LICE - Engineers Institute

JTO LICE ELECTRICAL INSTALLATION & MAINTENANCE

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LICE - JTO

Limited Internal Competitive Examination

SAMPLE STUDY MATERIAL

ELECTRICAL INSTALLATION & MAINTENANCE



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L.I.C.E. JTO

All types of motor and generators-AC & DC transformers, starters is a part of Electrical Machine i.e.

added into separate booklet (Electrical Machine)

Syllabus:

Single-Phase supply vs. 3 Phase supply, Star Delta connections, relation between phase &line voltage

power factor, rectifiers, inverters, batteries. Installation, commissioning, earthing, insulation testing and

maintenance, preventive maintenance, electrical accidents and safety measures, switchgear, sub-stations,

maintenance of relays and circuit breakers. A.C. Circuits, Circuit Theorems, Four Terminal Passive

Networks, Coupled circuits and their analysis, Passive filters, Lightening protection, power electronics

application in control of drivers, Refrigeration & air-conditioning.



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C O N T E N T

1. PHASE CONTROLLED CONVERTERS ………………………. 05-28

2. INVERTERS …………………………………………………………. 29-62

3. NETWORK LAWS AND THEOREMS ………………………… 63-84

4. COUPLED CIRCUIT AND AC CIRCUIT ……………………. 85-98

5. TWO PORT NETWORK OR FOUR TERMINALNETWORK ………………………………………………………….. 99-148

6. CIRCUIT BREAKER & POWER SYSTEMPROTECTION …………………………………………………….. 149-189

7. REFRIGERATION AND AIR CONDITIONING……………. 190-235



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1. PHASE CONTROLLED CONVERTERS

Phase controlled converter are used to convert fixed ac input to variable ac output converter has

application in dc machines drives HVDC system.

Type of Controlled Rectifiers:

1. Single Phase Controlled Converters

(a) Single phase half wave controlled rectifier

(b) Single phase full wave centre top converter.

(c) Single phase full wave bridge the semi-controlled converter

(d) Single phase full wave bridge type fully controlled converter.

2. Three Phase Converters

(a) Three phase half wave converter

(b) Three phase semi controlled bridge type converter.

(c) Three phase full controlled bridge type converter.

3. Dual Converters

(a) Single phase dual converter

(b) Three phase dual converter.

Some Important Parameter (Performance)

(a) Efficiency ac

ac

P (output power)

P (input power)

(b) From factor2 2

rms rms av

avg. avg.

V V V. .

V Vo

o

f f

(c) Ripple factor ripple rms

avg.

VR .

Vo

f

2R . . 1f f f

(d) Transformer Utilization Factor (TUF)

dcPTUF

V Is s



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V , Is s are rms value supply.

dcP dc. Power available at output of converter.

(e) Displacement Factor: The cosine of phase difference fundamental supply voltage and fundamental

supply current of the converter.

DF cos

= Phase difference between fundamental component of source voltage and fundamental of source

current.

( f ) Current Distortion Factor: Ratio of rms fundamental current to total rms supply current.

1I

CDSIs

s

(g) Total Distortion Factor:

THD =Total Harmonic current on source side

Fundamental current on source side

THD = 1

1

2 2I I

I

s s

s

THD =1

2I

1I

s

s

21

THD 1CDF

CDF Current distance factor.

(h) Supply Side Power:

1P V I cos V I coss s s s

cos = Power factor on supply side

cos= Displacement factor

1I

cos cosIs

s



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1. Single Phase half Wave with Resistive Load

The thyristor commutated Naturally due to line commutation (due to line voltage).

(i) Voltage Output Voltage:

V V sin V sins m mt

Average value of a periodic output voltage waveform

T

avg

0

1V V( )

Tt dt Let 0t

Voltage across thyristor T ON TV 0 (S/C)

~

+

–

VT

VS= V sin wtm

Vo

io

+

–

V sinm t

V sinm

VT

io

V sinm

Vs

0

Firing pulses

2

t

t(4 + ) (2 + )

2

2 3 4

t

t

tc

Vo

Vm

V /Rm

ig

–Vm

t



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T OFF TV V Vs o

T is fired at firing angle

During thyristor on S/C V Vo s V

Ro

oi

During thyristor off O/C = V 0o 0oi

PIV Vm ct

2ct f

1

2ct f

Let f = 50 Hz

10 m sec.ct

Let SCR turn off time gt 12 m sec.gt

If c gt t At naturally and after word it is kept reversed biased during ct they will be

commutated if .c gt t It is called natural or line commutation.

