Index

A

Accelerated commutation, 282–84

AC machines, EMF generated in, 242

Air blast cooling

for high-capacity transformers, 50

and oil-immersed self-cooled transformer, 49

Air gap, 230

All-day efficiency of transformer, 89

Alternator

equivalent circuit, 433

excitation circle, 476–77

infinite bus, 482

input power equation, 458–59

reactive power input, 459

real power input, 459

load characteristics, 454–55

load distribution, 488–89

losses and efficiency, 468–69

output power equation

maximum power output, 457

power output equation, 457–58

reactive power output, 457

real power output, 456–57

parallel operation

conditions, 483–84

identical frequency requirement, 484

identical phase sequence, 484

identical voltage requirement, 484

in-phase requirement, 484–85

prime mover torque speed, 484

reasons, 483

phasor diagram

lagging power factor, 434

leading power factor, 435

unity power factor, 435

powers sharing, 478–82

prime mover characteristic, 477–78

voltage equation, 434

voltage regulation determination, 337, 447–53

Ampere-turn method, 443–47

ASA method, 453–54

direct loading, 438

emf/synchronous impedance method, 438–43

Alternator at lagging power factor, 450

Ampere-turns (AT), 9

Armature core, 188–89

Armature mmf wave, 470

Armature reaction

in DC machines, 270–74

unity power factor load, 431–32

zero lagging and leading, 432

Armature resistance measurement, 440–41

Armature torque of motor, 339–40

Armature windings, 189, 219–21

leakage reactance, 431

resistance, 430–31

Automatic starters, 360

back emf, 361–62

series current-limit, 363–64

shunt current-limit, 362–63

time element, 361

Autotransformers

advantages of, 100–101

applications, 101

construction, 97–99

conversions, 100

copper saving, 99–100

disadvantages of, 100–101

B

Booster transformer, 111–12

Brake test of DC motor, 372–73

Breather, 51

Bright lamp method, 485, 486

Brushes

and bearings, 190

drop, 262

shift on terminal voltage, 300

Brushless DC motor

bipolar/full-wave, 396

bipolar or full-wave, 396

features, 396–97

features of, 396–97

unipolar/half-wave, 394–96

Buchholz relay, 52

Bushings, 47

C

Capability curves, 470–74

Circle diagram of polyphase induction motors

approximate equivalent circuit, 618

exciting current, 618

maximum quantities, 620–21

no-load test, 619

short-circuit current, 620

short-circuit test, 619

stator current phasor, 617

stator-resistance test, 619

Circuit connection and open-circuit characteristic, 439, 440

Co-energy of system, 26–27

Coil arrangement and waveform of mmf, 270, 271

Commutation, 277–79

accelerated, 282–84

improving methods

emf commutation, 286–87

resistance commutation, 285–86

linear, 279–81

retarded, 281–82

sinusoidal, 284

Commutator, 189

Compensating winding, 277

Complex power, 12–13

Compound generator, 301–3

parallel operation, 308–10

Compound motors, 343–44

characteristics of, 346

Compound-wound generator, 261

Concentric windings, 45

Conductors

current in, 1

force, in magnetic field, 2–3

magnetic flux, 1–2

Conservator, 51

Construction of DC machines, 186

armature core, 188–89

armature windings, 189

brushes and bearings, 190

commutator, 189–90

essential parts of, 190

magnetic frame/yoke, 187

pole coils, 188

pole cores and pole shoes, 187–88

Continuous disc windings, 46

Continuously variable reactor, 106

Cooling of transformer, 49–50

Copper loss, 266

Copper saving in autotransformer, 99–100

Core-type laminations, 41–43

Corkscrew rule, 1–2

Coupling angle, 530

Coupling field energy, 23–24

Crawling, 630

Cross-field generators, 391–94

Cross-magnetizing Ampere-turns per pole, 275–76

Cross-over windings, 46

Current-carrying conductors

force between, 2

isolated, flux distribution of, 2

Current transformer, 107

Cylindrical rotating machine, 32–33

cases, 33–37

magnetic actuator, 36

pulsating torque, 34

synchronous motor/machine, 33

Cylindrical rotor, capability curve, 473

D

Damper windings, 219, 549–50

Damping effect, 550

Dark lamp method, 485, 486

DC compound motor, characteristics, 346

DC generators, 207–8

