Resistive vs Reactive
Reasons to Choose
Reactive Load Bank Testing Solutions
Introduction
Facilities managers within all types of businesses recognize the
importance of backup power systems. If utility power is interrupted for
any length of time, your company could suffer from lost productivity and
revenues, as well as incur damage to your expensive equipment.
Backup systems, such as generators, help provide protection for power
outages, but only if they are properly maintained and tested. Too often,
facilities managers fail to conduct complete testing of their power
generation equipment to uncover system weaknesses. They perform tests
on a component-by-component basis rather than on the entire system. As
a result, they lack a full understanding of the risks they face should a utility
power outage occur.
This eBook will discuss the importance of using load bank testing for a
facility’s entire emergency power generation system. It will provide an
overview of load bank testing, explain the different types of load banks and
outline the most beneficial load bank solutions for most applications.
Specific topics include:
●●Load Bank Primer
●●What is a Load Bank?
●●Why Conduct a Load Bank Test?
●●Why is an On-Site Load Test Necessary?
●●What Happens During a Load Bank Test?
●●What Industries and Applications Use Load Bank Testing?
●●Types of Load Bank Testing Solutions
●●Resistive Load Banks
●●Reactive Load Banks
●●Reactive/Inductive
●●Reactive/Capacitive
●●Resistive/Reactive Load Banks
●●The Drawbacks of Resistive-Only Load Testing
●●Making the Case for Reactive Load Bank Solutions
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Load Bank Primer
What is a load bank?
A load bank is a self-contained electrical device that accurately mimics the behavior of the actual load of an
electrical system. It provides an organized, contained and controllable load. Through these simulations, load
bank testing protects, supports and ensures the reliability of a system.
Why conduct a load test?
A load bank test simulates real-world scenarios that can be used to confirm proper functionality. Load
testing validates the operational performance of electrical and mechanical systems, including generators,
uninterruptible power supply (UPS) equipment, power distribution units (PDUs), battery backups and cooling
systems. These systems are critical to ensuring business continuity during power outages.
Load testing is conducted during commissioning of a facility and/or equipment. It is also performed as part
of a comprehensive preventative maintenance program. Proper load testing allows for replacement of any
equipment not performing to specifications.
The main goal of load bank testing is to uncover problems in a controlled situation rather than during an
actual power failure. It is the only way to verify a backup power system will operate during an outage. With a
more reliable operation, you minimize the risks associated with unplanned downtime.
If equipment is tested at the factory, why is an on-site load test necessary?
Although your facility’s equipment may have been tested at the factory, many variables can affect the on-site
installation. For example, your system’s emergency generator may be calibrated in different altitudes and
ambient temperatures. The equipment may also be affected by installation variables involving air intake,
fuel, exhaust, cooling and contractor configuration.
Load bank testing can validate the operation of your complete system after installation within your
facility. You’re able to account for the vast range of variances that may exist between your site and the
manufacturer’s operating environment.
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What generally happens during a load bank test?
During a test, the load bank develops an artificial electrical load, that is applied to an electrical power source
and converts or dissipates the resultant power output of the source. The timed test gradually changes the
kilowatt (kW) load in specific increments to create a simulated load profile for the system. The load profile
represents the load levels over a period of time for an electrical power source and converts or dissipates the
resulting power output of the source.
Load bank testing verifies all equipment is properly integrated and tests all critical components for
operation and efficiency. It uncovers issues before the system is operational, allows for regular equipment
maintenance, and helps ensure your systems will perform as required.
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What industries and applications use load bank testing?
Regardless of your industry, reliable power is a critical success factor. Facilities managers, engineering firms
and/or commissioning agents in a wide range of industries rely on load bank solutions to test their mission
critical systems.
Load banks are used in a variety of applications, including factory testing of turbines and engine diesel
generator sets, periodic operating of backup generator sets, testing of battery and UPS backup systems,
ground power testing, load optimization in prime power applications and load rejection testing. Regular load
bank testing can prevent the build-up of carbon on piston rings and reduce wet stacking problems common
with generators (wet stacking occurs when some of a diesel generator’s fuel remains unburned and it
accumulates in the exhaust system).
