design of electrical works for projects

7/29/2019 Design of Electrical Works for Projects

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[ELECTRICAL WORKS FOR PROJECTS] 2013/2014

Eng.M.Tharwat 1


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Eng.M.Tharwat 2

Introduction

This course covers three main areas of the Electrical Contracting Process:

1. Basics of Electrical Works Design.2. Shop drawing and Site Works.3. Tendering of Electrical Projects.The Course requires pre-knowledge of [AutoCAD].

A project naturally progresses from design to the actual building going through the

following stages:

As the previous chart suggests, the electrical design is the first step of any electrical project, this

step has two major concerns besides the basic knowledge of electrical engineering which are

basic knowledge ofElectrical Safety and Economical Design.

Where the design aspect of this course covers areas like: Interior Lighting design, Socket

distribution, panel Boards design, cables selection, etc.

To

Contractors

Consultant

Approval

Tender selection

(Contractor)

Project as an idea

Planning Civil & Architecture Design Electro-Mechanical Works Design

Electrical Works Plumping works Design HVAC works Design

B.O.Q Preparation Tendering & Analysis

Shop DrawingImplementation Process

So on


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The second phase of the course addresses electrical site works supported with figures and videos

that introduces the student to real world experience of Sites Electrical Works and how to prepare

shop drawings for a given project.

Then the third phase, introduces the student to the basics of tendering and preparing a project bill

of quantity (B.O.Q).

At the end of this course, the student will have a head start extensive knowledge of how the

electrical contracting process works and will able to use this knowledge whenever facing an

electrical project.

With all respect

Eng .Mohammed Tharwat


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Part One

Interior Lightning Design


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I nteri or lighting Design

While the most important aspect of this area of design is determining the

desirable lux according to Egyptian, international codes and standards to match

your project needs, whether your project is a bank, school or even a hospitalthere are some basic rules to go by while determining the lux value of a given

area.

Lumen (lm):The unit of luminous flux is a measure for the quantity of luminous energy emitted per second by a lightsource.

Luminous I ntensity (I ):Light flux irradiated through a tri dimensional angle (solid angle) directed by the magnitude of the referredangle.

L= (Q/w) Lm/Seta radians

I L luminance (Lm/M2):The quantity of incidental light falling onto a given surface per unit area of the suface taking into

consideration that, it is uniformly illuminated.

E=Q/A Lux

To have a better understanding of the role of lux in lighting designs consider the

following example:

A lamp connected to a power source, the lamp will emit many lighting lines as

shown in the figure:

The lighting lines that illuminates 1 m2 is a simple definition of Lux

Lux = lumen/m2

Lighting lines

Lumen


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So if we say that an office needs 300 lux to be illuminated.

This simply means each 1 m2 requires 300 lumen.

The required lux depends on the application or usage of this area.

Some Lighting Parameters:

Colour Render ing I ndex (CRI ):A measure of the degree to which the appearance of a surface colour under a given light sourceCompares to the same surface under a CIE reference source. The index has a maximum value of 100.

Colour Temperature (K):All materials emit light when heated (e.g. metal glows red through to white as the temperatureIncrease). The temperature to which a full radiator (or black body) would be heated to achieve theSame chromaticity (colour quality) of the light source being considered, defines the correlated colour

temperature of the lamp, quoted in degrees Kelvin.

Luminance (L):

L=I/A (Cd/m2)

Luminous Ef fi cacy (lm/W):

The ratio of light emitted, to the power consumed by a lamp.


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The following tables show required lux for many appli cations:


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Types of lamps:

