Motor Starters

More Information about Motor Starters

When using a reduced voltage starter, like a star-delta starter, it is beneficial if the starting torque and current demand during startup can be reduced. Large induction motors benefit most from this concept. Because of their size, these motors naturally have high starting torques and current demands. A star-delta starter reduces both of these quantities noticeably when starting such motors. An added benefit is that low-voltage protection commonly is built into motor starters to protect against power fluctuations or failures that may occur in the supply system and thus against damage to the motor.

FAQs

Does the motor starter provide manual speed control and starting torque control of the electrical device (electric motor) through the power circuit?

No, the motor starter typically does not provide manual speed control and starting torque control; these functions are generally managed by devices like variable frequency drives (VFDs) or dedicated motor controllers, while the starter primarily handles safe starting, stopping, and protection of the motor.

What do magnetic motor starters consist of?

A magnetic motor starter consists of a contactor for switching the motor on and off, an overload relay for motor protection, and often auxiliary contacts for control circuit functionality.

Do manual motor starters have short circuit protection for the electrical power that runs them?

Yes, manual motor starters typically include short circuit protection to safeguard the motor and electrical power circuit.

Motor Control Basics

Motor control allows operational control of electrical motors in various environments. 

Motor control circuits provide a safe way to operate electrical motors. Back when motor control circuits were in their infancy, it would have been common to see a simple disconnect switch that would be used to turn on and off a motor. Depending on the size of the motor and how much voltage was required, operating this disconnect would have been dangerous, with a very high possibility of arcing or electrocution. Not to mention that when the disconnect was actuated, the large amount of inrush current would have damaged the motor over time.

In today's motor control circuits, there are a few common pieces of hardware. 

A circuit breaker is used to protect the motor and any hardware downstream. A contactor and an overload relay are connected together and function in tandem to allow for remote and safe operation of the motor. The contactor functions much like a relay, allowing for a smaller electrical circuit to remotely close the motor contacts, starting the motor. The overload relay is designed to protect the motor in the case of a prolonged overcurrent event. These two devices are wired in series, so that if the overload relay detects an overcurrent event, the contactor will open the motor contacts, shutting off power to the motor.

The other two most common types of motor control hardware are a soft starter and a Variable Frequency Drive (VFD). 

Both of these devices function in a similar way to the motor circuit with some added functions. The soft starter is designed to reduce large inrush current to the motor upon startup. This “soft starting” of the motor will prolong its life and allow for safer operation. The VFD performs the soft start functions, but also allows for speed control of the motor. This speed control is critical in many different environments and has made VFDs one of the most common and safe to use motor control circuits today.