4 Point Starter

A 4 Point Starter is almost similar in functional characteristics like 3 Point Starter. In the absence of back EMF, the 4 Point Starter acts as a limiting current device while starting of the DC motor. 4 Point Starter also acts a protecting device. The basic difference in 4 Point Starter as compared to 3…

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3 Point Starter

3 Point Starter is a device whose main function is starting and maintaining the speed of the DC shunt motor. Mainly there are three main points or terminals in 3 point starter of DC motor. They are as follows L is known as Line terminal, which is connected to the positive supply. A is known…

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Armature Reaction in a DC Generator

Armature Reaction is the effect of magnetic flux set up by armature current upon the distribution of flux under the main poles. The 2 pole DC generator is shown in the figure below. When there is no load to the generator, the current in the armature conductors is zero. As a result, there exists only…

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Four Quadrant Operation of DC Motor

Four Quadrant Operation of any drives or DC Motor means that the machine operates in four quadrants. They are Forward Braking, Forward motoring, Reverse motoring and Reverse braking. A motor operates in two modes – Motoring and Braking. A motor drive capable of operating in both directions of rotation and of producing both motoring and…

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Hopkinson’s Test

Hopkinson’s Test is also known as Regenerative Test, Back to Back test and Heat Run Test. In Hopkinson Test, two identical shunt machines are required which are coupled both mechanically and electrically in parallel. One is acting as a motor and another one as a generator. The input to the motor is given by the…

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Electrical Braking of DC Motor

Electrical Braking is usually employed in applications to stop a unit driven by motors in an exact position or to have the speed of the driven unit suitably controlled during its deceleration. Electrical braking is used in applications where frequent, quick, accurate or emergency stops are required. Electrical Braking allows smooth stops without any inconvenience…

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Plugging or Reverse Current Braking

In Plugging or Reverse Current Braking the armature terminals or the supply polarity of a separately excited or shunt motor when running are reversed. Therefore, in Plugging the supply voltage V and the induced voltage Eb which is also called back EMF will act in the same direction. Thus, during plugging the effective voltage across…

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Dynamic Braking or Rheostatic Braking of DC Motor

In Dynamic Braking, a braking resistor Rb is connected across the armature as soon as the DC motor is disconnected from the supply mains. The motor now works as a generator, producing the braking torque. For the braking operation in Dynamic Braking, the motor is connected in two ways. Firstly the separately excited or shunt…

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Swinburne’s Test

Swinburne’s Test is an indirect method of testing of DC machines. In this method the losses are measured separately and the efficiency at any desired load is predetermined. Machines are tested for finding out losses, efficiency and temperature rise. For small machines direct loading test is performed. For large shunt machines, indirect methods are used…

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