Aux 1 Unit 15 Q3

AC generators must be synchronized before connecting in parallel to avoid severe electrical and mechanical stresses that can damage the generators and disrupt the power system. Synchronization ensures that the incoming generator’s voltage, frequency, and phase angle match those of the existing system (the busbar or grid).  

1. Part 7 – Parallel Operation of Generators – eCampusOntario Pressbooks

2. What is Generator Synchronization? – Woodstock Power

Consequences of Unsynchronized Paralleling

1. Large Circulating Currents:

• Voltage and Phase Differences: If the incoming generator’s voltage or phase angle doesn’t match the busbar, a large circulating current will flow between the generator and the system.
• Equipment Damage: This circulating current can be several times the generator’s rated current, causing overheating, potential damage to the generator windings, and tripping of protective devices.

2. Mechanical Stress:

• Frequency Difference: If the incoming generator’s frequency is different from the busbar frequency, it will experience a sudden change in speed when connected.   1. 3 Consequences Of Improper Generator Synchronisation www.mes.com.sg
• Shaft and Coupling Stress: This abrupt change in speed can cause severe mechanical stress on the generator’s shaft, coupling, and prime mover (engine or turbine).
• Potential Damage: This stress can lead to damage to these components, potentially resulting in costly repairs or even catastrophic failure.

3. System Instability:

• Power Fluctuations: Connecting an unsynchronized generator can cause significant power fluctuations and voltage dips in the system, affecting the operation of other connected loads.
• Protective Device Tripping: The large circulating currents or power fluctuations can trigger protective devices, leading to unwanted shutdowns or disruptions in the electrical supply.

Conditions for Synchronization:

To avoid these problems, the following conditions must be met before connecting an AC generator in parallel:

• Equal Voltage: The generator’s terminal voltage must be equal to the busbar voltage.
• Equal Frequency: The generator’s frequency must be the same as the busbar frequency.   1. Synchronization (alternating current) – Wikipedia en.wikipedia.org
• Same Phase Sequence: The phase sequence (order of phases) of the generator must match that of the busbar.   1. What is Generator Synchronization? – Woodstock Power woodstockpower.com
• Phase Angle Coincidence: The phase angle of the generator’s voltage should be close to or coincide with the phase angle of the busbar voltage.

Synchronization Process:

The synchronization process involves adjusting the generator’s speed and excitation to match the busbar parameters. This is typically done using a synchronizing panel or controller that displays the relative phase angle and frequency difference. The generator breaker is closed only when these parameters are within acceptable limits.

Importance of Synchronization:

• Safe and Smooth Connection: Proper synchronization ensures a smooth and safe connection of the generator to the busbar, preventing damage and system instability.
• Efficient Operation: Allows multiple generators to operate in parallel, sharing the load and optimizing fuel efficiency.   1. What are synchronize generator systems? What are their advantages? www.emsa.gen.tr
• Redundancy and Reliability: Provides backup power and enables maintenance or repairs on individual generators without disrupting the overall power supply.

In conclusion, synchronizing AC generators before paralleling them is a fundamental practice in electrical power systems. It ensures the safe and stable operation of the generators, protects the electrical system from damage, and enables efficient and reliable power generation and distribution.

Several devices are used to ensure the correct synchronization of AC generators before connecting them in parallel to a busbar. These devices measure and compare critical parameters between the incoming generator and the existing power source (busbar), allowing the operator to make necessary adjustments before closing the breaker.  

1. Synchronization (alternating current) – Wikipedia

Here are some key devices commonly used for ensuring correct synchronization:

1. Synchroscope:

• Function: Displays the phase angle difference between the incoming generator’s voltage and the busbar voltage.   1. Synchroscope – Electro-Meters www.electro-meters.com
• Indication: A rotating pointer or a digital display indicates whether the generator is running faster (“fast”) or slower (“slow”) than the busbar, and when the phase angles are nearly in phase (ideal for closing the breaker).   1. Synchronization (alternating current) – Wikipedia en.wikipedia.org

2. Voltmeters:

• Function: Measure and display the voltage of both the incoming generator and the busbar.
• Importance: It’s essential to match the voltages before paralleling to avoid large circulating currents.

3. Frequency Meters:

• Function: Measure and display the frequency of both the incoming generator and the busbar.
• Importance: Frequency matching is critical for stable parallel operation and preventing mechanical stress on the generators.

4. Synchronizing Lamps (or Light Bulbs):

• Function: An older but still used method, involves connecting lamps across the generator and busbar phases.   1. Generator synchronization | PDF – SlideShare www.slideshare.net
• Indication: The lamps’ brightness and flickering pattern indicate the phase relationship.
• Ideal Condition: The lamps should be dark (or very dim) when the generator is in phase with the busbar, indicating the correct moment to close the breaker.

5. Automatic Synchronizer:

• Function: A sophisticated electronic device that automates the synchronization process.   1. Fundamentals and Advancements in Generator Synchronizing Systems – Schweitzer Engineering Laboratories selinc.com
• Operation: It monitors the voltage, frequency, and phase angle of the incoming generator and the busbar, and automatically adjusts the generator’s speed and excitation to achieve synchronization.   1. (PDF) Automatic synchronization unit for the parallel operation of synchronous generators www.researchgate.net
• Benefits: Reduces human error and ensures precise synchronization, particularly in complex systems or situations where manual synchronization might be challenging.

Additional Considerations:

• Check Synchronizing Relays: These relays can be used as a backup or additional check to prevent the breaker from closing if the synchronization parameters are not within acceptable limits.   1. Synchronization (alternating current) – Wikipedia en.wikipedia.org
• Communication and Coordination: Clear communication between the person operating the synchronizing equipment and the person controlling the generator is crucial for a successful and safe paralleling operation.
• Manual vs. Automatic: While automatic synchronizers offer convenience and precision, it’s important for operators to understand the manual synchronization process using synchroscopes and lamps, especially in case of equipment failure or for troubleshooting.

In summary, various devices and instruments are employed to ensure the correct synchronization of AC generators before paralleling them. These include synchroscopes, voltmeters, frequency meters, synchronizing lamps, and automatic synchronizers. Proper use of these devices and adherence to established procedures are critical for achieving a safe and stable parallel operation, preventing damage to the generators and ensuring a reliable power supply.  

1. Synchronization (alternating current) – Wikipedia

2. Fundamentals and Advancements in Generator Synchronizing Systems