Normal

Incident

Lamp

Tungsten

Halogen

Lamp

Low

Pressure

Mercury

Lamp

High

Pressure

Mercury

Lamp

Metal

Halide

Lamp

Low

Pressure

Sodium

Lamps

High

Pressure

Sodium

Lamps

Theory Of

Operation

Black Body

Radiation

Black Body

Radiation

Quantum

Theory

Quantum

Theory

Quantum

Theory

Quantum

Theory

Quantum

Theory

Color

Rendering100% 100% 50-95% 15-50% 65-90% 0 25-85%

Luminous

Efficacy8-17 13-25 60-95 40-60 70-95 125-200 40-90

Lif e Time 1000-2000 hr 2000-4000 hr 8000 hr 5000-24000 hr

3000-12000

hr 5000-20000 hr 6000-24000 hr

DimmingCan be

Dimmed

Can be

Dimmed

Can`t be

Dimmed

Can be

Dimmed

Can be

Dimmed

Can`t be

Dimmed

Can be

Dimmed

Application Indoor Indoor Indoor Outdoor Outdoor Outdoor Outdoor

In order to reach a satisfactory lux value for a given area, It`s required to use number of

lighting fixtures.

While the number of lighting fixture is dependent on a set of parameters which can be illustrated

in the following equation:

N =

Where:

N number of lighting fixtures. Q lumen for lighting unit.E required lux. n number of lamps per unit.

A. Area of room. utilization factor.F clearance factor. K. Maintenance Factor [0.8].


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A)Area of room (A):A = L.W

B)Clearance factor (F ):It is the factor that affect of num. lighting fixture according to

room clean degree.

For an open lighting fixture in a computer lap room and under a clean room condition,

clearance factor is 1.27

C)Number of l amps (n):

L

W

n = 4

n = 2

4 x 18

2 x 36

n = 1

n = 1

100

60

Spot light:


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D)Uti li zation factor ():For a certain lux value to be reached in a given room (area) there are some

parameters that affect the quantity of lumen per lamp, those parameters are

better illustrated as follow:

1. Room index:

Where:

KrRoom indexL.Room length

wRoom widthHmdistance between the

lighting fixture & working

plan.

S/Hm Parameter means the ratio between Mounting Height & distance between

lighting fixtures which give us the ratio between Emin & Emax

For Example:

S/H = 1.75 which mean ratio of [Emin / Emax= 75%]

S/Hm Ratio is a given value in lighting fixture data sheet.

Hm2Hm1

Hf

Hw

Hm1 = Ht Hw , Hm2 = Ht - (Hw + Hf)


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2.Reflection factors: ( )Depending on wall, ceiling, ground colors and materials, Reflection factor can be

determined by using the following tables:

Uti li zation factorcan be one from the following tables by using both ofRoom indexand

Reflection factors.

Now that we have reached this point, we know all the required parameters to get the desired

number of lighting fixtures in a specified room.


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Lumen per lighting lamp:

Can be determined by the following table according to lamp type:


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Design lighting for the following project:

L = 15 m

W = 8 m

H = 4 m

Work plan = 85 cm

The above data is for a Conference room, with a white colored ceiling, its required that you

determine the number of lighting fixtures that achieves the desired Lux.

Solution

A = L.w = 15 x 8 = 120 m2

From tables: conference room has an E = 500 lux

The owner choose fixture (E). so, lamps = 2 x 36 watt , n = 2

From application: for a clean room, F = 1.33 (clearance factor = 1.33)

From lumen table: Q = 3250 lumen

From wall and ceiling color: Hm = Ht(Hs + Hw) lighting fixture will be on false ceiling (Hw = 0.7 m)

Hm = 4(0.85 + 0.7) = 2.45 m Hm = 2.45 m

Kr= Kr= 2.12

From tables:

(Uf= 0.52)

N =

N = 23.6 units 24 units

L

W


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Arrangement of lighting fixture

From the previous example the required number of lighting fixtures is 24 unit, now

the question is how they can be arranged?

(4x6) or (3x8) or (12x2) or .etc

So we will arrange those as (4x6) units

As shown in the fig. below, The distance between each lighting fixture and the

other is double the distances between the lighting fixture and the wall to avoid a

blind spots.

12X = 10 x = m

8y = 8 y = 1 m

10 mX 2X 2X 2X 2X 2X 2X 2X X

8 m

y

y

2 y

2 y

2 y


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Control of lighting circuits

Lighting circuits can be controlled by lighting switches.

L ighti ng switches can be classif ied into:

One way, one gang.

One way, two gang.

One way, three gang.

Two ways, one gang.

Two ways, two gang.

Two ways, three gang.

