Load Bank Sizing Calculations – Part Three



In Article “Load Bank Sizing Calculations – Part Two”, We indicated the different types of load banks, which are:
  1. According To the Load Element Type,
  2. According To Portability,
  3. According To Cooling Method,
  4. According To Method of Control,
  5. According To Operating Mode,
  6. According To Application,
  7. According to no. of Load Steps,
  8. According to Load Bank Voltage and Frequency.
And we explained the first type; According to the load element type in this Article.

Today, we will explain the other types of Load Banks.



Second: According to Portability and Site Consideration




When selecting a load bank, considerations must be given to site space, access and setup.  According to the portability and site consideration, the load banks can be categorized to:
  1. Small Portable,
  2. Rack-Mounted Portable,
  3. Large Portable,
  4. Stationary,
  5. Stationary – Radiator/duct Mount,
  6. Trailer.


Note:
Some small AC Load Banks can be networked in groups and connected in parallel to provide a total, aggregate load (for example using 5 nos. 200 KW load banks to obtain 1000kw for than using a single large 1000 KW load bank).

A- Small Portable

Small Portable Load Bank - AC

When a load bank needs to be moved frequently, it is better to use a small portable type which will be Hand-carryable or wheeled units.
Portable load banks are Resistive type and can be rated up to 150 kW, AC or DC and it will be air-cooled type. A properly designed portable load bank should have overall dimensions small enough to fit through a man door or freight elevator.
Portable load banks are used in a wide variety of service and rental applications for the temporary Testing and maintenance of small generators and power systems like:
  • Residential standby,
  • Contractor generators,
  • Marine generators,
  • RV generators,
  • Contractor generators,
  • Small wind turbines,
  • 120/240v panelboards and distribution,
  • Inverters,
  • Small UPS.


Small Portable Load Bank - DC


Low voltage DC Load bank for testing and maintenance of:

  • Battery systems,
  • Rectifiers,
  • Battery chargers, Power Supplies, Hybrid vehicles.


Notes:

Digitally controlled, up to 40 units may be networked to achieve desired capacity:

  • Field testing & maintenance,
  • Product line testing,
  • Large systems via networking.


Small Portable Digitally controlled Load Bank 


B- Rack-Mounted Portable


Rack-Mounted Portable Load Bank

A rack-mounted load bank is a specific type of temporary portable load bank that is occasionally employed during data center commissioning to more accurately simulate the electrical and heat load of the critical computer systems prior to the computers actually being installed. In particular, where the data center computer cabinets are direct-ducted to a cooling system exhaust plenum, rack-mounted load banks may be the only practical way available to truly validate that the facility’s cooling systems perform as designed prior to full data center occupancy.


C- Large Portable

Large Portable Load Bank


A comprehensive line of large portable load banks which will be
Resistive type with ratings from 150kw to 1000kw, AC to 600v, DC to 800v can be used for Testing and maintenance of:

  • Mid-range generators when used as a single unit,
  • Large generators,
  • Large distribution systems; single or paralleled,
  • Shipboard generators,
  • Shipboard systems,
  • Oilfield systems,
  • UPS systems.


Note:

The Large Portable load bank can be network capable, digitally controlled for field or line testing of generators.


D- Stationary


Stationary Load Bank

Stationary Load banks are typically permanently mounted on concrete pads next to a generator set being served. They produced with heavy duty bases with fork pockets and lift frames.  These load banks can either be used in highly mobile environment via fork lifts, cranes, road trailer, or can be permanently installed on a concrete base for applicable static applications.
If the installation is indoors, the load bank can be enclosed in a NEMA-1 cabinet. For outdoors installation, a NEMA-3R enclosure is typically used.

Stationary load banks can be resistive, inductive, and or capacitive load banks for factory or field use and rated from 5kw to 5mw, AC to 600v (low voltage), to 15kV (medium voltage via transformer), DC to 800v.

Stationary load banks can be used for Testing and maintenance of:

  • Engine generator sets,
  • UPS systems,
  • Large AC generators.


Note:



Connecting multiple load banks


Stationary load banks may be combined and networked for unlimited system capacities.


E- Stationary – Radiator/duct Mounted


Stationary – Radiator/duct Mounted Load Bank


Radiator/Duct-Mounted load banks are custom built for each application, matching the generator set’s radiator core height and width. They will be resistive type only.

They are mounted directly to the generator set radiator and utilize the engine fan for cooling (Radiator Airflow Cooled type). These load banks are commonly installed inside the engine generator’s outdoor enclosure. The primary benefit of this approach is to conserve space.

They can be provided for indoor, duct-mounted, or outdoor locations.


F- Trailer

Trailer Load Bank


When there is a need to test large load ratings and there is no stationary load banks are installed, we can utilize load banks mounted on trailers or service vehicles.

Trailer Load Banks purpose-built for heavy-duty, field use Rated from 250kw to 3000kw, AC to 600v, DC to 800v with A wide selection of connection and control options.