abnormal sound, causes, 312

armature, heating causes, 312

armature reaction, 270–74

characteristics, 287

classification, 261–62

condition for maximum efficiency, 268–70

efficiency, 267–68

emf generated in, 246

excessive heating, causes, 311

external and internal characteristic

with armature reaction, 299

neglecting armature reaction, 298–99

internal/total characteristic, 297–98

overload, indications and causes, 310–11

parallel operations, 303–4

power stages, 267

rapid brush, reasons, 312

sparking at brushes, 311

two-segment commutator, 209–13

types, 261

uses, 310

voltage regulation, 297

DC machines construction, 186

DC motors

armature torque, 339–40

automatic starters, 360

back emf, 361–62

series current-limit, 363

shunt current-limit, 362–63

time element, 361

back emf, 338

brake test, 372–73

compound motor, 343

Field’s test, 386–88

Hopkinson’s test, 377–80

manual starter

four-point starter, 359–60

three-point starter, 358–59

maximum mechanical power, 339

principle, 213–14

retardation/running test, 383–86

rotational losses, 341–43

separation of losses, 380–83

series motor characteristics, 345–46

shunt/separately excited, characteristics, 345

speed control

armature resistance, 347–50

field resistance, 350–55

speed regulation, 347

speed with back emf and flux, 344–45

starter, 357

Swinburne’s test, 373–75

generating mode, 375–76

motoring mode, 375

torque and speed, 347

uses, 388–89

voltage equation, 337–38

ward-leonard control/voltage control, 355–57

DC series motor, 345–46

DC shunt motor starter design, 364–66

DC windings types

simple lap, 196–200

wave, 200–205

Deep-cage rotors, 631

Delta connections, 16

currents and power, 18–20

phasor diagram, 19

voltages, 18–20

Delta–delta connection, 158–59

Delta–star connection, 160–61

Delta–zig-zag star connection, 161–62

Diametrical connection, 171–72

Direct testing of polyphase induction motors

autotransformer, 616

drum radius, 616

efficiency, 616

input voltage, 616

operating slip, 616

output power, 616

performance characteristics, 617

Disc coils, 47

Distribution factor, 238–39

Double-cage rotors, 631–32

Double-delta connection, 171

Double-layer spiral coil, 46

Double-layer winding, 223

Double-star connection, 171

Doubly excited systems, 31–32

Drooping, 477

Drum windings, 192–94

armature conductors, 195

coil sides per layer, 194

coil span, 194–95

commutator pitch, 195

winding pitch, 195, 196

Dry-type transformer, 49

Dummy coils, 207

Dynamically induced emf, 5–6

Dynamometer, cross-field machines, 390–91

E

Eddy current loss, 266

Efficiency of transformer, 85

all-day, 89

maximum, conditions for, 86

kVA supplied, 87–88

load current, 87

Electrical and mechanical degrees, 234–36

Electrical energy input, 27–28

Electrical faults, 498

Electric braking, 366

of polyphase induction motors

dynamic braking, 644–45

plugging/counter-current braking, 643–44

regenerative braking, 643

of series motors, 368–69

of shunt motors, 367–68

Electromagnetic torque, 184–85

Electromagnetism, 1

mechanical forces in system, 28–30

Electromechanical energy conversion system, 24

Emf commutation, 286–87

Emf equation

long-shunt compound generator, 263

series generator, 263

short-shunt compound generator, 263–64

shunt generator, 262

Emf generated in AC machines, 242–43

Emf generated in DC generator, 246

Energy

conversion principle, 22–23

in coupling field, 23–24

Equalizer rings, 287–88

Equalizing connections for lap winding, 205–7

Equivalent circuit of polyphase induction motors

rotor, 596–99

stator, 596

F

Faraday’s first and second laws, 4–5

Field energy, 24–26

Field flux and flux distribution, 270, 271

Field’s test, 386–87

Fleming’s left-hand rule, 3

Fleming’s right-hand rule, 6

Flux density, 8

Flux per pole, 240–41

Four-point starters, 359–60

Fractional slot winding, 224–27

Full-pitched coil, generated emf in, 241–42

G

Generated emf in full-pitched coil, 241–42

Generator phasor diagram, 472

Generators protection, 497–99

H

Helical windings, 46

Hopkinson’s test (back-to-back test), 377–79

Hunting

