EE015-Electrical Control 2-Th-Inst.pdf

7/25/2019 EE015-Electrical Control 2-Th-Inst.pdf

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SRI LANKA INSTITUTE of ADVANCED TECHNOLOGICAL

EDUCATION

Training Unit

Electrical Control 2

Theory

No: EE 015

ELECTRICAL and ELECTRONIC

ENGINEERING

Instructor Manual


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Training Unit


Theoretical Part

No.: EE 015

Edition: 2008Al l Rights Reserved

Editor: MCE Industrietechnik Linz GmbH & CoEducation and Training Systems, DM-1Lunzerst rasse 64 P.O.Box 36, A 4031 Linz / Aus triaTel. (+ 43 / 732) 6987 - 3475Fax (+ 43 / 732) 6980 - 4271Website: www.mcelinz.com


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ELECTRICAL CONTROL 2

CONTENTS Page

LEARNING OBJECTIVES...................................................................................................3

1 SCHEMATIC DIAGRAMS ............................................................................................4

1.1 Wiring diagram.....................................................................................................4

1.1.1

Hints for the design of wiring diagrams ............................................................7

1.2

Single line diagram ............................................................................................13

1.3 Complete circuit diagram ...................................................................................14

1.4 Lay-out diagram .................................................................................................15

1.5

Equipment diagram............................................................................................15

1.6

Terminal table ....................................................................................................16

2 TYPES OF CIRCUIT CONSTRUCTION ....................................................................17

3

WIRING OF CIRCUITS ..............................................................................................18

4 ENVIRONMENTAL EFFECTS ...................................................................................19

4.1.

Protection against climatic influences ................................................................19

4.2. Protection against vermin ..................................................................................19

4.3.

Protection against corrosion ..............................................................................19

5 FAULT FINDING ........................................................................................................ 20

5.1. Tips for remedying faults....................................................................................20

6

SUMMARY OF SWITCHING SYMBOLS ...................................................................24

7 IDENTIFICATION LETTERS FOR GENERAL FUNCTIONS .....................................33

8

GLOSSARY OF ELECTRICAL TERMS.....................................................................35

8.1. Definition of characteristic quantities .................................................................35

9

OPERATING EQUIPMENT........................................................................................36

9.1. Designation of operating equipment ..................................................................36

9.1.1. Designation block "type, number, function"................................................36

9.1.2. Designation block "plant" ...........................................................................37

9.1.3.

Designation block "location".......................................................................37

9.1.4.

Designation block "connection"..................................................................38


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LEARNING OBJECTIVES

name and describe schematic diagrams.

draw wiring diagrams complying with standards.

recognize switching symbols and design simple contactor circuits.

state the difference between wiring diagram and complete circuit diagram.

produce a terminal table.

list the types of wiring.

recognize and find minor faults.


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1 SCHEMATIC DIAGRAMS

These are used to represent electrical devices by means of symbols. Operating

equipment can be shown in a simplified form.

Schematic diagrams always show the equipment de-energized, in the mechanically non-

activated condition.

1.1 Wiring diagram

This is the most frequently used representation of a circuit in electrical engineering.

The current paths should be drawn in straight lines, as far as possible, and without

crossovers.

The spatial position and mechanical interconnection of individual parts are not taken into

account.

The wiring diagram should show the method of operation and switching sequence of a

control system clearly and unambiguously.

The magnet coils (contactor coils) should be arranged in such a way that one terminal is

directly connected to the neutral line of the control circuit. The input to the coil is

connected to the other control line via various switching elements (contacts) of the

switchgear (pushbuttons, overcurrent relays etc.).

All contacts operated by one contactor have the same designation as the contactor itself.

Terminals are shown, and are given the same numbers as on the terminal table and the

circuit diagram.

For large circuits it is recommended that the wiring diagram should be divided into current

paths.

The equipment diagram of switchgear can be shown below the current path (as shown on

page 8).

The switch contact types, whether they are normally closed or open, the section in which

they are found and whether any of the contacts are free.


