Short-Question

What will happen if we run a DC series motor without load?

What will happen if we run a DC series motor without load?

Thus from equation (2), it is clear that speed of DC Series Motor is inversely proportional to Armature Current Ia. Therefore if the DC Series Motor is started at No Load then the speed of DC Series Motor will become dangerously high which will definitely damage the DC Series Motor.

Why is it dangerous to operate at no load condition in DC motor?

A series motor should never be started at no load. With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by overspeed.

Why should DC series motor started with load?

At the starting of the motor there is no back emf, so large current current flows cause high starting torque. This starting torque leads to very fast acceleration of motor if shaft is not connected to any load. This fast acceleration cause motor to damage. So series motor are always started with load.

In what two ways may the rotation of a shunt connected DC motor be reversed?

Detailed Solution. The direction of rotation of DC shunt motor can be reversed by reversing either field terminals or armature terminals but not both. The torque can be changed by changing either field flux or armature current. Hence the motor will rotate in the same direction by changing the supply connections.

What is the main disadvantage of a series motor?

The series motor has poor speed regulation. When the load speed of the machine increases, the DC shunt motor keeps its constant speed from no load to full load. The dc series motor’s Torque drops sharply when the speed increases.

What happens when the motor runs on no load?

When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude. This cause again increases the speed so the back emf.

What is no load in DC motor?

No Load Speed: Speed of a motor (ω [rad/s]) with no load applied. This can also be described as the maximum speed of the motor. Stall Torque: The amount of torque (τ [Nm]) needed to fully stop the rotation of the motor.

What happens when DC supply is given to rotor in induction motor?

Question: What happens when DC supply is given to rotor in induction motor? It acts as synchronous motor It acts as induction motor D. It acts as generator For a synchronous generator, which of the statement is NOT CORRECT A Increasing field current will result in leading power factor B.

Why does Series motor tend to race at no load and light loads?

This can be seen from the speed-armature current and the speed-torque characteristics that on low armature current and low torque condition motor shows a tendency to rotate with dangerously high speed. This is the reason why series motor should never be started on light loads or no load conditions.

What will happen if the supply terminals are reversed in case of DC shunt motor?

When both (the direction of the field as well as that of armature current) are reversed the direction of rotation will not change. So in the case of DC shunt motor, if the supply terminals are interchanged, there is no change in the direction of rotation.

What will happen if you reverse the power source polarities for a DC shunt motor?

Armature connection changed to give opposite direction of current in armature while maintaining field direction results in clockwise rotation. Reverse field polarity and armature polarity from middle diagram will result in the same clockwise direction of rotation.

• It is an easy assembly and simple design.
• Vast starting torque.
• Protection is very easy.
• It is cost-effective.
• Series wound motors can use for AC or DC supply so it is also known as universal motors.
• Compare with shunt motor DC series motor develop power for the same construction size.

Why should a DC series motor never be started on no-load?

When a series motor is started without load, there is no counter EMF in the field windings, so there is nothing acting against the initial starting torque developed in the motor. This means that the motor will spin faster and harder as the operating current continues to develop the magnetic field and no counter EMF develops to oppose it.

How is armature current determined in DC series?

In case of DC Series motor armature current is decided by the load. On light load or NO load, the armature current drawn by the motor is very small. Φ α Ia (or) Flux ( Φ) is directly proportional to armature Current ( Ia). On No load as Ia is small hence flux produced is also very small. N α 1/Φ as Eb is almost constant.

Why is the speed of a DC motor limited?

In other words, as the AC frequency through the armature increases as the speed increases, the inductance of the windings causes the current to decrease with rotational speed. The thing that limits the speed of the motor is the fact that the motor acts as a generator, bucking the source of power.

Where does the current come from in a series motor?

In a series motor, all of the current through the field winding comes from the armature, and as the speed of the motor increases and the current gets smaller, the magnetic field from the field winding gets smaller as well.