The difference between one way & two way switches is that the one way switch controls the

circuit from one location. However, two way switches controls the circuit from two locations.

Two way switches used in bed rooms, corridors.etc.

One way switch:

Two way switch:


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Part Two

Basics of Street lighting Design


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Street Lighting Design

Lighting is a vital rule to describe the importance of major

and minor roads, which constitute the lifelines of

communication in the motorized world today.

Good street lighting is aiming to:

Reduce traffic accidents Combat crime Respect the environment

For good street lighting design there are some parameters

must be taken:

Area Classification.

Road way Classification. Street Width. Poles height.

A) Area Classif ications:

Commercial Intermediate Residential


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B/Roadway Classif ications:

Freeway Expressway Arterial Collector Local Alleys

Poles height and street width affect li ghting arrangement

Street Lighting Arrangement:

1/Single sided:

This type of arrangement, in which all luminaries are

located on one side of the road, is used only when the width

of the road is equal to, or less than the mounting height of

the luminaries.

W


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2/Staggered:

This type of arrangement in which the luminaries are

located on both sides of the road in a staggered, or zigzag,

arrangement is used mainly when the width of the road is

between 1 to 1.5 times the mounting height of the

luminaries.

W=1~1.5 H

3/Opposite:

This type of arrangement, with the luminaries located on

both sides of the road opposite to one another, is used

mainly when the width of the

road is greater than 1.5 times

the mounting height of the

luminaries.

W>1.5H


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4- Span wire

This type of arrangement, with the luminaries suspended along

the axis of the road, is normally used for narrow roads that have

buildings on both sides.

I f Road is curved:

Single Sided:

If the radius is Small & The length is 300 m.

Opposite:

If the radius is Large & The length > 300 m.


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Types of lamps used in Street lighting

1- H igh pressure sodium lamps (H ighway Streets):

It is suitable for such kinds of lighting even in cloudy weather.

2- Low pressure sodium lamps (Tunnels):

This type of lamp is used in tunnels and closed public places. They also have

relatively long life.

3- Metal halide lamps.

4- Mercury lamps (I nternal Streets):

It gives a bright white light thus it could be used in illumination of open places

such as large stadiums since this type of lamps have strong glass.

Methods of switching of lamps

There are various methods, some of which are:

- Photo cell.

- Control switch.

- Timer.


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Street Lighting System

The distr ibution lighting network consists of:

- Lighting distribution box

- Poles

- Lighting luminaries

- Cables

Design of the street l ighti ng scheme:

Where:

F: is lamp flux in lumens.

C.F: is the clearing factor, taken about 0.6.

M.F: is the maintenance factor, taken about 0.7.

S: is the space between the poles in meter.

W: is the street width in meter.

E: is the illumination level of street in lux.


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Part Three

Electrical Sockets & Power Calculations


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Electri c sockets

Types of Electri cal Sockets:

Single & Duplex Socketsare used for low current applications, as in TVs, DVDs, computers, laptops,mobile chargers, cassettes, videos, and home instruments.etc.

Power socketsare used for heavy loads as Boilerssmall motor pumpswater heatersetc

Fuse Switch Disconnect Switch

Applications Used for [A/C-W.HETC] as a isolatorswitch & protective switch against overcurrent by using to rapture fuse

Used for [FCU-AHU-Pumps-Elevators-

..ETC] as isolator switch only.

Poles Number Double Poles Only Single, Double & Three PolesCurrent Rating 26A-32A 16A20A32A40A60A80A100A125A150A200A250A -320A-400A-

800A

All previous socket types are available with high IP for protection against water and dust in wet

and open or landscape areas.

Sockets distribution:

Socket distribution for a given room is dependent on the following factors:

1- Room application2- Room furniture3- Each 3 meters put a single or duplex socket (in case of no furniture DWG)4- For kitchens, there must be at least one power socket.

HD

Single Socket

Hand Drier

Fuse Switch or

Disconnect Switch

Duplex Socket

Power Socket


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Power calcul ations

A) For lighting:

- Incident lamps or spotsP = 20 200 watts.

