In the event of a motor being started in an industrial setting, it can result in a sudden flow of electricity and mechanical strain. This could impact the motor, equipment connected to it and the electrical system. A soft starter can to solve this issue by gradually increasing the voltage that is supplied to the motor in the beginning of its operation. It helps the motor achieve its speed of operation smoothly instead of launching with an abrupt mechanical and electrical impact. Soft starters are typically employed with fans, pumps and compressors, conveyors and various other motor-driven devices. However, how does a soft starter function and do you need to use it instead of VFDs? In this article we’ll go over the basic workings of a soft starter and the key advantages, as well as applications, and differences between a softer starter and a VFD.
What Is a Soft Starter and Why Is It Used?
Soft starters are an electric device used to regulate the start and stop for the AC induction motor. Its primary purpose is to minimize the abrupt electrical current and mechanical shock that could be experienced when a motor is started.
If a typical motor is plugged directly over the lines, it could draw more than its normal full load current for an indefinite period. This is referred to as beginning or inrush. A high current at the start can cause voltage drop in the electrical system, and add additional strain to the motor and equipment connected to it.
Soft starters minimize this effect by regulating the voltage that is supplied to the motor at startup. Instead of putting on the full voltage at once you gradually increase the power. As the voltage increases it accelerates the motor until it reaches its normal operating speed.
The same concept can be applied to stop. Soft starters can gradually lower the voltage of motor which allows the motor to reduce speed more easily. The typical soft starter employs semiconductor devices known as thyristors or SCRs to regulate the amount of voltage supplied into the motor. The controller regulates their firing angles to regulate the voltage when it is in use during the acceleration as well as deceleration. Soft starters are especially useful when the primary need is for a smooth motor’s starting and stopping, not constant motor control.
What Problems Does a Soft Starter Solve?
Soft starters are a great way to with a myriad of motor-starting problems:
- High-starting Current
- Sudden voltage drops
- Mechanical shock
- Stress on couplings and belts
- Pumping systems that use water hammer
- Sudden pressure changes
- Excessive wear on motor-driven equipment
- Regular maintenance is a result of difficult starting conditions
Take, for example, an enormous water pump. The sudden start of the pump can trigger a rapid pressure shift within the pipeline system. With a soft start, the motor is able to accelerate slowly and help the pump operate more quickly. Similar principles apply in conveyor systems. A sudden motor’s start-up can cause the product to move or belts to snap, or mechanical components to undergo unneeded stress.
Main Components of a Soft Starter
The exact layout of the product depends on the model and manufacturer. A soft starter usually contains:
1. Power semiconductor devices:
SCRs or thyristors control the voltage supplied to the motor. Also known as thyristors or SCRs, determine the voltage to the motor.
2. Control circuit:
The control system regulates the beginning and stopping of the process in accordance with the program parameters.
3. Protection functions include:
A lot of modern soft starters offer protection against certain conditions like overload or phase loss, high current, or overheating.
4. User interface:
Based on which model they choose, customers can adjust parameters via the use of a display, keypad, software, or a communication system.
5. Bypass the Contactor:
Certain soft starters employ a bypass contactor once the motor has reached full speed. This permits the motor to operate directly from the power source instead of continually moving through semiconductor components, which helps to decrease the amount of heat generated and loss.
The specific features will depend on the soft starter, therefore the motor’s power and application, the current, voltage, and the required safety functions must be considered prior to purchase.
How Soft Starter Works: Working Principle Explained
Understanding how a soft starter functions becomes much easier when you consider the process that takes place during motor startup. A soft starter doesn’t typically control the speed of the motor in the same manner as a VFD. It instead controls the voltage that is supplied to the motor when it is in deceleration and acceleration.
Step 1: Motor Receives Reduced Voltage
When the motor is given an order to start then the soft starter provides a controlled, lower voltage. The motor, therefore, will not be able to receive the full supply voltage right away. This lowers the initial voltage that is drawn from the electrical system.
Step 2: Voltage Gradually Increases
The soft starter will then increase the voltage gradually in line with the ramp time that is set. When the voltage rises, the motor produces more torque and speeds up towards the normal speed of operation. The time for acceleration can typically be set based on the motor and the application. A conveyor, pump, or compressor could require different characteristics for starting.
Step 3: Motor Reaches Operating Speed
When the motor is at its normal operating state and the soft starter is completed, it will complete this acceleration procedure. In systems with bypass contacts the bypass contactor could be shut in this moment. The motor will then get the normal supply immediately, and the soft starter’s semiconductor devices are shut off.
Step 4: Controlled Stopping
Soft starters can offer the ability to stop with a timed stop. Instead of cutting off the power at once the device gradually lowers the voltage being supplied to the motor. This lets the motor reduce its speed more easily. This feature is particularly helpful in pump settings in which an immediate stop could result in pressure surges or water hammer.
Why Does Reduced Voltage Reduce Starting Current?
