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How to Test AC Sources with an AC Electronic Load

2019-07-18  |  App Notes





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How to Test AC Sources with an AC Electronic Load


Testing AC power sources, such as uninterruptible power supplies, can be a real challenge. Find out how to overcome that.


These products are often tested with resistive load banks, but this approach does not simulate real-world conditions such as switching DC/AC converters found in many AC powered products.

As a result, using resistive load banks does not fully exercise the equipment under test (EUT) under worst case operating conditions. High peak currents and low power factor loads can significantly impact the operating characteristics of a UPS or AC power product.

A better way to test these products is with an AC electronic load, such as the California Instruments 3091LD AC eLoad. An AC electronic load can simulate high crest factor and variable power factor load conditions in addition to providing a purely resistive load, effectively simulating real-world conditions and significantly increasing product reliability. Product defects that result in costly field returns are detected well before a unit reaches a customer site.

An AC electronic load should have the following modes:



Constant Power (CP)

This mode effectively emulates constant power loads such as switching power supplies.

Constant Resistance (CR)

Emulates a conventional resistive load or power resistor. A programmable range from 2.5 Ohms to 1000 Ohms covers a wide range of applications. This mode can be used to replace conventional resistive load banks.

Constant Current (CC)

Provides a constant current load. This mode may be used to simulate both linear (resistive) and nonlinear (active) loads for voltage regulation testing.

Constant Voltage (CV)

This mode emulated a shunt regulator load and may be used to test current source products.

Short Circuit (SC)

Test the short circuit protection mode of the EUT by providing a short condition. The 3001LD can handle surge currents of up to 300 Amps for up to 50 msec and sustained currents of 30 Amps in this mode of operation. The low voltage cut-off of the load can be programmed from 50 Volts up.

When operating in constant current or constant power mode, the electronic load supports crest factor control by narrowing the conduction angle of the current waveform in order to match the requested crest factor. Thus, the peak current is increased while retaining the RMS current level. While the apparent power remains constant, the true power decreases.

This results in a reduced true power factor. Consequently, as the crest factor is increased, the true power factor automatically decreases. The load further controls power factor by shifting the current with respect to the input voltage (displacement power factor). Both leading and lagging power factor control is available. A phase shift of the current is only possible if the crest factor is higher than 1.414.

When selecting an electronic load, make sure to choose one that can dissipate all the power that your source can generate. The 3091LD AC eLoad is capable of dissipating 3000 W of single-phase AC power. For higher power or three-phase applications, a 3091LD master unit can be combined with one or more auxiliary units.

Another consideration might be how easily you can use the load in an automatic test station. If this type of operating is necessary, make sure that the load has the right type of computer interface, and that measurements made by the load can be read over the interface. This functionality may allow you to eliminate the need for additional test equipment such as meters, power analyzers, and oscilloscopes.



Read on to find out more about the Asterion AC power source from Ametek Programmable Power.


How to Test AC Sources with an AC Electronic Load



| Asterion AC Power Source




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✔ (500 VA - 36000 VA, 200 / 400 Vac, 250 / 500 Vdc)
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✔ 1U models - single phase
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