Examples of industries regularly
using load bank testing include:
●●Commercial Power/Utilities, including
substations, solar, wind, nuclear and
onsite generation
●●Maritime
●●Data Center
●●Government/Military
●●Oil & Gas
●●Hospitals/Healthcare
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Types of Load Bank Testing
Load banks come in an assortment of sizes and configurations. They measure commercial loads, which
usually consist of a combination of motors, heating, transformers and lighting. The type of load bank used
will depend on the application and specific site requirements.
Three main load bank testing solutions exist: Resistive, Reactive, Resistive/Reactive and RLC:
Resistive Load Banks
The most common type, resistive load banks mimic the operational load that a power source will see in
actual use. They convert electrical energy (current) into heat using power resistors and dissipate the heat
using air or water.
Some common examples of resistive loads generated in your home come from incandescent light-bulbs,
devices with heating elements, such as space heaters and hot plates.
Several versions of resistive load banks are available, including small DC portable units, small AC portable
units, large AC portable units, trailer-mounted AC units, permanent AC units, radiator-mounted units and AC
water-cooled units.
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Reactive Load Banks
These solutions are used to simulate systems affected by electric motors or other electromagnetic devices
on a power network. Typically, facilities have a significant amount of motor-driven devices, transformers and
capacitors. If this is the case, then the load banks used during the test equipment requires reactive power
compensation.
A reactive load bank changes the lagging power factor, known as inductive, or the leading power factor,
known as capacitive. Reactive load banks can simulate either an inductive or capacitive load depending on
the type of load expected on the power system.
Reactive/Inductive Load
Reactive/Capacitive Load
Measured in kVAR (Kilo Volt Amperes
Reactive), a reactive/inductive load converts
current into a magnetic field. Inductive
reactance resists the change to current,
causing the circuit current to lag voltage.
The inductive power factor is the most
common reactive load. However, no purely
inductive loads exist in the real world
because the device always performs some
amount of work, even if only heat generation.
Measured in kVARc (capacitor kVAR rating
at the system voltage) a capacitive load
charges and releases energy. Capacitive
reactance resists the change to voltage,
causing the circuit current to lead voltage.
Examples of devices producing reactive/
inductive loads include motors, transformers
and chokes. Reactive/inductive load bank
testing is routinely required in government
agencies with critical facilities and off-shore
maritime applications using heavy inductive
loads
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A reactive/capacitive load bank is similar
to a reactive/inductive load bank in rating
and purpose. However, with leading power
factor loads created, reactive power is
supplied from these loads to the system. An
improvement in power factor results. The
electronic and non-linear loads simulated are
typical of the telecommunications, computer
or PS industries.
In addition, reactive/capacitive load testing
is also used in applications requiring
heavy inductive loads and/or power factor
correction, such as in the manufacturing and
mining industries.
Resistive/Reactive Load Banks
These solutions combine both resistive and reactive elements in one load bank package. Resistive/reactive
loads are able to mimic motor loads and electromagnetic devices within a power system, as well as provide
purely resistive loads by allowing to set a specific power factor.
Many backup generators and turbines need to be commissioned at nameplate capacity using a combination
of resistive and reactive load to fully qualify their operating capability. Using a resistive/reactive load bank
enables comprehensive testing from a single unit. A range of resistive/reactive load banks are available
to simulate these types of loads on a power source and the transformers, relays and switches which will
distribute the power throughout a facility.
Resistive/reactive load banks are great choices for testing turbines, switchgear, rotary UPS, generators and
UPS systems. They can also be used for integrated system testing of utility substation protection systems,
particularly for more complex relays like distance, directional overcurrent, power directional and others. And,
a resistive/reactive inductive and/or capacitive load is often required to test solar inverters to ensure solar
panels can be stopped from producing electricity in the event of a power outage.
RLC Load Bank
Resistive, inductance and capacitance (RLC) load banks are commonly used in type testing.
Renewable systems require an inverter to convert the DC source from solar or wind energy into
usable AC power. Inverters and converters must be type-tested for safety according to UL-1741. The
fundamental test required in this certification is the anti-islanding test. This test ensures the system
will not export power to a utility circuit that is not energized (a power “island”), thereby protecting
utility linemen who may be working on a circuit.
