11-Dc Mot Series

8/10/2019 11-Dc Mot Series

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DC MOTOR

Soedibyo


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References

1. Theraja, B. L., Electrical Technology, S. Chand

& Company Ltd., 1978.

2. Schmidt-Walter, H., Kories, R., Electrical

Engineering: A Pocket Reference, Artech HouseInc., 2007.


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DC Motors Outlines

10: .Dc motor:

..dc motor parts & works

..back emf

..motor equivalent circuit

..characteristics of dc motor: Ta~Ia and n~E/

.Dc shunt motor:

..characteristics of dc shunt motor

..speed control of dc shunt motor: n ~ (VIaRa)/

11: .Dc series & compound motor

.speed control of dc series motor

12: .Braking & starting of dc motor

.Dc motor power stages


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dc motor parts How dc motor works

E

V

Ia

Ra

Rf

If

Ff

Vf

motor equivalent circuit V E = IaRa


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dc motor parts How dc motor works

E

V

Ia

Ra

Rf

If

Ff

Vf

motor equivalent circuit V E = IaRa


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Review: dc shunt motor

V

Ff

Ta/Iacharacteristic

Ia

Ta

n

Ia/n characteristic

Ia

No-loadoperation

Ta/n characteristic

n

TaNominalpoint


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DC Series Motor

.field winding is connected in series to

the armature winding..this causes the magnetic flux to be

proportional to the armature

current -> ~ Ia

which leads to a very high torque for

high load currents.

V

Fs


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Characteristics of DC Series Motor (1)

.As field windings also carrythe armature current, ~Iaup to the point of saturation.

.Hence, before saturation:

Ta~Ia -> Ta~Ia2

.After saturation, is almost

independent of Ia-> Ta~Ia

Ta/Iacharacteristic

Ia

Ta

*While discussing motor characteristics,

these should be kept in mind*:Ta~Ia and n~E/


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Characteristics of DC Series Motor (2)

n~E/

.Ia , .

Hence, n (speed varies inverselyas Ia)

(change of E for various load current

is small and may be neglected.)

n/Iacharacteristic

Ia

n

Starting point

Nominal point

nn

In

n/Tacharacteristic

n

Ta

.Its starting torque is very high.

.For no-load operation the series motor

reached very high speeds.

. the motor will be severely damaged due

to centrifugal force.. some type of protection: A centrifugal

switch can be connected to the motor to

de-energize the motor starter coil if the

rpm exceeds the set amount. Other

sensors can be used to de-energize the

circuit if the motor's current drops while fullvoltage is applied to the motor.


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DC Series Motor Speed Control (1):

Flux Control Method

a. Field Divertors b. Armature Divertors

V

V

c. Tapped Field Control

V

F

E~n


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DC Series Motor Speed Control (2):

Variable Resistance in Series with Motor

V

F

E~n


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Comparison of Shunt & Series Motors (1)

Shunt

.speed of motor is sufficiently constant.

.for the same input current, its starting torque is not as

high as that of a series motor.

Hence its used:

.when the speed has to be maintained constant from no-

load to full-load, i.e. for driving a line of shafting.

.when its required to drive the load at adjustable speeds

.Lathes, centrifugal pumps, blowers & fans,

Battery fan Battery blower

No-loadoperation

Ta/n characteristic

n

TaNominalpoint
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Comparison of Shunt & Series Motors (2)

Series

.high starting torque

.low speed at high loads & dangerously high speedat low loads.

Hence its used:

.when a large starting torque is required i.e. fordriving hoists, cranes, trams, starter motor.

n

Ta

hoist cranesDinamo starter /

Motorcycle

starter motor


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**DC Compound Motor (1)

.Shunt motor can provide smooth operation

at full speed, but it cannot start with a

large load attached.

.Series motor can start with a heavy load, but

its speed cannot be easily controlled.

.The cumulative compound motor takes the

best characteristics of both the seriesmotor and shunt motor, which makes it

acceptable for most applications.

V

Ff

V

Ff

Fs

http://zone.ni.com/devzone/cda/ph/p/id/39

Such machines are also used:

where series characteristics are required and

where, in addition, the load is likely to be removed totally.

Due to shunt windings, speed wont become excessively high.

But due to series windings, it will be able to take heavy loads.


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**DC Compound Motor (2)

.The machine has two field windings: One

connected in series; the other in

parallel.

.Due to shunt windings, speed wont become

excessively high.

.But due to series windings, it will be able to

take heavy loads.

.The characteristics lie between those ofshunt and series motor.

V

Ff

V

Ff

Fs

http://zone.ni.com/devzone/cda/ph/p/id/39

.cumulative compound:

series excitation helps shunt excitation.

