Separately Excited DC Motor

In this we will discuss about separately excited DC motor . Direct current (DC) motors converts electrical energy into mechanical energy and they works on dc supply.

Type of DC motors

1) Permanent magnet type dc motor

2) Separately excited dc motor

3) DC series wound motors

4) Shunt wound DC motor

5) Compound DC motor.

In this component we will separately talk about in regards to the excited motor that is dc. These engines provide both rotor and stator like other DC motors. Stator defines the component that is static of, including the industry windings. And so the rotor could be the armature that is contains which can be going windings or coils.

Individually motor that is excited is dc field coils just like that of shunt wound dc motor. The construction is preferred by the true title regarding the type of engine. Usually, in other DC machines, the field coil as well as the armature coil both are energized from the supply that is solitary. The industry of them doesn't have any excitation that is split.

But, in separately excited DC motor, split supply

Given to excitation of both industry coil and armature coil. Right here, the industry coil is energized from the DC that is voltage that is split the armature coil is also stimulated from another supply.

Armature voltage supply could be adjustable but, separate DC that is voltage that is constant for energizing the industry coil. Therefore, those coils are electrically separated from a single another, and this also connection could be the specialty of the type of DC motor.

Equations Of Voltage, current and power for DC motors

In a separately excited motor, armature and field windings are excited form two different dc supply voltages. In this motor,

Armature current Ia = Line current = IL = I

Back emf developed , Eb = V – I Ra

where V is the supply voltage and Ra is the armature resistance.

Power drawn from main supply , P = VI

Mechanical power developed , Pm = Power input to armature – power loss in armature = VI – I2 Ra = I ( V – IR a) = Eb I

Operating characteristics of Separately excited dc motor

Both in shunt wound dc motor and separately excited dc motor field is supplied from constant voltage so that the field current is constant. Therefore these two motors have similar speed -armature current and torque – armature current characteristics. In this type of motor flux is assumed to be constant.

Speed – armature current (N – Ia) traits: we understand that speed of dc motor is proportional to back emf / flux or in other words Eb / φ . Whenever load is increased Eb that is back emf and flux decrease because of armature resistance fall and armature response correspondingly .However right back decreases that are emf more than φ to make certain the rate with this engine notably decreases with load.

Torque – armature current ( τ Ia that is : Here torque is proportional towards the armature and flux current . Neglecting armature reaction, flux φ is constant and torque is proportional to your armature present Ia . τ – Ia characteristics is a lien that is directly through the foundation. Through the curve we're able to see that current that is huge had a need to begin loads that are hefty. And this variety of engine will not starts on hefty lots.

Speed control of separately excited DC motor

Rate of this type of dc shunt engine is managed by the strategies that are after Industry control techniques: Weakening of industry causes increase in cost connected with engine while strengthening the field causes decreases the speed. Speed modification of the type of engine is achieved through the strategy being following

Field rheostat control: - here a opposition that is variable connected in series with the industry coil that is current. Ergo the rate is managed by way of flux variation. Reluctance control variation that is involving of of magnetic circuit of engine. Field voltage control by varying the voltage at industry circuit while maintaining armature terminal voltage constant.

Armature control methods: Speed modification of separately excited DC motor by armature control is had by any certainly one of the following techniques :

i. Armature resistance control: - the following, the price is handled by varying the origin voltage to armature. Generally, a opposition that is adjustable supplied the armature to alter the armature opposition.

ii. Armature terminal voltage control variation that is involving of of voltage in armature circuit.

Applications OF DC Motors

Independently dc that is excited have actually applications which are industrial. These are typically generally used as actuators. This kind of motors can be used in trains as well as for automatic traction purposes.