System

The 3091LD is designed to provide precisely controlled non-linear loads for testing AC power generation equipment such as UPS’s, AC sources, electrical switches and circuit breakers. The ability to simulate high crest factor and variable power factor AC load conditions provides an effective method of testing these and other AC products against real-world conditions and can significantly increase product reliability.

Traditionally, many of these products are tested using resistive load banks. This approach does not simulate real-world conditions such as switching AC inputs found in many AC powered products. This type of conventional testing does not fully exercise the equipment under test (EUT) against 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. Unless properly exercised, product defects may go undetected until a unit is used at a customer site, resulting in costly field returns.

Operating Modes

The 3091LD can be used to emulate a wide variety of AC load conditions to support real-world testing and evaluation of UPS and AC source products. Specifically, the following modes can be selected:

Control

The AC load can be operated from an easy to use, menu driven front panel. Product tests can be performed quickly in an R&D setting by punching up specific load conditions on the front panel and reading the measurement screen of the 3091LD. This fast interactive front panel control mode can be used during a product’s early development cycle to isolate potential performance problems before the product leaves the engineering lab.

Software

All AC load modes are easily set from the front panel using a menu-driven user interface. The large LCD screen is used to display setup information as well as measurement data. Measurements include volt RMS, volt peak, current RMS, current peak, crest factor, true power, apparent power, power factor and frequency. Both voltage and current waveforms at the load input terminals can be digitized and displayed on the front panel graphical LCD. This allows EUT output behavior to be analyzed quickly without the need to hook up additional test equipment. A Windows graphical user interface (GUI) is provided to expand the measurement and display capabilities of the 3091LD. The GUI can be used to save and print test results for report purposes.

The 3091LD can be deployed in ATE test stations using either IEEE-488 or RS232C remote control. The industry standard SCPI (Standard Commands for Programmable Instrumentation) protocol is used and instrument drivers are available to ease test software development. The built-in metering functions of the 3091LD AC load can be used to eliminate the need for additional test equipment such as meters, power analyzers and oscilloscopes. This and the reduced size of the 3091LD compared to passive load banks, represents a savings in both cost and rack space.

Configuration

Each 3091LD 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 Auxiliaries. The controller in the master 3091LD unit provides the required consolidated measurements so the test system controller or operator need only interface to the master unit, regardless of the specific configuration. Single or three phase configurations can be software configured from the master controller.

Crest Factor
When operating in constant current or constant power mode, the 3091LD 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 power factor. Consequently, as crest factor is increased, the 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. Thus, crest factor and power factor control ranges are coupled.