Power soft starter

Types of Power Soft Starter

A power soft starter is an electrical device used to reduce the starting torque and current of an electric motor. This allows for a more controlled and smooth start-up process. The power soft starter achieves this through different techniques:

• Voltage Control Soft Starters: These are the most common types of soft starters. They work by reducing the voltage supplied to the motor during the start-up phase. This gradual voltage increase allows the motor to accelerate smoothly without causing mechanical stress or pulling excessive current from the power supply. Voltage control soft starters can be further divided into two: V-Start and V-Stop. V-start provides a ramp-up voltage to the motor during the start phase. On the other hand, V-stop soft starters allow the motor to run at a preset voltage and stop at a predetermined voltage level.
• Current Limit Control Soft Starters: Current limit control soft starters limit the inrush current to the motor during start-up. They achieve this by continuously monitoring the motor current and controlling the power delivered to the motor. This ensures that the motor current does not exceed the predefined limit, thus protecting the motor and associated mechanical systems from damage due to high current. Current limit control soft starters are suitable for applications where maintaining current is critical, such as in pumping or fan systems.
• Torque Control Soft Starters: These types of soft starters are mainly used in applications where precise control of the motor's starting torque is required. They allow users to set the desired starting torque level, and the soft starter adjusts the power delivered to the motor accordingly. Torque control soft starters are beneficial in applications with high inertia loads or where precise control of the process is essential.
• Frequency Drive Soft Starters: Although primarily used for speed control, variable frequency drives (VFDs) can also function as soft starters. By gradually ramping up the frequency and voltage supplied to the motor, VFDs provide a smooth and controlled start. This is particularly useful in applications where precise speed control is essential right from the start.

Specifications and maintenance of power soft starter

A power soft starter is an electrical device that controls the voltage supplied to an electric motor. It gradually increases the voltage, allowing the motor to start smoothly without jerks or shocks. The specifications and maintenance of power soft starters are essential for ensuring their reliability and optimal performance.

Specifications

• Voltage rating

  The soft starter has a voltage rating that matches the motor's operating voltage. The rating is available in different levels, such as 230 V, 400 V, or 690 V. The voltage rating ensures the soft starter can control the motor's power without causing damage or performance issues.

• Current rating

  The current rating of a power starter is selected based on the maximum motor full load current. The current rating is expressed in amperes (A). For example, a soft starter with a current rating of 100A can be used with a motor that has a full load current of 100A. The current rating prevents overload and ensures the soft starter can handle the motor's starting and stopping operations.

• Control voltage

  The control voltage is the voltage used to control the soft starter. The control voltage must be compatible with the control system of the motor. The control voltage is available in several options, such as 24 VDC, 110 VAC, or 230 VAC. The control voltage ensures communication between the soft starter and other control components, such as a programmable logic controller (PLC) or a motor control panel.

• Starting mode

  A power soft starter has different starting modes to meet various applications and requirements. The starting modes include:

  - Soft start: The voltage increase is smooth and continuous during the starting period.

  - Torque control: The soft starter controls the motor's torque during the start, keeping it constant.

  - Pump control: For pumping applications, the soft starter uses a specific starting profile to prevent water hammer and abrupt pump surges.

• Protection features

  The power soft starter comes with built-in protection features to safeguard the soft starter and the motor from damage. The protection features include:

  - Overload protection: It detects overload conditions and automatically disconnects the motor from the power supply.

  - Phase failure protection: It protects the soft starter and motor from phase failure or imbalance in the power supply.

  - Short circuit protection: It prevents damage from short circuit faults with an integrated short circuit protection function.

Maintenance

• Regular inspections

  Inspections should be done regularly to ensure the soft starter's reliability and performance. The inspections should include checking the wiring, connections, and components for signs of wear, damage, or looseness. The soft starter should be inspected for dust, moisture, and environmental factors that may affect its performance.

• Cleaning

  Cleaning the power soft starter is essential for preventing dust and contaminants from affecting its performance. A soft cloth or a soft brush can be used to clean the soft starter and its components. When cleaning the soft starter, avoid using moisture or conductive materials.

• Firmware updates

  The firmware of the power soft starter should be updated according to the supplier's instructions. The firmware updates provide enhancements, optimizations, and new features to improve the soft starter's performance and reliability.