- For florescent lamps2 x 36 watt

4 x 18 watt

2 x 55 watt

- For chandeliersP= 400500 watt

B) For sockets:

- Single socket........................200 VA- Duplex socket ......................400VA- Power socket.2000-2500VA- Hand driver1500VA-

Fuse switches

A.C W.H

1 HP....... ......1000 VA

1.5HP... 1500 VA

1500 VA

Up to 2000 VA

2.25 HP.2250 VA

3 HP .3000 VA

4 HP..4000 VA

5 HP..5000 VA


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Power Factor:

It`s a percentage of used active power.

Where:

P ==== Active Power

S==== Apparent Power

For all cables and C.Bs calculations, power must be in (VA)

For lighting, power must be in VA but its data is given by watt so:

For fluorescent lamps PF = 0.45 = 0.6

For halogen or spots PF = 1

For current calculations:

Single phase loads

I (Amp) = 4.5 Skva

Three phase loads

I (Amp) = 1.5 Skva


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Electrical Loads Estimation

According to Egyptian Company for Distribution maximum demand load (VA) is calculated by

knowing the area and building application as following:

A) For buildings less than 15 floors:The following table gives required KVA for each 100 m2:

Application Type Residential Building Commercial Building

Low Density 1.5-2 6-12

Medium Density 2.5-4 6-12

High Density 6-10 6-12

B) For buildings more than 15 floors:The following table gives required KVA for each 100 m2:

Residential Building Commercial Building

8-10 12

Height of building is calculated by 1.5 of street width.


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Electric li nes calculations

After Distributing lighting fixtures and sockets, it must be fed from a main panel board.

Each group of lighting fixtures or group of sockets has one line to the main panel board.

For lighting lines:

For socket lines:

For power socket lines:

For hand drier:

For air conditioners:

Each unit takes a separate line:

16 AmpEach line 1500 VA 2.5 mmNo more

Than

With wire

Size

With

MCB

20 AmpEachline 2000 VA

3 mm

No more

Than

With wire

Size

With

MCB

25 AmpEach line 2000 VA 4 mmNo more

Than

With wire

Size

With

MCB

25 AmpWith

MCB

Each unit

takes a

separate line

1500 VA 4 mmNo more

Than

With wire

Size

25 Amp1, 2.25, 3 HP 4 mm

32 Amp4 - 5 HP 6 mm


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Load schedules

Project Name: MCB:

Panel Name: cable: size:

Breaking cap.:

Circuit

NumberType

Cable

sizeMCCB

Three phaseNotes

R Y B

R1 Lighting 2.5 mm2

16A 800

Y1 Lighting 2.5 mm2

16A 600

B1 Lighting 2.5 mm2

16A 990

R2 Socket 3 mm2

20A 1600

Y2 Socket 3 mm2

20A 1800

B2 A.C 4 mm

2

25A 1500R3 Spare 16A

Y3 Spare 20A

B3 Spare 32A

Total connected load 2400 2400 2490

Load balancing:

Given that the network is featuring a star connection.

Its important to achieve I1 I2 I3 to reach an IN of nearly equal zero.

R

Y

B

N

I1

IN

I2

I3

R

BY


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Balance Check:

For any panel board, there is a balance check for three phase loads due to reducing nuteral

current & unbalanced stresses on circuit breakers.

Unbalance ratio can be calculated by:

Unbalance Ratio (%) mustnt exceed a value of5% of total three phase load.

For above panel bard unbalance ration will be:

Unbalance Ratio (%) = 3.62% so the above its balanced panel board.

Diversity factor:

It`s the percentage of expected on line loads connected at the same time.

- For lighting .. ....0.7 1- For all sockets............................... 0.6 0.9- For Air conditioners .. 1- For heaters and hand drier . 1

Circuit breaker capacity calculations:

After conducting load and diversity factor calculations, now we consider C.B capacitycalculations which are as follows:

IC.B = =


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Circuit breaker standard:

1016202532405060637580100125160200250320400

50063080010001250160020002500320040005000-6300 Amp.

