zxc ® 09-Oct-2012 20:13

Практика устранения неисправностей электрооборудования и цепей управления / Practical Troubleshooting of Electrical Equipment and Control Circuits

Year: 2005
Language: english
Author: Mark Brown
Genre: Troubleshooting
Publisher: Newnes
ISBN: 0 7506 6278 6
Format: PDF
Quality: OCR without errors
Number of pages: 248
Description: There is a large gap between the theory of electron flow, magnetic fields and that of troubleshooting
electrical equipment and control circuits in the plant. In this book, we try to avoid or at least minimize discussions on the theory and instead focus on showing you how to troubleshoot electrical equipment and control circuits. The book helps to increase your knowledge and skills in improving equipment productivity whilst reducing maintenance costs. Reading this book will help you identify, prevent and
fix common electrical equipment and control circuits. The focus is ‘outside the box’. The emphasis is on practical issues that go beyond typical electrical theory and focus on providing those that attend with the necessary toolbox of skills in solving electrical problems, ranging from control circuits to motors and variable speed drives.
This book focuses on the main issues of troubleshooting electrical equipment and control circuits of today to enable you to walk onto your plant or facility to troubleshoot and fix problems as quickly as possible. This is not an advanced book but one aimed at the fundamentals of troubleshooting systems.
The book is very practical in its approach to troubleshooting and the examples you will be shown are applicable to any facility.
We would hope that you will gain the following knowledge from this book:
• Diagnose electrical problems ‘right-first-time’
• Minimize the expensive trial and error troubleshooting approach
• Reduce unexpected downtime on electrical motors and other equipment
• Improve plant safety
• Learn specific techniques to troubleshoot equipment and control circuits
• Analyze equipment problems
• Determine causes of equipment failure
• Troubleshoot electrical equipment and control circuits.
Typical people who will find this book useful include:
• Plant Electricians
• Mechanical Engineers
• Production Operators and Supervisors
• Utilities Maintenance Personnel
• Plant Engineers.
A basic understanding of electrical theory and problems you have encountered in the past would be
helpful but a basic review is undertaken at the beginning of the book.

Contents

Preface................................................................................................................................. vii
1 Basic principles ......................................................................................................... 1
1.1 Introduction ................................................................................................. 1
1.2 Basic principles of electrical machines ....................................................... 12
1.3 AC power systems ..................................................................................... 19
1.4 Meters used in troubleshooting................................................................... 22
2 Devices, symbols, and circuits.................................................................................. 24
2.1 Devices and symbols.................................................................................. 24
2.2 Electrical circuits......................................................................................... 24
2.3 Reading and understanding electrical drawings.......................................... 28
2.4 Reading and understanding ladder logic .................................................... 36
2.5 Wires and terminal numbering.................................................................... 39
3 Basic troubleshooting principles ............................................................................... 42
3.1 Introduction ................................................................................................ 42
3.2 Basic principles in using a drawing and meter in troubleshooting circuits ... 43
3.3 Checks for circuit continuity with disconnected supply................................ 44
3.4 Checks for circuit continuity with live supply ............................................... 47
3.5 Tests and methods..................................................................................... 48
3.6 Testing devices .......................................................................................... 49
3.7 Circuits ....................................................................................................... 61
3.8 Accurate wiring of circuits and connections ................................................ 62
3.9 Tests for installation and troubleshooting.................................................... 66
4 Troubleshooting AC motors and starters .................................................................. 68
4.1 Introduction ................................................................................................ 68
4.2 Fundamentals of three-phase AC motors ................................................... 68
4.3 Fundamental of single-phase AC motors.................................................... 78
4.4 DC motors .................................................................................................. 81
4.5 Motor enclosures........................................................................................ 85
4.6 Motor terminal identification and connection diagram................................. 86
4.7 Motor rating and insulation types................................................................ 88
4.8 Operating a motor for forward and reverse operation ................................. 90
4.9 Motor braking methods............................................................................... 91
4.10 Motor testingt ............................................................................................100
4.11 Measurements used for a motor................................................................106
