In Article “Load Bank Sizing Calculations – Part Two”, We indicated the different types of load banks, which are:
- According To the Load Element Type,
- According To Portability,
- According To Cooling Method,
- According To Method of Control,
- According To Operating Mode,
- According To Application,
- According to no. of Load Steps,
- 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
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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:
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
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:
Low voltage DC Load bank for testing and
maintenance of:
Notes:
Digitally
controlled, up to 40 units may be networked to achieve desired capacity:
B- Rack-Mounted Portable
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
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:
Note:
The Large Portable
load bank can be network capable, digitally controlled for field or line
testing of generators.
D- Stationary
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:
Note:
Stationary load
banks may be combined and networked
for unlimited system capacities.
E-
Stationary – Radiator/duct
Mounted
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
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:
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.
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Third: According To Cooling Method
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Cooling methods for Load elements in the
load bank can be:
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 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/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 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:
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:
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.
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Fourth: According
To Method of Control
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Load bank
control can be classified according to type of control to:
A- Mechanical Control:
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:
Disadvantages:
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Fifth: According
To Operating Mode
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Load bank
control can be classified according to operating mode to:
A- Automatic
operating mode:
Automatic operating mode gives Wide variety of auto control available
including:
B- Manual
operating mode:
Manual
operating mode can be via local and remote manual control:
Manual
operating mode has only the following features:
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Sixth: According
to Application
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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:
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Seventh: According to no. of Load
Steps
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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
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There
many types of load banks according to their voltage and frequency as follows:
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:
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:
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:
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
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Article
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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
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Types of Load Banks:
First: According to
the Load Element Type
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