What is Generator Synchronization?

Daylight savings time has a way of throwing people out of sync, especially if they forget to change their clocks. Just like people need to sync their clocks to the rest of the world, generators need to be synchronized if they are removed from the service and connected back to the power system during variations of the load, emergency outages, maintenance, and in other situations. This helpful article from Woodstock Power explains what you need to know about generator synchronization.

What is Generator Synchronization?

Generator synchronization is the process of matching parameters such as voltage, frequency, phase angle, phase sequence, and waveform of alternator (generator) or other source with a healthy or running power system. This is done before the generator is reconnected to the power system. Once a generator is synchronized with the parameters of another generator, alternator, or bus bar, the system can run smoothly again.

Generator synchronization to a power system must be conducted carefully to prevent damage to the unit, as well as the power system itself. When synchronizing a generator to a power system, the frequency and voltage of the generator must match closely. The rotor angle and the instantaneous power system phase angle must be close prior to closing the generator breaker and connecting the isolated generator to a power system.

In the majority of cases for generator synchronization, the synchronization process is automated via an automatic synchronizer with manual control capabilities that can be used in backup situations. Synchronizing panels generally indicate any adjustments that the operator should make in regards to the governor and excited and when it’s deemed acceptable to close the breaker.

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Why is Generator Synchronization Needed?

A generator cannot deliver power to an electrical power system unless all the aforementioned parameters exactly match those of the network. The need for synchronization arises when two or more alternators work together to supply the power to the load. Since electrical loads do not remain constant, the two or more generators supplying the power need to be interconnected and operate in parallel to handle larger loads.

Using a series of small units instead of a single generator is known as parallel operation. Synchronization is critical for parallelization, and many commercial plants prefer this setup for its:

• Reliability: With multiple alternators, parallel operation is much more reliable than single-unit generators. In a single-unit system, the whole setup will shut down if the alternator fails. In parallel systems, one alternator can fail and the other units will keep the system active.
• Continuity: If a unit needs maintenance, the other systems can stay up and running to prevent your entire operation from stopping.
• Load: Your load requirements may vary throughout the day. Adjust your parallel system to accommodate higher and lower loads with more or fewer active systems.
• Efficiency: Generators run at the highest efficiency when they operate at their load rating. By adapting to load changes, your system can remain efficient at all times.
• Capacity: Bigger operations require more power. With more generators, systems have more alternators for increased capacity.

Requirements for Synchronization of Generators

During your generator synchronization procedure, you’ll need to make sure four parameters align between your generators. These parameters are:

1. Phase sequence: The three phases of the alternators in your system must have the same phase sequence as the phases of your electric grid or bus bar.
2. Voltage magnitude: Voltage magnitude can cause significant disruptions if the alternators and bus bar are not parallel. When alternator voltage is higher than the bus bar, you’ll create a high reactive power in your grid that could pose safety concerns. If the alternator voltage is lower, the generator will absorb high reactive power from the bus bar and potentially fail.
3. Frequency: When frequencies are unequal, they create an unstable flow of energy. This instability may lead to damaged equipment.
4. Phase angle: The phase angle of the bus bar and generator alternator must be zero.

Your generator synchronization procedure will help you determine if these parameters are equal between your bus bar and generator alternators.

Techniques for Synchronization

Generator synchronization can be a complex idea to understand, but here are the basics of three techniques for generator synchronization:

• Three Dark Lamps Method – uses bus bar to synchronize second generator; cannot provide information on generator and bus bar frequency.
• Two Bright, One Dark Method – measures frequency but cannot check the correctness of the phase sequence.
• Synchroscope Method – indicates whether the alternator frequency is higher or lower than the bus bar frequency

Modern synchronization equipment automates the entire synchronization process in order to avoid manual lamps and synchroscope observations. These methods are far more reliable.

Faulty Generator Synchronization

If generator synchronization with a power system is done incorrectly or poorly executed, there is the potential for:

• Generator & prime mover damage due to mechanical stress caused by rapid accelerator/deceleration need to bring the rotating masses in synch.
• Damage to the generator and step-up transformer windows due to the high currents
• Disturbance to the power system, such as oscillations and deviating voltages that are not nominal
• Keeps the generator from staying online and pick up loads when the protective relay determines the generator is running in abnormal operating conditions, which can cause the generator to shutoff

With all the possible risks of faulty synchronization, it’s critical for all operations to take the appropriate measures during the process. Consult a professional if you’re unsure about the steps to take, and they’ll help you keep your system up and running.

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