“Be prepared.” For critical facilities threatened with the possibility of a power cut-off or a community that could face a blackout, the best form of preparation is a backup genset, generator, turbine, or battery. But what about the backup preparation itself? How does an operator know that the backup will be ready when the time comes? Backup power sources tend to sit unused for long periods of time. Therefore, under normal operating conditions, the system operator can never be completely sure that they will be ready when needed.
But these emergency power sources are only needed under the abnormal conditions of a power outage. And it is neither practical nor even possible to actually shut off an entire electrical supply system, even for a short period of time, to allow for the testing of a backup power supply. Such an approach would put at risk both the operating system and the backup power source itself. And it is extremely risky for an operator to test his genset’s capabilities just as it is required to operate. So, how can a system operator provide the necessary assurance that the backup power system won’t fail just when it is needed? The answer is loadbanks.
A loadbank is a standalone electrical power testing unit that mimics the anticipated load (electrical demand) of the facility or system that will require a backup energy source in an emergency situation. These facilities can be an entire neighborhood, small town college campus, factory complex, shopping mall, office building commercial enterprise, residential unit, industrial center, or a critical emergency facility (such as a city traffic control system, hospital, emergency medical services, fire station, or police department). Loadbanks can test both alternating current (AC) and direct current (DC) power sources.
They typically are specifically designated for the testing of the backup generator sets (gensets) slated for emergency use. And though primarily used for emergency backup power, gensets can also be used as the primary electrical power sources in off-grid applications or even local microgrids. Though often small enough to be portable, gensets can be large units operating as fixed facilities. These gensets are typically diesel reciprocating engines or turbines. These gensets are in storage or prepositioned to generate electrical power as soon as the main power source or the local grid goes down. In addition to testing gensets to ensure that they are ready to go if needed, there are several other forms of testing performed by loadbanks.
Load optimization under ideal operating conditions can be simulated by the use of loadbanks. Loadbanks are used as part of manufacturing quality control, performing tests on gensets at their factory, making sure they are properly functioning prior to shipment and delivery to a customer. Loadbanks can be used to test the readiness of gensets to support partial shutdowns of critical sub systems such as the air conditioning systems needed to keep servers and data centers operating.
In addition to testing the operating capabilities of a genset, loadbanks can be used for analyses and to help eliminate “wet stacking” issues that can occur when a genset is operating at a lighter load. Under a light load condition, reciprocating engines have a tendency to not burn their diesel fuel completely and the result is an oily exhaust. Similarly, running the genset under a loadbank allows for the cleaning and removal of built up carbon from the diesel engine’s piston rings.
In addition to measuring performance, loadbanks can be used to perform safety testing of underground power conditions, measuring the ground resistance for an earth electrode system. This testing will ensure that the ground electrode’s resistance does not increase over time and present a safety hazard. Alternatively, loadbanks can be used to simulate the sudden loss of load and see if the genset can recover from the shock and return to normal functioning.
The Basic Design and Standard Operation of Loadbanks
Testing alternate power sourced by simulating actual electrical load conditions under various scenarios is what loadbanks do. But how do they do it? A loadbank is internally configured to simulate the load of the electrical system being protected. Its inner workings provide the identical resistance to an electrical supply that the operating system would offer. In other words, its system of circuits and resistors will convert and dissipate the supplied electrical power as if the operating system’s controls, communications, heating, lighting, machinery, equipment, and appliances were being operated. In doing so, it provides the most realistic simulation possible to mimic actual operating conditions in order to accurately test the genset’s operating capabilities and performance characteristics.
To add a further level of realism, loadbanks are operated to reflect the real world where actual electrical power demand will vary over time. During the course of any work day or operating shift, the amount of electricity required for proper functioning can vary considerably even over short durations. During the course of a test, the loadbank operator can manually vary the load banks’ resistance characteristics in order to simulate everything from low-level baseline electrical demand to peak operating conditions.
There are various types of electrical loads that can be examined in addition to the variable loads from the designated operating system. The most basic load testing is performed to test batteries that supply steady direct current (DC) power. These batteries will be tested under a variety of load conditions. Loadbanks can also be used to test critical equipment, key control systems, and even laboratory apparatuses. Most critical are the power generation systems used by advanced, high-technology aerospace applications and systems. Another extreme condition involves the testing of major electrical power system components such as breakers and relay stations.
A Matched Pair—Gensets and Loadbanks
While the use of loadbanks can ensure that gensets can meet demand when necessary, protecting both the genset themselves as well as the operating system, there is the problem of properly pairing up loadbanks with the correct gensets.
