Parallel Operation - TM-55-1930-209-14P-9-4

TM-55-1930-209-14P-9-4 Water Purification Barges (NSN 1930-01-234-2165) Electric Power System Manual
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Parallel Operation 3. After the engine has run long enough to warm up, bring it up to synchronous speed (the same frequency as the unit on the line). The synchronizing lights will begin to blink. 4. Using the governor control adjust the speed until the lights blink very slowly. 5. The lights are off when the voltages of the two units are in phase. At this point very quickly close the breaker while the lights are out. 6. Use governor controls to share KW load between engines 7. After generator temperature has stabilized (1 hr.), adjust the droop control of each generator so as to share the reactive load and to limit the circulating currents. Less droop (moving control CCW) increases the reactive current carried by the generator. The frequency of the incoming unit should be slightly greater than the line frequency. This will allow the incoming unit to assume some of the load rather than add to the system load. Load Division--(Speed Droop) Once two units have been paralleled their share of the load is determined by the governor control setting. If two units of the same capacity and the same governor characteristics have the same governor control settings they will share the load equally. To transfer the load from one engine to the other follow this procedure: The total load must not exceed the capacity of the engine. 1. Increase the governor speed control of one unit to increase the load. 2. Reduce the governor speed control of the other unit to decrease the load on that unit. 3. Raise or lower the governor speed control of both units to change system frequency. Circulating Currents When two units are paralleled there will be circulating currents. These currents are not doing useful work, but are flowing between the generators. By determining the total generator amperage and subtracting the amperage going to the load, the amount of circulating current can be determined. Circulating currents are caused by voltage differences between the two units. With cold generator sets, circulating current may be as high as 25% of rated amperes, without being considered harmful. Circulating current is part of the total generator current and this total must not exceed the amperage rating. As the generators warm, the circulating currents will decrease. The ammeter readings should decrease slightly, but the voltage meter readings should remain constant. 16

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