causes, 492

effects, 492–93

reduction, 493

Hydrogenerators, 218

Hysteresis loss, 266

I

Incoming machine and bus, voltage diagrams, 487

Induced EMF, 5

and current, 3–4

Induction generator

advantages and applications of, 642

circle diagram of, 641–42

disadvantages of, 642

excitation current and rotor current, 641

rotor emf, 641

Induction machines, 243–44

Induction motors

electrical braking of polyphase

dynamic braking, 644–45

plugging/counter-current braking, 643–44

factors governing performance

air-gap length, 634

rotor resistance, 634

slots and teeth shapes of, 634

operating conditions effects

break in one phase effects, 634

line frequency and line voltage, variation, 634

loading, 634

unbalanced supply voltage, 634

Infinite bus, 482

Inherent voltage regulation of transformer, 78

In-phase and out-of-phase condition, 484, 485

Inrush phenomenon, 112–13

Integral slot winding, 223–24

Isolated current carrying conductors, 2

K

Kapp’s regulation, 84

L

Laminations amalgamation, 40

Lap winding, 196–200

equalizing connections, 205–7

uses, 207

Lenz’s law, 5

Linear commutation, 279–81

Linear induction motor

applications of, 641

disadvantages of, 641

induced currents, 639

short-single primary, 639

slip, 640

synchronous speed, 640

thrust-speed characteristics, 640

Linear systems

magnetic force estimation, 30

Load angle, 530

Loaded and unsaturated DC machines, 273–74

Load sharing by transformers

equal voltage ratios, 92–94

unequal voltage ratios, 95–96

Long-shunt compound generator, 263

Losses in DC generator, 266

constant/standing, 267

copper, 266

core loss, 266

iron loss, 266

magnetic loss, 266

mechanical, 266

stray, 266

Losses in transformer, 84

copper loss, 85

core/iron loss, 85

M

Magnetic circuit, 7

Magnetic field intensity, 8

Magnetic flux, 8–9

Corkscrew rule, 1–2

right-hand rule, 1

Magnetic force, in linear systems, 30

Magnetic frame or yoke, 187

Magnetic locking (cogging), 630–31

Magnetomotive force, 7

Magnet withdrawn, 4

Manual starters

four-point, 359–60

three-point, 358–59

Maximum torque of polyphase induction motors

condition, 583–84

rotor resistance effect, efficiency, 589

Maximum voltage regulation, 79

Mechanical faults, 498–99

Mechanical forces, in electromagnetic system, 28

cases, 29–30

Mechanical losses, 266

Moving coil reactor, 105

Moving shunt reactor, 106

N

Negligible armature resistance, output power, 540

No-load curve for self-excited generators, 290–93

No-load release-type series motor starter, 364

O

Off-load tap changing transformers, 108

Oil-immersed forced air-cooled transformers, 50

Oil-immersed forced oil-cooled transformers, 50

Oil-immersed self-cooled transformers, 49–50

Oil-immersed water-cooled transformers, 50

On-load tap

changer with single primary, 109–10

changing transformers, 109

Open-delta connection, 163–65

Operating conditions effects of induction motor

break in one phase effects, 634

line frequency and line voltage, variation, 634

loading, 634

unbalanced supply voltage, 634

Output power equation of alternator

maximum power output, 457

reactive power output, 457

real power output, 456–57

Overloaded generators indications, 310

causes, 311–12

P

Parallel operation of alternator

conditions, 483–84

identical frequency requirement, 484

identical phase sequence, 484

identical voltage requirement, 484

in-phase requirement, 484, 485

prime mover torque speed, 484

reasons, 483

Parallel operation of single-phase transformer, 92

Performance and circle diagram of synchronous motor

constant excitation, 543–44

constant power developed, 541–43

constant power input, 541

Permeability, 9

Phasor diagram of alternator

lagging power factor, 434

leading power factor, 435

unity power factor, 435

Phasor diagram of mmf, 453

Phasor diagram, synchronous motor

equivalent circuit model, 528

lagging power factor load, 528–29

leading power factor load, 529

loading effect, 528

unity power factor load, 529–31

Pigtail brush, 190

Pitch factor, 236–37

Plugging/reverse current braking, 368

Polarity test of single-phase transformer, 90

