Amplidyne 4zh1v

Amplidyne Characteristics Introduction: An Amplidyne is a rotating amplifier. It is a prime-mover-driven d.c. generator whose output power can be controlled by a small field power input. An amplidyne is capable of giving a controlled power output in 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 control system.

Objective: Study of amplidyne whose output power can be can be controlled by a small field power input. For studying the characteristics: 1) We plot a graph of Output voltage against effective field current with no load, full load(500 W), and without compensation winding effect. 2) We draw the schematic diagram of an amplidyne system.

Principle of operation: The principle of operation of an amplidyne is simple. In the figure, a d.c. generator with a control field current If and the resulting control field flux f is shown. If the armature is rotated as shown a voltage will be induced in the armature and the resulting induced current through the armature and conductors will set up an armature reaction flux q at right angles to f. The reaction flux q is called the quadrature flux. In conventional generators, this armature reaction flux is suppressed, but in amplidyne a magnetic path is provided to encourage it. Moreover, the brushes are short-circuited so that maximum amount of q will induce voltage ed in the armature conductors in a direction as shown in the figure, and is called the direct axis voltage. A second set of brushes(called the direct axis brushes) is used to connect this to the load. Since q eq. f(as obvious from the above discussion), ed When the output brushes are connected to the load, the resulting load current Id will again rise to an armature reaction flux which obviously opposes the original control field flux f. The load current will thus be limited to a value such that mmf of this armature reaction is equal to the mmf by the control field current If. Thus the machine will act like a constant current generator - the load current depending only on the field current and independent of the speed and direction of rotation of armature(this is known as Rosenburg Generator, used in train lighting). In control system, such constant current feature is undesirable and the armature reaction flux due to the load current is compensated by the use of a compensating winding. Such a machine is called amplidyne. The compensating winding is placed in

A

IL

R1

A

S5

F1 F2

E S2

I1

30 V

R2

A

F4

I2

A1 Field winding

C1

S3

V

S1

F3

S4

200W100W200W

C2

Compensating winding

M

115V 50 c/s 3 phase

series with the load and is designed to produce a flux as nearly as possible equal and opposite to the flux produced by the direct axis armature current. The machine will thus give a voltage that is only moderately affected by the load current. The amplidyne is essentially a two-stage generator and combines two stages of amplification. The control field current causes a heavy current through the short circulated brushes to produce a very high quadrature flux. This flux acts as the effective input to the second stage giving amplified output across the direct axis brushes.  Drawbacks of Amplidyne: 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.

Other Essential Components: 1) D.C. Generator - A d.c. generator is used here for producing a d.c. voltage. A basic d.c. generator has four basic parts: (i) Magnetic field (ii) A Single Conductor, or Loop (iii) A Commutator (iv) Brushes

A single conductor, shaped in the form of a loop, is placed in between the magnetic poles. As long as the loop is stationary, the magnetic field has no effect(no relative motion). If we rotate the loop, the loop cuts through the magnetic field, and an EMF(voltage) is induced in the loop. EMF depends on the field strength and the rate at which the flux lines are cut. The stronger the field or the more flux lines cut for a given period of time, the larger the induced EMF is, as given by the equation: Eg = K φ N Where, Eg = generated voltage K = fixed constant φ = magnetic flux strength N = speed in rpm

2) A.C. Motor - Three phase a.c. induction motors are widely used for high power amplifications, including heavy industry. An a.c. electrical motor consists of two main parts: (i) Armature or Rotor: It is usually cylindrical that rotates about the axis of the motor‘s shaft. The rotor usually completes one revolution for each cycle of the a.c. electrical supply.