4.12 Motor failures and methods to extend its life..............................................106
vi Contents
4.13 Motor control trouble–remedy table .......................................................... 107
4.14 Motor starter check chart .......................................................................... 109
5 Switches, circuit breakers and switchboards........................................................... 112
5.1 Introduction............................................................................................... 112
5.2 Switches and circuit breakers ................................................................... 112
5.3 Overloads and fault protection .................................................................. 118
5.4 Switchboards............................................................................................ 119
5.5 Motor control center.................................................................................. 120
6 Troubleshooting variable speed drives.................................................................... 121
6.1 The need for VSDs ................................................................................... 121
6.2 Basic VSD ................................................................................................ 121
6.3 Power electronic components................................................................... 123
6.4 Electrical VSDs......................................................................................... 132
6.5 Power electronic rectifiers (AC/DC converters) ........................................ 135
6.6 Gate-commutated inverters (DC/AC converters) ...................................... 149
6.7 Overall protection and diagnostics............................................................ 157
6.8 Installations and commissioning ............................................................... 160
6.9 Power supply connections and earthing requirements .............................. 163
6.10 Precautions for start/stop control of AC drives .......................................... 166
6.11 Control wiring for VSDS............................................................................ 169
6.12 Commissioning VSDs ............................................................................... 170
7 Troubleshooting control circuits .............................................................................. 173
7.1 Basic control circuits................................................................................. 173
7.2 Ladder logic circuits .................................................................................. 177
7.3 Two-wire control ....................................................................................... 178
7.4 Three-wire control – start/stop .................................................................. 179
7.5 Jog/inch circuits ........................................................................................ 180
7.6 Sequence start and stop........................................................................... 181
7.7 Automatic sequence starting..................................................................... 183
7.8 Reversing circuit ....................................................................................... 183
7.9 Plug stop and anti-plug circuits ................................................................. 187
7.10 Two-speed motor control .......................................................................... 189
7.11 Overload protection .................................................................................. 189
7.12 Troubleshooting examples........................................................................ 190
7.13 Troubleshooting strategies........................................................................ 192
7.14 Ladder logic design exercise .................................................................... 194
Appendix A: Units and abbreviations ................................................................................. 195
Appendix B: Troubleshooting............................................................................................. 196
Appendix C: Low-voltage networks.................................................................................... 213
Index ................................................................................................................................. 232
Preface vii
Preface

Basic principles

Objectives
• To refresh basic electrical concepts
• To define basic concepts of transformer
• To refresh single-phase power concepts
• To refresh three-phase power concepts.
1.1 Introduction
A significant proportion of industrial electricity is about single-phase and three-phase
transformers, AC and DC machines. In this context, we will study the electrical circuits
and their construction, design, testing, operation, and maintenance.
For troubleshooting electrical equipment and control circuits, it is important to
understand the basic principles on which the electrical equipment works. The following
sections will outline the basic electrical concepts.
1.1.1 Basic electrical concepts
In each plant, the mechanical movement of different equipments is caused by an electric
prime mover (motor). Electrical power is derived from either utilities or internal
generators and is distributed through transformers to deliver usable voltage levels.
Electricity is found in two common forms:
• AC (alternating current)
• DC (direct current).
Electrical equipments can run on either of the AC/DC forms of electrical energies. The
selection of energy source for equipment depends on its application requirements. Each
energy source has its own merits and demerits.
Industrial AC voltage levels are roughly defined as LV (low voltage) and HV (high
voltage) with frequency of 50–60 Hz.
An electrical circuit has the following three basic components irrespective of its
electrical energy form:
• Voltage (volts)
• Ampere (amps)
• Resistance (ohms).

