|
|
Understanding
Portable Generators
 |
| Agdex#: |
771 |
| Publication Date: |
06/00 |
| Order#: |
00-057 |
| Last Reviewed: |
06/00 |
| 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 |
Table of Contents
- Introduction
- Table 1. Generator Feature/Benefit Analysis
- Table 2. Generator Feature/Benefit Check List
- Related Links
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. OMAFRA 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.
| Top of Page |
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 colourful 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. |
| Top of Page |
| 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. |
| Top of Page |
| 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. |
| Top of Page |
| 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.
|
| Top of Page |
| 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. |
| Top of Page |
Table 2. Generator Feature/Benefit
Check List
| |
1st Unit
|
2nd Unit
|
3rd Unit
|
Comments
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| |
|
|
|
| Top of Page |
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.
| Top of Page |
Related Links
For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
|
This site is maintained
by the Government of Ontario 
Queen's
Printer for Ontario 