Soft Starter | Soft Starter Working | Siemens Soft Starter | ABB Soft Starter | Allen Bradley Soft Starter | Soft Starter vs Vfd | What is a Soft Starter| Motor Soft Starter | Soft Starter Working Principle

Soft starters are essential components in many industrial applications, providing a cost-effective and efficient way to control the starting and stopping of electric motors. Unlike traditional motor starters, which use direct-on-line (DOL) switching to start the motor, soft starters gradually ramp up the voltage, reducing the inrush current and protecting the motor from damage. This not only extends the lifespan of the motor but also reduces energy consumption and wear and tear on other components in the system. In this article, we will explore the benefits of soft starters, how they work, and some common applications in which they are used.

Soft Starter | Soft Starter Working

1. Soft Starters are devices used to reduce the starting current and torque of electrical motors.
2. They work by gradually increasing the voltage to the motor, thereby reducing the initial surge of current that can cause damage to the motor or other components in the circuit.
3. Soft Starters also help to prolong the lifespan of the motor by reducing wear and tear on the mechanical components.
4. These devices are particularly useful for motors that are started frequently or in applications where the starting torque needs to be controlled, such as conveyor systems, pumps, and fans.
5. Soft Starters can be configured to provide a range of features, including ramp-up and ramp-down times, current limiters, and overload protection.
6. The device monitors the current and voltage of the motor during the starting process, and adjusts the voltage accordingly to ensure a smooth and controlled start.
7. Soft Starters are typically easy to install and operate, and can be integrated into existing electrical systems with minimal disruption.

Before learning in detail about Soft Starter we will see overview of 3 popular makes of Soft Starters 

(We have explained in detail about Soft Starter after Siemens, ABB & Allen Bradley Soft Starters decription)

Siemens Soft Starter

The SIRIUS Soft Starter ES engineering tool, which is based on the TIA Portal, makes it easy to parameterize, monitor, and diagnose SIRIUS general and high performance soft starters. We can set device parameters directly on your PC and transfer them to the soft starter via Ethernet cable or a PROFINET connection. With this tool, we can quickly and easily optimize your soft starter's performance, ensuring it operates smoothly and efficiently. Its user-friendly tool is designed to simplify the process of configuring and maintaining SIRIUS soft starters for an engineer or technician

Most commonly used Siemens soft starter series:

Sirius 3RW30: This is a compact and easy-to-use soft starter series that is ideal for controlling standard AC motors. It offers a range of features, including overload protection and flexible parameter settings.

Sirius 3RW40: This series is designed for use with high-performance motors and offers advanced features like torque control and integrated fieldbus communication.

Sirius 3RW44: This series is ideal for use with demanding applications that require precise speed control and high levels of protection. It features built-in motor overload protection and an optional bypass contactor for high reliability.

Sirius 3RW50: This series is designed for use with large motors and provides advanced features like soft stopping and a built-in bypass contactor. It also has a high degree of flexibility in terms of control options.

Sirius 3RW52: This series is similar to the 3RW50, but with additional features like S-bus communication and a power range of up to 630 kW.

ABB Soft Starter

ABB's softstarter is a highly advanced electrical device that provides superior motor protection by effectively minimizing electrical stress on the motor. This not only increases the motor's lifespan but also ensures its smooth operation. The device is equipped with numerous built-in motor protection features, making it a reliable and safe solution for your motor. The user-friendly design of the softstarter makes it simple to learn and set up, ensuring that we can easily optimize the device for your specific application. 

ABB's popular soft starter series:

PSR Series: The PSR series is a compact and efficient soft starter designed for various industrial applications. It provides smooth and reliable motor control with a range of features such as built-in bypass contactor, torque control, and underload protection.

PSE Series: The PSE series is a user-friendly and cost-effective soft starter with a built-in bypass. It features an intuitive interface and advanced motor protection features, making it ideal for use in pumps, fans, and conveyors.

PSTX Series: The PSTX series is a versatile and high-performance soft starter that can control motors up to 3000 kW. It has advanced motor control and protection features, such as built-in thermal overload protection, motor current monitoring, and fault detection.

PST Series: The PST series is a reliable and efficient soft starter with a built-in bypass. It features a user-friendly interface and advanced motor protection features, such as overload protection, phase loss protection, and overtemperature protection.

PSS Series: The PSS series is a high-performance soft starter designed for use with medium and large motors. It has advanced control features, such as soft start and soft stop, adjustable starting and stopping torque, and overload protection.

