Workshop Technology

Different circuit elements used:

Push button:

It is used in door bells. It interrupts single line. It is a handy but weak mechanism.

Resistors:

Opposition to flow of charges is offered by resistors.

Inductors:

In inductors, energy is stored in magnetic field.

Capacitors:

In Capacitors, energy is stored in electric field.

RLC has great effect on electric circuits.

Let us consider three feeder lines...

As these three lines have some length so they have the ability to oppose the flow of charges, hence they contain resistance.

As current changes inside wires, due to which magnetic field is produced and change in magnetic field gives rise to magnetic flux and store energy so it contains inductance.

Now conducting plates placed close to one another act as capacitors and thus contain capacitance.

Although wires don’t contain resistors, inductors and capacitors yet they show their combined effect. In order to minimize LC effect, we use DC source.

Electrical power System:

Introduction:

E.P.S is a combination of different electrical components, devices and a network of conductors to generate electricity, to transmit it to near centers and finally distribute it.

Main components/Sections:

Generation Section:

Generation Station is a station where we generate electricity. We can’t make electricity but can convert other forms of energy to electricity.

Generator /Alternator (3 phase up to 22 kV) +transformer (step up).

Without transformer, we can’t transmit electricity up to few kilometers. Our intention isn’t to increase voltage but current.

Transmission Section:

Conductors (Materials of high conductivity).

Those areas where electricity is consumed are called electrical load centers. They can’t move generation section towards distribution section because of our limitations and hazards.

Distribution Section:

It helps to distribute power. Conductors & Transformers are used and are also known as feeder lines. For passage of AC, we use combo of wires called stranded wires to minimize skin effect. It increases flexibility.

Difference between feeder and transmission lines is their capacity.

Capacity of transmission line>>Capacity of feeder lines

Transformers used here is step down.

It decreases 11kV to 220V.

Grid Station:

It is a help station which helps to control voltage and other electrical parameters.

Representation :( Single Line Diagram)

All circuit elements are 3-phase but represented by single-line.

Types of Electrical Power System:

Independent/Isolation:

This system independently produces electricity, transmits and distributes. It doesn’t connect itself with other electrical systems.

Above diagram is an example of independent /isolation E.P.S.

Interconnected E.P.S:

These power systems are all over the world. These are the systems which are connected to other electrical power systems. Most of power stations around the world are interconnected E.P.S.

All power stations are connected to one another through feeder lines/transmission lines. They cover major cities including urban areas.

Comparison on Basis of reliability and economy:

• Cheaper electricity. • Economical process. • Interconnecting different E.P.S brings security. • Machines used are electromechanical electromagnetic and require

maintenance. • Controlling of load becomes easy because of single location called Central

Control Location. • In off-week seasons, we can turn off costly generation stations. • All important decisions are taken at National Power Control System

(NPSC). • It allows us to take quick decisions. • Whenever a big system is out, switching takes place. E.g. Last few days due

to blast in thermal power station in Central Punjab, frequency decreased and electricity malfunction occurred. Due to this blast Mangla and Tarbela couldn’t cope up with demand and underwent disorder.

Distribution transformer internal connection:

The main function of core used inside transformer is to provide enhanced magnetic field. Its secondary side is earthed for safety purpose.

How to get single and three phase supply?

This 400V is called line-to-line voltage. Between any two lines, we get same voltage i.e. 400V so it is called phase-to-phase voltage.

When a neutral wire is involved, we call it phase voltage or line-to-neutral voltage. If a person is involved in getting single phase he will use neutral and any one (B, R or Y). A big advantage of 3 phase supply is that even in case of damage of single phase, other two can be used.

V (line-to-line) =√3*V (line-to-neutral)

Safety & Protection:

Transformers (in windings of core) heat up because of electrical load. We have electrical and mechanical losses. They dissipate energy in form of heat.

For safety and protection, we use transformer oil and radiating pipes. When transformer heats up, coil expands upwards and gives heat to surroundings.

Protection:

Overload (Current):

For prevention from overload, we use fuses also known as links across high tension (HT) wires.

