Case study of overload service power quality incidents
There was a problem with six air handling units on a busy trading floor, all powered by a 480V, 400 amp power supply. The unit malfunctioned, stalled, and sometimes failed to start, causing the temperature in the control room to rise to unacceptable levels. A German GMC-I Dranetz power platform, a PP4300, was installed for two weeks to evaluate the voltage and current of the 400 amp service.
Based on the data collected, we learned about the following power quality issues:
- The graph at the top shows the voltage, which averages around 450V instead of the expected 480V. This results in a persistent undervoltage condition that makes the system more sensitive to depressions.
- Three large depressions appeared, greater than 10% of the nominal (see purple arrows), and many more depressions, about 5% of the nominal.
- The diagram below shows the current, which is expected to be 400 amps. As you can see, in many cases, it will exceed 400a, and in some cases it will reach 500a.
- A rise in current can be associated with a drop in voltage.
In the graph above, we see that both the voltage (red) and the current (blue) are decreasing, indicating that the source of the sag can be found upstream of the monitoring point. The final result of the investigation was that the two air handlers were transferred to different services, eliminating the overloaded circuit conditions and the source of the voltage sag.
The MAVOWATT 230 power quality tester enables safe, intuitive and flexible analysis of power quality as well as power consumption requirements.
■ Meets all functions of Class A (4U/4I)
■ Load curve analysis and energy measurement
■ Comply with EN 50160 voltage quality standard, exclusive reporting function
■ Ultra-high sampling: 512 samples per cycle
■ Two test frequency bands: 162/3Hz and 50/60 Hz
■ Event logging: RMS value and raw waveform
■ Pre/Post Trigger: Up to 100 cycles
■ Snapshot function
■ USB and Ethernet interfaces
■ Time synchronization via GPS clock (optional)