Trailer Load Banks can be used for Testing and maintenance of:

  • Mid-range generators when used as a single unit,
  • Large generators,
  • Large distribution systems,
  • Shipboard generators,
  • UPS systems,
  • Other power systems.


Note:

Trailer load banks also can be Network capable and digitally controlled types to test large power systems.

Also, as per site consideration, the load banks can be categorized to:

A- Indoor
If the installation is indoors, the load bank can be enclosed in a NEMA-1 cabinet.

B- Outdoor
For outdoors installation, a NEMA-3R enclosure is typically used.




Third: According To Cooling Method




Cooling methods for Load elements in the load bank can be:
  1. Natural Convection Air,
  2. Integral Fan Forced Air,
  3. Radiator Airflow, or
  4. Water Flow.


A- Natural Convection Air

Natural Convection Air Systems may be used with load banks rated up to a 20 KW maximum.
B- Integral Fan Forced Air


Integral Fan Forced Air Load Bank


Integral Fan Forced Air Systems for resistive load elements consist of an aluminum fan blade (shrouded for high efficiency) directly driven or belt driven by a motor. The fan motor is energized by a control contactor and protected by a circuit breaker.
While Integral Fan Forced Air Systems for Reactive Load Banks (inductive or capacitive) utilize a system which consists of fan shutter assemblies.
Motors for outdoor Load Banks are totally enclosed. Motors for indoor Load Banks are open-drip-proof.

C- Radiator Airflow

Radiator Airflow Load Bank

Radiator/Duct-Mounted load banks are custom built for each application, matching the generator set’s radiator core height and width. They will be resistive type only.

They are mounted directly to the generator set radiator and utilize the engine fan for cooling (Radiator Airflow Cooled type). These load banks are commonly installed inside the engine generator’s outdoor enclosure. The primary benefit of this approach is to conserve space.

They can be provided for indoor, duct-mounted, or outdoor locations.


D- Water Flow


Water Flow Load Bank

Water Flow Systems consist of one or more water-cooled load modules supplied via an open loop water system. The pump/motor set delivers water to the load module.

Water-cooled load banks allow for indoor installations in controlled environments with the following advantages:
  • They are completely quiet,
  • They are highly compact and maintenance free,
  • They are ideal for installation in buildings in central-city areas, industrial parks or office complexes where an outdoor air-cooled unit would be impossible to install due to space or noise restrictions.


Water-cooled load banks are rated to 600vAC, to 3000kw, using fresh-water, glycol, and cooling tower (high flow/low rise) with high-pressure (to 1500PSI) are needed.

Water-cooled load banks can be used for Testing and maintenance of:

  • Large AC generators,
  • UPS systems,
  • Other power systems.


Water-cooled load banks are also Fully networkable for digital control of single or multiple units from a single operator HMI or remote station therefore they can be used for  Commissioning and testing applications of Data-center chiller.



Fourth: According To Method of Control




Load bank control can be classified according to type of control to:
  1. Mechanical Control,
  2. Electronic Control (Digital Control).


A- Mechanical Control:



Decade switch local control panel


The load bank will be controlled via Physical toggle switches, pilot relays, decade switches, indicator lights and alarms.

B- Electronic Control (Digital Control):

Electronic load banks are programmable and can be employed to test all sizes of generator systems in any given industry. They use a Programmable Logic Controller (PLC) to translate digital commands into mechanical switching.

Advantages:

  • The electronic load bank is superior and results in more precise data than the results derived from the mechanical control.
  • Adding a remote controller with a color touch screen allows even further enhanced control and user capabilities.
  • Having PC based software which provides increased sophistication for control along with transient speed instrumentation, full data acquisition reporting with graphical displays. Real time data such as crest recovery times and percentage error necessary for testing to ISO8528 should always be used for witness testing and product verification.
  • They can communicate via MODBUS allowing the load bank to be integrated into building management systems for control and monitoring through PLC, HMI, or SCADA systems.
  • Site load correction or automatic load control is also possible and maintains the required levels of loading especially on generator sets to prevent the problems associated with light load, such as wet-stacking.
  • The ability to network load banks brings many potential benefits not only from the ease of use where one remote controller or PC can control multiple linked units to allow higher capacity testing. Furthermore this also allows flexibility of load bank utilization and use in restrictive areas where the ability to use a single unit to carry out the test is not achievable.


Disadvantages:

  • The disadvantage is in the price where electronic load bank testing is more expensive.





Fifth: According To Operating Mode




Load bank control can be classified according to operating mode to:
  1. Automatic operating mode,
  2. Manual operating mode.



