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Gen-sets represent an increasingly important market place for diesel and gas engines, with a demanding customer base.  Developing world economies and recently more common power outages are fuelling the massive demand for standby power. Customers continually expect more from these products in terms of power density, load acceptance, emissions, fuel consumption, noise, cost of ownership. The customer needs a tailored product.

What is a gen-set and how does it differ to the industrial engine on which most are based? The following list sets out to explain many of the basic terms applicable to gen-set design, development and ownership.

ElectropaK -  A fixed speed diesel engine with ratings to suit a gen-set application. Comes complete with radiator, cooling group and fan.

Electrounit - An ElectropaK without radiator, cooling group and fan. Suitable for individually installed Combined Heat & Power setups. 

IOPU - Industrial Open Power Unit. These are multi speed non vehicle power units. The are normally sold with radiator, cooling group and fan, and typically share ratings from their off highway derivatives. Typical applications include pumps and compressors.

Operating Speed - Gen-sets are normally governed to fixed speed running. 1500 rpm to produce 50Hz electrical supply for European market and 1800 rpm to produce 60 Hz for US market. 60Hz supply can be achieved at 1200Hz with some alternator sets- this is uncommon.

kWe - Kilowatts electrical is a measure of electrical power produced by a gen-set. 60Hz generator sets are usually marketed in terms of kWe.

kVa - Kilovolt amps is a measure of electrical power produced by a genset. 50Hz gen-sets are usually marketed in terms of kVa. As gensets produce an alternating current P=VI doesn't hold true. Voltage and current follow sinusoidal wave forms with a phase shift due to the reactance (generated by inductance & capacitance) of the load on the alternator, and hence a power factor is used. Industry assumes a 100% resistive load for which a 0.8 power factor is used. This relates kWe to kVa by the following:

kWe = kVa x 0.8

Marketing - As a general rule of thumb, a gen-set will produce X kVa at 50Hz and X kWe at    60Hz. So we owe the confusing nomenclature to marketing who would like to sell, for example, a 100kVa (50Hz)/100kWe(60Hz) gen-set.

Fuel Coolers - Gen-sets are normally fitted into a frame, which holds a small fuel or "day tank" for limited time running. If the gen-set operates in elevated ambient temperatures, or the engine has a high fuel spill ratio, the temperature of the fuel will often be controlled by a small fuel cooler (air-to-fuel) mounted on the cooling group. The cooler prevents rises in "day tank" temperatures preventing fuel injector damage.

Fans - All Electrounits are fitted complete with fans to provide cooling to the radiator and charge cooler if fitted. Two versions of fans are normally offered for gen-sets and IOPU's, pushers (which blow air through the radiator) and pullers (which pull air through the radiator). The customer is able to specify the type most relevant to their application/installation. The type of fan used will affect the ambient air temperature the bulk of the engine will see, and may have consequences on the engines rating and performance.

Fan Power (Fp) - Depending on the size of the gen-set, the power required to drive the fan will vary between 10% for smaller gen-sets (<10L) and 5% for larger gen-sets ( />10L).

Alternator Efficiency (ha) - The alternator on the gen-set converts the mechanical energy delivered by the engine into electrical energy, and has an associated efficiency. Typically alternators have an efficiency of 0.95 (95%).

kWm - Gen-sets are marketed in terms of the electrical power which they produce. However engine manufacturers are more interested in the mechanical power which their engine needs to deliver to the alternator to provide the quoted electrical power. This includes fan powers and alternator efficiency:

kWe = (kWm -Fp) x ha      or   kWe = kWm x 0.90 x 0.95 (<10L engine)
kWe = (kWm -Fp) x ha      or   kWe = kWm x 0.95 x 0.95(>10L engine)

Emissions- Genset emissions are complicated and specific to the country in which they operate. Generally requirements are less demanding than other off highway equipment, but are often driven by marketing rather than legislative needs. Legislative limits are complicated, determined by introduction date, engine powers and power rating. The three most important limits are listed below with links to sites where full documentation can be found.

European Limits (Directive 97/98/EC)

Commonly referred to as EU Stage 'X' Emissions

www.dieselnet.com/standards/eu/offroad.html

North American Limits (Federal Regulations 40 CFR Part 89)
Commonly referred to as EPA Tier 'X' Emissions
 


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