A Soft Starter Syncing Line Power?

A Soft Starter Syncing Line Power?

The purpose of using a soft starter is to decrease the mechanical shock to the motor by reducing the starting voltage, current and torque to the application.

As a result, the motor will smoothly ramp up to speed according to plan.

Taking that smooth start philosophy a little further, you could apply it to connecting an induction generator from a wind turbine to the power grid.

The wind turbine blades capture the wind energy and begin to turn the shaft of the generator via a gear box up to synchronous speed.

Synchronous speed is the speed at which power is neither consumed nor created and slip of the motor is zero.

At or near synchronous speed is when the generator could be connected to the grid.

Once connected to grid or line power, reactive power is supplied to the generator.

Below synchronous speed, the generator would be acting as a motor, thereby consuming energy.

So why would you want to use a soft starter in this application?

The generators come in two common types, asynchronous squirrel cage induction and doubly fed induction.

Without a mechanism to bring on the generator softly, there is a potential to create a flickering or brown-out for users of the grid caused by the starting current of the generator, especially if it is a large turbine.

To make that happen smoothly and without mechanical or electrical stress, a soft starter could be utilized while connecting the generator to the grid.

It would provide reduced current and line synchronization between the grid and the generator.

After the soft starter completes the start and synchronization of the generator, a bypass contactor can be brought in.

Using a hybrid softer (contactor internal to the soft starter) reduces the need for an external bypass, saving space.

This same methodology can take place for any other energy source.

For example a wood, coal or gas fired burner creating steam to drive a generator.

The same can be said for hydropower or an engine.

It’s all the same philosophy as wind power – the source of the generator power does not matter, it is the synchronization/connection of the generator to the grid that matters.

Although a soft starter can work, it should be noted that some soft starters perform better than others.

This is based on the soft starter algorithms and functional capabilities. The power generation method and the specific soft starter should be examined in detail to match the appropriate soft starter.

Soft starters may not be the only solution devices for energy applications, but they do represent another option for connecting generators to grid power.

The specific application would need to be assessed for proper device selection.

We offer an SMCTM Soft Starter Portfolio to fit many applications in addition to motor control.

Think outside the box!

Bill Bernhardt
Posted June 5, 2017 By Bill Bernhardt, Senior Commercial Engineer, Rockwell Automation
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