GROUNDING (cont)

TM-55-1930-209-14P-9-4 Water Purification Barges (NSN 1930-01-234-2165) Electric Power System Manual
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GROUNDING TESTING AND ADJUSTING 3. There have been reports of excessive circulating neutral current occurring when two or more generators are operated in parallel. Generators should be installed with the assumption that no excessive circulating neutral current will occur with the generators paralleled at full load. The phase current should not exceed 100% of the generator nameplate ampere rating. In those cases where excessive neutral currents are encountered, either a neutral lead reactor or selective grounding of the neutrals may be used. If selective grounding of one generator neutral is used, a disconnect switch should be installed in each generator ground lead. The disconnect switch should have about 25% more current carrying capacity than the generator line ampere rating. NOTE: Three phase, "Y"-connected generators can have a third harmonic voltage that does not cancel at the neutral. It is this voltage that causes the excessive circulating neutral current that can occur when operating in parallel. 4. Instructions concerning excessive neutral current and grounding the generator neutral also apply to former model generators. 5. Most radio and audio frequency interference problems are corrected by proper grounding of the generator frame. In other instances, the cause is not the generator set, but equipment that may be related or unrelated to it. A small, hand-held battery- powered radio is a useful tool in locating the source of interference. Tune the radio receiver to the frequency of the interference and use the receiver as a probe around pipes, conduits, or other metal parts. Emitted noise will increase as the source is approached. Pipes rubbing together can cause radio frequency interference. Instances have been known where steel and galvanized pipe connections create interference even though the joint is mechanically sound and leak proof. In areas adjacent to high power radio frequency generators(transmitters, heating equipment, etc.), a partial or corroded joint or connection acts like a very poor rectifier, and can emit interference at frequencies different from the exciting frequency. The solution in all such instances has been physical bonding of the joint or conduit. A clean copper strap bridging the joint normally clears up the interference. 121

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