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Criteria & Definition

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Power Factor
Load Types
Decibels    

 

Terminology and Technology you need understand.

Decisions...

STAND-BY OR PRIME?

Will you require stand-by or prime power supply? Simply stated, prime power is required when you have no other source of power.

 

A stand-by generator set is a backup to utility power

 

Why differentiate?  The rating of a generator for backup power assumes the generator will be in occasional use for periods of several hours or days. Prime power generators are expected to run 7/24 for 365 days per year.  Generators are rated are higher for backup use than for prime power.

USED as an Option

There are good deals to be found within the used market.  We come across generators which have been installed for many years as backup with incredibly low hours on the equipment.  However, if your application is critical or you require the unit for prime power you must understand that parts, although available, may not be readily available or on hand at your local engine dealer for older engines.

GENERATOR TYPES & FEATURES

Generator sets produce either single or three phase power. Choose a single phase generator if you do not have any motors above five horsepower. Three-phase power is better for motor starting and running. Homeowners usually require single phase whereas industrial or commercial applications frequently require three phase power.

Three phase generators are set up to produce 120/208 or 277/480 or 347/600 volts. Single-phase sets are 120 or 120/240. Large heaters, stoves and dryers frequently use 240V volt power. 120V is the voltage available at your normal household electric outlets.

GENERATOR RATINGS

Generators are rated in either kVA (Kilovolt amperes) of kW (kilowatts), Kilo meaning 1000.   kVA is always higher than the kW.  All of our three phase water-cooled generators are rated with a power factor of 0.8 and single phase generators have a power factor of one.

GAS OR DIESEL?

Diesel generators while initially more expensive are frequently the best alternative due to their longevity and lower operating costs. Modern diesels are quiet and normally require much less maintenance than comparably sized gas (natural gas or propane) units. Fuel costs per kW produced with diesels is normally thirty to fifty percent less than gas units.

  • 1800 rpm water cooled diesel units operate on average 12-30,000 hours before major maintenance is required. 1800 rpm water cooled gas units normally operate 6-10,000 hours because they are built on a lighter duty gasoline engine block.

  • 3600 rpm diesel generators.  It is difficult to categorize 3600 rpm diesel generators because there is a huge spectrum of engines within this category.  Generally, small light-weight 3600 rpm diesel engines are not as durable as 1800 rpm engines. However, companies such as Deutz and Lombardini make excellent and durable air cooled units, some of which are designed to operate at 3600 rpm.

  • 3600 rpm air-cooled gas and gaseous units are normally replaced – not overhauled at 500 to 1500 hours depending on manufacturer.

  • No matter which manufacturer you use, you will get substantially shorter longevity from the gas and gaseous fuelled engines than diesel powered units because the gas units are built in a lighter fashion and because they burn hotter (higher BTU of the fuel).

OPERATING SPEED

Electric equipment in North America is designed to use power with a fixed frequency: 60 Hertz (Hz); and 50 Hertz in Europe, Africa and Australia. The frequency output of a generator depends on a fixed engine speed.

Frequency (Hz) is measured in Hertz (cycles per second) and basically it is the number of times that an AC supply oscillates in one second. The standard frequency in Canada and the US is 60Hz.  Frequency is held constant by the mechanical and or electronic governor mounted on the generator. An excellent level of frequency control is 1% while a 2-5% level of control is usually adequate.

To produce 60 Hz electricity, most engines operate at 1800 or 3600 RPM. Each has its advantages and drawbacks:

  • 1800 RPM, four pole gensets are the most common in larger units and in quality generators and are more expensive to manufacture. They offer the best balance of noise, efficiency, cost and engine life but are heavy and are only considered portable when mounted on trailers.
  • 3600 RPM, two pole sets are smaller and lightweight, frequently best suited for portable, light-duty applications.

    • 3600 rpm engines tend to use more fuel than 1800 rpm engines per kilowatt hour produced by about 10 to 15% (not usually an issue for a backup generator)
    • 3600 rpm engines  almost always produce more horsepower from the same size engine running at 1800 rpm.  This means a smaller engine can drive a bigger generator.  Smaller engines cost less than larger ones, saving money.
    • 3600 rpm engines are usually about 4X noisier than 1800 rpm engines (usually 85dB vs 76dB)
    • We have not noticed a difference in longevity within 3600 vs 1800 diesel engines when two quality engines from the same company are compared.

In simple terms it’s like operating your car at 90 mph, versus 45mph – at 45mph your car will last longer, is quieter, less maintenance and longer life. Most 3600 rpm units are twin or single cylinder gasoline powered air cooled lawnmower engines, while the water cooled 1800 rpm units are comparable to those found in forklift and tractor engines…the 1800 rpm water cooled units will last longer, offer less maintenance problems and be more fuel efficient.

FEATURES & BENEFITS TO LOOK FOR

ENGINE

Engine block: Select four cycle, liquid cooled, industrial duty diesel engines for long life and quiet operation.

Air or liquid cooling: Air-cooled engines require a tremendous amount of air and may require ducting. They're noisier too. Liquid cooling offers quieter operation and more even temperature control but these units weigh and cost more.

  • DC electrical system. Standard 12 volt system should include:

  • Starter motor and battery charging alternator with a solid state voltage regulator

  • Diesel units may come with a pre-heat switch and start/stop switch.  Pre-heating comes in many forms including glow plugs to warm the combustion chamber and manifold pre-heaters to warm the incoming air.

  • Safety shutdown system to protect the engine in case of oil pressure loss, generator overspeed or overcrank and high water temperature

  • DC system circuit breaker to protect the battery charging system.

GENERATOR UNIT

AC generator should have at least a 4-pole revolving field. Automatic Voltage Regulator (AVR) provides “clean” power. Normal utility power is +/- 5% voltage regulation; our 1800-rpm models are even better +/- 2%! All of our models offer AVR – Automatic Voltage Regulation

ENGINE ACCESSORIES AND CONTROLS

After determining the generator size you will need, make a list of optional and installation equipment you require. For noise abatement, we recommend purchasing a sound attenuated generator. A good primary fuel filter/water separator is a must to protect your engine's fuel system.

AC SWITCHGEAR AND CONTROLS

Switchgear can be as simple or complex as you want or can afford. As complexity increases, so does cost. Balance and a good electrical advisor are the keys here.

All generator systems require a circuit breaker and a distribution panel.

  • The circuit breaker protects the generator set from short circuit and unbalanced electrical loads.

  • The distribution panel divides and routes the connected loads and includes circuit breakers to protect these loads.

  • Stand-by systems also require a main circuit breaker between the utility source and the transfer panel. The transfer panel switches power from the utility to the generator unit and back so that both aren't on at the same time.

Auto-start, auto-transfer systems are available but are costly. Your contractor can help you determine what you will need.


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Last modified: April 17, 2010