The Power Quality of Life

By Richard P. Bingham | Apr 15, 2004
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Hospitals have a priceless ‘product’—human life

When people think of high-reliability facilities, most often it is the financial data centers and the semiconductor plants that come to mind. While these types of facilities can experience very costly downtime, the medical facilities have a far more valuable “product”—human life.

Hospitals are highly dependent on sophisticated electronic equipment in the laboratories, intensive care and even for administrative tasks being carried out by the medical staff at the hospital bed. What is the price tag for data corruption that results in the wrong medicine request being formulated in the pharmacy; or loss of access to EKG and other patient monitoring equipment at the nurse’s station in SICU; or loss of power to the operating room during a transplant procedure? You can’t put a price on poor power quality.

Many hospitals are older facilities that have grown with the needs of increased medical care. The wiring and electrical infrastructure were often put in place well before the proliferation of electronic monitors, computers and large inrush generating electric loads such as MRI, X-ray, and CT scan equipment, that can become both a source and victim of power quality phenomena. The same rules of Ohm’s Laws and Kirchoff’s Laws don’t change in the presence of the Hippocratic Oath. The large current draws from an MRI machine can cause the electrical ground references to change from this “ground bounce.” The result can be the malfunction of other equipment. This current is often rich in harmonics, which can create the same problems of overheated neutrals and transformers as in an industrial facility.

The chart shows the current from an X-ray machine as it cycles through its program. Not only did the current rise from 20A to 100A on a 380V system, but the current contains substantial even harmonics with current THD of 65 percent on a heavily loaded circuit. A harmonic filter was purchased that injected compensating current, improved the quality of the supply to the X-ray, as well as putting less stress on the UPS that feed the diagnostic lab.

These harmonic problems weren’t discovered until a severe power quality damaged X-ray equipment, costing nearly $100,000. The source of the problem was the switch over from utility to generator power, which occurs during regular testing and emergency situations.

Such problems, unfortunately, are not rare in medical facilities. Since many hospitals are required to periodically test their backup power systems, one would think that the problems would be detected and corrected during commissioning or in the monthly test. In another medical facility, the problem didn’t become apparent until a thunderstorm rumbled through the area. A nearby lightning strike resulted in a fault on the electrical distribution system, which in turn caused the operation of a re-closure of the utility feed to this large city hospital. The hospital had invested substantial capital in a UPS and emergency generation system that should allow for “bumpless” or smooth operation from the utility power to the UPS to the generator. The UPS was designed to carry the load until the generator was up to speed several seconds later. Instead, in this situation, when the distribution breaker opened to clear the fault from the lighting, the power was interrupted to critical medical diagnostic equipment, including the angio suite, cath lab X-ray systems, MRI and CT scan devices.

The hospital had not made the small investment into a power quality monitoring system to verify the proper ongoing operation of its expensive backup power supplies. When such a system was eventually installed on the input and output of the UPS, they found out that the UPS worked properly. However, 20 seconds passed before the emergency generator came on-line, causing downtime and confusion. The PQ monitoring system showed the facility operations personnel that the X-ray Emergency Power Off switch was being incorrectly fed directly by emergency power, rather than feeding the UPS as was specified in the hospital’s power system design.

Whereas hospitals and other medical facilities are constantly striving to improve the quality of the care provided to their patients, care must be taken to ensure the quality of the electrical supply that feeds the diagnostic and life-support equipment in such facilities, as well as the administrative IT equipment. Providing the best medical care is quite difficult if the lights are out and the monitor screens are blank.

BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.


About The Author

BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.

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