Case Studies

UPS Operation

A single-phase UPS was monitored by PQPro™ power quality analyzer/data recorder to characterize the performance of the backup system. The voltage and current were monitored by the AC input, AC output as well as the DC voltage and DC current of the internal battery. The PQPro™ was configured to record Continuous Waveform data with a resolution of 65 microseconds (256 samples/cycle) as well as AC RMS and DC voltages and currents with a resolution of 200 milliseconds (RMS update every 12 cycles). Input AC voltage was removed twice during the recording.

The UPS monitored was inexpensive with a square wave output when input voltage was removed. When input voltage was present the UPS inverter was bypassed.

Figure 1: Input (Red) and Output (Black) AC RMS Voltage and Current

Figure 2: Battery Voltage (Green) and Current (Black)

Figure 3: Input (Red) and Output (Black) Voltage at the Time of Input Disconnect. Note: Input Voltage was Measured on the Line Side of the UPS Input Disconnect Switch

Figure 4: Input (Red) and Output (Black) Voltage at the Time of Input Re-Connect

Figure 5: Input (Red) and Output (Black) Current at the Time of Input Disconnect

Figure 6: Input (Red) and Output (Black) Current at the Time of Input Re-Connect

Figure 7: 3rd Harmonic Output Voltage (Red) and Current (Black) Trend