Index

AC machines:
squirrel-cage induction motor, 18
synchronous motors, 19
wound rotor motor, 18–19
AC motors, 68
connections:
dual-voltage, 89–90
multispeed, 89
single-phase:
induction, 78–9
series-wound/universal motor, 80
synchronous, 80–1
types, 78
speed control, 134–5
three-phase:
fundamentals, 68–9
induction, 69–73
synchronous, 69, 73–6
wound rotor induction, 69,
76–8
AC power systems:
single-phase, 19–20
three-phase, 20–1
measurement, 21–2
Air Cooled transformer, 5
Ammeters, 22, 51–4
Analog ohmmeters, 23
Anti-plugging see Plug stop/anti-plug
circuits
Automatic sequence starting, 183
Autotransformer 3ø starter, 176–7
full voltage configuration, 177
reduced voltage configuration, 177
working, 177
Bipolar junction transistors (BJT), 127
Braking see Motor braking
Cathode ray oscilloscope (CRO), 56
features, 56
operating, 56–7
Choppers, 122–3
Circuit breakers, 113–14
air-circuit, 115
high-resistance interruption, 113–14
high-voltage, 116–17
low-resistance of zero-point extinction, 114
miniature, 114
molded case, 114
motor, 117
oil, 114
SF6, 116
vacuum, 115–16
Circuits, 61
accurate wiring, 62–3
optional tests, 64–6
conducting an insulation-resistance test, 63–4
continuity:
checks with live supply, 47
test, 44–6
different wiring diagrams, 61
reading, 61
troubleshooting, 42–3
continuity test, 44–6
insulation test, 46–7
using a drawing and meter, 43–4
Clip-around/clamp-on ammeters, 22
Commissioning see Installations/commissioning
VSDs
Index 233
Commutation, 135–8
see also Gate-commutated inverters (DC/AC
converters); Line-commutated thyristor
rectifier bridge; Line-commutated diode
rectifier bridge
Connections:
accurate wiring, 62–3
optional tests, 63–4
cable connection requirements, 163–4
cables between converter and motor, 165
common cabling errors, 166
conducting an insulation-resistance test,
63–4
control cables, 165
fault finding on underground cable, 66
power supply cables, 164–5
see also Earthing
Continuity testers, 23
Control circuit, 26
automatic sequence starting, 183
basic, 173
autotransformer 3ø starter, 176–7
DOL (Direct-On-Line) starter, 173–5
star–delta 3ø starter, 175–6
input contact, 26
jog/inch circuits, 180–1
ladder logic, 177–8
NC (normally closed), 26
NO (normally open), 26
AND operation circuit, 27
OR operation circuit, 27
output coil, 26
overload protection, 189–90
plug stop/anti-plug circuits, 187–9
reversing circuit, 183–7
sequence start and stop, 181–2
troubleshooting:
examples, 190–2
strategies, 192–3
two-speed motor control, 189
two-wire control, 178
AND with OR operation circuit, 27
Control wiring for VSDs, 169
hard-wired connections to PLC control systems,
169–70
remote operation, 169
serial communications with PLC control
systems, 170
Converters, 122
AC to DC, 122
cycloconverter, 123
DC to AC converters/inverters, 123
DC to DC (choppers), 122–3
Copper brush switches, 113
Core type transformer, 5
CRO see Cathode ray oscilloscope (CRO)
Current Transformer (CT), 5
DC machines, 17
shunt motor, 17
compound motor, 18
self excited, 17
separately excited, 17–18
series motor, 18
DC motors, 81
braking methods, 99
characteristics, 81–2
connection, 87
forward/reverse operation, 90
speed control, 133
testing:
direct loading/brake test, 100–2
Field’s series test, 105
Hopkinson test on shunt motors, 103–4
retardation test, 104–5
Swinburne test, 102–3
types, 81–2
adjustable-voltage shunt-wound motor drive, 83
compound-wound, 83
separately excited, 81
series, 79–80
shunt, 82
Devices, 24, 25
Diagnostics see Protection and diagnostics
Digital capacitance meters, 23
Digital frequency meters, 23
Digital ohmmeters, 23
Digital voltmeters, 23
Diodes, 124
Direct-On-Line (DOL) starter, 173
main circuit, 173–4