.differential compound:

series excitation opposes shunt excitation.


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Comparison of DC Motors

Cumulative Compound

Used when:

.series characteristic is needed & the load is likely to be

removed totally, such as: in some types of coal cutting

machines.


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Battery drillBattery screwdriver

Battery toothbrush

**For instance, an electric screwdriver

has a very large gear reduction becauseit needs lots of torque to turn screws,

but the motor only produces a small

amount of torque at a high speed. With

a gear reduction, the output speed can

be reduced while the torque is

increased.
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-Ende-

24-12

24-23

25-16


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-Ende-


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**DC Series Motor Speed Control (2):

Variable Resistance in Series with Motor

V

.By increasing the resistance in series with

the armature, the voltage applied across thearmature terminals can be decreased.

.With reduced voltage across the armature,

the speed is reduced.

.However, it will be noted that since full motor

current passes through this resistance, thereis a loss in it.

F

E~n


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A lathe(pronounced IPA: /le/) is amachine toolwhich spins a block of materialto perform various operations such ascutting, sanding, knurling, drilling, ordeformationwith tools that are applied to theworkpiece to create an object which has

symmetryabout an axis of rotation. Lathes are used in woodturning,

metalworking, metal spinning, andglassworking. Lathes can be used to shapepottery, the best-known design being thepotter's wheel. Most suitably equippedmetalworking lathes can also be used toproduce most solids of revolution, planesurfaces and screw threads or helices.Ornamental lathes can produce three-dimensional solids of incredible complexity.The material is held in place by either one ortwo centers, at least one of which can bemoved horizontally to accommodate varyingmaterial lengths. Examples of objects thatcan be produced on a lathe include

candlestickholders, cue sticks, tablelegs,bowls, baseball bats, crankshaftsandcamshafts.

http://en.wikipedia.org/wiki/Lathes
http://en.wikipedia.org/wiki/Help:IPA_English_pronunciation_keyhttp://en.wikipedia.org/wiki/Machine_toolhttp://en.wikipedia.org/wiki/Cuttinghttp://en.wikipedia.org/wiki/Sandinghttp://en.wikipedia.org/wiki/Knurlinghttp://en.wikipedia.org/wiki/Drillinghttp://en.wikipedia.org/wiki/Deformationhttp://en.wikipedia.org/wiki/Rotational_symmetryhttp://en.wikipedia.org/wiki/Axis_of_rotationhttp://en.wikipedia.org/wiki/Woodturninghttp://en.wikipedia.org/wiki/Metalworkinghttp://en.wikipedia.org/wiki/Metal_spinninghttp://en.wikipedia.org/wiki/Potteryhttp://en.wikipedia.org/wiki/Potter%27s_wheelhttp://en.wikipedia.org/wiki/Solid_of_revolutionhttp://en.wikipedia.org/wiki/Candlestickhttp://en.wikipedia.org/wiki/Cue_stickhttp://en.wikipedia.org/wiki/Furniturehttp://en.wikipedia.org/wiki/Bowl_%28vessel%29http://en.wikipedia.org/wiki/Baseball_bathttp://en.wikipedia.org/wiki/Crankshafthttp://en.wikipedia.org/wiki/Camshafthttp://en.wikipedia.org/wiki/Camshafthttp://en.wikipedia.org/wiki/Crankshafthttp://en.wikipedia.org/wiki/Baseball_bathttp://en.wikipedia.org/wiki/Bowl_%28vessel%29http://en.wikipedia.org/wiki/Furniturehttp://en.wikipedia.org/wiki/Cue_stickhttp://en.wikipedia.org/wiki/Candlestickhttp://en.wikipedia.org/wiki/Solid_of_revolutionhttp://en.wikipedia.org/wiki/Potter%27s_wheelhttp://en.wikipedia.org/wiki/Potteryhttp://en.wikipedia.org/wiki/Metal_spinninghttp://en.wikipedia.org/wiki/Metalworkinghttp://en.wikipedia.org/wiki/Woodturninghttp://en.wikipedia.org/wiki/Axis_of_rotationhttp://en.wikipedia.org/wiki/Rotational_symmetryhttp://en.wikipedia.org/wiki/Deformationhttp://en.wikipedia.org/wiki/Drillinghttp://en.wikipedia.org/wiki/Knurlinghttp://en.wikipedia.org/wiki/Sandinghttp://en.wikipedia.org/wiki/Cuttinghttp://en.wikipedia.org/wiki/Machine_toolhttp://en.wikipedia.org/wiki/Help:IPA_English_pronunciation_key

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11-Dc Mot Series