Procedure: The setup consists of an Amplidyne armature, which is driven by a 3-phase motor. Two potentiometers R1 and R2 are for adjusting the two control-field currents. 3 lamps of 100 W, 200 W and 200 W are connected across the output as loads. The 115V, 50 Hz, 3-phase supply to the motor is supplied from a 400V, 3-phase supply through a step-down 3-phase transformer. (I) Run-1: No load characteristics (a) Switches S1, S2, S3 and S5 are kept in OFF and S4 in ON position. The battery(30 volts) is connected. R1 and R2 are varied so that both I1 and I2 need 2mA. The voltage V0 is measured. (b) Keeping I1 constant(i.e. at 2mA), I2 is increased in steps of 1mA by decreasing R2 and V0 is measured in each step until it reaches 150V(but not exceeding 250V in any case). Next I2 is reduced in steps of 1mA till it comes down to 2mA. In each step, output voltage V0 is noted. (c) Next, I2 is held constant at 2mA and I1 is varied by varying R1 in steps of 1mA just like the previous step. In each step V0 is noted. (II) Run-2: Full load characteristics -

(a) Switches S1, S2, S3 and S4 are kept in OFF and S5 in ON position. (b) Keeping I1 constant(i.e. at 2mA), I2 is increased in steps of 1mA by decreasing R2 and V0 and load current IL is measured in each step until it reaches 150V(but not exceeding 250V in any case). Next I2 is reduced in steps of 1mA till it comes down to 2mA. In each step, output voltage V0 and load current IL is noted. (c) Next, I2 is held constant at 2mA and I1 is varied by varying R1 in steps of 1mA just like the previous step. In each step V0 and load current IL is noted. (III)

Run-3: Characteristics without compounding winding (a) Switches S1, S2, S3, S4 and S5 are kept in ON position. (b) Keeping I1 constant(i.e. at 2mA), I2 is increased in steps of 1mA by decreasing R2 and V0 and load current IL is measured in each step until it reaches 150V(but not exceeding 250V in any case). Next I2 is reduced in steps of 1mA till it comes down to 2mA. In each step, output voltage V0 and load current IL is noted. (c) Next, I2 is held constant at 2mA and I1 is varied by varying R1 in steps of 1mA just like the previous step. In each step V0 and load current IL is noted.

(IV)

Run-4: Obtaining the power gain The power gain of an amplidyne is defined as the ratio of the power output to the power input to any single control field with other field de-energised. (a) Switch of S4 to disconnect the control field F3-F4. (b) Switch on S1, S2 and S3 leaving S5 in OFF position. Adjust R1 so that I1 is 5mA. (c) Connect a voltmeter across F1 and F2. (d) Measure V0, IL and voltage V1 across F1 and F2.

Experimental Result: RUN I I1(amp)

I2(amp)

I1-I2

V0(volt)

2(fixed)

2 3

0 -1

-2.0 -5.3

2(fixed)

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 22 18 17

4 5 6 7 8 10 12 14 15 17 18 20 17 16 15 14 13 12 11 10 9 8 7 6 5 4 4 2 2(fixed)

-2 -3 -4 -5 -6 -8 -10 -12 -13 -15 -16 -18 -15 -14 -13 -12 -11 -10 -19 -8 -7 -6 -5 -4 -3 -2 -1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 16 15

-20.4 -29.0 -39.5 -54.1 -69.4 -89.5 -104.0 -116.5 -125.3 -137.0 -144.6 -150.3 -138.6 -134.0 -126.4 -124.4 -116.5 -111.8 -101.4 -91.4 -81.5 -72.0 -61.6 -50.5 -39.9 -29.7 -12.7 -5.8 -5.8 2.2 5 16 28.1 38.9 50 60.6 76 82.2 91.7 107.0 112.6 120.0 127.3 132.4 136.0 141.0 155.0 141.0 135.0

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

2(fixed)

126.0 118.8 112.0 107.0 103.7 93.6 85.1 69.9 60.3 52.1 31.9 25.6 15.1 7.0 -3.2

RUN II I1(amp)

I2(amp)

I1-I2

V0(volt)

IL(amp)

2(fixed)

2 3 4 5 6 7 8 9 11 12 13 12 11 10 9 8 7 6 5 4 3 2 2(fixed)

0 -1 -2 -3 -4 -5 -6 -7 -9 -10 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 0 1 2 3 4 5