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Each piece of equipment is lettered to indicate its type. 1f here are several items of the

same type of equipment, they are given consecutive numbers. A further letter indicates its

general function, e.g., K 2 A auxiliary contactor and K 4 M main contactor (motor

contactor).

a) Main circuit wiring diagram


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b) Control circuit wiring diagram


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1.1.1 Hints for the design of wiring diagrams

When designing a wiring diagram, the following points should be observed.

a) The current paths are drawn vertically, in between the horizontally drawn bus bars.

b) Switching appliances, switchgear and initiating equipment must be drawn at right

angles to the current path.


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c) The direction of the current flow should always be from top to bottom.

d) Crossover of lines should be avoided.


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e) Apparatus and equipment must be represented in zero volt condition (switched off).

Exceptions have to be clearly indicated (i.e. arrow).


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f) Control equipment e.g. coils, signal lamps must be connected directly to the neutral

conductor, or in case of an earthed supply system, to the potential earth neutral (PEN)

conductor.


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g) Current paths must be numbered consecutively, circuit elements must be placed from

left to right, depending on their sequence of operation. Circuit elements must be

provided with code letters and consecutive numbers.

For clean representation of the various circuit elements, a table can be added below

the wiring diagram.


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1.2 Single line diagram

This is a simplified, single-phase representation of the circuit.

F1 = motor fuses

F2 = overcurrent relay

K1 = motor contractor

M1 = 3-phase AC motor


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1.3 Complete circuit diagram

This is the representation of a circuit in all its details.

As both main and control circuits appear in one diagram, this can become unwieldy and

makes fault finding more difficult.

F1 = motor fuses K1 = motor contractor

F2 = overcurrent relay M1 = 3-phase AC motor

F3 = control fuses S1 = ON-OFF-pushbutton


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1.4 Lay-out diagram

This is a document for wiring up the components. All equipment is shown in the correct

position.

1.5 Equipment diagram

This gives information on electrical switchgear (contactors, controllers, and master

switches etc.), but not on its construction. The switch positions and contacts must havethe same designation on the wiring diagram.


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1.6 Terminal table

The terminals shown in the wiring diagram and complete circuit diagram are compiled in

the terminal table into terminal strips. The terminal table contains the cable or wire

numbers, the terminal number, the origin and the destination.


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2 TYPES OF CIRCUIT CONSTRUCTION

Small circuits are built up on boards and are installed in the places provided on the

machines, e.g., star-delta starter circuit.

Cubicles are fixed directly to the machine and contain all control and switching devices.

Freestanding cubicles for large machine tool controls contain e.g. measuring equipment,

switching devices and control devices.

Freestanding contactor boards are used for extensive electrical plants, e.g., rolling mills

and cranes etc.

Contactor boards are erected separately in the switchgear rooms provided.

Control desks contain all the Instruments and control devices on one board, in order to be

able to control a plant from a central position.


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3 WIRING OF CIRCUITS

Wiring in ducts:

This is affected by laying wired in plastic ducts. Note:

Always make the ducts large enough.

Back-panel wiring:

Wires are connected on the back of panels.

Note:

When wiring is taken through a panel, grommets should be used, otherwise the wiring

insulation will be damaged.

Flat wiring:Individual wires are laid next to and above one another in layers.

Round bundle wiring:

Bundles of wires are bunched with string or held together by tapes.

Laced wiring harness:

This is a preformed and tied bundle of wires.

Quick wiring:

The wires are laid from terminal to terminal (by the shortest path).


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4 ENVIRONMENTAL EFFECTS

4.1. Protection against climatic influences

The required control devices may be affected by local conditions. This means that the

prevalent climatic conditions have to be taken into consideration in advance.

The control devices have to work satisfactorily in temperate and dry climates, as well as in

hot climates with high air humidity. If water condenses in a control cubicle due to frequent

temperature changes at high air humidity (changing climate), then control devices will not

function properly. Heaters may be employed to ensure that water is not deposited in the

equipment.

