power quality

Solving Issues with Electrical System Power Quality

Thursday, August 9, 2018

It was a step towards sustainability that almost became a stumble. Shortly after a Canadian hospital invested in an energy-efficiency upgrade, the facility began experiencing significant issues with its critical equipment. System malfunctions and complete shut-downs began affecting treatments and day-to-day operations, causing delays, frustrations, and sizable headaches for both staff and patients alike.

After some investigation, they reached the conclusion that it was a power quality issue. Soon after, the hospital reached out to Schneider Electric Services to do a thorough investigation.

Diagnosing the disturbances

Schneider Electric was no stranger to the facility, having worked with the hospital on several prior initiatives. As such, its Power Quality (PQ) team jumped in with an acute understanding of its electrical configuration.

power qualityThe initial review and analysis of the site were completed using the existing Schneider Electric Power Management System (PMS). This helped immensely to review the site’s electrical grid parameters and narrow down the likely sources of the power quality issues. Ultimately, three PQ disturbances were identified: voltage distortion (THD or VTHD), voltage sag, and zero crossover point distortion for voltage.

The cause of the voltage distortion and multiple zero cross-over points was determined to be tied to the lighting ballasts and variable frequency drives (VFDs) that were installed as part of an energy retrofit. While the existing PMS provided Schneider Electric’s PQ team with a general direction of where to look, further analysis was required to determine the source and quantity of harmonic current being generated and to evaluate the cost and time required to implement the recommended solutions.

Soon after, Basillio Binghay, a Power Quality Specialist with Schneider Electric Power, arrived to conduct a full power quality audit. He set up the appropriate tools at the various nodes within the electrical system and began logging the various parameters and disturbances such as sags, voltage spikes, voltage, and current distortion levels. Over a period of several months, the data was compiled and a report was drafted and delivered to the facility manager which indicated some of the substations had significant levels of voltage distortion.

Based on the data observed, the PQ team concluded that the main source of harmonic current was the variable frequency drive (VFD) loads. The harmonic current produced by the VFDs was significant and it was causing voltage distortion throughout the entire electrical distribution system. A Reactive Compensation and Harmonics Filtering Activity Simulation report was then prepared which summarized the findings, modeled the system and – more importantly – simulated the results of different filtering and compensation techniques. By applying the various compensation remedies, the harmonic current was calculated to be greatly reduced and in turn, the Voltage Distortion at the main incoming feeders would be reduced to below 3 per cent. This would meet or exceed guidelines as per IEEE 519-1992 guidelines.

Taking action

  1. Install input line reactors (3 per cent Imp) for the VFDs rated 10 HP and above. Additional input impedance on a VFD will reduce harmonic currents and add protection to the VFDs from external transients.
  2. Install Active Harmonic Filters at four locations on the 600 V Main Incoming system. These filters monitor the status of the grid and actively compensate for variation in the distortion levels on the grid and will further reduce voltage distortion to acceptable levels as per IEEE-519-1992 guidelines.
  3. Install an isolation transformer at each of the main feeder circuits for the critical equipment to provided additional impedance during high-frequency switching, etc.

A simplified line diagram was then produced along with detailed mapping of the various feeders, transformers, MCCs, and electrical panels. This allowed the team to visualize what was needed and where. A plan of attack began to form.

The second part of the project included installing, testing, and commissioning the needed equipment. Schneider Electric won the bid which included not just the installation, but also project management, equipment supply, commissioning, and testing.

power quality

Since the equipment was installed, ongoing monitoring has shown that the power quality has improved significantly and the sensitive equipment is no longer shutting down or causing issues with patient treatment. Throughout the project, the power management system was configured to ensure the facility manager can review the progress and the system at any time, monitoring levels of power quality and disturbances. It is set up to alarm the team if anything in the system gets out of hand (i.e., voltage distortion on a particular feeder).

No cookie-cutter cure

An electrical system is like a living organism. And, like in healthcare, each treatment is unique to the patient. First, it is necessary to diagnose the symptoms and get to the root of the issue. Then, identify the culprits, and only then can you tailor a solution for the grievance at hand.

It’s true that the cost of addressing issues such as these can be intimidating at first and it can be a challenge for organizations to receive funding for improvements. That’s why it’s critical to be armed with the best information available to enable success.

Power Quality issues can look daunting and it can manifest itself through strange and seemingly non-related occurrences like essential equipment shut-downs, electronic and electrical equipment failure, and the tripping of critical circuits. With the right tools and skillsets, however, these adversaries can be exposed, measured, and treated.

References:

IEEE Std. 519-1992: Recommended Practicesand Requirements for Harmonic Control in Electrical Systems.

To contact a Power Quality specialist, visit us at www.schneider-electric.ca/pqs.

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