Pole

coils, 188

cores and shoes, 187–88

Polyphase induction machines

air gap, 230

squirrel-cage rotor, 228–29

wound rotor, 229–30

Polyphase induction motors

applications, 633

blocked-rotor/short-circuit test, 614–15

circle diagram

approximate equivalent circuit, 618

exciting current, 618

maximum quantities, 620–21

no-load test, 619

short-circuit current, 620

short-circuit test, 619

stator current phasor, 617

stator-resistance test, 619

direct testing

autotransformer, 616

drum radius, 616

efficiency, 616

input voltage, 616

operating slip, 616

output power, 616

performance characteristics, 617

efficiency, 592

electrical braking of, 643–45

equivalent circuit

rotor, 596–99

stator, 596

factors governing performance of, 634

full-load and maximum torque, 586–87

losses, 591–92

maximum torque

condition, 583–84

rotor resistance effect, efficiency, 589

no-load test/open-circuit test, 613–14

operating conditions effects, 634

power factor

rotor resistance and reactance, effect, 589–90

power stages, 592

ratings of, 634–35

rotor current

electromagnetic force (emf), 577

rotor power

air gap power, 579

mechanical power, 580

phase power input, 579

stator input, 580

rotor resistance and reactance, effect, 590

slip measurement

electromechanical counter, 594

mechanical differential counter, 594–95

stroboscopic method, 595–96

starting load torque and maximum torque, 587

starting of, 604–605

starting torque

change in supply voltage, effect, 582

condition, 588

slip-ring motor, 582

squirrel-cage motor, 582

synchronous watt, 594

Thevenin’s equivalent circuit of, 600–603

torque and slip

change in supply frequency on, 591

change in supply voltage on, 583, 591

characteristics, 584–86

torque expression, 581–82

Potential transformer, 107

Potier method, 447–53

Potier triangle, 448–51

Power angle, 530

Power factor of polyphase induction motors

rotor resistance and reactance, effect, 589–90

Power triangle, 12

Preventive autotransformer, 110–11

Pull-out torque, 544

Pulse transformer, 102

response characteristics, 103–104

usage of, 104

R

R–C series circuit, 10

Reactance voltage, 284–85

Regenerative braking, 369

Reluctance, 9

torque, 185

Resistance commutation, 285–86

Retardation/running test, 383–85

Retarded commutation, 281–82

Rheostatic/dynamic braking, 367–68

Right-hand rule, 1

Ring windings, 190–92

Rotating electrical machines

classification, 184

constructional features, 185–86

electromagnetic torque, 184–85

reluctance torque, 185

Rotating magnetic field concept, 246–49

Rotational losses of DC machines, 341

Rotatory electromagnetic system, 31

Rotor

currents, 31–32

faults, 498

frequency, 233–34

of polyphase induction motors, emf, 577

salient pole-type, 216–17

smooth cylindrical, 217

speed of MMF, 234

Rotor power of polyphase induction motors

air gap power, 579

mechanical power, 580

phase power input, 579

stator input, 580

Rotor side speed control of induction motor

cascade connection, 624–26

injecting voltage in rotor circuit, 627

rotor rheostat control., 623–24

Running torque, 544

S

Salient-pole alternator

losses and efficiency, 468–70

maximum reactive power, 468

torque-angle characteristic, 464–67

two-reaction theory, 460–64

Salient-pole synchronous motor, 544

lagging power factor, 545

leading power factor, 546

power developed, 547–48

stability and maximum load angle, 548–49

unity power factor, 546–47

Salient pole-type rotor, 216–17

Sandwich windings, 47

Saturable reactor, 106

Schrage motor, 636

advantages of, 639

block diagram of, 637

phasor diagram, 638

power factor compensation, 639

two-pole DC generator, 638

Scott connection, 165–67

Self-excited generator, 261

no-load curve, 290–91

Separately excited DC motor, 345

Separately excited generators, 261

advantages and disadvantages, 294

internal and external characteristic, 290

no-load saturation characteristic, 289

Separation of losses in DC machine, 380–83

Series generator, 263

circuit diagram, 301

parallel operation, 307

Series motor, electric braking