A- Automatic operating mode:



Automatic operating mode


Automatic operating mode gives Wide variety of auto control available including:

  • Generator exercise, control from remote control contacts,
  • Automatic exercise/test via programmable microprocessor control,
  • Automatic load leveling/load regulation to maintain preset load on generator by sensing of total load and automatic addition or subtraction of load bank component,
  • Reverse power/regenerative power protection of generator by sensing power direction and magnitude and automatic addition of load bank component to act as a power sink.


B- Manual operating mode:

Manual operating mode can be via local and remote manual control:

  • Local control:  Control panel self-contained in Load Bank,
  • Remote control: Control panel placed in a location away from the physical load bank.


Manual operating mode has only the following features:

  • Generator exercise and testing via local or remote manual control,
  • Minimum loading of generators,
  • Malfunction Detection.





Sixth: According to Application




The load bank classification and Type will depend on the sector or application in which it will be used. Typically load banks can be categorized into the following classifications as in Tables 1&2 below:

Table-1: Load Bank Type according to Application
Generator Capacity
Load Bank Type
Application
< 100 kVA
Resistive Only Portable, Small Generators and UPS System (120/208, 240 VAC, 60 Hz)
< 200 kVA
Resistive
Only
Small Generators and UPS Systems (480VAC, 60Hz)
>200 kVA
combined Single Units (480VAC, 60 Hz)
1MVA – 6MVA
combined
Single Units (480/5kV/15kV, 60 Hz)
>6 MVA
combined Multiple Units Combined
(480/5kV/15kV, 60 Hz)

Table-2: Load Bank Type according to Classification
Load Bank Classification
Load Bank Type
Radiator Mount
Resistive
Portable (DC or AC)
Resistive
Mobile/Static
Resistive / Capacitive / Inductive / Combined
Static Only
Resistive
Container
Resistive / Combined
Medium Voltage
Resistive / Combined






Seventh: According to no. of Load Steps




Load banks can be categorized as per the included no. of load steps to:

A- Single Block:

Entire capacity of load bank applied, on/off, in one step increment.

B- Multiple Steps:

Load bank capacity is divided into discrete increments for application in steps;
defined in terms of Load Step Resolution, which is the smallest step increment of load control.
Steps can be coarse (50%, 33%, 25%) or fine (5KW, 1KW).




Eighth: According To Load Bank Voltage And Frequency




There many types of load banks according to their voltage and frequency as follows:

  1. Single or multiple Frequencies,
  2. Single or multiple voltages,
  3. Low or medium voltage.


1- Single or multiple Frequencies:

A- Single Frequency 
Designed for a specific frequency.

B- Multiple Frequencies
Capable of multiple frequency or AC/DC operation (Typical frequencies: 50-60-400HZ, DC)


2- Single Or Multiple Voltages:

A- Single Voltage:
Designed for a specific voltage, typical of exercise load banks to 15KV.

B- Multiple Voltages: 
Capable of dual or quad voltages; (Typical voltages—60HZ: 120/240, 208-240, 416-480; 50HZ: 190-220, 380-420; DC: 12-60, 125, 250) to 15KV.


3- Low Or Medium Voltage:


A- Low voltage:
Typically load banks are low voltage from 220V to 690V.


B- Medium voltage:

Medium voltage (MV) power supplies are now one of the most common load bank test applications. Many facilities require MV supplies to power their equipment and matched MV load banks are specified to ensure back-up power supplies are kept in optimum condition.

There are three main types of medium voltage load banks:


A- Low voltage (LV) load bank with a step-down transformer on a common skid:
Low voltage (LV) load bank with a step-down transformer on a common skid

A common configuration mounts a three-phase step-down transformer and one or more load banks on a structural skid, as shown in the image below. The transformer secondary voltage on these skid mounted units are usually rated at 480 or 600 volts. These higher secondary voltages result in lower current, and will require less interconnect cabling when compared to designs that use 208 volt or 240 volt secondary voltage.


B- Containerized Solution:


Containerized Solution

Load bank manufactures often install large step-down power transformers and LV load sections inside 20-foot and 40-foot ISO-style containers. Unlike skid-mounted models, containerized load banks can offer both resistive and reactive loads, typically with variable power factors. The capacity of the 0.8 PF medium voltage containerized load banks range between 2 to 5 MW and are perfectly suited to heavy-duty load test applications.


C- Direct Connection Solution:


Direct Connection Solution

True direct connect medium voltage load banks accept medium voltage power directly onto their input busses, and do not require any step-down transformers. The absence of transformers allows any additional space to be dedicated to increasing kW capacity. While typically offered in capacities up to 6000 kW, these units can sometimes offer higher capacities (depending on the application and the required voltages).




In the next article, we will explain components, safety precautions and some design aspects of Load Banks. So, please keep following.

The previous and related articles are listed in below table:

  
Subject Of Previous Article
Article
What is a Load Bank?
Why we don’t use the actual facility loads to test the power source?
Wet Stacking Problem
Load Bank Applications
Applicable standards for Using load banks with emergency power generating systems



Types of Load Banks:
First: According to the Load Element Type


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