StartYwinding

(b) General arrangement

shift

b

.. _..

lr

(c) Phasor diagram Low starting and running torques

Figure 1.23 Since there is only one winding and the poles are already shaded at one particular end, the direction of the rotating flux is fixed and so is the direction of rotation of the rotor. The direction of rotation cannot be altered as in the earlier cases. Since there is only one winding and no need of a speed-operated centrifugal switch, these motors require almost no operational maintenance.

5 Universal motors

These are series motors and are relatively compact and lightweight compared to an a.c. motor. The use of such motors is therefore common for hand tools and home appliances and also for such applications that require a high speed (above 3200 r.p.m) which is not possible in an a.c. machine. Likely applications are polishers, grinders and mixers. This motor runs equally well on both a.c. and d.c. sources of supply.

t

3 P

COT,

Tsi

I

Centrifugal switch opens here

Speed Nr ---+ 7 5 8 5 % N, (d) Speed-torque characteristics of a split phase motor

(e) Split phase 1-4 motor [Courtesy: AUE (GE Motors)]

Split-phase winding

The motor is designed conventionally, with a laminated stator, a static magnetic field and a rotating armature, as shown in Figure 1.27(a) and (b). The armature and the field windings are connected in series through two brushes, fitted on the armature extended commutator assembly, to obtain the same direction of field and armature currents. Thus, when the direction of the line current reverses, the field and armature currents also reverse. When operated on a.c., the torque produced is in pulses, one pulse in each half cycle as illustrated in Figure 1.27(c). The normal characteristics for such motors are also illustrated in Figure 1.27(d).

The no-load speed may be designed very high, to the order of 2000-20 000 r.p.m. but the speed on load may be around 50-80% of the no-load speed due to windage and friction losses, which constitute a higher percentage for such small to very small motors (l/lo to 1 h.p.). The required output speed for the type of application can be obtained through the use of gears.

Main I, I m winding

- - -

Start hinding (a) Schematic diagram

Disconnect switch

ImiL

!

-

r I,

-

Y

Start winding (b) General arrangement

(c) Phasor diagram High start but low running torques

Centrifugal switch

E T -

e

1

0

Nr

Centrifugal switch

E T -

e

1

0

Nr

@ Capacitor start and run windings

@ Run winding

@ Capacitor start and capacitor run windings (d) Speed-torque characteristics of capacitor start and

capacitor run motors

(e) Capacitor start or capacitor start-capacitor run 1-0 motor

Figure 1.24 Capacitor start winding

Theory, performance and constructional features of induction motors 1/31

r

-

^VW-S)

- 7 - y

Vr(1-d

- 7

- -

_L

L1 C

I I

-

w

(ai) Schematic diagram

Main

Start winding Cz = 5 to 6 times Cl (a2) Schematic diagram

vr(l-$) winding

Start winding

-

Start winding

General arrangement (bl) Low start but high running torques

Cl = Run capacitor C, = Start capacitor General arrangement (b2) High start and high running torques Figure 1.25 Capacitor start and capacitor run windings

Shading coil (copper ring) Laminated stator core Squirrel cage rotor 7

Shading coil (copper ring) Figure 1.26(a) General arrangement of a shaded pole motor

Figure 1.26(b) Shaded pole 1-g motor [(Courtesy: AUE (GE Motors)]

1/32 Industrial Power Engineering and Applications Handbook Rotating

Static armature series field

0 m

.

* Vr(a.c. or d.c.) (a) Schematic diagram

I I

1/

No-load ,feed

0 Tr

Torque (T)

-

T,, I, and N, are the rated values (d) Characteristics of a universal motor

Positive half cycle'

I I i

Negative half cycle

*

ax. 1-@

or d.c.

(b) Theory of operation

'-G

^{I I} _I

Time

-

Negative half cycle

(c) Pulsating torque on 1-0 a.c. supply Figure 1.27 Theory of operation of a universal motor

Theory, performance and constructional features of induction motors 1/33 Relevant Standards

IEC Title IS BS I S 0

60034-1/1996 60034-5/199 1

6OO34-6/199 1 60034-711 992

60034- 12/1980

60038/1994 60072- 1 / I 99 1

60072-2/1990

60072-3/1994 60529/1989 60617-1 to 13 -

-

Rotating electrical machines Rating and performance Rotating electrical machines.