0 -7.0 -18.0 -28.5 -37.5 -45.8 -59.7 -69.2 -83.9 -88.0 -97.8 -90.0 -86.0 -78.0 -73.0 -64.3 -51.3 -43.7 -33.3 -22.6 -12.9 -4.0 -4.0 0.7 9.2 17.6 27.5 37.7

-0.145 -0.254 -0.707 -0.846 -1.010 -1.214 -1.403 -1.487 -1.746 -1.780 -1.885 -1.816 -1.729 -1.693 -1.626 -1.507 -1.340 -1.172 -1.069 -0.881 -0.679 -0.422 -0.422 0.090 0.320 0.790 0.857 1.134

2 3 4 5 6 7

8 9 10 11 12 13 12 11 10 9 8 7 6 5 4 3 2

2(fixed)

6 7 8 9 10 11 10 9 8 7 6 5 4 3 2 1 0

47.3 57.0 62.6 68.9 73.6 87.8 75.4 70.3 66.3 59.5 50.2 43.1 34.3 24.1 15.4 6.4 0

1.239 1.419 1.529 1.600 1.654 1.781 1.672 1.575 1.527 1.427 1.313 1.207 1.070 0.900 0.727 0.489 0.024

I1(amp)

I2(amp)

I1-I2

V0(volt)

IL(amp)

2(fixed)

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 19 20 19 18 17 16 14 13 12 11

0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -16 -17 -18 -17 -16 -15 -14 -12 -11 -10 -9

-0.0 -0.1 -0.4 -0.7 -0.8 -1.3 -1.5 -1.7 -2.0 -2.4 -2.7 -3.1 -3.4 -3.8 -4.4 -6.6 -7.1 -8.2 -7.3 -6.4 -5.3 -5.1 -3.8 -3.4 -2.9 -2.5

-0.001 -0.010 -0.049 -0.077 -0.106 -0.151 -0.195 -0.210 -0.246 -0.283 -0.330 -0.358 -0.379 -0.412 -0.446 -0.523 -0.564 -0.564 -0.540 -0.510 -0.477 -0.459 -0.394 -0.366 -0.329 -0.298

RUN III

2(fixed)

2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 22 18 17 16 14 13 12 11 10 9 8 7 6 5 4 3 2

10 9 8 7 6 5 4 3 2 2(fixed)

-8 -7 -6 -5 -4 -3 -2 -1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 14 15 16 17 20 16 15 14 12 11 10 9 8 7 6 5 4 3 2 1 0

-2.1 -1.8 -1.6 -1.4 -1.2 -1.0 -0.6 -0.3 -0.0 -0.0 0.0 0.3 0.6 0.9 1.2 1.4 1.6 1.8 2.1 2.3 2.6 3.1 3.8 4.3 5.2 6.0 9.1 5.7 5.1 4.5 3.3 2.9 2.6 2.0 1.7 1.5 1.2 1.0 0.7 0.6 0.4 0.0 -0.0

IL(amp)

V1(volt)

I1(amp)

RUN IV V0(volt)

-0.260 -0.235 -0.200 -0.167 -0.133 -0.109 -0.071 -0.038 -0.008 -0.008 0.004 0.042 0.072 0.112 0.138 0.161 0.196 0.242 0.266 0.300 0.333 0.360 0.405 0.432 0.481 0.503 0.610 0.479 0.461 0.432 0.360 0.338 0.311 0.274 0.236 0.219 0.183 0.153 0.114 0.080 0.062 0.016 -0.006

61.7

1.47

0.005

 Calculation:

Power Gain(P.G.)

2485

Graphical Analysis:

No Load and Full Load Characteristics

7.3

Characteristics without Compensation Winding

Conclusion: From the above experiment that we could conclude that the output voltage of amplidyne is not linearly varies with effective field current. When an amplidyne is used in a control system, the dead band tends to reduce the loop gain. The accuracy comes near to zero field.

Application: Amplidyne is used in a field of control system. It is used as a voltage regulator. Speed control of paper mills, positioning control in machine tool control systems, power factor control of synchronous machines etc.