| History: |
Original Factsheet
|
| Written by: |
Steve Clarke - Rural/Environmental Engineer
(Provincial Crop Engineering Specialist)/OMAF; Allen
Hills - College Senior Instructor (Engineering
Research)/University of Guelph; Ben Hawkins - Associate
Director (Academics & Engineering Research)/University
of Guelph |
Introduction
The prolonged power outage in Eastern Ontario and
Southwestern Quebec during the 1998 Ice Storm, and the concern
surrounding potential power outages caused by Y2K, have combined
to create significant interest in the purchase of standby
generators. Farmers across Ontario have been reassessing their
need for emergency electrical power supplies. This Factsheet
looks at some of the factors you should think about in
purchasing and operating portable generators in the 3 to 12
kilowatt (kW) size to ensure production of Quality Power. OMAF
Factsheet Tractor-Driven Generators: Producing Quality Power,
Order No. 00-059 provides a more detailed review of power
quality and looks at the issues surrounding the use of
tractor-driven PTO generators of 15 kW and larger.
Figure 1. Portable generator with plug-in voltage
frequency meter.
Portable generators are available from a number of
manufacturers, in many sizes, with a whole range of features.
Different terminology is often used to describe the same feature
and the same terminology may describe different features. Your
challenge is to understand the terms manufacturers use to
describe the features of their respective units. The process is
further complicated by the fact that manufacturers and retailers
promote product features, while purchasers are looking for user
benefits. These marketing features and user benefits all meet in
a retail store where, too often, the sales person has limited
knowledge to assist in translating one to the other.
Table 1, Generator Feature/Benefit
Analysis is designed to aid in developing an understanding
of the relationship between features and benefits. With this
table and Table 2, Generator
Feature/Benefit Check List on page 6, you will be able to
sort through the features and determine their benefit to your
operation. At the very least this Factsheet should provoke a
through discussion with your supplier before you make a
purchase. The decision of what features you need is a compromise
or balance between price and perceived need.
This Factsheet is intended to help you select a small
portable generator where the most urgent need is to run a water
pump to supply water for livestock, and light and heat for the
residence. Specific details for the operations of generator are
available from manufacturers, distributors and electrical
contractors. Always use a qualified electrical contractor when
installing a generator into your electrical service.
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Table 1. Generator Feature/Benefit Analysis
| Feature |
Benefit |
| Continuous Rating is the amount
of wattage the generator can supply on a continuous
basis. This is where you start when you talk about the
size or capacity of the generator. Check the
manufacturers' specification plate for this rating. The
big colorful model number on the side is probably not
the continuous rating. |
This is the electrical load
that the generator can support on a continuous basis.
Continuous means for periods of a few hours at a time,
not 24 hours a day for days at a time. Generators
manufactured to higher quality standards (Heavy Duty)
would be expected to run for longer periods of time. |
| Maximum Rating is
the amount of wattage the generator can supply for short
periods of time. |
This is the electrical load
the generator can support for short periods of time.
Short periods of time means from 2 or 3 seconds to 5 or
10 minutes every hour. Most generators restrict the
extra current needed for starting electrical motors to
this maximum. Ask your retailer "How much, for how long,
how often?" to get a true sense of this value. |
| Surge Rating is the
amount of wattage the generator can supply for a very
short term, as when starting an electric motor. |
Most manufacturers of small
portable generators do not quote or support a surge
rating. Where quoted, a surge rating is typically in the
range of 2 times the maximum rating for 2 to 3 seconds.
A high surge rating ensures that you can start larger
induction motors that have a high starting current
requirement. |
| Brush or Brushless
Design describes the method used to transfer
electric current from or to the rotating component of
the generator. |
There are no significant
differences in performance between the 2 design types.
While there may be minor advantages and disadvantage to
each type this does not need to be an issue when making
your purchase of an emergency use generator. |
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| Feature |
Benefit |
| Voltage Regulator or
Voltage Regulation addresses a feature of generators
designed to regulate the output voltage being produced.
Ideally, output voltage should be at or close to 120 or
240 volts. Ontario Hydro's extreme range for voltage at
a rural service entrance is 212 to 254 volts. Without
regulation, voltage would change as the load and/or
engine speed (frequency) change. |
The ability of a generator
to maintain voltage in a narrow range around 120 or 240
volts is critical in situations where loads
(particularly electric motors) are regularly cycled on
and off. The effectiveness of voltage regulation is
designed into each generator model, and varies
significantly from model to model. Higher priced units
generally (but not always) will have better regulation.
