Paralleling Procedures

Figure 3-20.—Parallel operation connection diagram. SYNCHRONIZING LIGHTS (fig. 3-19) will bring the phase and frequency into exact agreement. As the phase and frequency approach the same value, the SYNCHRONIZING LIGHTS will gradually turn on and off. When the blinking slows to a rate of once per second or slower, close the main circuit breaker of the incoming set while the SYNCHRONIZING LIGHTS are at a point of being dark. The phase sequence relates to the order in which the generator windings are connected. If the phase sequence is not correct, the SYNCHRONIZING LIGHTS will not blink on and off together. When the incoming set is first connected to the load through the appropriate switchgear (fig. 3-20). you should observe one of four occurrences. When the phase sequence, voltage, frequency, phase, and engine performance are the same, the changeover will be smooth with only the slightest hesitation in engine speed; if each output is slightly out of phase, one of the engines will shudder at the point of changeover; if the phase sequence or voltage levels are incorrect, the reverse power relay will trip on one of the generator sets and open its main circuit breaker contactors; if the incoming generator set loses speed significantly or almost stalls, the incoming engine may be defective. CAUTION Should either generator set lose speed, buck, or shudder when the incoming set is connected to the distribution feeder lines, immediately flip the CKT BRK switch of the incoming set to open, and then recheck the paralleling set-up procedures. Refer to figures 3-19 and 3-20 to set up the generator sets for parallel operation. WARNING When performing step 1, make certain that the incoming set is shut down and that there are no voltages at the switchgear terminals being connected to the incoming set. Do not take anybody’s word for it! Check it out for yourself! Dangerous and possibly deadly voltages could be present. Take extreme care not to cross the LO (neutral) with any of the other phases (L1, L2, or L3). Paralleling Procedures 1. Connect the incoming set, as shown in figure 3-20. 2. Make certain that the voltage change board (reconnection board) (fig. 3-12) of the incoming generator is set up for the same output voltage as the on- line generator. 3. Set CKT BRK switch on the incoming set to OPEN. When the incoming set circuit breaker is open (CKT BRK indicator light will be out), operate the load switchgear so that the on-line output voltage is present at the voltage change board of the incoming set. 4. Set the PARALLEL OPERATION-SINGLE UNIT operation switch on both sets to PARALLEL OPERATION. 3-25