Download - Design of Electrical Works for Projects
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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
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Also there is the resistance of wire thats connected between electrodes (Rh)
Rh =
Where:
.soil resistivityL.wire length
.utilization factor.
Total Earth Resistance
Rt = .