maintained contactor control, 173–4
momentary contactor control, 174
Drawings see Electrical drawings
Dip meter, 23
Earthing, 166
see also Connections
Electric fields, 13
Electrical circuits, 24
control, 26–8
power, 24, 26
Electrical drawings:
reading/understanding, 28
inverter drive, 33–5
things to look for, 29–35
234 Index
Electrical drawings (Continued )
three-phase motor with DOL starter, 30–1
three-phase motor with star–delta starter,
31–2
Electrical energy, 3
Electrical machines:
basic principles:
electromagnetism, 13–14
electromechanical energy conversion, 12–13
generator, 15
idealized machines, 15–16
motor, 14
windings, 17
characteristics, 19
types
AC machines, 18–19
DC machines, 17–18
Electrical VSDs, 132–4
AC motor speed control, 134–5
DC motor speed control, 135
armature voltage, 135
field flux, 135
Electricity:
basic concepts, 1–2
electrical energy, 3
percentage voltage regulation, 2
power, 2
types of circuit, 3
Electromagnetism:
magnetic field produced by current-carrying
conductor, 13
magnetic/electric fields, 13
Electromechanical energy conversion, 12–13
Electrostatic voltmeters, 22
Energy meter, 22
Fault protection see Overloads and fault protection
Field controlled thyristors (FCT), 127
Field effect transistor (FET), 129–31
Field’s series test, 105
Forward/reverse operation:
DC motors, 90
induction motor, 89–90
Gate-commutated inverters (DC/AC
converters), 149
operating principle, 149–50
single-phase pulse width modulation (PWM),
152–5
single-phase square wave, 150–2
three-phase, 155–7
Gate turn-off thyristor (GTO), 126–7
Generator, 15
Hand-driven insulation/continuity tester, 58
Hazardous areas, 163
Heterodyne wavemeter, 23
Hopkinson test, 103–4
Human interface module (HIM), 157–8
Idealized machines, 15–16
Inch circuits see Jog/inch circuits
Induction motor:
braking methods
counter current braking/plugging, 97–8
dynamic, 95–7
regenerative, 92–3
forward/reverse operation, 90–1
single-phase, 79
capacitor-start, 79
capacitor-start/capacitor-run, 77
repulsion-start, 80
shaded-pole, 80
single-value capacitor/capacitor split-phase, 79
split-phase, 79–80
three-phase:
losses and efficiency, 72
principle/operation, 69–70
speed–torque characteristics, 70–1
startup, 71
Installation tester, 60
Installations/commissioning VSDs:
correct application settings selection, 171
correct parameter settings selection:
acceleration time, 172
basic, 171
current limit, 171
deceleration time, 172
maximum speed, 171
minimum speed, 171
rated current of motor, 171
starting torque boost, 172
de-rating for high altitude, 161
de-rating for high temperature, 161
environmental conditions, 160
environmental requirements, 160
general safety conditions, 163
hazardous areas, 163
mounting/enclosures for AC converters,
161–2
purpose, 170–1
Insulated gate bipolar transistor (IGBT), 131–2
Insulation-resistance test, 63
Insulation-resistance testers/meggers, 57
battery-operated, 59
hand-driven, 58
multi-voltage digital, 59
Index 235
Insulation testers, 23
Isolation transformer, 5
Jog/inch circuits:
start/stop using push buttons, 180–1
operation, 180–1
start/stop using selector switch, 181
Knife switches, 112
Ladder logic:
basic terms:
execution conditions, 37
logic blocks, 38
normally open/normally closed
conditions, 37
operands, 38
END instruction, 39
instructions, 38
examples of simple, 39
reading/understanding, 36
diagram, 37
PLC terminology, 36–7
Ladder logic circuits, 175
digital inputs, 177
digital outputs, main contactor on, 177–8
troubleshooting strategies, 192–3
checklist, 192–3
Lamp indicators, 49
analog vs digital instruments, 51
applications, 50
checking three-phase supply voltage, 50–1
description, 49–50
testing of a motor, 50
Line-commutated diode rectifier bridge, 139