Overvoltage:

It occurs when load on secondary side of transformer increases.

For prevention, we use air gap arrangements. In horns, upper part is connected to live wire and lower part is connected to steel body. When there is a high voltage a spark is produced between adjacent horns and air gap between two horns get ionized and excess voltage passes through live wire to earth.

Hazards related to electricity:

Accident:

“Any unwanted/unexpected event/act which has harmful impacts.”

Electrical Accidents:

“Accidents in which human body is affected by electricity”.

According to particular statistics, # of deaths around the world through electricity is much greater. Electric current flows through human body because of presence of large amount of liquids.

The resistance of human body is about 1400 Ω to 2000 Ω. A current of 60mA is very dangerous for human body.

Factors affecting accident:

Time:

Longer the time, greater will be impacts on body and greater will be time taken by victim to recover.

Factors affecting resistance:

The resistance of human body depends upon:

• Thickness of skin (Thicker the skin, greater will be resistance). • Food intake. • R of wet skin<<<R of dry skin. • Wounds on human body decrease R up to 10 Ω.

Type based on phase involved:

Phase-to-neutral accident:

In this case current flows through whole body. It is most common form of accident. In this type of accident 230V is involved.

Phase-to-phase accident:

It is a case in which human body is isolated from surrounding and doesn’t involve any neutral. A person gets hold of two phase wires and gets a total of 460V shock.

Phase-to-phase and neutral accident:

In this case person standing on neutral catches a live wire and gets an electric shock. It is quite rare.

General Discussion on Effects of Electrical Accidents on Human Body:

When considerable amount of current passes through body, four major types of effects occur.

Breathing System:

It is also called pulmonary system. If current passes through body of human being, he/she will suffer from breathing disorder. It may be temporary or permanent. When a body gets a current for large amount of time, victim usually loses his voice. Due to this, condition becomes worse.

Cardiac System:

Due to electric current, blood in body of victim is converted to clot and when it travels through arteries, it blocks the arteries.

Sometimes phenomena ventricular fibrillation (extremely irregular heart beat) occurs due to which unconsciousness occurs.

Muscles Contraction:

Sometimes a phenomenon called muscles spasms (muscles become stiff and lose their flexibility) occur.

Nervous System:

Brain is affected.

Factor affecting the severity of electric shock:

Level of voltage:

Generally even 30-40 volt is dangerous. Greater the voltage greater will be damage. Higher voltage is much more dangerous because more current is flown through the body and it produces deep injuries.

Intensity of current:

Greater the intensity of current, greater will be danger risk.

Resistance of human body:

Skin offer maximum resistance. In order to find total resistance, we have to add resistance of human body, shoe sole and earth.

Time and current flows:

Greater the time, greater will be danger risk.

Body response:

The strength of a person also affects the severity of electric shock. If a person is sick, he will have greater effects on his body.

Surrounding effects:

Changing surrounding effects converts a healthy practice into hazard. Tripping of electricity occurs because of grounding effects.

Path of current:

If current flows through a path, which contains a sensitive vital organ, shock will be severe and vice-versa.

This type of data is obtained by experiment on animals and interview and conversation with victims.

Earthing and grounding of power system:-

Introduction:

These two effects are commonly used in those electrical devices which are exposed and we touch them in our day to day life.

For getting maximum efficiency, minimum loses from system, we check out proper rating of system which determines:-

• Voltage. • Frequency. • Wave form of sine wave

A slight change in frequency provides damage for electrical devices.

UPS (Uninterrupted power supply) increase frequency that is why heat and sound produced by electrical devices is increased.

Factors affecting sine wave of power supply:-

1) Internal factors:

These are factors which are produced internally (i.e. by components of electrical devices).

2) External factors:

External factors such as lightning strokes produce a complex wave which causes damage in transformer as well as loads.

3) Switching/operational factors:-

When we consider an isolated system (a system which is not grounded), and on/off switch, it produces fluctuation in voltage.

