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

This is an AMP page - Open full page! for all features.

Electrical Motors - Starting Devices

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

Sponsored Links

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.

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Share

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

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 the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Topics

Unit Converters

Temperature

oC
oF


Load Calculator!

Length

m
km
in
ft
yards
miles
naut miles


Load Calculator!

Area

m2
km2
in2
ft2
miles2
acres


Load Calculator!

Volume

m3
liters
in3
ft3
us gal


Load Calculator!

Weight

kgf
N
lbf


Load Calculator!

Velocity

m/s
km/h
ft/min
ft/s
mph
knots


Load Calculator!

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O


Load Calculator!

Flow

m3/s
m3/h
US gpm
cfm


Load Calculator!

3 10

This website use cookies. By continuing to browse you are agreeing to our use of cookies! Learn more