Electrical phase imbalance is a condition in a three-phase system where the amperage draw is uneven between phases A, B and C. This condition exists in most buildings, but if the imbalance is severe (more than 10% between phases), it can cause unexplained nuisance tripping on large breakers. Facility personnel should check periodically for phase imbalance. If it exists, have a trained professional carefully identify the problem and redistribute the load to make sure all phases are evenly distributed.
A northern New Jersey university was experiencing frequent electrical problems that were becoming very troublesome in one of its campus buildings, a six-year-old, four-story, 125,000 sq. ft. building that housed a large, open student center with cafeteria and several retail shops. Electronic distribution breakers were randomly tripping, turning off power and highly inconveniencing users and students. Omni Instrumentation & Electrical Services, Inc. was called in to diagnose and correct the issues.
Our technicians’ first action was to record voltages across various parts of the system, from phase to phase and phase to ground, finding them within 1-2.5%. Amperage readings, however, taken in different parts of the building at different times of day, clearly showed an imbalance. Phases A and B were within 1-2% of each other, but the C leg was carrying at least 10% more current than the other two, causing the electronic breakers to fault or trip to protect the circuit.
Next, we set out to find where the amperage phase imbalance was occurring. Working on off-hours, our technicians started from the top down, shutting off distribution and panel breakers one by one to see where the imbalance would point. Issues were found with distribution of the lighting load across phases, providing only a partial solution.
The main culprit was discovered in the mechanical penthouses when shutting off the breaker to the large HVACR packaged chillers immediately corrected the imbalance. The problem was narrowed down to a single faulty chiller that was promptly isolated and locked out, and the manufacturer was brought in to address electrical problems in the equipment. The Student Center was quickly back in business, and the client highly satisfied with our service.
About Omni
Omni Instrumentation & Electrical Services, Inc. is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.
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