UPS Testing and Static Transfer Switch Testing

UPS Load Testing

Dash 8Xe Monitoring UPS testing at the Liebert Delaware, Ohio Facility

The most important function of a UPS during power disturbances is to provide clean, usable power until utility power can be restored. For this reason, it is essential that the UPS has adequate load regulation. During load testing, load regulation is the ability to maintain a constant voltage level on all three phases of the output voltage as equipment is being switched on and off the UPS supply bus.

Liebert switches in various loads and monitors the three phases of output voltage for any transients or anomalies that can corrupt the power provided by the UPS. During UPS qualification, Emerson performs hundreds of load step tests to verify that the UPS performs to specification.

UPS Load Test (50% - 100% load)

The above figure is a screen shot from an Astro-Med Dash 8Xe showing the results of a 50%-100% load step and the corresponding stable three phase voltage output. The Dash 8Xe provides user configurable input modules for a variety of sensor and voltage measurements. Liebert’s Dash 8Xe units are populated with IHV2 and IHV1 voltage input modules. The IHV2 is rated for 600 VRMS, CAT II, which is ideal for measurement of the UPS voltage phase legs. The output current load step measurement employs an IHV1 input module rated to 250 VRMS, CAT II, along with an SR759 1000A current clamp.

The Dash 8Xe graphical user interface (GUI) allows easy setup of engineering units to convert the voltage output of the current clamp to units of current. The IHV1 and IHV2 provide channel-to-channel and channel-to-chassis voltage isolation to protect the unit and prevent crosstalk.

The two second load step test is performed hundreds of times. Using the Dash 8Xe touchscreen and GUI, Emerson created a custom Dash 8Xe test setup that can be saved and loaded when needed. The Emerson test setup has a sample rate of 10,000 samples per second per channel to assure that even the fastest transients are captured. Most importantly, the Dash 8Xe has a versatile trigger capability that allows Emerson to start recording at the appropriate time during the test. During the load test, the unit is set to trigger when the load rises above a predetermined current. The Dash 8Xe's circular buffer allows pre-trigger data to be recorded, so Emerson can capture one second before the trigger point and one second after it.

Upon completion of this test, the Dash 8Xe is set to automatically display the file on the screen. This allows Emerson to verify performance immediately. The Dash 8Xe advanced search utility allows Liebert engineers to quickly locate the trigger point in a file. Once the data review is complete, the unit is automatically re-armed and ready for the next test.