaseous fuels. Any fuel system must be installed in accordance with applicable codes, and this is especially important with an LPG system. Reputable manufacturers provide guidance in the design of fuel systems. An excellent source of fuel system design for LPG is NFPA 54, National Fuel Gas Code.
LPG presents the greatest hazard of any of the fuels because, being heavier than air, any vapors leaked or released will fill low areas such as basements and create an explosion hazard.
Gaseous fueled units must have depends able supply lines installed so as to protect them from damage. Underground lines should be installed away from high vehicle traffic areas. Outside lines should be protected from weather excesses, corrosives, and high heat.
Recent EPA rulings require stricter standards for installation of fuel tanks. An approved LPG fuel tank must be used to store the liquid propane. All of the appropriate shut-off valves and pressure gauges also must be included. An LPG tank should never be installed inside a structure; it should be installed outside, some distance away from any structures and away from open flames, sparks, or electrical connections.
In recent years, two standard systems have been used to identify generator leads brought out to supply loads: National Electrical Manufacturers Association (NEMA) and International Electrotechnical Commission (IEC). Generators built in the U.S. adhere to markings in NEMA Standard MG1. Here, the leads are typically identified with a "T" and a numeral. Fig. 2 shows NEMA markings for a typical generator, along with IEC markings that use a "U," "V," and "W" with numerals for identification.
Both NEMA and IEC standards specify that field leads be identified with an "F," with F1 being positive and F2 being negative. These leads may also be marked with a "+" or "POS" and "-" or "NEG."