Telephone company customers reported audible noise in their telephone service. Through measurements, analysis, and simulationns, 540 Hz noise was found to be coupling from power distribution to telephone cables in a shared underground right-of-way. The source of the noise was small single-phase electronic loads dispersed throughout the power distribution system in the area. A passive shunt filter was designed using an existing capacitor bank. Installation of this filter reduced the noise to acceptable levels.
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