Amplidyne

Submitted by By:

VIVEK KUMAR(20109018)

VINEET KUMAR SINGH(20108079)

Amplidyne

Introduction:

An amplidyne is a special type of motor-generator which uses regeneration to increase its gain. Energy comes from the motor, and the power output is controlled by changing the field current of the generator. In a typical generator the load brushes are positioned perpendicular to the magnetic field flux. To convert a generator to an amplidyne you connect what would be the load brushes together and take the output from another set of brushes that are parallel with the field. The perpendicular brushes are now called the 'quadrature' brushes. This simple change can increase the gain by a factor of 10,000 or more.

Historically, amplidynes were one of the first amplifiers to generate very high power (tens of kilowatts), allowing precise feedback control of heavy machinery. Vacuum tubes of reasonable size were unable to deliver enough power to control large motors, but vacuum tube circuits driving the input of an amplidyne could be used to boost small signals up to the power needed to drive large motors. Early (World War II era) gun tracking and radar systems used this approach.

Amplidynes are now obsolete technology. Modern electronic devices for controlling power in the kilowatt range include MOSFET and IGBT devices.

An amplidyne is capable of giving a controlled power outputin the range of a few hundred to few thousand watts with a power

amplification of the order of 10,000 or more and hence finds wide application in feedback control system.

Characteristics:The nature of external char. of cross-field generator with various degrees of compensation are shown in the figures below

It can be seen from the figure that for low values of compensation the machine gives an approximately constant current characteristics ,while for degree of compensation of the order of unity the machine gives approximately constant voltage characteristics.

Where C=Nc/Na

Nc=effective compensating winding turnsNa=effective d-axis armature turns

Applications: It is widely used for various purposes particularly in feed-back control systems where the regulated power requirement is in the range of 1 to 50 KW. It may sometimes be found economical to feed the field winding directly from the Amplidyne. It can also serve as a generator in Ward-Leonard system of speed control provided that the controlled DC motor rating is not very high. In general when the controlled power requirements are within the range of cross field machines ,Amplidynes competes favorably with other type of controlled configurations.

Advantages : 1. Amplidyne generate very high power ,allowing precise

feedback control of the heavy machinery.2. The resultant d-axis flux is equal to the field flux. In

other words the d-axis flux is completely under the control of field winding and unaffected by d-axis armature current.

3. Amplidyne circuit is also used by U.S. navy naval gun control. This is a high power position servo system.

Drawbacks:Main drawback of amplidyne is sparking at the brushes due to armature reaction on which the operation of the machine depends. Special brushes and construction of the field poles are used to alleviate this difficulty. It often sparks very severely at the quadrature brushes when delivering large output voltages

Questions

1. What is the difference between metadyne and Amplidyne? The main difference between metadyne and Amplidyne is that Amplidyne has the compensating winding while metadyne doesn’t.

2. When this machine is known as constant current source and when constant voltage source?

When degree of compensation is 0 the this machine is known as constant current ,when the degree of compensation is of the order of unity the this machine is known as constant voltage source.