Advantages of grounding:-

1. It reduces operational and maintenance expenditure. 2. It improves service reliability. 3. It provides greater safety for devices. 4. It provides better system and equipment over current protection by installing

fuses/circuit breakers.

5. It includes lightning protection. 6. It provides protection against static charges.

Types of grounding systems:

1) Solid ground:-

In solid ground common point of electrical device is directly connected to ground.

It is usually applied for low voltage and rating system, working at 2.2 KV and 5VA.When a short circuit appears, it is usually ground fault current. In this case, heavy current flows to ground and if wire doesn’t opposes specific internal resistance/impedance, a large amount of current flows through wire.

2) Resistance grounding:-

It is applied for medium voltage and rating system. It works at 11KV to 33KV and 5MVA. This resistance may be few kΩ to few MΩ depending upon internal resistance of system.

3) Reactance grounding:-

In place of resistance, we can also use inductor called reactance grounding. It isn’t normally used because of certain loopholes.

4) Resonance grounding:-

When XL=XC, it limits the earth fault current.

It is used for high voltage (in power system).

A transformer used practically for grounding is called ground transformer.

Safety or safe handling of electrical devices:-

Introduction/Definition:-

“Safety or safe handling means performing any task without any harm to personal and equipment/devices”.

OR

“End part of an activity in which status of the operator and equipment/devices remains unchanged”.

New trend in design of electrical devices:-

• In old days, safety system wasn’t much reliable but nowadays special attention has been given to it.

• Nowadays, body of washing machines is made up of plastic and has replaced metal.

• Electric socket in form of receptors are now replaced with shutters. • Nowadays, all devices are connected with three-pin shoe which are ground

and are used for safety purposes. • Nowadays a shoe with fuse is most commonly used.

Effecting factors:-

A. Proper insulation:-

Wherever we use eletricity, insulation is very necessary. Different types of devices which we use in our daily life become handy because of insulation. There are different types of insulation depending on environmental condition.

It should be kept in mind that for permanent purpose, we can’t use extensions because of mechanical and electrical losses. In sensitive loads, we should prefer fire-resistance wires in order to overcome problems of fire due to short circuit.

B. Proper grounding:-

Devices are grounded for safety and stability purpose. Mostly devices are solid grounded. In three pin shoe, upper socket’s hole is much thicker, provides less R and increase G.

C. Equipment Status:

This means that device which we use should be free of defaults.

When devices aren’t used regularly, their insulations lose their strength and break off causing problems. It is called aging.

In order to check whether there are problems with our device or not, we perform two tests:

i. Multimeter test: It shows zero R(short circuit) ii. Series test circuit: It shows infinite R(open circuit)

When we insert a high load in place of low load, switch can catch fire because of high power dissipation.

D. Personnel experience and learning:

In electrical field we need to concentrate on learning as well. Just to be dependent on experiments is a risky business.

E. Personal physical and mental condition:

For electrical we need to be physically and mentally normal. Electrical work isn’t allowed for people having mental abnormalities.

F. Follow the instruction manual:

Every electrical device comes in market with a catalogue known as user’s manual which should be read carefully before using device.

G. Surrounding conditions:

Changing surrounding conditions convert a safe operation into a hazard.

Electrification Designing:

Electrification:

“Electrification means feed an area or provide electricity to area under consideration.”

For any township (either commercial or residential), we need a proper electrification system.

Designing:

“Executing a job in systematic way is called designing.”

OR

“On technical basis, the general arrangement and plan for making electric circuit or electrical system is called designing.”

The systematic way should be reliable, economical and user friendly.

Types of Electrical Wiring Design:

1. New designing:

Area under construction is already developed.

2. Extension/Redesigning:

From area under consideration already developed, we evolve different extensions.

New designing is comparatively simpler than extension/redesigning.

Because in new designing we can start from bas while in redesigning we have to use limited methods and take care that our modifications don’t disturb already developed system.

Steps:

Prediction/Forecasting of electrical load:

It should be based upon previous records of electrical experiments and present trends. It allows us to know requirements of area (for residential or commercial purposes)

Receiving of application:

In this case, electrical companies receive applications regarding need of electricity for particular area.