An AC induction motor may draw a significant current as it begins because it is not rotating at all or even with a minimal speed. This voltage vs current relationship is roughly linear – by adjusting the voltage at the initial startup phase the soft starter is able to cut down on the amount of power that is drawn from the source. However, there’s one important thing to keep in mind that reducing voltage can also decrease the motor’s starting torque. Thus the soft starter has to be selected correctly to match the load and motor. Applications that require a high torque at the start may require an alternative motor control solution.
Soft Starter Starting Methods
Different soft starters may employ different methods of control and features. The most common methods are:
Voltage ramp –The voltage increases gradually in a time span that is set.
Current limiting: The soft starter limit that motor’s start-up current at a predetermined amount.
Soft stop: The voltage gradually decreases after stopping the motor.
Kick-start: Certain applications might require a brief increment in torque at the beginning to overcome the initial resistance. Certain soft starters offer the ability to kick-start to accomplish this.
The right method will depend on the specific application, motor characteristics and the load requirements.
Soft Starter vs VFD: What Is the Difference?
A frequently asked question in motor control is soft starter vs. VFD. Both can give better motor start-up but they’re designed to serve different purposes. A soft starter is utilized to control the beginning and stopping of motors. A VFD, also called Variable Frequency Drive, regulates motor speed by altering both the speed and frequency that is supplied by the motor. Soft starters are an ideal choice for motors that normally need to be running at maximum speed and the primary goal is to lessen the stress on starting.
A VFD is better for processes that require the motor to work at various speeds. For instance for example, a conveyor that has to be running at a fixed speed could have a smooth start in cases where smooth starting is the primary concern. A pump that has to alter its speed in response to flow requirements could be equipped with VFD.
C3 Automation’s current VFD panel describes how VFDs regulate the motor’s performance by altering the voltage and frequency delivered to the motor, allowing accurate speed control to devices like pumps, conveyors, HVAC systems, and different industrial machinery.
When Should You Choose a Soft Starter Instead of a VFD?
Select a soft starter:
- The motor is normally running at a predetermined speed.
- You need to be able to smoothly start and stop.
- You’d like to cut down on the starting current.
- You’re trying to reduce mechanical stress.
- You require a fairly basic motor-starting system.
- Continuous speed control isn’t needed.
You should choose a VFD if:
- Motor speed is required to be varied in the course of operation.
- The process requires precision control of the speed.
- The energy savings derived from variable speed operation are crucial.
- You’ll need more advanced motor control functions.
- The software requires the ability to adjust acceleration, deceleration as well as operating speeds.
The decision should be based on actual device rather than simply choosing the most advanced equipment.
Benefits and Applications of a Soft Starter
The primary benefit of soft starters is the ability to control engine acceleration as well as deceleration. This improves the efficiency and dependability of both the motor and the mechanical system.
1. Reduces Starting Current
A motor will draw a significant amount of current when it is first started. Soft starters regulate the voltage at which it is accelerated and helps decrease the initial demand for current. This could reduce the effect of motor startup on the electrical circuit particularly in the case of installations with motors larger than the ones in the installation.
2. Reduces Mechanical Stress
Motors that start suddenly can cause an intense mechanical shock. Belts as well as shafts, couplings, pumps, gears, and many other components can experience excessive stress. When you allow the motor to slowly accelerate and softly, a soft starter can help lessen the impact of these sudden forces. This may result in smoother operation of equipment, and possibly decrease mechanical wear.
3. Provides Smooth Motor Starting
Soft starters provide the ability to control the acceleration process. This is helpful when abrupt movements could impact the manufacturing process. Conveyor systems for instance are able to start with ease rather than jerking to a stop.
4. Provides Smooth Stopping
The controllable stopping function may be helpful in cases in which abruptly shutting off the motor may create problems. In pumping systems, gradual stopping can help reduce pressure surges. This could ensure the safety of valves, pipes and other parts that are connected to the system.
5. Helps Reduce Equipment Wear
Repeated hard starts can put more stress on mechanical parts. By reducing the impact in stopping and starting an engine, a soft start can aid in creating more comfortable operating conditions. This can lead to longer service lives for the equipment connected to it if the system is designed properly and maintained.
6. Simple Motor Control
In comparison to the VFD, a soft starter typically focuses on a smaller job: controlling a motor’s starting and stopping. If you are using a fixed-speed application, it could be an effective option in situations where speed control with advanced features is not needed.
7. Useful Protection Features
A lot of modern soft starters have built-in motor protection, monitoring, and safety functions. Depending on the model they could include:
- Protection against motor overload
- Phase loss protection
- Overcurrent protection
- Overtemperature protection
- Protection against underload
- Monitoring of motor-start
- Fault indication
The protection features available vary among products, and specifications must be reviewed prior to making a purchase.
Common Soft Starter Applications
Soft starters are commonly employed in situations where big motors require to be controlled in their acceleration, or when they need deceleration.
1. Pumps – Pumps are among the most popular applications. A soft starter may offer smooth acceleration and stop to prevent abrupt pressure fluctuations within the pipeline system. They are typically regarded as:
- Pumps for water
- Pumps for wastewater
- Irrigation systems
- Industrial process pumps
- Pumps for boosters
2. Conveyor Systems – Conveyors are often designed with smooth start to stop sudden movement of conveyor belts and other materials being transported. A soft starter will slowly get the conveyor motor to its operating speed, which helps to reduce the mechanical strain.
