As science spawns new innovative technologies to improve power quality (PQ), so too can new PQ issues emerge from such technologies themselves.
EPRI’s PQ Team has witnessed this phenomenon many times. For example, new inverter technologies—which can reduce the depth of voltage sags caused by the inrush current of motor-driven loads—can introduce high-frequency-switching interference onto distribution lines. Even the not-so-new capacitor bank technology —designed to correct power factor and optimize volt/var—can impose switching transients and resonance onto a power system.
Recently, Oak Ridge National Laboratory (ORNL) contracted EPRI's PQ Service Team to assist with a power quality issue that coincided with the operation of the world’s first and fastest exascale supercomputer, Frontier.
The Frontier system uses over 30 megawatts of power to operate at maximum load. During operation, with applications that generated large and high-frequency load swings, the LED lights in the building and nearby buildings serviced from the distribution circuit were observed to flicker. In addition, the mechanical cooling pumps for Frontier on that same distribution would frequently turn emergency power off, causing unscheduled outages.
Through PQ monitoring and waveform data analysis, the EPRI and ORNL team observed that, in the presence of system background harmonic distortion, there was less than optimal performance, leading to more severe harmonic fluctuations.
After studying the power supply and system operation, optimal performance was achieved by tuning the active power factor correction (PFC) for the power supply. Once the adjustments were made, the team noticed that the heavy voltage distortion and severe flicker issues were successfully eliminated. Any remaining minor flicker is being addressed with suggested LED lighting optimizations.
Active PFC is a high-frequency switching method that normally would be a highly distorted waveform and converts it into a near-perfect sinusoidal waveform—free of low-frequency harmonics that can cause numerous power quality issues. However, like other switching inverter technologies, the high-frequency component from this circuit could introduce other PQ issues. In this case, there was an issue with synchronizing the current with the voltage, which created other PQ issues.
Who knows when and where new enabling technologies will cause their own set of headaches for the industrial and commercial customers of electric utilities? What about other technologies that use active PFC, such as the boost converters of battery chargers in electric vehicles? If the background voltage is heavily distorted, will they also present switching issues?
EPRI will continue to investigate active PFC technology and determine how common an issue this could become.