Load Bank Basics
Why do I need a Load Bank?
A Load Bank is a critical piece of Test Equipment that provides accurate and consistent electrical loading of a power source. Load Banks are used in a variety of Applications/Markets including Power Generation, Data Centers, Aerospace, Wind Farms and Battery Discharge Testing (just to name a few).
A load bank converts electrical power into heat by using resistive elements that absorb the incoming power. The incoming power heats the resistors and cooling fans within the load bank safety exhaust the heat load.
The primary use of load banks is to provide proper loading on generator sets. The prime mover on most generators is the Diesel Engine which by design need a minimum load to operate efficiently. Diesel Generators that are not properly loaded will not reach proper operating temperature and therefore will allow a buildup of unburned diesel fuel. The effect of unburned diesel fuel on the genset results in poor performance, clogged emissions, and reduced turbo-charger performance. Long term effects of under loading on diesel generators are premature Valve, Piston, and Turbo blade failures.
Load Banks are also used to create specific heat signatures and are the perfect solution for testing HVAC systems. Today, many Data Centers utilize load banks to mimic server room heat parameters to ensure proper cooling and prevent overheating shutdown.
How do load banks work?
Resistive Load Banks are the most common type, and as stated above convert the kW Power under test into heat. There are three basic circuits that are used in Load Banks. These circuits are Control, Load and Cooling circuits.
- The Control Circuit provides power for the safety and operator interface.
- The Load Circuit utilizes contactors to activate the proper load value(s).
- The Cooling Circuit provides power to the cooling fans to discharge the hot exhaust.
Properly designed load banks offer continuous operation with little or no cool down period required after use.
Besides Resistive load banks there are also Resistive/Reactive combo units to properly test lagging power factor loads, Resistive/Capacitive combos for testing leading power factors. Direct Current (DC) Load Banks are also available for battery discharge testing and Ground Power Units.
Resistive, Reactive and Resistive-Reactive Load Banks
What is a Resistive Load Bank?
Resistive load banks are the most common kinds of load banks in use. They are used to test real-life resistive loads such as lighting or heating systems.
When an electrical current passes through the resistive elements inside the load bank, it creates a resistance, and places the electrical load on the power source. The resistance causes generation of heat, which must be dissipated through the cooling system of the load bank.
A Resistive load bank draws the full real power load, in kW, on the power source, such as a generator, and helps fully test its fuel, exhaust and cooling systems. However, Resistive load banks are not able to test the reactive load of the power source. To load the power source to its full kVA, a Reactive load bank is needed.
Resistive load banks are often used to prevent ‘wet-stacking’ in diesel generators – a phenomenon that occurs when they are operated at low loads, and unburnt fuel clogs up the engine. This may lead to lower fuel efficiency and cause more severe problems. Load banks can ‘exercise’ the generator, putting a greater load and achieving higher temperatures that burns away the excess fuel.
A Resistive load bank can be an AC load bank or a DC load bank. DC load banks are used for testing and maintaining large DC power systems, batteries, UPS systems, etc.
What is a Reactive Load Bank?
Reactive Load Banks simulate an inductive (lagging power factor) and/or capacitive (leading power factor) load.
Inductive loads are used to simulate real load from motors, transformers etc. This simulates real life mixed commercial loads like lighting, heating, motors and transformers with inductive or capacitive reactance that resist changes to current.
Capacitive loads are used to simulate real loads from electronic or non-linear loads usually found in telecommunication, computer or UPS markets.
What is a Resistive-Reactive Load Bank?
Resistive-Reactive Load Banks combine both resistive and reactive loads. These reactive loads can be inductive and/or capacitive depending on the application. , inductive and capacitive elements to test the widest range of applications.
A Resistive-Reactive (Inductive) Load Bank is a versatile load bank that can be used for a mixture of commercial loads such as lighting, heating, motors, transformers, etc.
Choosing the right load bank for your application
Determine the kind of load you are trying to simulate.
If testing a generator set, a resistive load bank can fully test the generator at 100% of the nameplate kW rating. It will fully load the generator cooling, fuel and exhaust systems.
