What is generator synchronisation?

Source : Woodstock Power blog

Genset synchronisation is the process of equalising parameters such as voltage, frequency, phase angle, phase sequence and waveform of the alternator (generator) or other source with a stable, running power system. This is done before the genset is reconnected to the power system. Once a genset is synchronised with the parameters of another genset, alternator or busbar, the system can operate correctly again.

Synchronisation of the generator set to a power system must be carried out with care to avoid damage to the unit, as well as to the power system itself. When synchronising a generating set with an electrical system, the frequency and voltage of the generating set must match closely. The rotor angle and phase angle of the instantaneous power system must be close before closing the generator circuit breaker and connecting the isolated generator to a power system.

In the majority of genset synchronisation cases, the synchronisation process is automated via an automatic synchroniser with manual control capabilities that can be used in emergency situations. Synchroniser panels usually indicate any adjustments the operator needs to make with regard to the regulator and energised and when it is deemed acceptable to close the circuit breaker.

Why choose to synchronise generators?

A genset can only supply an electrical network if all of the above parameters exactly match those of the network. The need for synchronisation arises when two or more generators operate together to supply the load. Since electrical loads do not remain constant, the two or more generators supplying the power must be interconnected and run in parallel to handle larger loads.

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

• Reliability Parallel operation: with several alternators, parallel operation is much more reliable than single-unit generators. In a single unit system, the whole configuration will shut down if the alternator fails. In parallel systems, one alternator can fail and the other units will keep the system running.
• Continuity If one unit needs maintenance, the other systems can remain operational to prevent your entire operation coming to a standstill.
• 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 Generator sets operate at peak efficiency when they are running at their load capacity. By adapting to changes in load, your system can remain efficient at all times.
• Capacity : Larger operations require more power. With more gensets, systems have more alternators for greater capacity.

Parameters for correct synchronisation

When synchronising your generator set, you will need to ensure that four parameters are aligned between your generators.

These parameters are :

• Phase sequence The three phases of the alternators in your system must have the same phase sequence as the phases of your electrical network or busbar.
• Voltage amplitude The amplitude of the voltage can cause major disturbances if the alternators and the busbar are not parallel. When the alternator voltage is higher than the busbar, you create high reactive power in your network, which could cause safety problems. If the alternator voltage is lower, the generator will absorb high reactive power from the busbar and may fail.
• Frequency When frequencies are unequal, they create an unstable flow of energy. This instability can lead to damaged equipment.
• Phase angle : the phase angle of the busbar and the generator alternator must be zero.
• Your generator synchronisation procedure will help you determine whether these parameters are equal between your busbar and the generator alternators.

Here's a video that explains it all.

Synchronisation techniques

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

• Three dark lamps method - uses a busbar to synchronise the second generator; cannot provide information on generator and busbar frequency.
• Two Bright, One Dark Method - measures the frequency but cannot check the accuracy of the phase sequence.
• Synchroscope method - indicates whether the alternator frequency is higher or lower than the busbar frequency

Modern synchronisation equipment automates the entire synchronisation process, eliminating the need for manual observations of lamps and synchroscopes. These methods are much more reliable.

Contact Unicompex for your synchronised generator set needs

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