4.2. Protection against vermin

Control devices may suffer adverse effects from vermin (e.g. termites). Components made

of materials containing cellulose should be avoided in electrical operating areas, and a

high degree of cleanliness and brightness of illumination should be ensured. It is useful to

employ encapsulated equipment in areas likely to be affected by vermin.

4.3. Protection against corrosion

There is a corrosive atmosphere in many plants due to the manufacturing processes e.g.

in chemical and electroplating works and steelworks etc.

The following information may serve as a rough guide:

In atmospheres in which human beings can exist, normal encapsulation of equipment will

provide resistance to corrosion.

Metal parts used as contacts must be suitable for the constructional and switching load

requirements. They are male of precious metals or appropriate alloys.

The above considerations do not only apply for contactors and switchgear, but for all

electrical machines and electrical installations.


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5 FAULT FINDING

For rated voltages above 42 V up to a voltage of 250 V to earth, work on live parts is only

permitted, if, in order to prevent danger or for other important reasons, it is impossible to

make those parts of the plant dead, on which work is to be carried out. Such work may

only be carried out by an "expert". An expert is one who can judge and recognize possible

dangers based on his technical training, knowledge and experience as well as his

knowledge of the appropriate regulations applying to the work entrusted to him.

Electricians with completed electro-technical engineering training fulfil these conditions.

Note:

Under no circumstances may apprentices work on live parts of a plant.

5.1. Tips for remedying faults

This table includes the faults which occur most frequently on contactors.

CAUSE REMEDY

Contactor does not switch on:

Control fuse burnt out. Fist remove cause of short circuit, then

replace the fuse.

Thermal overload relay has operated Wait for cooling period, press reset button.

Switch on again.

Coil defective Replace coil

Coil for wrong voltage, wrong

frequency or wrongly connected.

Replace coil. Change the circuit.


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Low voltage (permitted lower limit

0.85 x UC) particularly for DC operated

contactors.

Replace coil, use special coil for increased

voltage security

(0.75 x UC). Provide stable mains supply.

Low voltage 214 V. Note the voltage drop. If necessary, choose

higher control voltage.

Circuit errors. Look for and remove the cause. Go

through the wiring diagram step by step.

By-pass normally closed contacts in circuit,

one by one.

Broken wire. Pull the wires to check whether they are

broken inside the insulation. Frequently the

break in the wire, caused by incorrect

removal of the insulation, is inside the

insulation.

Contactor with thermal overcurrent device

trips

Thermal overcurrent trip not operating

correctly

Set trip to motor operating current. Note

that, in the delivered condition, the trip is

always set to the lowest current value.


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Long starting time due to starting against

the load, too low voltage.

Install thermal overcurrent

trip with saturation transformer. During start

up the load should be switched off

(coupling) so that rotary Pumps should not

be started against a closed gate valve.

Measure voltage at motor terminals.

Check cross section of wires (possibly

voltage drop). Thermal trips are by passed

during starting period.

Too high switching frequency. Use thermistor protection. Thermal

overload trips are only suitable up to 15

operations/ hour.

Bimetal strip has turned blue or burnt out;

overload due to too high current; short

circuit with wrong (too high) fuse ratings.

Change overload trip. Install fuses suitable

for overload trip.

Loss of one-phase (motor does not start - it

hums).

Possibly a burnt-out fuse, loose or broken

main connection to motor winding.

Contactor does not switch off

Contactor contacts welded together. Break the contacts apart and replace them.

Install bigger type of contactor.

The control wires between contactor and

operating device is too long (holds itself in

due to capacitive currents).

Lower the control voltage. Install contactor

with smaller holding capacity.


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Stop push Button is short circuited. Remove short circuit, break the contacts

apart, if necessary, and renew them.

Faulty star-delta circuit switching. Use timing relay with changeover time .of

40 - 100 s. Set timing relay to longer time

period. The motor must nearly reach the

nominal speed in the star circuit.

Contactor flutters. Ensure that the operating signal is correct.

Remove fault on operating elements.