With a resistive only load bank; it can only test 80% of the generator set nameplate kVA rating. Using an Inductive load along with the Resistive load will allow for the generator set to be tested to the full 100% kVA rating from the nameplate.
Determine the voltage, phase and kW or kVA requirement for the application
Voltage: Typically, load banks are offered in dual or multiple voltage ratings, such as 208 VAC and/or 240 VAC. The load, in kW for Resistive Load Banks, and in kVA for Resistive/Reactive Load Banks (kW or kVA) is specified for a specific voltage. If a different voltage is used, the load available will change.
Phase: You must also determine whether the application has a single-phase or a three-phase connection.
Load: Determine the load requirements for testing. Loads are specified in kW for Resistive Load Banks, and in kVA for Resistive/Reactive Load Banks
Determine where you will install the load bank.
Indoor or Outdoor: You will need to decide where you are going to install the load bank – will it be indoors or outdoors?
If you are planning to install the load bank outdoors, what kind of weather are you likely to face? If the load bank is likely to be exposed to heavy rain, snow or sleet, it must be available to withstand these elements. Load bank manufacturers, including ULB, specify what kind of NEMA rating the load bank’s enclosure is rated for. NEMA 1 enclosures are typically used for protecting controls and terminations from objects and personnel, while NEMA 3 enclosures are intended for outdoor use, primarily to provide a degree of protection against windblown dust, rain, sleet, and external ice formation.
Portable or Stationary: Load Banks come in two main types – ‘stationary’, also called ‘permanent’ load banks, and ‘portable‘ load banks that can be moved easily from one location to another. Portable load banks are typically meant for indoor or temporary outdoor use, and are fitted with lifting handles, caster wheels or fork truck slots to help move them easily.
Other things to remember: Ensure that the load banks has enough clearance on all sides for proper use and ease of maintenance. Also, keep in mind how the load bank will be cooled. Load banks are cooled either by air or by water (most ULB load banks are air -cooled). If air-cooled, larger load banks will typically have a vertical air flow (bottom to top) while smaller load banks will have a horizontal air flow (side to side).
Determine the type of controls and instrumentation you need
Will the load bank be primarily used with local controls at the load bank? Or will the load bank be used in a remote situation, where the user is away from the load bank?
ULB offers many different versions of control. All load banks offer local controls via lights/switches, and typically a local HMI and PLC. In many load bank versions, the HMI can be mounted up to 50 feet away for control (different lengths are available if required). If true remote control of the load bank is required, the user can connect to the PLC via ethernet.
Connecting your load bank
Types of connections
The two main types are either directly to the Copper Bus Bar within the load bank cabinet, or CAM-LOK connectors. ULB offers both types of connections.
Depending on the load bank, it can be connected in 3-phase or 1-phase configurations. Refer to the specific manual and nameplate on the ULB load bank to determine how to connect the load bank.
Connecting the load bank to the power source
There are two ways a load bank can be connected to a power source such as an emergency generator: either via a switch, or directly connected (if the load bank has automatic load sense and control).
Manual switch: A manual switch is turned on or off to bring the load bank into the circuit for testing or maintenance of the generator.
Automatic switch: An automatic switch turns off the load to the generator from the load bank.
Direct connection without a switch: The load is permanently connected to the generator, and it automatically adjusts the load.
Should you buy or rent your load bank?
Renting a load bank
The main advantage to renting a load bank is that the load bank rental company provides the load bank and its personnel will help you take maintain and take care of the load bank. The rental company typically provides trained and experienced technicians who are familiar with the load bank; they will connect, test and disconnect the load bank.
Purchasing a Load Bank
The main advantage to purchasing a load bank, and having it permanently with you is that you can use it for more than than testing generators. In many cases, regular usage of a load bank can extend the life of your equipment.
If the current generator is sized at a larger capacity, running it under capacity can damage them or decrease the life of the generator. Having a load bank will fill in the difference in load, making sure that the generator is not running under capacity. ULB, for example, offers load banks with Automatic Load Level controls. These controls will sense the difference between the demand and the optimal running load, and automatically apply that differential load.
Contact a ULB sales associate to help you determine which is best for your company and application.