Load Bank Installation
A load bank is an electrical machine that has multiple rows of resistor elements inside, controlled by toggle switches or a digital controller, that applies precise amounts of electrical load to the power source(s). Digital control panels now allow us to apply load to the power system, sometimes even controlling multiple load banks from one handheld controller. Think of a space heater, or a toaster, but much, much larger. Most load banks are air cooled, using fans and heat sinks to dissipate the heat from the resistor elements. Very few load banks are water cooled, but some of you may remember the brine tank load banks from way back in time; newer load banks allow for much more controlled load application to the generating set(s).
Load bank types can vary quite a bit and depend on what works best for your facility:
- “Suitcase” style – carried by hand or on wheels
- “Refrigerator” style – rolled around on wheels
- Trailer mounted
- Permanent installations
- Radiator mounted unit
- Pad mounted unit
Load banks also come in different configurations, although resistive load banks are the most common. Some other load bank types are capacitive load banks and resistive reactive load banks. Selecting a load bank other than resistive will allow testing of the generator set at a power factor other than 1.0 (Unity). This is beneficial because many of the building equipment today include generator leading power factor loads, so testing your generating systems at various power factors will ensure adequate performance under building load. This is often the case for data centers, as the UPSs and efficient lighting systems tend to generate more leading power factor. Medium voltage load banks are also available and will reduce set up time, since the cabling amount is greatly reduced.
What is a load bank connection cabinet?
Load bank connection cabinet, often called a tap box, can be installed to allow safe connection and quickly connecting of cables to the tap box. When designed and installed correctly within the electrical system, the tap box can also serve as a portable generator connection point, should the permanently installed standby generator fail or require down time for maintenance or repairs. During installation of the tap box, phase rotation will be permanently determined by the installing electricians and clearly identified at the docking station by colored cabling or specially configured camlock connections.
When configured as a portable generator connection cabinet, a temporary generator will be brought to the facility and parked near the connection cabinet. Cabling will be run from the portable generator to the tap box. Generator quick connections will be terminated at the tap box and any necessary shore power or remote start cables will also be ran to the temporary generator. Any necessary configurations of the breakers inside the facility may need to be adjusted, and then the portable generator will be supporting the emergency power loads, normally backed up by the permanent generator, through the automatic transfer switches.
Cabinets can be constructed of different styles, configurations, and materials. The majority of tap boxes are mounted outdoors, so NEMA 3R and Stainless Steel construction may be worth looking at for your project.
What is a resistive load?
Resistive load is a simple load that has a power factor of 1.0, or unity. This means that the voltage and current sine wave are both aligned, and their zero crossings meet at the same point in time. Understanding resistive loads is easier when we discuss what types of loads are resistive and inductive; for example, incandescent light bulbs, toasters, space heaters, hair dryers or hand dryers, are all resistive loads. Reactive, or inductive / capacitive, loads are motors (chillers, elevators, pumps, etc), VFDs, UPSs, efficient lighting systems, (sometimes) transformers.
What is the purpose of a load bank?
Load banks are primarily used as testing equipment but can also be integrated to power system design to balance uneven loads or to be used as power factor correction. Onsite power generation systems are more sensitive to an imbalance of power factor than the utility grid will be, since the emergency power source (generator) itself is much smaller than the generating equipment for the power company. If your facility has large amounts of reactive load that needs to be brought closer within the acceptable range of the capability curve for alternators, a permanently installed automatically loading load bank may be a good option.
Did you know? Load banks can be used for much more than just testing generators, including testing a Uninterruptible Power Supply (UPS) battery system or rotary system, testing circuit breaker operation, loading an automatic transfer switch power panel to rated capacity, and much more. LionHeart can help to perform each of these to ensure your facility is ready to handle the load when the time comes!
Why does it need to be installed?
Equipment for load bank testing is crucial to ensuring long-life and maximum reliability from the generator system. Building loads are typically sized to not heavily load the generator system and allow room for addition of electrical loads in the future. Additionally, very often, transferring critical loads to the generator for testing is not practical; these lightly loaded conditions end up creating wet-stacking conditions in diesel engines which can be harmful to the internals of the engine, as well as how light loads do not effectively test the cooling system operation, which may be masking an underlying problem with the cooling package.
Load bank equipment resolves each of these concerns by periodically testing the diesel engine to heavy loads, ensuring proper operation of the cooling package, as well as increasing exhaust temperatures above the manufacturers minimum exhaust gas temperature recommendation, which reduces the effect of wet-stacking in the engine.
How often should you load bank a generator?
Generators, particularly diesel engine powered sets, are normally load bank tested annually. During the initial start-up of a new generator set is also a great time to conduct load bank testing, to verify that the system operates as designed in the environment to which the installation has been completed.
Occasionally, a load bank test may be required after a repair is performed to verify system operation under heavy loads. For example, if engine thermostats were replaced to alleviate an overheating condition, we may need to load bank the generator to ensure that the overheating condition was corrected.