General Geographical Region:

It means that by surveying a particular area, we come to know about its need.

Statistical Method Field Survey Method It depends upon previous records. e.g. 5-10 years electrical load 5-10 years electrical power 5-10 years electrical energy

For purpose of electrification, designers visit area again and again and collect data.

We draw load curve by taking electrical power along Y axis and time along X axis and compare curve of last year with respective year. Comparing both, we get growth rate which depends upon various factors. “Predicting future curve by comparing any two past curves is called extrapolation of curve.”

Engineers involve themselves in studying physical characters of area which includes climate and its effect on electricity need, topography, population distribution, natural resources etc.

It isn’t recommended because of unseen factors i.e. because of deficiency of proper survey of area.

Electrification Wiring/ Electrification of buildings:

“Bringing electricity from transmission section to distribution section.”

Electric Load calculation:

For single phase system:

P=VIcos(ϑ)

Cos (ϑ) =% of useful power.

Three types of power:

Apparent power(S):

S=P+Qj

S=Complex quantity.

P=true power, watt full power, useful power

Q=apparent power, watt less power, reactive power.

In resistive circuit, P is used.

In capacitive and inductive circuits, Q is used.

Reactive Power:

“The rate at which L and C store power and give back to circuit.”

In ideal conditions: cos (ϑ) =1

In theoretical conditions: cos (ϑ) =0.9

Calculating current, we get:

I=P/V cos (ϑ)

For three phase system:

These equations are used only and only if devices are three phase:

P=3 VphaseIphase cos (ϑ)

Q= √3VlineI line cos (ϑ)

Electric Load types:

Light load:

All those devices whose capacity is less than 1000 W (Max I draw=5 A)

Heavy loads:

Refrigerators, AC, Ovens etc.

Selection of material:

A) Wire and Cable Selection:

We use stranded wires for AC passage to reduce skinning effect.

The wires through which switches are connected to loads are a wire of 3/29.

Switches are connected to electrical loads through electrical circuits which depend upon appliances.

For checking which wire should be used for connecting circuit of room to main switch, calculate total current of room and then select wires.

For connecting electric system of home with main electrical system we use cables.

Main panel Board:

In foreign countries two types of voltages are available.

1. 110 V for lighter loads. 2. 220 V for heavy loads.

For this purpose two independent electric circuits are developed and from here concept of “panel boards” comes.

Panel boards consist of:

Indicating lamps, Measuring devices, Recording instruments and Protective devices.

Ratted current:

“Amount of current passing through fuse without breaking it”

Fusing Current:

“That minimum current which will melt fuse and break circuit”

We use silver wire as it has much R. Circuit breakers come with heat sensing elements called thermistors or nowadays bimetallic strips.

Protection devices:

Fuse is considered as cheapest protective device because of inability to replace, it isn’t frequently used.

In residential areas fuses aren’t used but in automobiles they are used because of low rating which can’t be achieved by circuit breakers.

Circuit Breakers___Simple Mechanism:

They can sense thermal change and when they get specific amount of heat plates of Circuit Breakers are pushed away from one another thus creating an open circuit.

Two mechanisms followed by circuit breakers:

Bimetallic strips:

Two metals having different coefficient of expansion are used which expand at various temperatures and open circuit is formed.

Relation between voltage and current:

When V decrease, I increases which depends upon load.

In case of incandescent lamp, I will not increase. Similarly in case of dim lights we don’t switch off bulbs but we turn off refrigerators but in case of decreased V, I is increased to maximum.

When a normal amount of current passes through circuit, no change occurs and switch remains in on position. But in case of greater amount of I, bimetallic strips will heat up and switch will be in off position.

Types of circuit breakers:

In residential and commercial areas, no spark is produced in circuit breakers because of low I and V. In grid stations and substations, spark is produced because of large I and V. Due to this spark connection is produced between two plates and when electricity produced is moved forward, it produces noise and distortion.

1. Low voltage and current:( 11kV and 100A)

These circuit breakers are called air or vacuum circuit breakers.