The only meaningful way of expressing the level of
voltage regulation is as a + or - percentage above or
below the rated voltage. Fore example, 240 volts with a
rating of ±2% would mean the voltage range would be
235.2V to 244.8V. For units without a specific plus or
minus value it is not uncommon to find voltage output
varying by as much as ±15% to 20%. If your usage
involves significant variation in load values, or if you
will be running sensitive electrical equipment, or if
you plan to run the generator for significant numbers of
hours, voltage regulation in the ±2% to 5% may be worth
the extra cost. |
| Disconnect Breaker
is a breaker designed to shut off all power output from
the generator. |
A safety feature, designed
to switch off in a short circuit or significant overload
situation. Also allows power to be turned off during
connection to or disconnect from load. Not all portable
generators have this feature. In direct hookups to
electrical sub-panels this is the preferred system. |
| Circuit
Breakers have the same function on a generator as in
the regular electrical panel in your house. Generally
each circuit or plug has its own circuit breaker. |
Automatically
trips if there is a short circuit or an overload,
preventing damage to the generator or electrical
equipment connected to circuit. Some generators have a
main disconnect breaker as well as protection for each
circuit. This combination gives the greatest protection
for generator and personal safety. No fuses to replace. |
| Top of Page |
| Feature |
Benefit |
| Non-fuse Breaker is
another name for Circuit or Disconnect Breakers. |
No fuses to replace. |
Plug Type or Number
is the CSA number of the plug required to match the
receptacle on the generator. There are 3 types of plugs
with numerous capacity ratings commonly used on portable
generators.
Current CSA regulations require a 4 prong twist-lock
plug for hard-wiring into residence sub-panel. |
The plug number and its
matching receptacle number are identification numbers
accepted as industry standards. This insures only proper
capacity plugs are used. For example, a 125/250V 20amp
receptacle would need an L14-20R plug. The CSA number is
engraved into the plug and the receptacle for proper
identification. |
| Full Capacity Outlet
describes a receptacle, and its matching plug, which is
design to handle the maximum capacity of the generator.
Usually rated by amperage. The relationship between
current, voltage and wattage is shown as: Current (in
amps) x Voltage (in volts) = Wattage (watts)
Therefore, a 20 amp, 240 volt plug would be a full
capacity plug for a 4800 watt or smaller generator (20
amps x 240 volts = 4800 watts) |
Whether this is an
important feature depends on how you plan to use the
generator. If you will be plugging individual loads into
each receptacle then a full capacity plug is not an
issue provided you do not exceed the capacity of each
plug and that the total of all loads do not exceed the
capacity of the generator. However, if the generator is
to be connected directly to a sub panel or transfer
switch and the owner wishes to use the full available
power from one receptacle, then a full capacity outlet
is needed. |
| Circuit Selector Switch
allows directing full rated power to the outlet, which
is used for direct hookup through a transfer switch
connection. |
Flexibility in using power
output from generator while guarding against over
loading. Only certain receptacles can be used at any one
time. |
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| Feature |
Benefit |
| Ground Fault Circuit
Interrupter cuts off electricity if some of the
current tries to return to ground by a method other than
the neutral wire (a fault). It does this by measuring
current in the live wire and comparing it to the neutral
wire; when these 2 measurements are different; power is
disconnected from the receptacle.
|
Protects against the
hazards of grounding faults from defective tools, or
cords. If the ground wire does not make a perfect
contact to the ground, the leakage current will flow
through the operator to the ground. Of particular
importance when working in damp areas or conditions.
|
| Voltmeter - a meter
which measurers voltage. Can be built into the generator
or purchased as a hand held unit. |
Ensures that the voltage
produced is within acceptable range. See VOLTAGE
REGULATION for acceptable voltage range. Electrical
equipment can be damaged by voltage too high or too low. |
| Frequency Meter - a
meter for measuring frequency of alternating current. In
North America electricity is delivered at 60 cycles per
second (60 Hertz or Hz). |
Frequency is directly tied
to engine speed. By ensuring that frequency is at or
close to 60 Hz, (between 58 and 62) the correct engine
RPM can be maintained for optimum voltage output. |
| Insulation Class
identifies maximum allowable operating temperature. |
Insulation class is a
coding for generators and electric motors identifying
the maximum allowable operating temperature of the
windings. The higher the class, the higher allowable
temperature. Class A, B, F and H are the most common
classes encountered with maximum operating temperatures
of 105°C, 130°C, 155°C and 180°C respectively.
Generators and engines produce considerable heat, and
units built to higher insulation ratings will usually
carry a premium price. Ventilate properly to stay within
the proper operating temperature. |
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| Feature |
Benefit |
| Oil Alert is a
device designed to shut down the engine when the
crankcase oil drops below a safe level. Some systems use
a float in the engine crankcase to sense the oil level.
If the oil falls below a certain level during operation,
the float signals the engine to shut down. The indicator
light blinks on and off to indicate low oil. Another
type uses a sensor in a pressurized engine oil system.
