1 elect actuatlor

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May 25, 2012 PMI Revision 00 2

An actuator is a piece of equipment that produces movement when given a signal.Actuators are used in the computer control of an environment, industrial

automation and in robotics.

Signal Mechanical Movementor work

Actuators can be of

1. electrical2. hydraulic (work by liquid pressure)3. pneumatic (work by air pressure)

Devices that control the movement of mechanical actionof a machine indirectly rather than directly or by hand.


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Hydraulic actuator operates by liquid ( oil ) pressure.

Hydraulic actuators are of different :

Open-close type (On-Off type).

Controlling type.

Hydraulic actuator requires

Oil.

Oil tank. Pump. Motor. Actuator. Positioner (Servo-unit for controlling type). Solenoids (for On-Off actuator).


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Pneumatic actuator operates by air pressure.

Pneumatic actuators are of different :


Controlling type.

Pneumatic actuator requires

Air.

Compressor. Motor. Air receiver tank. E/P converter. Actuator. Positioner (for controlling type).

Solenoids (for On-Off actuator).


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Electrical actuator operates by electrical supply 3-.

Electrical actuators are of different :


Controlling type.

Electrical actuator requires

Electrical supply 415 V, 3-.

Control supply 240 V 1-. Motorised actuator.


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-


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Electromagnetic

Stator Winding

Housing

Bearing

Shaft

Rotor

Power

Connection

Fan


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0 0

CLASS-A CLASS-B CLASS-F CLASS-H

} 5

} 10 }10

} 15

60 RISE

80 RISE

105 RISE

125 RISEHOT SPOT

HOT SPOT

HOT SPOT

HOT SPOT

BEFORE MOTOR IS STARTED THE TEMPERATURE OF WINDING IS AT SURROUNDING TEMPERATURE( AMBIENTTEMP.). NEMA HAS STANDRDISED THE AMBIENT TEMP.=40 C OR 105 F.

NEMA HAS STANDERDISED FOUR INSULATION CLASSES WHICH ALLOW FOR FOUR DIFFERENT CLASSES.

FOR EXAMPLE: CLASS-F INSULATION ALLOWS MAXIMUMU 105 C.

THE OPERATING TEMPERATURE OF MOTOR IS CRITICAL TO EFFICIENT OPERATION AND LONG LIFE.

OPERATING MOTOR ABOVE THE LIMITS OF ITS INSULATION CLASS REDUCES LIFE EXPECTANCY.

FOR EXAMPLE: A 10 C RISE IN OPERATING TEMPERATURE CAN DECREASE LIFE EXPECTANCY AS MUCH AS 50%.


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A1

A2

C2

C1

B2

B1

IN DORDER TO CAUSE THE ROTOR OF AN AC MOTOR TO ROTATE, A ROTATING MAGNETIC

FIELD MUST BE PRODUCED IN THE STATOR.

LOOPS OF WIRE PLACED IN SLOTS IN THE MOTOR HOUSING CONSTITUTE THE STATORWINDINGS.

IN A THREE PHASE STATOR, THE PHASE WINDINGS A, B, AND C, ARE PLACED 120 APART.

IN THIS EXAMPLE, THERE ARE TWO SETS OF PHASE WINDINGS.

THE NUMBER OF POLES IS DETERMINED BY HOW MANY

TIMES A PHASE WINDING APPEARS, SO THE MOTOR

ILLUSTRATED HAS A TWO POLE STATOR.

WHEN AC VOLTAGE IS APPLIED TO THE STATOR, CURRENT

FLOWS THROUGH ITS WINDINGS.

THE POLARITY OF THE MAGNETIC FIELD DEVELOPED IN AWINDING DEPENDS ON THE DIRECTION OF CURRENT FLOW.

THE STRENGTH OF THE FIELD DEPENDS ON THE AMOUNT OF

CURRENT.

IN AN AC STATOR, THIS CURRENT IS CONSTANTLY

CHANGING IN BOTH MAGNITUDE AND DIRECTION.


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THE AMOUNT OF FLUX() LINES PRODUCED BY

THE MAGNETIC FIELD IS PROPORTIONAL TO THE

VOLTAGE (E) AND INVERSELY PROPORTIONAL TO

THE FREQUENCY (F).

= E/F

IN THIS FIGURE THERE IS NO CURENT FLOW IN

THE PHASE-A. PHASE-B HAS CURRENT FLOW IN

THE NEGATIVE DIRECTION, AND PHASE-C HAS

CURRENT FLOW IN THE PSITIVE DIRECTION.

IN PREVIOUS FIGURE- , B1 AND C2 ARE SOUTH

POLES, AND B2 AND C1 ARE NORTH POLES.

MAGNETIC FLUX LINES LEAVE THE B2 NORTH

POLE AND ENTER THE NEAREST SOUTH POLE

C2.

MAGNETIC FLUX LINES ALSO LEAVE THE C1

NORTH POLE AND ENTER THE NEAREST SOUTH

POLE B1.

A1

C2B2

B1C1

A2

ZERO CURRENT FLOW

NEGATIVE CURRENT FLOW

POSITIVE CURRENT FLOW

MAGNETIC LINES OF FLUX

RESULTANT MAGNETIC FIELD

C

A

B

START


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A1

C2

SN

B2

C1

N

B1S

A2

0 60 120 180 240 300 360

IF THE FIELD IS EVALUATED AT 60 INTERVALS, AT POINT 1 WE CAN SEE THAT THE THE FIELD

HAS ROTATED 60 DEGREES.

PHASE C HAS ZERO CURRENT FLOW,PHASE A HAS POSITIVE CURRENT FLOW.

PHASE B HAS NEGATIVE CURRENT FLOW.

NOW A1 AND B2 ARE NORTH POLES; A2 AND B1 ARE SOUTH.

AT THE END OF SIX SUCH INTERVALS THE FIELD WILL HAVE ROTATED ONE REVOLUTION, OR

360.

C

A

B


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The stator windings of an AC induction motor are distributed around

the stator to produce a roughly sinusoidal distribution. When threephase ac voltages are applied to the stator windings, a rotatingmagnetic field is produced.

The rotor of an induction motor also consists of windings or moreoften a copper squirrel cage imbedded within iron laminates. Only

the iron laminates are shown. An electric current is induced in therotor bars which also produce a magnetic field.

The rotating magnetic field of the stator drags the rotor around. Therotor does not quite keep up with the the rotating magnetic field ofthe stator. It falls behind or slips as the field rotates.

In this animation, for every time the magnetic field rotates, the rotoronly makes three fourths of a turn. If you follow one of the brightgreen or red rotor teeth with the mouse, you will notice it changecolor as it falls behind the rotating field. The slip has been greatlyexaggerated to enable visualization of this concept. A real inductionmotor only slips a few percent.


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M

OPB

CPB

G

R

RC5

FC5

FCC

RCC

RC4

FC4

OLSOTS

CTS CLS

ESPB

FC1

RC1

RC2

RC3FC2

FC3

R N Y B

F1 F2 F3 F4


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Push button

Indication lamp

NO contact

NC contact

Coil or Contactor

M Motor

Fuse


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M

OPB

CPB

G

R

RC5

FC5

FCC

RCC

RC4

FC4

OLSOTS

CTS CLS

ESPB

FC1

RC1

RC2

RC3FC2

FC3

R N Y B

F1 F2 F3 F4


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