Motor Starting Methods

Motor Starting Methods: Optimizing Performance and Efficiency

Electric motors are an essential part of many industrial, commercial, and residential systems. However, when starting an electric motor, the way you apply power can affect the motor’s performance, longevity, and energy consumption. Several methods exist for starting motors, each with its unique advantages and applications. This page will guide you through the most common motor starting techniques, helping you understand which one is right for your needs.

We are often asked “What’s the difference between Star-Delta and Direct-On-Line (DOL) Motor starting methods – “What are Variable Speed Drives (VSD) Variable Frequency Drives (VFD) and what is a Soft Starter”

Most Rotating equipment i.e. Pumps, Mixers, Fans, Gearboxes etc are motor driven by an electric motor… upon starting this draws significant levels electric current; this sudden demand for current may cause voltage drops with variable consequences, thus the correct means of starting should be considered – as this will affect the investment required for the Pump, Mixer Fans Gearbox Motors and Starter.

Direct-On-Line (DOL)

DOL starting is essentially starting in 1 step, unlike Star-Delta (2 steps).   DOL is generally only used for smaller current loading, as start current levels can exceed 8 to 10 times the running current. DOL starting is the simplest and lowest cost option for motor starting – due to high starting current cable is usually larger than Star-Delta. Motor protection usually consists of relay, and a contactor is used to switch power on/off.

Star-Delta

The Motor is wired in Star, this allows the motor to achieve an initial speed level meaning the current requirement is relatively low, this either time based, or speed based, it then switches to the normal delta mode.  Major benefit of this starting system is current is 1/3 of the rated motor current – usually reducing cables size in to the bargain, applications where the equipment is required to start under full load conditions i.e. a fully loaded conveyer or gearbox Star Delta is of no use.  These applications require Direct-On-Line starting as below.

Soft Start

A soft starter regulates the voltage flow to the motor during start-up. The voltage is delivered slowly to the motor rather like a clutch system in your car – These electronic devises are the favoured start method in industry as this method avoids instantaneous mechanical shock loads, some larger machines are stipulated to start this way as full load equipment is often more expensive.

Variable Speed Drives

VSD is an electronic device which gives full control over the way a motor starts and stops (like a soft start), Most VSD units offers further standard features such as constant pressure or a prespecified flow curve must be maintained.  VSD’s versatility and ever reducing prices means its becoming the standard for many water pressure boost pump systems – In a system where flow loading is variable it ensures minimal energy, simply put a VFD can reduce your running costs.