….is paved with good intentions. And the road to poor power quality is paved with power conditioning devices. Four examples:
1) Reviewing a power quality study, wherein the complaint is a chiller that is shutting down due to excessive voltage imbalance. The voltage imbalance chart showed unusual step changes in voltage balance, often exceeding 2%. The problem: the site had a tap-switch voltage regulator installed, and as individual phases were regulated, voltage balance jumped from relatively balanced to relatively imbalanced. The solution: Bypass the voltage regulator.
2) A second study, with imaging artifacts affecting an MRI system after several years of satisfactory service. The system is protected by a UPS, and shows a higher than typical number of load related events. The problem: the UPS requires the battery string to supply the maximum imaging system load. As the batteries have aged, they were unable to support the peak load. The solution: service the UPS / battery string; in all likelihood the battery string needs to be replaced. A different UPS, that did not rely on the battery supply peak power, would not have had this problem.
3) Finally, a site with repetitive (~ 10 minutes) and severe low frequency transients. A facility based capacitor bank, intended to correct voltage and power factor, is malfunctioning – the capacitors pull in, and then shut down 45 seconds later (for so far unknown reasons) – probably internal fault or error indications. Ten minutes later, the caps try again. A CT scanner has been damaged repeatedly by this problem.