Classification of degrees of protection provided by enclosures for rotating machinery

Rotating electrical machines. Methods of cooling (IC Code)

Rotating electrical machines. Classification of types of constructions and mounting arrangements

Rotating electrical machines. Starting performance of single-speed three-phase cage induction motors for voltages up to and including 660 V

IEC Standard voltages

Dimensions and output series for rotating electrical machines. Frame number 56 to 400 and Flange number 55 to 1080

Dimensions and output series for rotating electrical machines. Frame number 355 to 1000 and flange number 1 180 to 2360. Dimensions and output series for rotating electrical machines

Small built-in motors. Flange number BF I O to BF SO

Specification for degrees of protection provided by enclosures (IP Code) Graphical symbols for diagrams Preferred numbers

Dimensions of motors for general use

4122/1992 325/1996 4691/1985

6362/1995 225311974

8789/1996

123 VI991

123 1/1991

996/ 199 I 469111985 12032 107611985 8223/1976

BS EN 60034- 1/1995

BS 4999- 105/ I988

BS EN 60034 6/ 1 994 BS EN 60034.

7/1993 BS EN 60034- 12/1996

BS 5000-1O/1989 -

BS 4999- 14 1 / I 987

BS 5000-10/1989 -

BS 4999-103/1987

BS 5000-11/1989 BS EN 60529/1992 BSEN 606 17-2 to 13

BS 2045/1982 3,17,497

BS 2048-VI989 Related US Standards ANSJINEMA and IEEE

NEMAlMG 111 993 NEMAlMG 211989 NEMNMG 10/1994 NEMA/MG 11/1992 NEMA/MG l3/1990 ANSI C 84.111995

Motors and generators ratings, construction, testing and performance

Safety Standards (enclosures) for construction and guide for selection, installation and use of rotating machines Energy management guide for selection and use of three-phase motors

Energy management guide for selection and use of single phase motors Frame assignments for a x . integral horsepower induction motors Electric power systems and equipment - voltage ratings (60 Hz)

Notes

1 In the tables of relevant Standards in this book while the latest editions of the standards are provided, it is possible that revised editions have become available. With the advances of technology and/or its application, the updating of standards is a continuous process by different standards organizations. It is therefore advisable that for more authentic references, readers should consult the relevant organizations for the latest version of a standard.

2 Some of the BS or IS standards mentioned against IEC may not be identical.

3 The year noted against each standard may also refer to the year of its last amendment and not necessarily the year of publication.

Abbreviations ANSI

BS British Standards - UK IEC

IEEE

IS Indian Standards - India IS0

NEMA

American National Standards Institute - USA

International Electro Technical Commission - SwitLerland The Institute of Electrical and Electronics Engineers - USA International Standards Organisation - Switzerland National Electrical Manufacturers’ Association - USA

1/34 Industrial Power Engineering and Applications Handbook

List of formulae used

_{for S high, I , =}

_-

5s e2

E< x2

(1.7a)

(1.8) Theory of operation

Motor output and torque T = (Pm . [rr

$ = $,,, sin ^(ut T = torque developed

&,,

= maximum field strength I, = rotor current

(1.1)

P, = rotor power

(1.8a)

(1.9) P , = synchronous power

T . N p = -

974

P , - P, =

s .

^P,

P , - P, = slip loss P = rotor power in kW

T = torque in mkg N = speed in r.p.m.

(1.3) (1.10)

S = slip

R2 = rotor resistance per phase

,,X2 = standstill rotor reactance per phase and ,,e2 = standstill rotor induced e.m.f. per phase.

System harmonics

(1.3a) (1.1 1)

n

HVF = harmonic voltage factor V, = per unit harmonic voltages

n = harmonic order not divisible by 3 Tst = starting torque

(1.3b)

(a) Eddy current loss Le = t : . f 2 . B 2 I p

tl = thickness of steel laminations B = flux density

p = resistivity of the steel laminations T, = rated torque

e 2 = - z I . - dt) dt

(1.12) (1.4)

zr = number of turns in the rotor circuit per phase and d@dt = rate of cutting of rotor flux

e2 = 4.44 Kw

.

^{@,,, .} zr

.

,f, (1.5) Kw = winding factor

f, = rotor frequency = S . f

(b) Hysteresis loss

L h = f

.

( B m ) ' 3 ^to 2 (1.13)

N, = synchronous speed

N , = rated speed

Further reading

1 2 0 . f

N , =

-

r.p.m.

P (1.6a) ^{1 Golding, E.W.,} Electrical measurements and measuring

Instruments, The English Language Book Society and Sir Isaac Pitman & Sons Ltd, London.

Humphries, J.T., Motor and Controls for l - $ motors. Merrill, Columbus, OH.

Puchstein, A.F., Lloyd, T.C. and Conard, A.G., Alternating Current Machines, Asia Publishing House, Bombay (1959).

Say, M.G., The Perjkrmancr und Design ofAlternating Current Machines, Pitman & Sons Ltd, London (1958).

Smeaton, R.W., MotorApplication and Maintenance Hand Book, McGraw Hill, New York (1969).

2 3

4 5

f = frequency of the supply system in Hz p = number of poles in the stator winding Rotor current

(1.7)