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In this video, we are going to discuss the “Soft Starter” method amongst all other motor starting methods and we will cover the rest of methods in future videos.
Since Electric Motors often require large amounts of electricity during their accelerating to the nominal speed, a Soft Starter can be used to limit the surge of current known as “inrush current” and torque of the electric motors, resulting in a safer, smoother and gradual start-up.
Soft starters will protect your electric motor from possible damage and at the same time extend the lifespan of your electric motor and the whole system by declining the heating caused by frequent start/stops, reducing the mechanical stress on the motor, its shaft, and reducing the electrodynamic stresses on the power cables.
One example of this is an Air Scrubber or Dust Collector.
These will have large fans inside.
In this application, it will take some time to get the fan moving but once the fan is moving the current and torque load on the motor is reduced.
In the system, the fan will pull air into filters where dust particles are collected. Then the clean air is pushed back to the factory.
Water supply applications are another great use for soft starters.
When using pumps in a process you have to bring them up slowly. If not you will cause pressure surges in the water system that could lead to dangerous conditions.
The soft starter can be controlled either by a direct start/stop wiring or, it can be controlled over ethernet. Both control methods have their advantages and disadvantages.
Direct start/stop signals would not require a PLC. They would be less expensive. Using ethernet control, a PLC is required.
This will allow there to be feedback, which will give adjustable control and monitoring capabilities.
The main component of a soft starter is a Triac which is designed to limit the applied voltage to the motor.
Triac consists of two back-to-back Thyristors or SCRs. When an internal pulse is applied to its gate it allows current to flow which then sends current out to our motor.
The pulses are sent based on ramp time so the current will be slowly applied to the motor. This will allow our motor to start slowly reducing torque and inrush current.
When the motor reaches full speed the soft starter and DOL work the same. The difference is how they act while getting to full speed.
When comparing the voltage between a DOL starter versus a Soft Starter, we can see that there is a direct in rush of voltage on the DOL where the Soft Starter takes more time to get up to full voltage.
The current is more regulated using a soft starter. With a DOL there will be larger spikes in current as the motor starts.
With a soft starter, the time the motor gets us to speed is slower and more controlled.
Our Air Scrubber fan will be driven by a motor using belts and pulleys. Using a DOL can cause the belts to slip and wear.
With our water supply example, the DOL will cause pressure surges on the water lines. This can cause excessive wear which could lead to line breaks.
There are also electrical effects that we want to avoid by using a soft starter. The heavy current surges that a DOL can cause, can burn out contacts and motors.
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