assumptions, 139–42
Line-commutated thyristor rectifier bridge:
applications, 147–8
limitations, 144–5
reasons, 146
remedy, 146–7
operation, 143–6
Linear voltage differential transformer
(LVDT), 7
Logic analyzers, 23
Logic level probe testers, 23
Magnetic fields, 13–14
produced by current-carrying conductor,
13–14
Fleming’s left-hand rule, 14
flux, 14
right-hand rule, 13
Maintenance programs, 106
Megger testing:
cables/auxiliaries of three-phase system, 64
cables/auxiliary devices of a single-phase
system, 64
motor, 64–5
see also Insulation-resistance testers/meggers
Meters used in troubleshooting, 22–3
Modulation index, 155
Motor, 14
enclosures, 85
drip-proof, 86
pipe/duct ventilation, 86
protected-type, 86
splash-proof, 85–6
totally enclosed fan-cooled, 86
totally enclosed/non-ventilated, 85
failures/extension of life, 106
insulation, 88
characteristics, 88
classification/standardization, 89
material requirements, 89
permissible temperature rise, 88
nameplate, 86
rating, 88
terminal, identification/connection diagram, 86–7
testing, 100
DC machines, 100–6
Motor braking, 91–2
DC motors, 99
electrical, 92
counter current braking/plugging, 93–4
dynamic/rheostat, 94
electromechanical friction, 94
regenerative, 93
induction motors, 94–8
mechanical, 92–3
series motor, 100
shunt motor, 99–100
synchronous motors, 98–9
Motor Control Center (MCC), 120
Motor control trouble–remedy table:
coils open circuit, 108
contacts chattering, 107
failure of contact operation, 109
failure to drop-out, 109
limit switches, damaged parts, 109
magnetic/mechanical parts noisy magnet, 108
manual starters failure to reset, 109
overheated coil, 108
overload relay Tripping, 108
pickup and sealing failure, 108
pneumatic timers, erratic timing, 109
236 Index
Motor control trouble–remedy table (Continued )
short tip, life tip, overheating, 107
trip failure, 108
welding/freezing, 107
Motor starter check chart:
arc lingers across contacts, 110–11
burning of panel/equipment due to starting
resistor heat, 111
contact corrosion/welding, 110
contactor/relay closing failure, 109
contactor/relay fails to open, 110
frequent coil failure, 111
noisy AC magnet, 111
Multi-range voltmeters, 22
Multimeters, 22, 54–5
digital, 55
operating, 56
Neon Tester, 50
Ohmmeters, 23, 54–5
Oil-filled self-cooled transformer, 5
Oil-filled water-cooled transformer, 5
Oscilloscope, 23
Overloads and fault protection, 118, 189–90
bimetal relay with single-phasing protection, 118
motor circuits, 118
phase failure relays, 118–19
winding-protection relays, 119
Plug stop/anti-plug circuits, 187
anti-plugging, 188–9
plugging, 187–8
Potential transformer (PT), 5
Power:
apparent, 2
factor, 2
reactive, 2
real/true, 2
relationship between, 2
Power circuits, 24, 26
Power electronic components, 123–4
gate-controlled, 126
power diodes, 124–5
fast recovery, 125
line-frequency, 125
Schottky, 125
power thyristors, 125–6
Power electronic rectifiers (AC/DC
converters), 135
assumptions, 135–8
line-commutated diode rectifier bridge, 139
line-commutated thyristor rectifier bridge, 142–8
quadrant thyristor-controlled, 148–9
three-phase commutation with six-diode bridge,
138–9
Power factor meter, 21–2
Power transformer, 5
Programmable Logic Controllers (PLCs), 36
terminology, 36–7
Protection and diagnostics, 157
operator information/fault diagnostics,
157–60
internal/external, 159–60
levels, 158
parameters/conditions, 159
Pseudo wattmeters, 23
Q meter, 23
Quadrant thyristor-controlled rectifier, 148
operation, 149
Reversing circuit, 183
jog type for/rev/off circuit using selector switch,
184–5
latch type for/rev/stop circuit using pushbuttons,
185–7
Safety:
general recommendations, 163