Check rated voltage of the contactor coil.

Contactor hums

Coil of wrong voltage or wrong frequency. Replace coil.

Magnet surfaces dirty or corroded (after

long period of shutdown).

Clean magnet surfaces. Do not file, do not

grease them.

Short circuiting ring broken. Replace contactor.

Foreign bodies in air gap. Switch on and off several times.

Remove foreign bodies.


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6 SUMMARY OF SWITCHING SYMBOLS

Contacts with two or three positions Description

Symbol Description


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Wiring contacts with two positions

Leading and lagging contacts


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Contacts showing delay in actuation and resetting

Contacts with automatic and non-automatic resetting


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Switches

Symbols Description


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Switches, which are actuated by pushing or pulling, normally have an inherent reset force.

It is therefore not necessary to draw the symbol for automatic reset.

In exceptional cases, where switches have latching qualities, the symbol for latching is to

be used.

Switchgear

Symbol Description


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Electromechanical and electromagnetic drives

Symbol Description


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Fused and fuse switches


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Electrical machines and transformers


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7 IDENTIFICATION LETTERS FOR GENERAL FUNCTIONS

Letter General function

A Auxiliary function

BDirection of movement (forwards, backwards, raising, lowering,

clockwise, anticlockwise)

C Counting

D Differentiation

E ---

F Protection

G Test

H Alarm

J IntegrationK Pushbutton operation

L ---

M Main function

N Measurement

P Proportional

Q Condition (start, stop, limits)

R Reset, cancel

S Storage, indication

T Time measurement, time delay

U ---

V Speed (acceleration, braking)

W Addition

X Multiplication

Y Analogue

Z Digital


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For example:


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8 GLOSSARY OF ELECTRICAL TERMS

8.1. Definition of characteristic quantities

Rated insulation voltage

Uiis the standardised value of voltage for which the insulation is suitable.

Rated voltage (rated operating voltage)

Ueis the reference voltage for switching.

Continuous current (thermal rated current)

Ith2is the current which the switchgear can carry for an unlimited period of time in normaloperating conditions, without the controls having to be cleaned and without the limiting

maximum temperatures being exceeded.

Rated operating current

Ieis the current reached in normal operation

Mechanical life span

The mechanical life span in expressed by the number of switching cycles possible under

no-load condition.

Life span of switching contacts

The life span of switching contacts is determined by the number of switching cycles which

can be achieved under full load conditions.

Frequency of switching

Frequency of switching is the number of switching operations (number of switching cycles)

per hour.

Rated actuating voltage UC

Control voltage is the voltage for which the coil or the tripping mechanism is suitable. It is

also called the coil rated voltage.


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9 OPERATING EQUIPMENT

9.1. Designation of operating equipment

The complete system of designation contains four blocks. Each block has a prefix for

designation.

Prefix Information in identification block

- Type of operating equipment Consecutive number Function

= Plant

+ Location

: Connection

The four designation blocks can be arranged in any sequence. i.e.:

: A 1 = B4 + D1 K 3 A

or

- K 3 A + D1 = B4 : A1

For small units it is sufficient to quote one or two designation blocks. Normally only the

designation block "Type of operating equipment - consecutive number - function" is used,

so that the prefix can be omitted.

i.e.: instead of - K 3 A only K 3 A

9.1.1. Designation block "type, number, function"

For the designation of "type" an identification letter from the table "identification letters for

type of equipment" must be used.

The consecutive number is obligatory, and must always be stated. In some cases the

number alone might be sufficient to designate operating equipment.

The function relative to other operating equipment is indicated by a letter from the table

"identification letters for general functions".


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The designation of the function may be omitted if is not required. However it is not

permitted to use the designation "function" by itself.

9.1.2. Designation block "plant"

The designation "plant" is written down only once in a suitable place on the switching

document. The designation of the plant may be omitted if not required.

9.1.3. Designation block "location"

The designation "location" states, where the operating equipment is located. The

designation of location may be omitted if not required.


