Page 4 - Load Bank Rentals

Fundamentals ®

of Load Bank Rentals
Insight Onsite

Load Bank Testing of Electrical Load Test Capacity Low Power Factor Testing
Power Sources The desired capacity of the load test is By adding an inductive load to the resistive
Any device which generates electricity expressed in kilowatts (KW). KW corresponds load, lagging power factor can be obtained.
may require load testing. This can be for directly to engine HP (.746 HP = KW) and Commercial loads, as well as generator sets,
product development, production line testing, is developed exclusively by the resistive are rated at the nominal power factor of 0.8
product demonstration, commissioning of load bank. Adding reactive load changes the lagging. This number is the cosine of the
a new installation or for periodic service, total KVA of the load, but does not alter the angle made between the KW and the KVA in
maintenance or trouble shooting. Although KW or HP load. A purely resistive load bank the diagram below:
the most common use of load banks for provides a realistic and effective test of the
testing is with engine generator sets, in fact, prime mover and causes full load currents to kVA
any device which generates electricity may be developed by the generator. The engine
require a load bank for testing, service or will develop full rated HP, operating pressures kVAR
calibration. This includes UPS, batteries, and temperatures, and the performance of
power supplies, fuel cells, solar cells, wind the governor will be fully evaluated. Adding
turbines, hydro generators, etc. A load bank inductive load allows for the full KVA capacity kW
provides a stable, known, controllable and of the generator to be developed for a full
relatively “harmless” load for these purposes. functional test of temperature rise, waveform COS = Power Factor
That is, if the performance of the generator quality, voltage regulator response and KW
is not known, it is better to evaluate the reactive load sharing. PF = KVA
performance with a load bank than with
critical facility loads. Voltage TAN x KW=KVAR
Low voltage AC systems are rated 120/240v, KVA= KW +KVAR 2
2
Load Bank Overview single-phase, 2 or 3 wire; 208-240/416-
Load banks simulate the “real world” loads 480/575-600/690vAC, 3 or 4 wire. Medium The magnitude of inductive load required
that the power source will experience. voltage systems are in the 5kV or 15kV class. to obtain 0.8 power factor is 0.75 X the KW
Electrical load can be broadly classified as DC systems can range from battery voltages (1000kw + 750kvar = 1250kva at 0.8 lagging
resistive, magnetic and capacitive. In the of 12/24/32v, 125/250v, or 350/700v, typically. power factor). As a point of interest, 0.75 is
real world, these components are mixed, Keep in mind that the AC load banks in this the tangent of the aforementioned angle.
as they are with a load bank, except with catalog are generally 3-phase, 3-wire loads, Keep in mind when sizing cables that the
the load bank, full control of the component meaning that a neutral is not required and full load current at the rated KVA must be
loads is possible. Resistive loads comprise that loads are applied in 3-phase balanced calculated.
incandescent lighting, electric heating and steps
other loads in which electrical energy is Leading Power Factor Testing
largely converted to heat. Magnetic loads Current The same rationale as above applies to
comprise motors, and other devices which Current, expressed in amperes, is found by leading power factor, except capacitive load
convert electrical energy to mechanical the following formula: is added. Leading power factor testing is
force and transformers which “step-up” rare and specialized. Most engine generator
/ “step-down” power from transmission KWx 1000 sets cannot tolerate more than a very small
to utilization voltages. Capacitive loads 3ph. A= degree of leading power factor.
comprise electronic loads. Although both AC (Vx 1.73xP.F.)
and DC systems power similar loads, most Portability and Site Conditions
of this discussion will involve AC systems. Current must be known in order to size
The most common load bank and the load connection cables. Keep in mind that When designing a load bank rental,
bank which is suitable for general load connection cables have a certain small considerations must be given to site space,
testing is the resistive load bank. A resistive resistance, and that a small voltage drop access and set up. All rental load banks
load bank converts electrical energy to heat. will be seen across the cable set and at listed herein can be networked in groups
Within the load bank, the load is divided the terminals of the load bank. Therefore, and connected in parallel to provide a total,
into discrete circuits or “steps” capable of although the generator instrumentation may aggregate load. It may be more workable to
stepwise, controlled application. The load indicate 480v, the load bank instrumentation network 10 Powerstar Load Banks to obtain
bank includes a means of cooling, most will measure the terminal voltage at the load 1000kw than rent a single 1000kw Load
commonly forced air, but also water. The bank, for example, 473v. Bank.
load bank also includes protective sensors,
circuit protection devices, instrumentation, an KW as a Function of Voltage Networking and Paralleling
operator interface and a means of connection Most rental load banks can be networked
to the generator. To simulate magnetic or KW varies as the square of the voltage: and paralleled to form larger systems.
motor loads, an inductive load bank is added therefore, in the preceding example, if the Powerstar and Infinity Load Banks can only
to the resistive load bank. This can take the load bank terminal voltage is reduced to be networked with other Powerstar and
form of an integrated, all-in-one package, or 473v, then the resultant KW will be 97% of Infinity Load Banks. All other digital models
separate units. Likewise, a capacitive load the rated KW. Where did that power go? It is can be networked and paralleled in any mix
bank can be added. Inductive and capacitive lost as heat in the connection cables. and match combination up to a maximum
load banks are always used in conjunction number of units. All control is centralized in a
with a resistive load bank-- there is generally single operator interface. All data is likewise
no reason to use one alone. Inductive and totalized to the operator interface. Networking
capacitive load banks, also known collectively is via data cables provided with the load
as “reactive” load banks, are only used on banks. Power cables are paralleled to the
AC systems and result in lagging or leading power source.
power factor for inductive or capacitive loads
respectively.

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