standards, measuring instruments, 57
Schottky diodes, 125
Sequence start and stop, 181–3
Series motor:
braking method
plugging/reverse current, 100
regenerative, 100
rheostatic, 99
Series-wound single-phase motor, 80
Shell type transformer, 5
Shunt motor:
braking methods
plugging/reverse current, 99–100
regenerative, 100
rheostatic/dynamic, 99
Hopkinson test, 103–4
Single-phase:
AC power systems, 19–20
cables/auxiliary devices, 64
induction motor, 78–9
series-wound, 80
square wave inverter, 150–2
synchronous motor, 80
transformer, 5
parallel connection of two, 6–7
series connection of two, 6
Index 237
Single-phase pulse width modulation (PWM)
inverter, 152–5
Spectrum analyzers, 23
Star–delta 3ø starter, 175
full voltage (delta configuration), 176
reduced-voltage configuration (tar
configuration), 176
working, 176
Start/stop control of AC drives, 166–7
problems:
contactor on motor side of the
AC converter, 168
contactor on supply side of the AC converter,
166–7
Steel wire armored (SWA) cables, 164
Swinburne test, 102–3
Switchboards, 119
direct-control panel-type, 119
direct-control truck-type, 119
electrically operated, 119
remote mechanical-control panel-type, 119
Switches, 112–13
Symbols, 24, 25
Synchronous motor:
braking methods
dynamic, 98
plugging, 98–9
regenerative, 98
single-phase, 80–1
three-phase, 69
hunting (phase swinging), 75–6
losses and efficiency, 75
principle/operation, 73–4
‘V’ curves, 74–5
Terminal numbering see Wires/terminal
numbering
Tests, 48
devices, 49
accessories, 58–9
CRO (cathode ray oscilloscope), 56–7
insulation-resistance testers/meggers,
57–8
lamp indicators, 49–51
multimeters and ohmmeters, 54–5
safety standards for measuring instruments,
57–8
voltmeters and ammeters, 51–4
installation and troubleshooting:
earth continuity, 66
electronic earth, 67
flash, 67
insulation, 66
Thermocouple meters, 22
Three-phase:
cables/auxiliaries system, 64
commutation with six-diode bridge, 138–9
induction motor, 69–70
inverter, 155–7
motor with DOL starter, 30–1
motor with star–delta starter, 31–3
power system, 20–1
measurement, 21–2
supply voltage, checking, 50–1
synchronous motor, 69, 73–4
transformers, 7
delta connection, 7–8
four-wire star connection, 7–9
possible combinations of star/delta, 9
wound rotor motor, 69, 76–7
Three-wire control (start/stop), 179
Thyristors, 125–6
Transformers, 3
basic principle, 3–4
current-induced, 4
potential-induced, 4
ideal, 5
power transmitted at higher voltages, 11
rating defined in kVA, 11
single-phase, 6–7
testing, 9–11
three-phase, 7–9
types:
application, 5
construction, 5
cooling, 5
important points, 5
Triacs, 126
True wattmeters, 23
Two-speed motor control, 189
Two-wire control, 178–9
Underground cable, fault finding, 66
Universal motor, 78
Variable speed drives (VSD)
basic, 121–2
control wiring, 169
converters, 122–3
electrical, 132–4
gate-commutated inverters (DC/AC converters),
149–57
installations/commissioning, 160, 170–2
need for, 121
overall protection/diagnostics, 157–60
power electronic components, 123–31
238 Index
Variable speed drives (VSD) (Continued )
power electronic rectifiers (AC/DC converters),
135–49
power supply connections/earthing requirements,
163–6
precautions for start/stop control of AC drives,
166–8
Variable voltage, variable frequency (VVVF), 134
Volt-ohm-milli-ammeter, 22
Voltage:
definition, 2
percentage regulation, 2
Voltage Tester see Lamp indicators
Voltmeters, 51–4
Wattmeters, 23
Windings:
coil, 17
commutator, 17
polyphase, 17
Wires/terminal numbering,
39–41
Wiring, accurate, 62–3
Wound rotor motor:
three-phase, 69
principle/operation, 76–7
startup, 77–8
Zero-speed switch, 187–8
Rating: 4.9 / 5 (Votes: 23)
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