Soft Starter Accessories
Motors require a great amount of energy when rapidly accelerating to full speed. Variable frequency drives (VFDs) and soft starters can be used to reduce inrush currents and limit torque. This reduces wear and tear caused by frequent starts and stops extending the life of the motor.
Soft starters are solid-state devices that protect electric motors from damage caused by limiting the inrush of current associated with motor startup. They ramp up the initial voltage to the the motor producing a gentle climb to full speed. Soft starters typically use a series of thyristors or silicon controlled rectifiers (SCRs) to reduce the voltage. In the normal “on" state, the SCRs allow current while in the normal “off” state, the SCRs restrict current. The SCRs are engaged during ramp up, and bypass contactors are used after maximum speed is reached. This significantly reduces motor heating.
Soft starters are a cost-effective choice for applications that require torque and speed control during motor startup. Soft starters can be utilized in conveyer belt applications where a gradual startup can prevent misalignment and stress to the belt’s drive components. They can also be used on motors that control pump applications where there is often a risk of power surges.
Motor Starters, Soft Starters and VFDs
Motor Starters
Motor starters safely start and stop a motor in industrial applications. They are designed with a contactor, overload and circuit protection. They are used when basic motor control is required, where torque on the motor is not a concern and speed control is not needed. The advantages of motor starters include: lower cost, allows for remote operation, allows for monitoring of motor state (with the use of auxiliary contacts) and they are safe and efficient. The disadvantages include: high inrush current that can cause fuses to blow and breakers to trip if the inrush is too high, and the starter will allow a full torque to start the motor which can cause the motor to ramp up to full speed very quickly potentially causing the motor to wear and degrade prematurely.
Soft Starters
Soft starters protect motors from inrush current by gently ramping up the motor to full speed. They provide all of the same functions as a traditional motor starter. The advantages of soft starters include: they are less expensive than a VFD when only startup control is needed, they are a smaller system than a VFD where space is a concern and they prevent unwanted torque upon startup, prolonging the life of the motor. The disadvantages include: they are more expensive than a traditional motor starter and they do not allow for full speed control.
VFDs
Variable Frequency Drives (VFDs) allow for the slow ramp up of a motor during startup and the slowing down of the motor during shutdown. They also allow for full speed control during the entire run cycle of the motor. VFDs provide the same functions as both the traditional motor starters and soft starters. The advantages of VFDs include: full speed control (start, stop and in-between), more custom control and monitoring, energy savings due to efficient motor usage and less wear and tear on the motors. The disadvantages include: they are more expensive and larger than other motor control options and they generate heat that may require fans or AC units.