Parallel Generators Synchronization free short guide.Full description
Parallel Generators Synchronization free short guide.
Parallel Operation of Generator
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The purpose of this discussion is to address the concerns of and the techniques required to successfully parallel synchronous generators to a network.
Parallel Operation of Synchronous Generators Requirements for parallel operation of synchronous generators:
Before any two generators can be connected together, the oncoming unit terminal voltages must: generator, 1. have the same magnitude as the running generator, 2. be in phase with the corresponding phases of the running unit, 3. have the same phase sequence as the running generator, 4. have slightly higher frequency than that of the running generator. If the requirements 1 through 3 are not met, there will be circulating current between b etween the generators sufficiently large that might damage the machines. The following discussion explains a method to check the above requirements: One “dark” two “bright” lamps method In this method, one lamp is connected con nected across the a-phase of the two generators, the second lamp between the b-phase of the running generator to the c-phase of the oncoming generator, and the third lamp between the c-phase of the running machine and the b-phase of the oncoming machine as shown in the following figure. With this arrangement, the generators are paralleled when one lamp is dark and the other two are bright.
Dark
A
Running Generator
Bright
B
A
B Bright
C
C
Oncoming Generator
Running Generator F2
A2 DC Motor Shunt Field
Synch. Gen.
A1
RL A
Field Winding
F1
RL
V
RL
If
A2
F2
DC Motor Shunt Field
F1
Synch. Gen.
A1 Field Winding If Oncoming Generator
Synchronizing Switch
Three-pahse Wattmeter
Procedure: 1. Couple one of the generators to the dc motor. Adjust its speed to 1800 rpm and its terminal voltage to rated value. Connect a 0.2 A resistive load. This generator will be the running generator. 2. Start the second generator and adjust its voltage and speed to rated values. This generator will be the oncoming generator. 3. Using the “combined Dark and Bright Lamp” method, parallel the oncoming generator with the running generator. Measure the line voltage, line current, and three-phase power. Also measure the field current of the generator. 4. If the two generators are properly synchronized, the oncoming generator w ill be “floating” neither supplying nor receiving power. 5. Increase the speed of the oncoming generator until it supplies half of the load p ower. Adjust the field current of the oncoming unit for unit y power factor. For both generators measure the speed, armature current, terminal voltage, field current, and d c motor field current.
6. Keep the field excitation of the oncoming generator constant and vary its input power (speed of the dc motor) such that its armature current varies from 10% to 150% of the generator rated current. Plot generator output power vs. dc motor field current. What is the significance of this curve? 7. Readjust the input of the generator for 25% of its rated current. Holding this input constant, vary the excitation of the generator and obtain data to draw curves of generator armature current as a function of its field current. What is the significance of this curve? 8. Reduce the speed of the running generator until it is “floating” on the other machine and open its line circuit breakers. Reduce the load to zero and shutoff the two machines.