“In this circuit breaker, spark travels through air”.

It can be reduced by increasing size of Circuit breakers but it will give rise to many other problems.

2. Medium Voltage and Current: (66kV-220 kV 1000A)

In this case plates of circuit breakers are dipped in oil and are called oil circuit breakers.

3. High rating Circuit Breakers: (220kV,500kV,800kV,1100kV I>1000A)

In this case plates of circuit breakers are dipped in gas (SF6) and are called gas circuit breakers.

Relay:

It is basically electromagnetic circuit breaker. It is used for switching purposes.

Capacity of relay to switch on and off is maybe in kV or MV, hence called amplified Circuit breakers.

Relay isn’t a protective device it just transmits a signal if something’s wrong.

Conduit Systems:

“Special pipes or arrangement to house electrical wiring systems or electrical conductors”

Types of Conduit Pipes on basis of environment:

Conduit Pipes are mostly made up of plastic pipes (PVC) or sometimes metals depending upon condition.

Insulating conduit pipes are used wherever there is great moisture and water like in marble factories.

Metallic conduit pipes are used when we want to save wires from external impacts such as coal mines.

Advantages:

1. It provides insulation.

2. It helps in beautification of buildings. 3. It helps in prolonging lifespan of wiring system. 4. It decreases cost of electrical wiring system. Because in its absence each

wire needs to be insulated separately this is a costly process.

Types:

Classification on basis of building. Classification on basis of wiring system.

Classification on basis of wiring system:

1. Surface(Conduit) wiring system

They aren’t used in residential/commercial area but in industrial areas.

2. Concealed (conduit) wiring system

Comparison:

• It is easy to replace, repair, maintain and make new connections from surface conduit wring systems.

• In concealed conduit, we get much safety and beauty.

Classification on basis of Application:

1. Rigid Conduit 2. Semi-rigid Conduit 3. Flexible Conduit

Rigid Conduit

Conduit wiring system fixed to specific place is called rigid conduit system e.g. fan from ceiling.

Semi-rigid Conduit

Conduit wiring system hanging from a specific place is called semi-rigid conduit system e.g. in industrial areas.

Flexible Conduit

Conduit wiring system free to move is called flexible conduit system e.g. iron I n our homes.

Filling of conduit:

Filling means how much wires should be inserted in conduit.

If a pipe is filled 100% there remains no place for new connections.

In case of power loss more heat is lost which results in V drop and this heat lost proves to be a decisive factor that how much pipe should be filled.

Experiments and past records show that 35% of pipe should be filled.

%age filling %age decrease in I 35% 0% 70% 50% 80% 60%

Electrical Connection__Jointing:

Wherever we use electricity, we need connection of electrical wiring system.

Junction:

“Junction is a common point where various wires meet each other.”

It is basically a node but every junction isn’t a node.

According to recent survey, most common causes of fluctuation in electricity are due to lose connections. Due to loose connections, sparking is produced. If sparking takes place for long time it can be reason for fire.

Properties:

1. The junction or joint should have long service life time and shouldn’t corrode when subjected to environmental conditions.

2. It should be able to withstand overload conditions without burning, melting or failure.

3. It must maintain contact integrity, electrical continuity. 4. When conducting current, its temp should be lower than conductor .This is

achieved by increasing cross-sectional area.

Technique 1:

If we have 2 or 3 wires of same material at a point, we form a junction by twisting them with hands or pliers. This is called slicing.

We may use process of soldering i.e. spread one layer of metal over another.

Technique 2:

If we have 2 or 3 wires of different material then they can’t be simply sliced because of different coefficient of expansion. In this case we use connector to make a junction which is used in houses where energy meters are hoisted on poles.

Junction Box:

It maybe circular or square and it shouldn’t be loose and air tight.

Size of junction box= largest pipe*safety factor+ (rest of pipe)

Angle of bent:

We can’t place a wire 900 sharp with anything because it increases mechanical and electrical losses.

Angle of bent shouldn’t be greater than 3600.