SECTION 5 - Fuel
For gasoline egine generators, Unleaded or Regular gasoline with a lower
octane rating than 85((RON/MON)/2) may cause pre-detonation (knocking) which
can damage the engine. Regular gasoline can be used, however, unleaded gasoline
is preferred because it reduces pollution and combustion chamber deposits.
See the generator's engine owner's manual for fuel information or contact
the generator set's manufacturer.
|ENGINE FUEL can cause fire or explosion.|
|POOR QUALITY, LOW OCTANE FUEL can damage the engine.|
5-2. Gaseous Fuels
Typically on LP Gaseous or Natural Gas powered unit the unit will run on
either vaporous fuel source. Most gaseous fuel units are set up for a specific
number of ounces of line pressure (a.k.a. as a corresponding number Inch
Water Column) with some type of threaded pipe hook up. Note: Use of gaseous
fuels decrease the amount of total power the generator is capable of producing
by as much as 20 percent, dependent upon thermal content of fuel in your
specific area. Refer to Section 8 for Gaseous Fuel Systems.
5-3. Diesel Fuel
Piping and Filtration
The basic requirements of a diesel engine fuel system are adequate piping,
proper selection of filters for the application and completely air-tight
joints, with a minimum number of fittings to prevent air from entering the
fuel lines, especially in installations where the fuel tank is lower than
5-3. A. Piping to the Tank
Vacuum at the transfer pump inlet must be avoided. If an auxiliary pump is
used, pressure at the transfer pump must not be less than 0 p.s.i. nor greater
than 5 p.s.i.(typical). Pressure after the return line connector assembly
must not exceed 5 p.s.i. unless called for in the pump or system
NOTE: The return line must never be piped back to the transfer pump inlet
side. Both supply and return line should be connected to standpipes in the
tank with the opening for each 2 inches minimum from the bottom of the tank
to allow space for water and sediments to settle and to eliminate siphoning
5-3.C. Maximum Pressure
Pressure drop across clean filters should not be more than 2.5 inches of
mercury (1.2 p.s.i.) at full load. Pressure drop in the supply system exceeding
10 inches of mercury (4.9 p.s.i.) because of dirty filters or other restriction
usually will affect pump and engine performance, (erratic operation, low
power, engine stall).
Fuel consumption is typically specified in the generator's user manual and
is specified in a quantity of fuel consumed per hour based on a specified
load. Refer to the generator's user manual for expected fuel consumption,
which is based upon a specific load. While the generator's manufacturer may
not be able to predict the consumption for your site because of the differences
in the typical load, by site, an estimate a full load is typically given.
A simple fuel consumption model that is a "ball park" predictor of fuel
consumption is as follows:
Based on experience, a generator at no load typically uses about half of
the fuel of a generator at full load. The ratio of output power from a generator
to the amount of fuel consumed is almost linear. Consumption on diesel fueled
generators is somewhat less than gasoline.
Fuel Consumption = (Estimated Load/Maximum Generator Power Output) X .5 X
Maximum Fuel Consumption + 50% of Maximum Fuel Consumption
Assuming Maximum fuel consumption = 1 Gallon/Hour
Minimum fuel consumption = .5 Gallon/Hour
At a 50% load, Fuel Consumption = (((50 Amps/100 Amps) X .5 Gallon) + .5
Gallon) = (((.5) X .5) + .5) = .75 Gal./Hr.
Other factors that need to be taken into account are the temperatures of
the areas where the fuels are stored are as follows:
SECTION 6 - Electrical
There are a number of different generator systems and typical loads in the context of electrical systems. Most systems, unless they contain automated swtich gear, have a means of disconnect between the generator and the load. This is typically a transfer switch or disconnect. Ensure the contacts on the switch are rated for the size of your system. System schematics are beyond the context of this tutorial at this time.
6-1. General (Electrical
Generators are rated for a maximum current in Amps and power output in Kilowatts.
Typically power outputs can vary between different models. The output is
dependent upon fuel type, ambient temperature and altitude of the installation.
Of same model types using different fuels, Gasoline units will have the highest
output followed by gaseous fuels (Natural Gas and Liquid Petroleum(Vapor
withdrawal). LP is about 95% of that of gasoline and natural gas at about
85% of gasoline. These units typically derate at about 3% per 1,000 ft (334
meters) starting at about 3,000 feet (1,000 meters) and an additional 1%
for every 10 degrees over 78 degrees F. This is fairly common for all asperating
Diesel units derate more for temperature and altitude. Diesels typically
derate at about 4% per 1,000 ft (334 meters) starting at sea level and an
additional 1% for every 10 degrees over 78 degrees F. At higher elevations,
this power loss can be significant.
Circuits to carry power from the generator needs to be sized accordingly. Distance of the generator to the load (Typically a UPS) will also effect wire size. The conduit entryway for the generator is typically specified for a nominal size and may need to be increased in size if you are required to go to the maximum wire size. Flexible liquid tight metallic conduit should be used.
Direct Current (D.C.) Generators typically require a significantly larger
cable size from the generator to the load (typically UPS batteries) in order
to compensate for voltage drop. Voltage drop is a function of the
resistance of the wire over the distance from the source to the load. The
typical recommedation for D.C. generators is to keep the generator as close
to the load as possible. Refer to the generators manufacturer's
recommendations. Refer to N.F.P.A. 70, also known as the National Electric
Code (NEC) for cable sizing tables.
When mounting electrical panels, a 3 foot clearance is required and the use
of an emergency light to illuminate the unit during operation is typically
required. Power for the emergency light should be from both the primary
utility and the generator. This is highly recommend so that in the event
of a malfunction there is a light source to see to work on the unit. Refer
to your local building and electrical codes to ensure compliance.
Use of powered exhaust fans and powered louvers for ventilation is typical
for indoor installations. Emergency power will be needed operate the
auxillary devices. Make sure the generator is sized large enough to
cover the load and the auxillary equipment.
6-2. Conductor Sizing
This information is dependent upon your generator output and intended load.
When connecting cables to the generator, unless instructed differently by
the equipment manufacture, make connections at the generator first. Make
the connections at the load last. Failure to do so may constitute a fire
or safety hazard.
All ampacities are typically calculated at 75 o C (Celsius)(167
o F(Fahrenheit) in the conductor size charts. Building wire conductors
should be rated at 90oC(194oF) to allow for different
ambient temperatures that these conductors may pass through.
All conductors are typically required by electrical code to be copper. The
recommended conductor sizes are based on maximum current. Ampacities are
found in NEC Article 310, Table 310-16. Conductor resistances are found in
NEC Table 8 "Conductor Properties".
Direct Current (D.C.) generators require larger output power cables than
comparable A.C. generators due to voltage drops in the cable caused by increased
Most A.C. Generators require the use of transfer switches. Refer to manufacturer's installation instructions and recommendations.
Return to Table of Contents
Go to Section 7
Tips on Hooking up a Generator (genset) to a Uninterruptible Power System (UPS)
Amazon.com now has tools, tooling and gas powered generators in their Amazon.com's Home Improvement Store. Click on Amazon.com's Home Improvement Store or the logo below to go there or use the Search feature.
Copyright © Dexter A. Hansen