Paralleling switchgear is basically a low-voltage switchboard used to control and synchronize different power sources being used on the same busbar. Such power sources could be generators using diesel fuel, natural gas, battery-powered energy storage units, renewable energy sources, or even the utility grid.

Differing from the traditional switchboard used to distribute electrical power, the paralleling switchgear controls how the power sources interact among themselves. It determines whether the generator starts or stops, synchronizes the generators that come on with the existing electrical system, equalizes the electrical load among the running generators, and safeguards the whole setup from any abnormal condition.

Picture it as the conductor in an orchestra. Each and every player is good at what he does, but without a conductor he could easily get out of sync. Likewise, several generators can not just be wired together and be expected to work in harmony. There should be synchronisation in the generation of power in terms of voltage, frequency, phase angle and phase sequence before they can be on the same electrical bus. Failure to coordinate properly could lead to mechanical strain, fault currents, tripping, or even equipment failure.

Why Is Paralleling Switchgear Becoming More Important?

The power generation process has undergone tremendous transformation over the last ten years.

Several facilities in Australia are no longer dependent only on the utility grid. Due to higher costs of power, the need for more resilient energy solutions, and the development of renewables, companies have been prompted to utilize various means of generating energy. Currently, it is quite usual that one facility has numerous diesel generators, solar photovoltaic, batteries, and the utility link.

The manual management of all these diverse forms of energy would be unfeasible. The operators would have to constantly monitor the electrical characteristics, start and stop the generator at the appropriate moment, regulate its capacity, and safely synchronize before connecting it to the system. Paralleling switchgear does all that automatically, and thus enables the whole electrical system to become dynamic in accordance with changing electrical loads.

Consider a large industrial factory starting its shift in the morning. At night time, only one generator is needed for powering essential equipment. However, as the production activity picks up, there is an enormous increase in electricity demand. Instead of putting excessive strain on the working generator, the paralleling switchgear will automatically start another generator, synchronize it with the existing electrical bus, close its circuit breaker in the right moment and share the load between two generators. The third generator will be brought in case the load increases further.

The opposite process takes place when production decreases. Without keeping redundant generators idle with low load consumption (which leads to fuel wastage and more engine wear), the load transfer to the rest of the generators and then turning off the redundant generators will take place. The automatic load management enhances efficiency and extends equipment life.

How Paralleling Switchgear Works

In spite of the advanced controllers and protection equipment in modern paralleling switchgear, there is a certain logical sequence in their operation.

Step 1: Detecting a Need for Additional Power

It all starts from observation.

The switchgear monitors the electrical load and condition of all available sources of electricity. When there is a failure of the utility supply or electrical load gets close to the operating generator capacity, the decision is made on the need for additional generating capacity.

Without waiting for any action from the operator, the control system continues the next step in the sequence.

Step 2: Starting the Generator

The chosen generator gets an order to start and starts increasing its speed up to the specified speed.

While this time, the generator control system checks the engine operation parameters, oil pressure, coolant temperature, fuel availability, and alternator power to make sure that the generator is working properly before connecting it to the power grid.

While the generator generates power, it stays isolated from the bus bar, as its electrical parameters are still different from the parameters of the active system.

Step 3: Synchronising with the Bus

This could be considered the most important phase of the whole process.

Prior to connecting the new generator, its electrical production should be identical to that of the current power generation system.

The controller keeps comparing four main factors:

• • Voltage
• • Frequency
• • Phase angle
• • Phase sequence

In case any of the above-mentioned parameters deviates from the acceptable synchronising time, the circuit breaker continues being open.

For synchronising process to be accomplished, the generator governor modifies the speed of the engine to balance the frequencies, and the automatic voltage regulator (AVR) regulates the voltage of the generator. The process is continued until the incoming generator turns with exact matching of the live bus.

At that very moment when the two waveforms match each other precisely, the synchroniser controller orders closing of the generator circuit breaker.

The process itself is quite accurate. Despite the fast actions of modern circuit breakers, there is always some time required to close the breaker contacts. This is taken into account by sophisticated controllers which provide for simultaneous occurrence of both events.

Step 4: Sharing the Load

After being connected, the newly installed generator does not suddenly take half of the total electrical load.

Rather, it increases the amount of power it supplies as the original generator decreases the proportion of power it is supplying.

The switchgear keeps checking the output of each generator to ensure that the kW and kVAR power is evenly shared among the generators in accordance with the load sharing scheme.

As a result, instead of one generator working at full power while the other works inefficiently, both generators operate together in harmony.