Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Electrical Motors - Starting Devices

Direct-on-line starters, star-delta starters, frequency drives and soft starters.

Commonly used starting methods for squirrel cage motors are

  • direct-on-line starters
  • star-delta starters
  • frequency drives
  • soft starters

Direct-on-Line Starters

The simplest and most common starting device is the direct-on-line starter where the equipment consists of a main contactor and a thermal or electronic overload relay.

The disadvantage of the direct-on-line method is very high starting current (6 to 10 times the rated motor currents) and high starting torque, causing

  • slipping belts, heavy wear on bearings and gear boxes
  • damaged products in the process
  • water hammers in piping systems

Star-Delta Starters

A star-delta starting device consists normally of three contactors, an overload relay and a timer for setting the time in the star-position (starting position).

The starting current is about 30 % of the direct-on-line starting device. The starting torque is about 25 % of the direct-on-line starting torque.

The stress on an application is reduced compared to the direct-on-line starting method.

Frequency Drives

With a variable frequency drive the electrical frequency to the motor is modulated between typical 0-250 Hz.

  • the rated motor torque is available at lower speed
  • the starting current is low - ranging 0.5 - 1 times the rated motor current

The frequency drive can also be used for soft stops.

Soft Starters

With soft starters thyristors are used to reduce starting voltage. With lower motor voltage

  • the starting current and starting moment can be very low compared to other methods

Stress on the application can be close to minimum compared to other methods.

Related Topics

  • Miscellaneous

    Engineering related topics like Beaufort Wind Scale, CE-marking, drawing standards and more.

Related Documents

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

Citation

This page can be cited as

  • The Engineering ToolBox (2008). Electrical Motors - Starting Devices. [online] Available at: https://www.engineeringtoolbox.com/electrical-motor-start-d_1441.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter


















































12.6.9

.