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9.1.4. Designation block "connection"

The designation "connection" has a colon as prefix. The designation of connection may be

omitted if not required.


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Examples of block combinations

Designation Block combination Explanation

= C 1 -K 5 A

= Plant

- Type, consecutive

number, function

Auxiliary contactor K 5 in plant C 1

+ L 2 : 3+ Location

: ConnectionTerminal 3 of component L 2

= B 2 + 2 D 4 = Plant

+ Location

4th component of control panel 2 on

floor D of plant B 2

- K 2 M. : 11

- Type, consecutive

number, function

: Connection

Terminal 11 of main contactor K 2

= B 3 B + D = Q

= Plant

+ Location

- Type, number, function

Circuit breaker Q of panel D, Plant B

3 B

+ A 2 - S 10 : 4

+ Location

- Type, number,

function

: Connection

Terminal 4 of push button S 10 on

control desk A 2

: A 1 = B 4+ D 1 - K 3 A

: Connection

= Plant

+ Location

- Type, number, function

Terminal A 1 of

auxiliary contactor K 3, control panel

D 1, plant B 4


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EE 015


Theoretical Test


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TEST 1

1. Explain the purpose of schematic diagrams.

2. Name the six different types of schematic diagrams.

3. Draw an equipment diagram for a contactor with three main contacts and four auxiliary

contacts (two normally closed and two normally open contacts).

4. What information is provided by a terminal table?

5. State how back panel wiring is carried out.

6. What is the purpose of a control desk?

7. State what is meant by the term "laced wiring harness".

8. The contactor of a switching circuit "hums". Name possible sources of error.


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TEST 2

1. State four points which have to be observed when designing a wiring diagram.

2. Describe the design of a complete circuit diagram.

3. Describe the term "flat wiring".

4. Draw an equipment diagram for a contactor with three main contacts and two auxiliary

contacts (one normally closed and one normally open).

5. Explain the term "frequency of switching" of a contactor.

6. Name the two main parts of a wiring diagram.

7. Trouble shooting in control circuits must be carried out by experts only. Which persons

qualify under the stipulation of operating instructions for the term "expert"?

8. The contactor of a switching circuit "flutters". Name possible sources of error.


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TEST 1

(Solution)

1. Representation of electrical installations through switching symbols. Simple

representation of operational equipment.

Schematic diagrams always show the equipment in a de-energized state, i.e. in the

mechanically non-activated condition.

2. Wiring-, single-line-, complete circuit-, lay out-, equipment diagram and terminal table.

3.

4. Cable or wire number, terminal number, the origin and the destination.

5. Wires are connected on the back of panels. Always use grommets through the panel.

6. All instruments and control equipment assembled on one panel for purpose of

controlling a plant from one central place.

7. This is a preformed and tied bundle of wires.

8. Coil on wrong voltage or frequency; dirt on the mating faces of the magnetic core;

short circuiting ring broken; foreign body in the air gap.


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TEST 2

(Solution)

1. The current paths are drawn vertically in between the horizontally drawn bus bars.

Circuit elements must be drawn at right angles to the current path.

The direction of current flow should always be from top to bottom. Crossovers of lines

should be avoided.

Circuit elements must be represented in zero volt condition (switched off).

Control equipment such as coils, signal lamps etc. must be connected directly to the

neutral conductor.

Current paths must be numbered consecutively, circuit elements must be provided

with code letters and consecutive numbers.

2. The complete circuit diagram is the representation of a circuit in all its details.

If the main and control circuits appear in one diagram, it can become unwieldy and

makes fault finding more difficult.

3. Individual wires are laid next to end above one another in layers.

4.

5. The number of switching cycles per hour.

6. Main circuit and control wiring diagrams.


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7. An expert is one who can judge and recognize possible dangers, based on his

technical training, knowledge and experience as well as his knowledge of the

appropriate regulations applying to the work entrusted to him. Electricians with

completed electro-technical engineering training fulfil these conditions.

8. The operating signal is not correct. Fault on the operating elements. Contactor coil

voltage is incorrect.


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