Page 4 - Load Bank Rentals
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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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