The test sequence requires a special load that includes resistance, inductance and capacitance load
that can be controlled as one unit. The test setup has to be tuned for the fundamental frequency and
for the kW rating of the system.
Figure 1 -- Unintentional Islanding Test Configuration
(Source: IEEE 1547.1 -2005 Standard Test Procedures for DR Connected to the Electric Power System)
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The Drawbacks of Resistive-Only
Load Testing Solutions
Business owners want to be sure their emergency power generation systems remain operational during a
utility service interruption. Many businesses, especially life-saving operations like hospitals, depend on an
uninterrupted power supply.
Although facilities managers may stringently follow manufacturer guidelines for testing individual equipment
components, they could still be without critical functions during a power outage. A well-managed
maintenance plan for only subsystems, such as alternators, regulators, switchgear, cabling, ventilation and
cooling, of the overall system is not sufficient.
Emergency power generation is a complex system consisting of many different parts. And, any single part is
subject to failure at any given time. In addition to testing the individual components, you need to ensure your
entire system functions as required.
Testing the entire emergency power backup system is more complex, time-consuming and expensive
compared to testing individual components. However, complete system testing is the only way to know
whether the individual components in the system will work together. Facilities managers can plan
appropriately and conduct a system-wide test when it’s most convenient for their business.
However, many facilities managers don’t adequately evaluate the stresses during an actual emergency.
They usually use a resistive load bank to test only the generator engine, which fails to simulate real-world
conditions. Because pure resistive loads comprise only a part of a facility’s total power consumption, they do
not adequately convey how well a business will be prepared in an emergency.
Why is this the case? Typically, incandescent lights and electric heaters are the only equipment operating on
a resistive load. Although this equipment draws a steady supply of electricity from a generator, it does not
draw large loads that realistically test a generator’s performance.
Using only resistive load testing cannot simulate how a facility’s equipment will operate under actual
conditions, including power outages caused by brownouts, blackouts and serious weather events. The entire
system must be tested simulating a real load situation.
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Making the Case for Reactive
Load Bank Solutions
In many facility applications, the more effective
load bank solution is reactive. Reactive solutions
simulate systems affected by electric motors or other
electromagnetic devices on a power network. And
resistive/reactive combination load banks can test the
entire generator system at its expected power factor.
Using a resistive/reactive test, facilities managers
can replicate a real power outage by manipulating the
power factor. Unlike resistive-only testing, a resistive/
reactive test can predict pending failures of the
multiple components making up the entire system.
Resistive-only testing cannot create the conditions
experienced during a real power failure.
The inductive load of a reactive test verifies proper voltage regulation by the emergency generator. Without
a working voltage regulator, a generator’s magnetic field would collapse and it would fail. The non-working
generator would also prevent other generators in the system from operating in parallel.
Only a properly configured resistive/reactive load test will ensure your system operates at an acceptable
level during an emergency. Facilities managers must confirm all system components work together
seamlessly and are able to produce the necessary power levels.
Even though a system-wide reactive load test will ensure the highest level of system performance,
you will still need to test individual components within the system, per the equipment manufacturer’s
recommendations. Regular, ongoing maintenance of equipment, along with system-wide, reactive load
testing, will indicate how well your system will likely perform during a power outage.
Proper resistive/reactive load testing of an entire system helps uncover weaknesses in your power
generation system and prevents unexpected failures during emergencies. To prevent catastrophes, you
must understand what load testing solutions to deploy and how to conduct effective testing. And, you need
to stay current with advances in electric power generation technology.
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ComRent Load Bank Testing Solutions
ComRent is a global leader in load bank rentals and service for testing
and commissioning mission-critical power generating equipment. With
more than 30,000 load tests performed and a 99.99% on-site performance
rate, we bring a level of service, expertise and experience unmatched in
the industry.
We add value by taking a consultative approach to every commissioning
and testing project. By getting involved early in a strategic process, we’re
able to integrate load bank test planning into the design, scheduling and
budgeting phase of each project.
ComRent’s team of experts is ready to help ensure your system is
successfully interconnected. We offer a complimentary consultation to
review your project and propose the right load bank solution for your
application. Contact us today at 888-881-7118 or visit our website for more
information on load bank testing.
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