Resistive Load Banks
Power Generation
Testing Load Banks
Industry trade organizations and
manufacturers both agree that a well planned
preventive maintenance program is vital to the
reliable operating of a standby generator. Load
Banks are a essential part of such a program.
Load Banks provide a practical means to test the
system without interruption to the critical loads.
The primary cause of diesel engine failure is “wet
stacking” (”wet” unburned fuel accumulating in the
engine “stack”). It is caused by under-loading of
the generator. Diesel engines that are lightly
loaded, or allowed to idle for long periods, never
reach their recommended operating temperature.
Over time, unburned fuel coats the combustion
chamber, reducing engine rating, efficiency, and
life span. A preventive maintenance plan that
includes load testing of a diesel generator set, will
reduce the harmful effects of “wet-stacking” and
increase engine life.
BOBWHITE
Load Banks are devices designed to provide
electrical loads for testing power sources such as
generators. Load banks are also used to reduce
“wet stacking” problems in diesel engines of backup
generating systems. The load bank should be used
in conjunction with a good preventive maintenance
schedule. A resistive load bank is equipped with
elements that “heat”, which provide a large amount
of resistance to the flow of electrons.
The Effects of West-Stacking
on a Diesel Engine
RENTALS
PO Box 2472 | Victoria, TX 77902
P: 361.570.5000 | F: 361.578.4456
bobwhiterentals.com
Load Banks For
Prevention Of
Wet-Stacking
in Diesel
Generator Sets
This information is general in nature and intended to give
the reader a overview of the issues involved. Specific
recommendations can only be made after a review of the
equipment involved, installation parameters, applicable
codes and national standards by competent personnel.
Please consult Avtron Manufacturing, Inc. with comments
or questions about the information contained herein.
Wet-Stacking
“Wet-Stacking” - The buildup of unburned
diesel fuel and carbon residues in the engine
and exhaust system causing 65% of
maintenance problems in generator sets!
PRINCIPLE CAUSE
The UNDERLOADING of the generator.
Operating at less than 50% of rated load.
Reduce the problem by increasing power
consumption above 70% of the rated load.
Periodic maintenance should include load
banking.
Not only does wet stacking damage the engine
but to much carbon buildup in the exhaust can
cause flameout (Flame shooting out the top of
the exhaust).
Wet-Stacking is a common problem with
diesel engines which are operated for extended
periods with light or no loads applied. When a
diesel engine operates without sufficient load it will
not operate at its optimum temperature. This will
allow unburned fuel to accumulate in the exhaust
system, which can foul the fuel injectors, engine
valves and exhaust system, including
turbochargers, and reduce the operating
performance. Our Preventive Maintenance
Program can save thousands of dollars in
costly repairs. Providing additional load from the
building load may not be practical with critical
computer, life safety or communication equipment.
Any interruption of power to these loads may cause
a loss of data, operations or jeopardize personal
safety.
In order for a diesel engine to operate at
peak efficiency it must be able to provide fuel and
air in the proper ratio and at a high enough engine
temperature for the engine to completely burn all of
the fuel. The proper load can be achieved by
adding additional building load or by providing
supplemental load through the use of a resistive
load bank. These can be small portable load banks
designed to be rolled up to the generator under test
or they may be larger trailer mounted load banks
for generator sets in the 1-3 MW range.
Wet-Stacking does not usually cause any
permanent damage and can be alleviated if
additional load is applied to relieve the condition. In
extreme cases it can cause the engine to run
backwards at shut down due to excess fuel buildup
in the exhaust system causing costly damage. It
can reduce the system performance and increase
maintenance. Applying an increasing load over a
period of time until the excess fuel is burned off
and the system capacity is reached usually can
repair the condition. This can take several hours to
burn off the accumulated unburned fuel.
BOBWHITE
RENTALS
Load Banks Use:
Diesel engine “Wet Stack” Prevention
Applies full KW load to engine
Bring to full load temp to burn out
carbon/fuel build up
35
Minutes
1
Hour
3
Hours
Operating diesel engines at low load will
cause increased lubricating oil consumption and
oil/fuel leaking from the exhaust. Engine internal
parts are designed to run under fully loaded
conditions. When an engine is run on low to light
load the proper engine temperature is never
reached. The tolerances of internal part are bigger
because the engine is not at full temperature. This
leads to lubricating oil passing thru the tolerances
in valves guides, stems, pistons and liners.
Heavy carbon buildup on pistons, in piston
ring grooves, valves and turbocharger
1. Heavy carbon buildup on pistons and in ring
grooves can cause piston seizure when
operating later at full load.
2. Low combustion temp will result in
insufficient burnt fuel, which will cause
diluting of the lubricating oil.
3. Bore polishing
4. Due to the low combustion temp, unburnt
fuel and lubricating oil will enter the exhaust
manifold and eventually leak out through the
joint in the exhaust manifold.