Gensets consist of three primary components: the dynamo, the power source, and the fuel supply. The dynamo is the source of the electrical current. As with any generator, this consists of a bundle of wires rotating rapidly relative to a set of fixed magnets. As the wires cross the magnetic lines of force, electrical current is generated in the wires as alternating current (AC). In effect, a dynamo transforms mechanical power of the rotation into electrical power. The mechanical power is provided by the genset’s second element, the power source, which is either a diesel reciprocal engine or gas turbine. By burning diesel fuel or igniting natural gas, the engine or turbine converts heat energy into mechanical energy and rotational motion. And the heat energy is derived from the latent chemical energy provided by the third component of the genset, the fuel source. Typically, gensets based on reciprocating engines utilize diesel fuel since diesel tends to have a higher energy density than gasoline, though other types of fuels are also used (propane, biodiesel, hydrogen, or even vegetable oils). Natural gas is the fuel source for turbine-based gensets.
Secondary genset components include a governor linked to the engine or turbine which regulates and smoothes out the genset’s operating speed (measured in revolutions per minute, RPMs). Additionally, a coolant system is required to keep the engine from overheating. Genset engines, depending on their size, can be either air-cooled or liquid-cooled. In both cases, a circulating fluid absorbs the waste heat radiated from the engine and carries it to a radiator where it is bled off to the ambient air. In addition to radiating waste heat, an engine has to vent off the exhaust fumes from the combustion of its fuel. Further regulating engine operations is a self-lubricating system to reduce friction and wear and tear on its moving parts, automatic starters, voltage regulators to prevent the voltage of the electric current from getting too high, fuel and air intake control mechanisms that regulate the engine’s fuel/air mix ratio, and the means to simultaneously disconnect the failed grid’s power system as the backup genset comes online.
The AC electrical power generated by a typical genset will be either single-phase for smaller mobile units or three-phase for larger fixed facilities. Small units are primarily used for individual homes or small commercial operations. Larger demands (from neighborhoods and towns, commercial buildings, offices, hospitals, etc.) require backup from larger three-phase gensets. Three-phase is also required for mixed-use from multiple loads such as motors, transformers, equipment, large HVAC systems, and commercial-scale lighting. The final goal of the genset design and installation is to match the backup electrical power supply with the anticipated power demands of the system it is serving. Conversely, the goal of loadbank design is to match its simulated demand load to the genset.
And loadbanks are not just used to test AC power created by genset. They can be designed to test both AC and DC power from a variety of renewable and distributed energy sources (such as hydroelectric dams, wind power farms, solar energy PVC arrays, batteries, and fuel cells, as well as inverters that convert DC to AC current). Gensets are typically required by the local electric code to be able to manage a variety of loads. This requirement exists to ensure that a genset can function properly for a wide range of possible load situations ranging from a light-demand load of partial failure or subsystem failure up to a heavy-demand load resulting from complete local grid blackout. The intent is to ensure that critical facilities like hospitals continue to function even if the worst happens.
A loadbank operates by receiving, converting, and dissipating as heat the electrical power supplied by the genset. This is exactly what the system being serviced does. In essence, a loadbank consists of a series of resisting load elements of various resistivity arranged so as to mimic the system’s operation. But to provide the variable loads for complete testing, loadbanks also include the controls necessary to adjust the test load. Simulating a variety of electric loads to properly test a backup genset requires a loadbank designed with the ability to vary its resistance to the electrical current. During the actual testing, the operators apply a series of variable and discrete electrical loads to the current received from the genset. During the tests, the operators measure the genset’s response endurance.
Types of Loadbanks and Their Applications
Unfortunately, there is no “one size fits all” type of loadbanks. There are three different categories of loadbanks, each with its own performance characteristics and testing applications. These three types are resistive, inductive, and capacitive loadbanks.
Resistive loadbanks are the most common. These consist of a battery or specially arranged resistors who act solely to convert electrical current into waste heat in imitation of the actual system (but without performing any useful work, of course). An integral cooling system (like the coolant system of a reciprocal engine) uses a working fluid that absorbs the resultant waste heat radiated by the resistors and carries it away to a radiator where it is vented to the air. The design of a resistive loadbank is comparatively simple with just a series of individual resistors aligned and connected so as to match a fixed DC load demand from either a battery or a genset that provides a consistent amount of electrical power. A battery or genset that produces 100 kW will be tested by a resistive loadbank that mimics a load demand of 100 kW.
Inductive loadbanks are used to augment the performance of resistive loadbanks. Inductive loads are created by currents that lag behind the applied voltage. This lagging effect is created by the application of a lagging load factor, generated by a reactive iron core that creates magnetic inductive loads when subject to an applied current. The resultant inductive load is usually set at a strength that is three-fourths of the resistive load (if the resistive load bank is designed for 100 kW, the inductive loadbank will create 75 kW of comparative reactive load). The application of an inductive load allows the loadbank to mimic mixed loads from variable industrial and commercial activities and is applicable to the testing of full power systems.