Allen Bradley Soft Starter

Allen Bradley is a popular brand that produces a range of high-quality soft starters for various industrial applications. The Allen Bradley soft starter is an advanced electronic device that is designed to reduce the stress on motors when they are started. By gradually ramping up the voltage, the soft starter is able to minimize the inrush current that can cause damage to the motor, resulting in a longer lifespan for your motor. The device is also equipped with numerous features that ensure the safety and protection of your motor. The Allen Bradley soft starter is easy to set up and use, and is available in a range of sizes and configurations to suit different applications.

Allen Bradley most popular series:

SMC-3 Soft Starters: This series is designed for applications that require a small, compact soft starter. It is available in a range of sizes, from 5 to 150 horsepower, and is ideal for simple, standalone applications.

SMC Flex Soft Starters: This series is designed for applications that require more advanced features, such as Ethernet connectivity, diagnostics, and communication capabilities. It is available in a range of sizes, from 5 to 1,500 horsepower, and is ideal for complex applications.

SMC-50 Soft Starters: This series is designed for applications that require a higher level of motor control and protection. It is available in a range of sizes, from 5 to 500 horsepower, and is ideal for applications that require a more advanced level of performance.

Softstarter Bulletin 150: This series is designed for applications that require a highly versatile and flexible soft starter. It is available in a range of sizes, from 5 to 3000 horsepower, and is ideal for demanding applications that require a high level of customization and control.

Induction Motor can be started  in following ways:

1. Direct On Line Starting By applying full load voltage at intervals of time

2. Star Delta Starter and Soft starter By applying reduced voltage gradually

3. Auto transformer starter By applying part winding starting

4. Variable Frequency Drive By applying variable voltage & Frequency

Types of Control using Soft Starter:

1) Open Loop Control: A start voltage is applied w.r.t time, irrespective of the current drawn or the speed of the motor. For each phase two SCRs are connected back to back and the SCRs are conducted initially at a delay of 180 degrees during the respective half wave cycles (for which each SCR conducts). This initial delay is gradually reduced w.r.t. time until the applied voltage ramps up to the full supply voltage. This is also known as Time Voltage Ramp System. 

2) Closed Loop Control: The motor output characteristic like the current drawn or the speed is monitored and the starting voltage is varied accordingly to get the required response.  The current in each phase is monitored and if it exceeds a beyond limit, then that time voltage ramp is halted.

Soft Starter Features:

Generally Suitable for 3 phase AC Induction motor up to 168KW (225HP) Back to back SCR modules (e.g. Semikron make SKKT series) It reduces starting current User select able configuration for 3 wire close delta (In line)  and 6 wire open delta (in-side line) User settable jump start and soft start / ramp time It can accept start and stop command from external potential free contact Provides Over load trip facility

Contactor bypasses output and Fault output Easy to install and maintain

Soft Starter Working Principle:

To gradually accelerate the speed of AC 3 phase induction motor it is required to feed increasing voltage to the motor and such behavior is only possible by connecting SCRs in series with the motor. The SCRs are controlled by firing card to generate the firing pulses giving the effect of soft start.

User has access to set the starting voltage to create the torque and to set the soft start time. For over load trip, the feedback it taken from 5A CT to monitor the load current and to generate the trip contact in case of over load condition. Once the motor achieves full RPM, it is not required to pass the current through the SCRs and hence these SCRs can be bypassed using external contactor. The bypass command is available in the form of potential free contact, once the full speed is achieved as indicated by LED. 

The START/STOP/RESET push buttons are accessible from front and parallel remote connections are available to user for external controls. The soft starter is built with thyristor firing card & suitable rated back to back connected SCR module (with electrically isolated base)- mounted on the forced air cooled heat sink, with copper/aluminum bus bars for incomer and motor connections. SCR modules are protected by thermal cutouts (Thermistors), RC-snubber and MOVs.

Max. Starting Current/ Continuous Current with Soft Starter

Motor Rating  HP	Motor Rating  kW	Max. Starting Current/ Continuous Current
1 -6	0.75 -4.5	20A/6.2A
7 -10	5 -7.5	32A/10.5A
11 -17.5	8 -13	55A/18A
18 -35	13.5 26	110A/36A
36 -75	27 -55	150A/75A
76 -110	56 -82	230A/115A
111 -150	83 111	310A/155A
151 -197	112.5 -147	410A/205A
198 -225	147.5 -168	470A/235A

Soft Starter vs VFD

Soft starters and variable frequency drives (VFDs) are both used to control the starting and stopping of electric motors, but they do so in different ways.

