For industrial motor control to accelerate the motor at maximum speed, a significant quantity of energy is frequently needed.
Both soft starters and VFDs are often utilised in the sector. Although they both function similarly in the starting and halting of an industrial motor, they both have unique qualities.
Why do we use Soft Starter and VFD?
An industrial motor would use a significant amount of inrush current (often 4 to 6 times its full load current) when using a DOL or other traditional starter. Frequent starts might shorten the life of the motors and stops.
To lower inrush currents and restrict torque, you can use soft starters and VFDs to safeguard your expensive equipment. Additionally, it lessens the heat produced by repeated start/stop operations, increasing the motor's lifespan.
The decision between a variable frequency drive and a soft starting depends on many factors, including the application, system requirements, and initial cost.
Soft Starters
An industrial motor is shielded from harm by abrupt power surges by the use of a solid-state device known as a soft starter. By lowering the voltage, a soft starter restricts the substantial inrush current during motor start-up. As a result, they are often referred to as decreased voltage soft starts.
Applications
- Only during start-and-stop are speed and torque control necessary.
- lowering a big motor's excessive initial inrush current.
- A soft start is necessary for mechanical equipment to reduce the stress and torque spikes that come with a typical beginning.
- Pumps and blowers are employed to reduce pressure spikes in pipe systems.
How does a soft starter work?
To start the motor smoothly, a soft starter employs six thyristors or SCRs in a reverse-parallel arrangement. The anode, cathode, and gate are the components of a thyristor.
The thyristor is in its ON state when there is a pulse at the gate terminal, allowing current to flow from the anode to the cathode. Additionally, the current flow is restricted when there isn't a pulse at the gate terminal. The thyristor is in its OFF state at this point.
Based on the ramp-up period, the pulses at the gate terminal are regulated, which in turn controls the applied voltage to an electric motor. Up until it reaches its maximum speed, the motor connected to the soft starter will start up smoothly with a nice, steady current.
Benefits of choosing a soft starter
For situations where speed and torque control are only necessary during motor beginning, soft starters are frequently the most cost-effective option.
Soft starters are still the greatest option when it comes to space because they take up less room than variable frequency drives.
Variable Frequency Drives
A device known as a variable frequency drive regulates the frequency and voltage of an electrical motor's power source to adjust the speed of the motor. To start and stop the electrical motor smoothly during the run cycle, the VFD also offers ramp-up and ramp-down features. AFDs, another name for VFDs, stand for adjustable frequency drives.
Applications
Applications for VFDs include:
- Complete speed control is required.
- Energy saving is the main goal.
- Custom control is required.
How does a variable frequency drive work?
- Purpose: A VFD is used to control the torque and speed of a motor. It is also known as an adjustable frequency drive or an inverter. By adjusting the frequency and voltage supplied to it, it can accurately control the motor's speed.
- Operation: A VFD converts the input AC voltage first to DC and then back to variable frequency AC voltage. By changing the voltage and frequency, it can control the motor's speed and torque.
- Speed Control: Due to the precise control that a VFD can provide over a motor's speed, a motor can operate at speeds other than its rated speed. When varied speeds are required, this is useful.
- Efficiency: Even though the conversion process may incur additional losses, VFDs can result in overall energy savings when the motor is operating at lower speeds.
- Applications: VFDs are used in HVAC systems, conveyor belts, industrial machinery, and other applications that call for variable speed control.
Benefits of choosing VFDs
- Energy Savings
- Reduces peak energy demand
- Reduces power when not required
- Controlled starting, stopping, and acceleration
- Dynamic torque control
- Provides smooth motion for applications such as elevators, escalators
- Advanced overload protection
- Communication with PLC, HMI, DCS, etc.
- Relay Outputs
Choosing between Soft Starter and VFD
- In comparison to VFDs, soft starters are less costly and smaller in size.
- While VFDs initially cost more than soft starters, they also offer energy savings of up to 50%, which adds to cost savings during the equipment's lifespan.
- VFDs may regulate the motor's speed at any time, not only when the motor is starting up like a soft starter.
- simply a soft starter is the most cost-effective option if the application simply needs current limiting at start-up and does not require continual acceleration control.
In conclusion
The choice between a soft starter and a VFD depends on the specific requirements of the application. If the main concern is reducing mechanical stress during startup, a soft starter may be sufficient. However, if precise control of speed, torque, and energy savings during operation is critical, a VFD would be the better choice.
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