Conversely, resistive loadbanks can be augmented by capacitive loadbanks that create leading loads where the current precedes the voltage. The result is a leading load factor load. These loadbanks are used to test non-linear systems such as advanced electronic controls, sensors, telecommunications, data storage, or computer systems.
Loadbank Testing Procedures
The goal of the testing is to ensure a viable backup power source or uninterruptible power supply (UPS). Loadbank testing can be performed by the owners of the loadbanks after purchase, or may be included as a service provided by the loadbank manufacturer. The first option saves on operational costs, but the second allows for testing without the need for a trained in-house staff.
Size also matters. Typically, small portable loadbanks are tested by the suppliers on loadbanks owned by the operator, and larger loadbanks are tested by larger units specifically rented for testing. Some time is typically required (weeks or months) between installation of the loadbank and the first series of tests. This waiting period is required to ensure that the backup batteries are fully charged and that the voltages across the bank of batteries making up the backup power supply has been equalized. Further testing is usually performed concurrently with anticipated maintenance downtimes, and after normal working hours so as to not interrupt the flow of work. A facility with multiple gensets will usually test them sequentially in order to isolate those worn-out batteries or faulty turbines/engines that require repair or replacement.
Connections between the loadbank and the genset being tested are made with rated power cables. For safety reasons, a minimum setback distance of 60 feet is maintained between the loadbank and the genset being tested. Noise abatement and heat generation can also be issues, and testers have to be prepared to manage both. Diesel power reciprocating engine gensets should be tested at least monthly. Testing should be at a power output equal to at least one third of the engine’s official name plate rating for a period of at least 30 minutes. NFPA 110 has established definitive standards for loadbank testing:
“Diesel-powered EPS installations … shall be exercised monthly with the available EPSS load and shall be exercised annually with supplemental loads [e.g., a loadbank] at not less than 50% of the EPS nameplate kW rating for 30 continuous minutes and at not less than 75% of the EPS nameplate kW rating for one continuous hour for a total test duration of not less than 1.5 continuous hours.”
To meet these and other industry standards, and ensure safety during testing, loadbank testing is performed in a series of steps:
- The loadbank load is connected to the circuit.
- The generator is started and run until temperature stabilizes.
- The manual or automatic switches are transferred to the backup power source.
- Step loading with the load bank until the power level required by the test is achieved. Results are measured and evaluated.
- Test results are recorded and archived.
- The loadbank load is removed from the circuit.
- All transfer switches are then switched back to normal operating positions and allow the genset to cool down and shut down in accordance with manufacturer’s specifications and guidelines.
New Applications—Data Centers
Data centers represent both a huge power load and a new field for loadbank testing. According to a report published by Centrica in October 2017, 32% of organizations do not have any form of energy resilience strategy in place; 52% of energy decision-makers believe they will experience an energy-related failure within the next year; 33% of energy decision-makers say their organization is not prepared for a disruption to their energy supply from a temporary grid failure; and 67% of businesses have experienced problems due to poor maintenance of equipment. Loadbanks remain the key to overcoming these deficiencies and hardening data centers against potentially catastrophic failure.
This testing is critical for keeping data centers operating. The rapid growth in this type of loadbank application reflects the need for ever more robust testing. Paul Brickman, Sales and Marketing Director at Crestchic, explains the reasons for this growth:
“One of our first ever loadbank customers was in fact an early data center at the Littlewoods head office in Liverpool more than 30 years ago. Since then, our presence in this sector has grown significantly. We have seen sales increase from six to seven units per annum to over 100 units per annum. Today, data centers account for 30% of our business. So, what is driving this growth? In today’s fast-moving world, we have all become accustomed to instant online access. We do our banking, renew our home insurance, and book hospital appointments online. We don’t even print photos anymore: we store them online and we think nothing of it. All around the world, power failure, even for a few minutes, can lead to the loss of highly valuable or even irreplaceable data. Healthcare, banking, insurance, and e-commerce are industries which rely heavily on reliable global data storage. Interestingly, 90% of all data generated up until 2013 was generated between 2011 and 2013. This huge increase in data generation led to the coinage of the term ‘Big Data’ and can be seen as the turning point for the data center industry as we know it today. The amount of power that data centers use is growing by the day, with the most recent report stating they use 3% of the world’s electricity, while IT as a whole is accountable for at least 10%.”
As the market for data centers expanded, the design and operation of data centers has had to evolve quickly to achieve ever higher levels of sophistication and reliability. Traditionally, these two attributes are considered to be at odds with each other; it is often assumed that a more sophisticated system is inherently less reliable. But to meet demand and function day to day, data centers have had to meet both of these goals simultaneously. To help them achieve this, without causing downtime (something a data center simply cannot tolerate since they must run continuously for their entire operational lifetime) or other operational risks, loadbanks are a necessity to ensure that reliability is maintained.