A soft starter is an electronic device that gradually ramps up the voltage to an AC motor, reducing the initial inrush current that can cause damage to the motor and other electrical components. This can be useful for applications where there is a need for a gentle start, such as pumping systems, compressors, or conveyor systems.

A VFD, on the other hand, is a device that can adjust both the frequency and voltage supplied to an AC motor, allowing for precise speed control of the motor. This can be useful for applications where speed control is important, such as in fans, pumps, and compressors. In addition, a VFD can also provide energy savings by reducing the amount of power used by the motor during operation.

Summary

While both soft starters and VFDs can be used to control the starting and stopping of electric motors, they are designed for different applications. Soft starters are typically used when there is a need for a gentle start, while VFDs are used when precise speed control is required and energy savings are important.

Frequently Asked Questions (FAQ)

What is difference between VFD and soft starter?

VFD (Variable Frequency Drive) and soft starter are both electrical devices used to control the speed and torque of AC motors, but they function differently. A VFD controls the frequency and voltage of the power supplied to the motor, allowing for precise control over the motor's speed and torque. On the other hand, a soft starter only controls the voltage supplied to the motor, reducing the initial voltage during startup to limit the motor's inrush current and reduce stress on the motor and connected equipment. While both devices can reduce energy consumption and extend the lifespan of the motor, a VFD is better suited for applications that require precise speed control, while a soft starter is ideal for applications where reducing inrush current is the primary concern.

What are soft starters examples?

Soft starters are electronic devices used to limit the inrush current and gradually increase the voltage applied to an AC motor during its startup, reducing mechanical stress on the motor and the connected equipment. Some examples of soft starters are the Siemens Sirius soft starters, ABB PSR soft starters, Schneider Electric Altistart soft starters, and Eaton S801+ soft starters. These devices are commonly used in industrial applications such as pumps, fans, compressors, and conveyors.

What is the disadvantage of soft starter?

Soft starters have some disadvantages, including higher cost compared to direct-on-line starters and increased complexity. Soft starters also typically generate more heat during operation, which can lead to reduced efficiency and a shorter lifespan for the device. Additionally, some soft starters may not be suitable for use with certain types of motors, such as synchronous motors, and may not provide the same level of control as variable frequency drives.

What is soft starter circuit?

A soft starter circuit is an electronic device that is used to gradually ramp up the voltage and current supplied to an electric motor during startup, rather than applying full voltage and current immediately. This helps to reduce the mechanical stress and wear on the motor, as well as limit the inrush current that can occur when starting a motor at full voltage. Soft starters are commonly used in applications where there is a need for precise control over motor acceleration, such as in industrial settings where heavy machinery is used.

Why soft starter is used?

A soft starter is an electronic device used to control the starting current of an AC electric motor. It gradually increases the voltage supplied to the motor, thereby reducing the stress on the motor during startup. This helps to prevent damage to the motor and increases its lifespan. Soft starters are commonly used in applications where large motors are being started, such as in industrial settings. They are also useful in reducing energy consumption and lowering maintenance costs. Overall, the use of a soft starter can improve the efficiency and reliability of motor-driven equipment.

What is benefit of soft starter?

A soft starter is an electronic device used to control the starting current of an electric motor. Its main benefit is that it reduces the stress on the motor during startup, which can extend the motor's lifespan and reduce maintenance costs. Additionally, soft starters can improve the efficiency of the motor by reducing energy consumption during startup, as well as improve the overall performance of the system by providing a smooth and controlled acceleration of the motor. Overall, using a soft starter can result in cost savings, improved reliability, and better performance for motor-driven systems.

Can we use VFD instead of soft starter?

VFD (Variable Frequency Drive) and soft starters are two different types of equipment used for controlling the speed and starting/stopping of electric motors. While both VFDs and soft starters can be used to achieve similar outcomes, they operate in different ways and have different features. VFDs are more versatile and provide greater control over motor speed and torque, making them suitable for a wider range of applications. Soft starters, on the other hand, are simpler and less expensive, and are primarily used to reduce the initial starting current of motors, which can be beneficial for certain applications. Whether to use a VFD or soft starter depends on the specific requirements of the application.