• Electrical tests

  Electrical tests should be performed on the power soft starter to check its performance and functionality. The tests include measuring the voltage and current during the start and stop operations to ensure they match the expected values. The electrical tests can help identify issues or abnormalities with the soft starter and allow for timely troubleshooting and repairs.

• Component replacement

  Any damaged or worn components of the power soft starter should be replaced promptly. The component replacement should be performed according to the supplier's instructions and using original replacement parts. Component replacement helps maintain the soft starter's performance and reliability.

How to Choose Power Soft Starter

Choosing the right power soft starter is essential for meeting specific application requirements while ensuring optimal motor performance and protection. Here are some key factors to consider when selecting a power soft starter:

• Voltage and Size

  It's important to select a power soft starter that has the same voltage rating as the electrical system to which it will be connected. If the voltage is not compatible, the performance might be affected and the equipment might even be damaged. Additionally, the soft starter should be selected based on the motor size and its full-load amperage (FLA). The soft starter's current rating should be higher than the motor's FLA to ensure that it operates without problems and to avoid any damage to the components.

• Control Method

  Power soft starters control the voltage that goes to the motor by using different methods. The most common methods are Voltage Ramp Control and Current Ramp Control. In Voltage Ramp Control, the output voltage gradually increases during the starting process, allowing for a smooth and controlled motor start. In Current Ramp Control, the motor's current gradually increases during the start, which results in a reduced torque.

• Bypass Contactor

  A power soft starter can come with an in-built contactor or be configured without one. If it has a built-in contactor, then the soft starter will be able to automatically disconnect itself from the circuit once the motor is running at full speed. This will help minimize the wear and tear and increase the lifespan of the power soft starter, while also maximizing its efficiency.

• Features

  A power soft starter comes with different features that help enhance its functionality and performance. For instance, it can have overload protection, under-voltage protection, or phase failure protection. Additionally, it can have a built-in timer that helps set the starting torque and ramp time, and a digital display that shows the various parameters and the soft starter's status.

How to DIY and Replace Power Soft Starter

Here is a step-by-step guide on how to replace a power soft starter:

• 1. Before replacing the soft starter, the parameters of the old unit should be checked and the new unit should be set to match them. This includes voltage, current, and control signal settings.
• 2. Disconnect the power supply to ensure safety during the replacement process.
• 3. Remove the cover of the old soft starter.
• 4>Remove all the connected wires from the old soft starter. It is important to take a picture or make a note of the wiring connections to ensure correct reinstallation.
• 5. Unscrew and remove the old soft starter from its mounting.
• 6. Place the new soft starter in its mounting location and screw it in place.
• 7. Connect the power supply, control signals, and output connections according to the wiring diagram made earlier.
• 8. Once the connections are done, the cover of the new soft starter should be replaced.
• 9>Reconnect the power supply and control circuits to the new soft starter.
• 10>Perform a test to ensure that the motor starts and stops smoothly, and that all parameters are set correctly.

Q and A

Q1. Can a power soft starter be used on all types of motors?

A1. Soft starters are designed for use with electric motors, particularly three-phase induction motors. They are not suitable for use with all motor types, such as synchronous motors or certain types of variable frequency drive (VFD) systems.

Q2. Does a power soft starter consume more energy during operation?

A2. Power soft starters do not significantly increase the energy consumption of a motor. Their primary function is to manage the motor's start-up process, reducing mechanical stress and improving system reliability. Any minor energy losses associated with the soft starter's control circuitry are typically offset by the motor's efficient operation during the start-up phase.

Q3. Can multiple motors be controlled by a single power soft starter?

A3. While it is technically possible to connect multiple motors to a single power soft starter, this arrangement is generally not recommended. Each motor may have different start-up characteristics and load requirements, making it challenging to optimize the soft starter settings for all connected motors. Additionally, the soft starter's capacity must be sized appropriately for the total combined motor power.

Q4. Do power soft starters require regular maintenance?

A4. Power soft starters have maintenance requirements, but they are generally low. Keeping the soft starter clean and free from dust and debris, inspecting electrical connections for tightness and integrity, and periodically checking control parameters are essential to ensure optimal performance.

Q5. Can a power soft starter be integrated into existing motor control systems?

A5. Power control soft starters are designed to be easily integrated into existing motor control systems. They can be connected to the motor's power lines and wired to the control circuit, allowing for seamless integration without significant modifications to the existing system.