plugging/reverse current, 368

regenerative, 369–72

rheostatic, 368

Series R–L–C circuit, 11

Series R-L circuit, 9–10

Series-wound generator, 261

Shell-type transformers, 41–44

Short-circuit ratio, 495–97

Short-circuit test, 67–68

Short-shunt compound generator, 263–64

Shunt generator, 262

conditions for, 295

failure reasons, 295

internal and external characteristic, 295–97

parallel operation, 304–6

voltage build-up, 294

Shunt motors

characteristics, 345

electric braking

plugging/reverse, 367–68

regenerative, 368

rheostatic/dynamic, 367

Shunt-wound generator, 261

Simple DC generator and two-segment commutator, 209–12

Single-layer windings, 221–23

Single-phase circuits

series L-C-R circuit, 11

series R–C circuit, 10

series R–L–C circuit, 11

series R-L circuit, 9–10

Single-phase transformer, 39–41

core-type transformer, 41–43

parallel operation of, 92

polarity test of, 90

shell type, 43–44

spiral core type, 44

Single-turn generator, 208

Singly excited machine, 229

Sinusoidal commutation, 284

Six-phase star connection, 171

Slip in induction motor, 232–33

Slip measurement of polyphase induction motors

electromechanical counter, 594

mechanical differential counter, 594–95

stroboscopic method, 595–96

Slip-ring induction motors

starting of

approximate ratio, 612

full-load current, 611

resistance steps for three-phase, 610

stud, 611

Slip ring rotor, 229–30

Slip test connection diagram, 470

Smooth cylindrical type rotor, 217

Speed control of DC motors

armature resistance control, 347–49

field resistance control, 350–51

Speed control of induction motor

rotor side, 623–27

stator side, 627–29

Speed of rotor mmf, 234

Speed regulation, 347

Speed–time curve, 384

Spiral core-type transformer, 44

Spiral windings, 45

Squirrel-cage motors

autotransformer, 607–608

direct-on-line, 605–606

star-delta, 608

stator resistor, 606–607

Squirrel-cage rotor, 228–29

Standing losses, 267

Star connections

currents and power, 16–18

domestic and industrial load, 20

phasor diagram, 17

voltages, currents and power, 16–18

Star–delta connection, 159–60

Star–star connection, 156–58

Starter principle, 357

Starters for DC series motors, 364

Starting/breakaway torque, 544

Starting torque of polyphase induction motors

change in supply voltage, effect, 582

condition, 588

slip-ring motor, 582

squirrel-cage motor, 582

Statically induced emf, 6–7

Stator, 215–16

faults, 498

Stator side speed control of induction motor

changing number of poles, 627–29

changing supply frequency, 627

Steam supply, effect of change, 489

Step-up and step-down transformer, 39, 56

Stray losses, 266

Sumpner’s test, 91

Swinburne’s test, 373–75

generating mode, 375–76

motoring mode, 375

Synchronizing power

coefficient units, 492

and synchronizing torque coefficient, 489–91

Synchronizing procedures, alternator

frequency synchronization, 488

in-phase determination, 486–88

phase sequence matching, 485–86

synchroscope synchronization, 488

voltage matching, 485

Synchronous condensers, 554–55

Synchronous generators, 244–46

armature reaction

unity power factor load, 431–32

zero lagging power factor load, 432

zero leading power factor load, 432

armature winding, parameters of

leakage reactance, 431

resistance, 430–31

capability curves, 471–76

determination of, 470–71

reactance and impedance, 433

short-circuit ratio, 495–97

sudden short circuit, 494–95

Synchronous-induction motor, 633

DC Excitation to rotor winding, 645, 646

slip-ring induction, 645

starting characteristics, 646

Synchronous machines

armature windings, 219–20, 243

double-layer winding, 223

fractional slot winding, 224–27

integral slot winding, 223–24

single-layer, 221–23

classification, based on prime mover

hydrogenerators, 218

turbogenerators, 218

construction of, 214–15

rotor, 216–18

stator, 215–16

damper windings, 219

excitation system, 218–19

field winding, 243

frequency and synchronous speed, 219

Synchronous machines oscillations, 493–94

Synchronous motors, 33

applications of, 553–54

armature reaction, 527

classification, 218