3. Fans and Blowers – Large blowers and large fans may require substantial starting current. Soft starters can give controlled acceleration, and without constant adjustments to speed.
4. Compressors – Compressors may require demanding starting conditions. A soft starter that is suitable can aid in controlling motor speed as well as reduce the mechanical and electrical effects of the process of starting. However, the type of compressor along with load characteristics and the manufacturer’s requirements must be taken into consideration prior to selecting which motor’s starter.
5. Crushers and Other Industrial Machinery – Certain fixed-speed industrial equipment could benefit from motor starting controlled. The applications could include mixers, crushers, grinders, and many other machines in which a sudden start can put stress on mechanical parts.
Factors to Consider When Selecting a Soft Starter
Selecting the best soft starter is crucial for a reliable operation. Take note of these factors prior to buying.
Motor power: Examine the motor’s HP or kW rating.
Motor voltage: Ensure that you have a soft starter that is at the right voltage for the operating motor.
Full-load current: Soft starters should be selected based on the motor’s rated current as well as the application conditions.
Starting load: Different load types need various starting forces. A high-load motor may need a different rating for soft starters than a motor that is lightly loaded.
Starting frequency: Think about how often the motor is started every hour or throughout the day.
Ramp-up and ramp-down requirements: Find out how fast the motor must be able to accelerate and stop.
Safety requirements: Determine if the soft starter is equipped with the security functions needed by your application.
Bypass requirements: If your software requires a bypass contactor verify if it is integrated in the soft starter or requires an additional installation.
Environmental conditions: The temperature and humidity, dust, enclosure requirements, as well as locations of installation can influence your choice of product.
Is a Soft Starter the Same as a VFD?
No. Soft starters and VFD serve different purposes. A soft starter is primarily responsible for the voltage when motors are moving between stops and starts. When the motor is at its maximum operating speed, it typically operates at the usual power supply speed and frequency. A VFD regulates voltage as well as frequency. It can change the speed at which motors operate in normal operation. In simple terms: Soft starter = smoother stopping and starting. VFD means variable motor power and features advanced technology for control. The best choice is based on the process requirements.
Can a Soft Starter Save Energy?
A soft starter may help lessen the stress and losses caused by starting, but it is not an exact substitute for a VFD if you are looking to make significant energy savings with variable speed operation. A motor that is operating at a constant speed will typically function at the speed it was set with an in-built soft starter. If the process doesn’t require continuous full-speed operation constantly it is possible that a VFD can offer more energy-saving potential by adjusting the speed of the motor according to demand. Therefore, efficiency in energy should be assessed based on the entire application, not the starter itself.
Why Proper Soft Starter Selection Matters
The choice of a soft starter solely by motor horsepower isn’t enough. Two motors that have the same power rating may have different requirements for starting, based on the load being used. Pumps, conveyors, compressors, crushers, and conveyors could put different requirements on the motor in acceleration. A mistake in selection could lead to:
- Problems with starting
- Heating too much
- Fault causes
- Longer time for acceleration
- Problems with motor performance
- Reliability of equipment is reduced
Always confirm the nameplate of the motor the load characteristics, the operating conditions, the frequency of starting and the specifications of the manufacturer before choosing a soft starter. For projects involving industrial automation, choosing the right motor control equipment is just as crucial as selecting the appropriate protection and control equipment.
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Conclusion
Soft starters are functional motor control devices created to make moving and stopping easier. By adjusting the voltage that is supplied to the AC motor, it will lower the beginning electrical current, mechanical shock, and strain on the equipment. It is particularly useful for conveyors, pumps, compressors, blowers, fans as well as other applications in the industrial sector that are fixed-speed.
Knowing the way that a soft starter operates can help you determine if it is the right choice for your specific system. If you are only looking for an easy stopping and starting process the engine, a soft starter could be a good option. If you require continuous control of the speed, VFDs are generally the best choice. When comparing the soft starter and VFD, concentrate on the motor’s and process requirements, rather than selecting solely on the features. Making sure you select the appropriate configuration and rating will ensure a reliable and efficient motor operation.
FAQ
1. How do I pick the best soft starter?
Think about the motor’s capacity, power and voltage, full-load current, the type of load the frequency of start-up, as well as the starting requirements.
2. Can you use a soft starter for industrial purposes?
Yes. Soft starters are commonly employed in industrial applications in which smooth motor starting and stopping are needed.
3. What is a Soft Starter?
The soft starter is a device that increases motor voltage to allow smooth starting and lower the current at which it starts.
4. Does a soft starter regulate the speed of motors?
No. Soft starters are primarily used to control the acceleration of motors and their deceleration, but not the continuous speed of operation.
5. Can a soft starter cut down on the energy use of a home?
Soft starters can help minimize the risk of starting, but it doesn’t offer the same benefits.