MCB MCCB VACUUM ELCB

AbbreviationMiniature

Circuit

Breaker

Molded Case

Circuit

Breaker

Vacuum

Circuit

Breaker

Earth Leakage

Circuit

Breaker

Nominal Current 10125 A 321600 A 16005000 A 10100A

Short Circuit Current 630 KA 1080 KA Up to 150 KA 630 KA

Num.Poles SPDPTP- FP TP - FP FP DP

Adjustment FixedFixed -

AdjustableFixed Fixed

For pervious load, there will be a panel board to feed these circuits, Single line

diagrammed for panel board required to represent panel specifications and component as

following:

16A20A32A16A20A32A

X3X2X1X1X1X1

LightingSocketA.CSpareSpareSpare

40A

[4x10]+10 mm CU/PVC

380V,50HZ,Isc


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Motors Panel Boards

Circuit Breakers of each motor should be greater than starting current of the motor.

Starting Current of motors can be determined by Code-letter method according to the following

table:

Code LetterKVA/HP at

startingCode Letter

KVA/HP at

starting

A 1.6 L 9.495

B 3.29 M 10.595

C 3.72 N 11.845

D 4.25 P 13.25

E 5.3 R 14.995F 5.95 S 16.995

G 6.1 T 18.995

H 6.7 U 21.195

J 7.55 V 22.4

K 8.495

As an example:

A 3 phase, 380V, 50HZ, 5KVA motor with code letter J, Required calculating Ist?

From above table:

Code letter J mean KVA) st = KVA) motor * 7.55

= 5 * 7.55 = 37.75 KVA

So:

Ist= 1.5 * 37.75 = 56.625 Amp,

So the circuit breaker rating will be = 60A


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Distribution Board for group of motors:

For distribution board, feed group of motors, the sub circuit breakers ratings should be larger

than starting current of each motor.

To determine the rating of main circuit breaker:

IM.C.B= Ist-largest+ D.F ( IRating-except largest )

Where:

D.F is a diversity factor & can be calculated from following table:

No. Motors Type of drive Demand Factor1:5 Individual Drive 1

6:10 Individual Drive 0.75

11:15 Individual Drive 0.716:20 Individual Drive 0.65

21:30 Individual Drive 0.6

Less than 5 Group Drive 1

5:10 Group Drive 0.85

More than 10 Group Drive 0.7


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Part Four

Cables Selection


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Cable selection

Power cables are used to feed circuits with the required power.

So, cables selection must be according to transfer a full power to certain load, that mean the

cables must transfer the full current with no or limited voltage drop to ensure full power transfer.

Cables can be classif ied as following below:

Operating & Meggered Voltages 600/1000 450/750

Conductor Type Copper Aluminum

Insulation Material PVC XLPE

Number of cores Single Multi core

ArmoredArmored

[STASWA]

Non-

Armored

Neutral Size Reduced NeutralNon-

Reduced

Neutral

To select a cable for a certain load like below:

ELECTRICA

L LOAD

AC Source

380 V, 50HZ


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The above mentioned cable should transfer full power from

source to load, so it must stand full load current with limited

voltage drop.

To ensure carrying full load current [Derating Factors] must be

taken in consideration.

Derating factor :

Derating factors are the factors that affect cables life time

and their standing current and its dependant on cable laying

methods.

From Cables catalogue we can obtain the Derating factors

ratings


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Df= D1 x D2 x D3 x D4 x D5 x D6x..Dy

Icable = Voltage Drop:

A long distance cable and its internal impedance may

cause a voltage drop more than the allowed percentage.

Voltage Drop Percentage mustnt more than 5%.Voltage drop calculations:

VD% =

Where:

VD% Voltage Drop Percentage Voltage Drop for a certain cable[Obtained from cables catalogues]

Circuit Breaker Current Cables Length


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Part Five

Emergency Loads

Generators & UPS


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Generators and UPS

In some projects, power continuity is required for many different reasons

like:

(1)Data loss as in banks(2)Emergency as in hospitals(3)Production quantity as in factoriesetcSo the important loads must be fed by a stand by source.

In case of power interruptions, another source will feed these loads

There are two devices that ensure power continu ity:

(A) Generators(B) UPS

Difference between Generators and UPS:

Generatorsare used as a standby power source with a delay time

between current interruption and continuity.