If the oil pressure falls below the preset value during
operation, the engine ignition is grounded out and the
engine shuts down. A time delay allows for low pressure
during engine starting. If the oil system doesn't build
sufficient pressure quickly enough to close the oil
sensor switch, the engine will not continue to run.
|
This will help prevent
engine damage from low oil situations. The oil
pressure sensor system is a much more robust and
accurate system. The float system can be affected by
cold weather operation, cold oil does not flow as freely
as warm oil and float may give erroneous shut down
readings.
If your intended use involves long periods of
unattended running of the generator this may be a
worthwhile feature. |
| Automatic Idle Control
reduces engine speed when all electrical loads have been
turned off and automatically returns to rated speed when
loads are turned back on. |
Reduces fuel consumption.
While generally viewed as a good feature, this is not
always true. Delays in responding to load demands,
particularly during electric motor start up, could lead
to premature motor failures. On units with poor voltage
regulation: as the engine speed drops, voltage levels
may fall below 100 volts from a 240-volt output. If
electronic controls or components are still being
powered (thermostats, clocks, etc.) but are not drawing
enough power to trigger idle control off, damage may
occur. If your generator has this feature, review usage
and monitor voltage carefully before activating it. |
| Splash Lubrication -
lubrication system where the rotating engine parts
splashes and throws oil around the inside of the engine
for lubrication. |
Economical. |
| Pressure Lubrication
- lubrication system where an oil pump forces oil
throughout the engine. |
Longer engine life.
Increased cost. |
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| Feature |
Benefit |
| Automatic Decompression
- a feature that reduces the amount of compression in
the engine cylinder during start-up. Returns to normal
compression after engine starts. |
Decompression makes it
easier to pull the starter rope. This is most beneficial
for engines with higher horsepower ratings (8 hp and
over). |
| Governor Type -
describes the type of governor used to control the speed
of the engine as electrical load changes. An
air-governor uses the amount of air flow produced by
the flywheel to change the throttle setting. If the
engine slows down because of an increased load, the
reduced air flow allows the throttle to open to speed up
the engine. An increase in speed produces more air flow
that closes the throttle.
A mechanical-governor uses a set of weights to
control speed. The faster the weights spin the further
out they are flung shutting down the throttle. When the
speed drops the weights return closer to their turning
axis and the throttle opens. |
Maintaining the correct
engine speed (3600 RPM) is required to generate
electrical power at 60 Hertz. The correct speed is
required to insure the proper voltage levels. The
governor of an engine is the device that keeps the speed
at or near 3600 RPM. The more sensitive the governor is
to changes in speed as loads change the closer frequency
will stay to 60 Hz. Mechanical-governors tend to be
more effective at maintaining the required engine speed.
|
| OHV - overhead valve
engine. The intake and exhaust valves are located, over
the cylinder, in a separate component of the engine
called the head. |
An engine with OHV is
generally considered to be of better quality than units
with the valves in the block. Benefits include improved
combustion efficiency, reduces fuel and oil consumption,
and the increased ability to rebuild engines for longer
life. |
| Cast Iron Cylinder(s)
- describes the material used in constructing the
cylinders of the engine. |
Engines with cast iron
cylinders generally give longer engine life, and are
often considered better quality than aluminum. |
| Fuel Tank Capacity
indicates how much fuel the tank holds. |
A large capacity tank
allows the generator to run longer without refueling. |
| Run Time at Specified
Load is an estimate of the amount of time the
generator will run with a specific percentage of rated
load. i.e.: 8 hours @ 50% load. |
This specification gives
the operator some indication of how long the generator
will run at the specified load. Use this as an estimate
only. |
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Table 2. Generator Feature/Benefit Check List
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1st Unit
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2nd Unit
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3rd Unit
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The information in this Factsheet has been condensed from
several sources, including operator manuals, generator testing,
and interviews with generator manufacturers. It is not intended
as a substitute for professional advise from a manufacturer or
supplier of generators. Always consult your electrical
contractor. All installations of electrical equipment are
subject to inspection requirements contained in the Ontario
Electrical Safety Code.
Funding for this project has been provided under the
Canada-Ontario agreement for the Ice Storm Recovery Assistance
Program, Annex A, Assistance for the Agricultural Sector and
Rural Communities in Eastern Ontario. This program is jointly
funded by the Government of Canada and the Government of
Ontario.
Funding for this project has been provided under the
Canada-Ontario agreement for the Ice Storm Recovery Assistance
Program, Annex A, Assistance for the Agricultural Sector and
Rural Communities in Eastern Ontario. This program is jointly
funded by the Government of Canada and the Government of
Ontario.
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