Frequency of output1 1

T Too s

f f

Ripple frequency , 2 , 3 ........... , 2 , 3 .......o o of f f f f f

Lowest ripple frequency is f, so we designed filter at frequency. at F.

V sinV

0 elsem

o

0

1 1V V V sin

2 2o o md d

VV (1 cos )

2m

o

Total RMS Voltage

2 2V average of Vor o

22 2 2

0

1 1V V (V sin )

2 2or o md d

22 21

(V sin )2 m d



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1

2V 1V ( ) sin 2

22m

or

The value of rms current Ior is

VI

Ror

or

Power delivered to resistive load (rms load voltage) (rms load current)

22V

V I I RR

oror or or

Input power factor =V I VPower delivered to load

Input VA V I Vor or or

ss or s

1

21 1P.F ( ) sin 2

22

The circuit turn off time2

ct

Note: For proper function of converter the circuit turn off time should be more than the thyristor turn of

time.

2. 1 - half wave with R – L load



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IL

dv

dt

Stored energy 21( ) LI

2sw

if I = constantI

0d

dt and P = 0

constantsw

If I increaseI

ved

dt

IV L ve

P VI ve

d

dt

i.e., energy consumed

If I decrease

Ive

d

dt

IL ve

dv

dt

P = VI = –ve

i.e. Power delivered i.e., L release energy

~

+

–

VT

VS= V sin wtm

Vo

io

+

–

is

TR

L

V sinm t

V sinm

VT

i , is o

V sinm

V sinm

V sinm

Vs

0 2

t

t

t

tc

Vo

Vm

ig

–Vm

t

3 4



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onT V Vo s V V sino m t

L R V V sinoio o m

dit

dt

LV

A sin( )2

tm

oi e t

L V Roo

di

dt is

If Vo is high

L vedi

dt oi increase

If Vo is low

L vedi

dt is decrease

LV ve

So, if LV ve thyristor latched into conduction even after due to inductor voltage reversal,

thyristor is latched.

We can say current will decrease at finite rate.

V veo veoi

P V I veo o

For

V veo veoi

P V I veo o

Power flow from load to source

From tο stored energy of inductor partially consumed in R and partially returned to supply sV



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2

0

1 1V V V sin

2 2o o md d

VV [cos cos ]

2m

o

2c

2ct

2ct

:ct Circuit turn off time

2 2 21V V sin

2or m d

1

2V 1V ( ) [sin 2 sin 2 ]

22m

or

2. Half Wave Controlled Rectifier with RLE load with free wheeling diode

VL

T

–+ –

+

R



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T ON V Vo s

At V ves

veoo

dii

dt LV ve

FD ON and T OFF V 0o

L R E 0oo

dii

dt V 0o

E Rve

Lo o

o

di ii

dt

Vba

Vba

VT3 VT4

Io

V sinm

V sinm

Vs

t

t

t

tc

Vo

E

–Vm

t

(3 4

t–Vm

T1T2

T1T2

VT1 VT2

T3T4T3T4

T1T2 T3T4

Voltageacross T1 or T2

Source current

32(2(

is

Outputcurrent

Outputvolatge Vab

Vab

Vo0

T3T4

T1T2

T3T4

+

–

VS Vo

io

+

–

is

iT1

T1 R

L~

T3

T2T4 E



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During free wheeling mode stored energy of inductor is consumed in load itself it is not returned to

supply.

Hence power delivered to load increased and such power factor improved.

Let L (inductor so large) oi is continuous

If 2 oi discontinuous

2 oi continuous

2

0 0

1 1V V 1 cos V

2 2o o od d

VV (1 cos )

2m

o

Advantage of Free Wheeling Diode

Supply P.F. improved

Any Vo increase

oi waveform improve (closed to dc)

1- Full Wave Center Top Converter:



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Figure: Single-phase full-wave mid-point converter

Assumption: Load current is continuous mean load inductance is very large.

Circuit turn off time =2 ( )

ct

ct

V1V V sin [ cos( ) cos ]m

o m d

2VV cosm

o

2 2 21V V sinor m d

1

2V sin 2( ) sin 2V

2 4 4m

or



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ct

ct


o m d

2VV cosm

o

2 2 21V V sinor m d

1

2V sin 2( ) sin 2V

2 4 4m

or



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ct

ct


o m d

2VV cosm

o

2 2 21V V sinor m d

1

2V sin 2( ) sin 2V

2 4 4m

or

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