complex power input, 535–37

complex power output, 538

conductor current, 526

constant excitation, 543–44

constant load operation, 532–34

constant power developed, current locus, 541–43

current locus, constant power input, 541

curves, 535–36

hunting/surging, 550–51

input reactive power at negligible armature resistance, 540–41

leading current, demagnetizing effect, 527

maximum output power, 538–40

motor characteristics, 541–44

operation principles, 526

performance and circle diagram, 541–44

periodicity of hunting, 551–52

power output at negligible armature resistance, 540

rotating magnetic field and rotor field poles, 526–27

starting methods, 553

torque, 544

Synchronous speed, in induction motor, 232

T

Tap changing transformers, 108

Tapped reactor, 105

Tapping, 48

Terminal voltage, brush shift effect, 300

Testing of DC machines, 372

Three-phase circuits, 13–15

advantages of, 15

generation of voltage, 14

interconnection of, 15

phase sequence, 15

phasor diagram, 14

power, measurement of, 21–22

waveform diagram, 14

Three-phase induction motors

common faults, 635

principle of operation, 230–32

Three-phase transformers

advantages of, 154

connection

delta–delta, 158–59

delta–star, 160–61

delta–zig-zag star, 161–63

star–delta, 159–60

star–star, 156–58

connections, 173–76

construction of, 155

core-type, 156

shell-type, 156

open-delta/V–V connection, 163–65

operation principle, 154–55

parallel operations of, 170

rating, 176

Scott connection/T–T connection, 165–67

six-phase conversion

diametrical connection, 171–72

double-delta connection, 171–72

double-star connection, 171

star connection, 171–72

two-phase conversion, 167–70

Three-point starters, 358–59

Three-winding transformer, 173

Three-wire generator, 389

Torque and slip of polyphase induction motors

change in supply frequency on, 591

change in supply voltage on, 583, 591

Torque and speed of DC series motor, 347

Torque angle/angle of retardation, 530

Transformers

air blast and oil-immersed self-cooled transformer, 49, 50

Buchholz relay, 52

bushings, 48

conservator and breather, 51–52

cooling of, 49–50

definition, 38

efficiency of, 85–86

all-day efficiency, 89–90

maximum efficiency condition, 86–89

emf equation, 54–56

equivalent circuit, 64–66

equivalent reactance, 61–62

equivalent resistance, 60–61

exact voltage drop, 73–74

leakage reactance and impedance voltage drop, 77

on load, 59

load sharing, 92–96

losses in, 84

copper loss, 85

core/iron loss, 85

magnetic leakage, 61

methods of cooling, 50

no load, 57–59

oil, 51

open circuit test/no-load test, 66–67

per unit resistance, 77

principle, 38–39

rating, 176

resistance and leakage reactance, 63–64

separation of core/iron losses, 70–72

short circuit/impedance test, 67–69

step-up and step-down transformer, 56–57

Sumpner’s test, 91

tank, 52

tapping, 48

terminals and leads, 48

theory of, 53

total approximate voltage drop, 72–73

types of, 39

unequal voltage ratios, 95–96

voltage regulation

calculation for, 78–84

inherent voltage regulation, 78

Kapp’s regulation, 84

voltage regulation down, 78

voltage regulation up, 78

Turbo alternators, 217

Turbogenerators, 218

Two bright and one dark lamp method, 486, 487

Two current-carrying conductors, 2

Two-reaction theory, 460

Two-wattmeter connection, 21

Two-winding transformer, 41

V

Variable excitation, 532–34

V curves experimental set-up, 536

Voltage regulation determination

Ampere-turn method, 443–47

AS A method, 453–54

direct loading, 438

direct load testing circuit diagram, 438

synchronous impedance method, 438–42

zero power factor method/Potier method, 447–53

Voltage regulation down/up, 78

W

Ward-Leonard control, 355

Wave winding, 200–203

uses, 207

Welding transformers, 104

reactors, 105–6

Windings, 44–45

concentric, 45

continuous disc, 46–47

cross-over, 46

factor, 240

helical, 46

sandwich, 46–47

spiral, 45–46

Wound-rotor, 229–30

and cage-rotor induction motors, 629

Wound-rotor induction motor, 229

Z

Zero power factor method, 447–53

Zero voltage regulation, 79