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Page 279

| units are much affected by line-of-sight limitations, several units may be required for long transmission lines. The intermediate stations receive their signals and retransmit them to the next unit, referred to as relay stations. These relay the radio signals and are not to be confused with other relay functions connected with the power lines. |

| Ground Relays |

| Another scheme measures the flow of so-called ground current and employs overcurrent relays. In a three-phase circuit or piece of equipment, the currents flowing in each of the conductors are usually fairly well balanced in magnitude. When wye-connected, the neutral or ground conductor carries little or no current. By measuring this current directly, or by measuring each conductor and determining the difference, this unbalance or ground current can be made to actuate relays whenever it exceeds certain predetermined values. Figure 14-12 shows a relay using ground-fault detection and illustrates |

| Figure 14-12 Ground relaying. |

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