Synchronizing AC Generators for Parallel Operation
(a) Importance of Synchronization:
AC generators must be synchronized before connecting them in parallel for several crucial reasons:
- Frequency Matching: Generators need to be operating at the same frequency to avoid damaging currents flowing between them. If the frequencies differ, the generators will try to “fight” each other, causing unstable voltage and current fluctuations that can damage the generators and connected equipment.
- Voltage Matching: The voltage output of each generator needs to be the same magnitude and in phase to ensure smooth power sharing when connected in parallel. Unequal voltages can lead to circulating currents between the generators, causing inefficiency and potential overheating.
- Phase Sequence Matching: Three-phase generators also require matching phase sequences. This ensures that the peaks and troughs of the AC voltage waveforms from each generator coincide, preventing destructive interference within the combined system.
Connecting unsynchronized generators can lead to:
- Large circulating currents: These currents can damage windings, bearings, and other components in the generators.
- Voltage and frequency instability: This can disrupt power quality and damage connected equipment.
- Potential equipment failure: Severe cases of unsynchronized operation can lead to complete generator failure.
(b) Devices for Ensuring Correct Synchronization:
Two primary devices are used to ensure proper synchronization before connecting AC generators in parallel:
- Synchronizing Lamps (Synch Lamps): These lamps are connected between corresponding phases of the generators being synchronized. As the voltage and frequency approach synchronization, the lamps will flicker at a decreasing rate. When the lamps reach a steady illumination, it indicates the generators are in phase and ready for paralleling.
- Synchroscope: This is a more advanced instrument that provides a visual representation of the phase difference between the generators. It displays a rotating pointer and a stationary scale. When the pointer aligns with a specific mark on the scale (typically zero), it signifies that the generators are in phase and ready for paralleling.
(c) Indications of Correct Synchronization:
The devices listed in part (b) indicate correct synchronization using the following observations:
- Synchronizing Lamps: When the lamps achieve a steady illumination, without flickering, it indicates that the voltage and frequency of the generators are matched and in phase.
- Synchroscope: When the rotating pointer on the synchroscope aligns with the designated mark (usually zero) on the stationary scale, it signifies that the phase difference between the generators is zero, and they are synchronized for paralleling.
By utilizing these devices and observing the proper indications, operators can ensure safe and reliable parallel operation of AC generators.