Chapter One
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Introducing Froment Load Banks
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Load Bank Applications
The main application for a load bank is for use during generator testing. However, load
banks are versatile devices and they have a number of useful applications that can be
applicable during the installation, commissioning and ongoing operation of a generator.
Generating set testing
The specific tests that need to be carried out for a particular installation depend on local
regulations, the application, the type of equipment involved and the requirements of
insurance companies, local authorities and other interested parties.
The requirements for the testing of engine driven generators are described in ISO 8528
part 6. This document explains the general test requirements and describes both a
functional test and an acceptance test. Functional tests must always be done and usually
occur at the manufacturer’s factory. Acceptance tests are optional and are often done on
site, witnessed by the customer or his representative.
ISO 8528 part 5 defines three performance classes - G1, G2 and G3, each with dierent
criteria:
• G1 is the least stringent and applies to small generating sets intended to supply simple
loads.
• G2 is broadly equivalent to commercially available power.
• G3 is intended for sets which are powering loads which particularly require a stable
and accurate power supply.
A further class, G4, allows for performance criteria agreed between the supplier and the
buyer.
In addition to the testing that is carried out immediately after installation, it is important
to carry out regular tests as part of an ongoing maintenance program. This is particularly
important for emergency power supplies that may have long periods of non-operation.
The type of tests carried out include:
• Load duration tests (also known as a “heat run”), designed to record steady-state
voltages, frequency, and also to calibrate instrumentation and measure emissions and
fuel consumption.
• Load acceptance tests, which check changes in frequency and voltage regulation due
to sudden load changes. These tests ensure that the rise and fall of the generator’s
output voltage and frequency remain within limits as load is applied and removed.
Testing UPS systems and batteries
Uninterruptable power supply systems consisting of a generating set combined with a set
of batteries are a common feature of data centres and other installations where maintaining
a constant power supply is critical. In the event of a power failure the batteries provide an
immediate source of power whilst the generator is automatically started, synchronised to
the correct frequency and put online.
Regular testing of the batteries, generator and its automatic control gear is extremely
important, but testing using the site load could put critical systems at risk and may not
provide suicient load for a complete test. Load banks provide an ideal solution because
they will allow the operation of the UPS to be fully tested without posing any risk to the
site load.
Site load correction
In many applications a generator may be required to run for extended periods with little or
no load applied. For a diesel generator this may mean that the engine does not reach its
optimum operating temperature and this can cause a problem sometimes known as “wet
stacking” – so called because unburnt fuel can make its way through to the exhaust stack.
This can lead to serious maintenance problems, including high levels of cylinder wear,
excessive fuel consumption and high levels of emissions.
Froment load banks provide a function known as Site Load Correction (SLC) which provides
an automated solution to this problem. This is where the load bank automatically adds and
removes load to keep the generator running at an optimal temperature.
There are many applications for Site Load Correction. Figure 1-10 shows an example
scenario where a site that is usually supplied by the public utility supply makes use of a
backup generator. The system is designed so that, if the utility supply fails, the generator
will start up and supply power to the site until the utility supply is restored.
Note: The specific
details regarding the
frequency and type of
test required may also
be specified by local
regulations or other
interested parties.
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