Data centers requiring loadbank testing have in the past been those servicing the healthcare, government, and finance industries. In addition to these traditional uses, today data centers are used for e-commerce, social media, and every smart application. In order to stay one step ahead of anticipated needs, loadbanks are now more frequently being specified at the front end of data center concepts by specialist designers and consultants.
The testing requirements for data centers have several unique characteristics compared with traditional loadbank testing, and include three main applications: commissioning of backup power at build stage, heat load testing during the commissioning phase, and periodic testing of standby power systems. During the commissioning of a data center backup system, the operators of the loadbank and genset have to take into account the unique characteristics of a center’s cooling, fuel, and exhaust systems.
In addition to these unique subsystems, data centers produce enormous amounts of heat. Therefore, loadbanks are used to heat load test the data center’s air conditioning system to ensure that the backup power systems can cope with the massive heat output of the servers. The heat problem is exacerbated by three operational factors: loadbanks are more compact and can produce more heat using a smaller footprint, loadbanks are highly controllable and can be programmed more accurately than electric heaters, and multiple loadbanks can operate in parallel and be controlled using a single remote terminal.
In order to protect millions of dollars invested in advanced data technology (and the equally valuable data itself), air conditioning systems must be able to maintain stable temperatures in the server halls under all conditions. Resistive-only loadbanks provide an easily portable and controllable (at 1 kW increments) heat source to test the air conditioning systems against. Multiple loadbanks can serve to test the system with variable heat loads that can be increased or decreased over the course of the test. The resultant heat is then measured by a battery of temperature sensors and probes, or by thermal mapping devices, to ensure that the air flow and cooling is evenly distributed and that there are no “hot spots” around any vital equipment enclosures.
Recent Advances in Loadbank Technology
In addition to new and expanding applications, loadbank technology itself continues to advance. Though the physics of loadbank technology is well established, there have been enormous strides in the field of loadbank operational controls and measurements. Early loadbanks were operated via manual switch controls. Newer features have been developed to assist with load testing: remote controls, pre-setting, real-time data, and synchronous load modifications. Remote control reduces the number of load test operators required, thus reducing labor costs, and can allow for instantaneous operations up to a kilometer away. Pre-setting voltages and frequencies saves time and reduces testing errors. Real-time data increases the confidence level that the resultant data is accurate. Synchronous load changes provide real-life demand load simulations and support the genset’s reaction load.
The data is now displayed graphically showing selected voltages, power, and frequency and their interrelationships. Testers can easily select key settings during the test for diagnostic comparisons. The data is collected, collated, and organized by data capture algorithms. This allows an operator to pinpoint the causes of the exact moment of test failure at a certain day, time, voltage, frequency, and power setting—and understand the reasons for the failure. This data can be gathered simultaneously from multiple units via networking. It also allows for ease of setup and installation (instead of utilizing a 10,000-kW loadbank, the operator can connect 10 1,000-kW loadbanks to get the same result). The use of multiple smaller units also allows for finer load resolution than would be possible with a single large loadbank.
Specializing in loadbank manufacture since 1983, Crestchic Loadbanks is a leading manufacturer of loadbanks with major worldwide operations servicing the data center market. Crestchic are the largest loadbank specialists in the world. They have the expertise and capability to develop tailor-made testing solutions that meet a wide range of loadbank requirements, from standard size resistive and reactive loadbanks to custom-designed and built loadbanks of any size at any voltage and frequency. Crestchic loadbanks have been operationally successful in all seven continents and are reliably testing power supplies every day in locations and climates all around the world, from temperate to jungle, desert to snow, offshore to high altitude. They design and manufacture a wide range of air-cooled resistive loadbanks in standard frames sizes and containers, from 10 kW to 6000 kW, built to specific voltage, frequency, and phase requirements. Their resistive loadbank operates at voltages from 110 V to 690 V, at one- or three-phase and from 50–60 Hz. For test conditions requiring a lagging power factor, a resistive-reactive loadbank designed by Crestchic is available that operates from 50 kVA to 6250 kVA with the option for specific voltage, frequency, and phase requirements. All of the loadbanks are available in permanent or transportable models, and they meet IP55 standard protection requirements. They can be controlled with multiple 1-kW load steps and work in ambient temperatures of 45°C.
Eagle Eye Power Systems provides loadbanks for testing both AC and DC backup power sources: their LB-Series AC load banks and LB-Series DC loadbanks, with over 150 models available across both product lines. The LB-Series DC loadbanks are used to test the capacity of battery systems for acceptance testing. Options include wireless or wired cell voltage monitoring during a discharge test, and software solutions for discharge test recording and reporting, as well as custom discharge current and voltage configurations. Their LB-Series AC has a number of different series of loadbanks, each designed for a different application testing of backup generators and turbines.