Types of Starters for 3 Phase Induction Motors: DOL, Star Delta & Auto Transformer

When AC voltage is directly applied to the stator windings of a 3 phase induction motor, the motor draws a high starting current which may disturb the system voltage. The starting current can be 6 to 7 times the full load current of the motor. To reduce this starting current, different types of motor starters are used in industrial applications.

TYPES OF STARTERS:

DIRECT ONLINE STARTER (DOL):

AC voltage is directly applied to the stator windings.
No effort is made to reduce the starting current.
DOL starters are generally used for motors up to 10 HP.
Control Circuit: The control circuit of a DOL starter includes a contactor, overload relay, and push button switches.

STAR DELTA STARTER:

Initially, the stator windings are connected in star configuration.
Once the motor reaches 2/3rd of its normal speed, the stator windings are switched to delta connection.
This reduces the starting current to 1/3rd compared to a DOL starter.

Types of Star Delta Starters:

Manual
Semi automatic
Fully automatic

Star delta starters are used for motors ranging from 12.5 HP to 30 HP.

Auto Transformer Starter:

Uses an auto transformer with 70% tapping initially connected to the stator windings.
Once the motor reaches 2/3rd of its normal speed, the connection shifts to 100% tapping.
The starting current is reduced by √3 times compared to a star delta starter.
Auto transformer starters are normally used for motors above 30 HP.

4. Thermal Overload Relay:

These starters have thermal overload relays to trip the motor in case of overload.
Bi metallic relay elements carry the motor current.
When the current exceeds the preset value, these elements bend and open a normally closed contact in the relay.
This disconnects the electricity supply to the contactor coils, preventing damage to the motor.

Comments

Fire Extinguishers: Types, Operation & Best Uses for Fire Classes

A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. Typically, a fire extinguisher consists of a hand held cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire. There are two operation types of fire extinguishers: i. Stored pressure ii. Cartridge operated Stored Pressure In stored pressure units, the expellant is stored in the same chamber as the fire fighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, nitrogen is typically used; water and foam extinguishers typically use air. Cartridge Operated Cartridge-operated extinguishers contain the expellant gas in a separate cartridge that is punctured prior to discharge, exposing the propellant to the extinguishing agent. This type is not as common, used primarily in areas such as industrial ...

Important components of a Diesel Engine - Turbocharger

Important components of a Diesel Engine Turbocharger A turbocharger can significantly increase an engine’s horsepower without adding significant weight. It enhances engine performance by forcing more air into the combustion chamber, enabling better fuel combustion. A turbocharger is made up of two main sections: The turbine and the compressor. The turbine consists of the turbine wheel and the turbine housing. It is the job of the turbine housing to guide the exhaust gas into the turbine wheel. The energy from the exhaust gas turns the turbine wheel, and the gas then exits the turbine housing through an exhaust outlet area. The compressor also consists of two parts: the compressor wheel and the compressor housing. The compressor’s mode of action is opposite that of the turbine. The compressor wheel is attached to the turbine by a forged steel shaft, and as the turbine turns the compressor wheel, the high-velocity spinning draws in air and c...

Sewage Treatment Plant - Filter Feed Pumps Types and Operation And Maintenance Considerations

FILTER FEED PUMPS Filter Feed Pumps are used to draw water from the clarified water sump and pass it through the Pressure Sand Filter (PSF) and Activated Carbon Filter (ACF), which are installed in series to improve water quality. PRESSURE SAND FILTER (PSF) Working Principle: The upper layers of sand perform the actual filtration function, while gravel layers provide physical support. Specialized sand with a specific particle size is used to trap solid impurities present in water. The particles get entrapped in the spaces between sand grains, eventually blocking water flow. When the pressure drops beyond a set limit, the sand is cleaned by backwashing with water. Backwashing reverses the flow, fluidizing the sand bed and removing lighter solid particles as waste. Operation And Maintenance Considerations Filtration is followed by a short backwash sequence. The filter requires backwashing when the pressure drop across the filter reaches 0.5 kg/cm². Best practice: Backwash once per shift,...

FM Techie

Search This Blog