On the other hand, UPS are used as a power source without any

time delay between current interruption and current continuity.


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Theory of operation:

G

UPS

1

3

2

L5

Main power source is on:

S1 is on S2 is on S3 is off

Power interruption:

S1 is off S2 is on S3 is on

For load (5): Power continuity is needed without time delay so a UPS is

used to feed the load till the Generator starts up.

UPS is connected before load.


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A controller of three switches called (ATS)

ATS panels:

Its a panel that consists of three switches one is connected to the mainsource, the second one is connected to the Generator and the third one is

connected to the load through a controller Microcontroller, PLCEtc

Generator selection:

Generators are selected according to emergency loads power rating (KVA).

UPS selection:

A UPS is selected according to emergency load power rating (KVA) and dischargingtime of back up batteries.

Co-ordination between Generator starting up time and backup battery discharging time is

crucial as to assure the continuity of power.

The UPS discharging time must be selected to cover the delay time between current

interruption and continuity.

ATSG

Load

Main source


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Part Six

Short Circuit Current


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Short cir cui t current

In case of short circuit, there is a large current value passing through protective devices.

If these protective devices fail to stand the current value, damage occurs in circuit

components which might cause fire or complete damage of the electrical system.

The power systems must be designed to stand short circuit currents for a short period of

time before the trip process takes place.

While the types of trips performed by a circuit breaker are:

Thermal trip: Responsible for protection against over load currents.

Magnetic trip: Responsible for protection against short circuit currents.

Ikis the maximum current capacity that a device stands before damaging.

Short circuit current calculations:

It = ISC + IL

At short circuit (IL = Zero):

IS.C =

Vphphase voltage

Zttotal circuit impedance

Thermal trip

Mag. trip

ISC IK

ZCab

ZLoad

ZCab

ZLoad

It

Isc

IL


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For the following circuit:

A)For part a:IS.C =

=

B)For part b:

IS.C =

=

a

b


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Impedances Calculations:

1/Ring Main Units:

Power Rating Reactance Value

250 KVA0.633 m

500 KVA0.316 m

1000 KVA0.158 m

2/Transformers:

Power Rating Reactance Value

25 KVA 256 m50 KVA 128 m

100 KVA 64 m160 KVA 40 m200 KVA 32 m250 KVA 25.6 m

315 KVA 20.3 m400 KVA 16 m


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500 KVA 12.8 m630 KVA 10.16 m

800 KVA 9 m1000 KVA 8 m1600 KVA 7.35 m

3/Circuit breaker:

XC.B = 0.15 m4/Bus Way:

Xb.w= 0.15L mCables:

XCable = 0.08L mResistances are negligible.

Shor t cir cuit current can be calculated by another method

Up and Down Stream Tables


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Part Seven

Earthing Systems


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Earthing systems

There are two types of ear thing systems:

(1) Function earthing(2) Protection earthing

(1)Function earthing:

This is the earthing of neutral points.

A neutral point is connected to the earth point to get the potential of the neutral point to be zero.

(2) Protection earthing:

This is the earthing of the electrical equipment body for human protection.

Earthing system design:

The following shape shows electrical equipment having a current leakage problem while a human is

touching the equipment body.

The above circuit can be represented by:

Rh.. Human Resistance.

Re.. Earthing Resistance.

The sole purpose of any earthing system is to protect humans from (I1)

So for I1


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Earthing Systems Resistance Calculation:

Re =

Where:

Re . Electrode Resistance

Soil ResistivityL..Earth Electrode Length

Soil resistivity depends on soil type as show in table (1)

Rv = Where:

Rv Total earth resistance

ReEarth resistance for each electrode

L..Electrode length

SDistance between electrodes

N.Number of electrodes

..Utilization factor which calculated by tables (2), (3), (4).

L

L

SS


63/65


Eng.M.Tharwat 63


64/65


Eng.M.Tharwat 64


65/65


Also there is the resistance of wire thats connected between electrodes (Rh)

Rh =

Where:

.soil resistivityL.wire length

.utilization factor.

Total Earth Resistance

Rt = .

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