Design Of Electrical Systems For Projects.pdf

Electrical Systems Design For Projects

EEE-Electrical Engineering Encyclopedia Facebook.com/EEEncyclopedia

Eng.M.Tharwat

2016/2017

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Introduction 

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 of Electrical Safety and Economical Design.



This course is orientated around a number of major projects where students work in teams to design and develop a specified product, device or system.



Each project itself involves both management and engineering components. It requires students to utilize knowledge from a range of disciplines including some or all of: Electrical, Electronics, Communications, Computing, Software, Signal Processing, Control and Mechanical systems.



On successful completion of this course, you will be able to: 

Select suitable electrical components and equipment for a new building.



Carry out basic calculations associated with the electric power demand in a building.



Utilize the applicable Standards in the process of designing.



Prepare basic technical documentation of a new building services system.

In the end I hope to enjoy your training with me.

With all respect …

Eng .Mohammed Tharwat

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Chapter One Interior Lightning Design

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Interior 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 hospital there are some basic rules to go by while determining the lux value of a given area.

Lighting Parameters:  Lumen (lm): The unit of luminous flux is a measure for the quantity of luminous energy emitted per second by a light source.

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

L= (Q/w) Lm/Seta radians

 IL luminance (Lm/M2): The quantity of incidental light falling onto a given surface per unit area of the surface taking into consideration that, it is uniformly illuminated.

E=Q/A Lux

A lamp connected to a power source, the lamp will emit many lighting lines as shown in the figure:

Lighting lines “Lumen”

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

Lux = 𝐀 lumen/m2

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.

 Colour Rendering Index (CRI): A measure of the degree to which the appearance of a surface colour under a given light source Compare to the same surface under a CIE reference source. The index has a maximum value of 100.

 Colour Temperature (°K): The temperature to which a full radiator (or ‘black body’) would be heated to achieve the Same 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)

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 Luminous Efficiency (lm/W): The ratio of light emitted, to the power consumed by a lamp.

 S/H Parameter: Means the ratio between Mounting Height & distance between lighting fixtures which give us the ratio between Emin & Emax.

For Example: S/H = 1.56 78% This mean when the ratio between Mounting Height & distance between lighting fixtures is 1.56 , Emin = 0.78 Emax.

Notes: Emin/Emax should be more than 0.5.

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The following tables show required lux for many applications:





:





:





































































:





















:





:























:

 Eng.M.Tharwat







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Types of lamps: Low

High

Low

High

Pressure

Pressure

Pressure

Pressure

Mercury

Mercury

Sodium

Sodium

Lamp

Lamp

Lamps

Lamps

Black Body

Quantum

Quantum

Quantum

Quantum

Quantum

Radiation

Radiation

Theory

Theory

Theory

Theory

Theory

100%

100%

50-95%

15-50%

65-90%

0

25-85%

8-17

13-25

60-95

40-60

70-95

125-200

40-90

1000-2000 hr

2000-4000 hr

8000 hr

5000-24000 hr

3000-12000 hr

5000-20000 hr

6000-24000 hr

Normal

Tungsten

Incident

Halogen

Lamp

Lamp

Theory Of

Black Body

Operation

Metal Halide Lamp

Color Rendering Luminous Efficacy Life Time Dimming

Application

Can be

Can be

Can`t be

Can be

Can be

Can`t be

Can be

Dimmed

Dimmed

Dimmed

Dimmed

Dimmed

Dimmed

Dimmed

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=

𝑬.𝑨.𝑭 𝑸.𝒏.𝑼𝒇. 𝑲

Where: N… number of lighting fixtures. E … required lux. A…. Area of room. F… clearance factor.

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Q… lumen for lighting unit. n… number of lamps per unit. 𝑼𝒇 …utilization factor. K…. Maintenance Factor.

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Area of room: L

W

A = L.W

Clearance factor (F): It is the factor that affect num. lighting fixture according to room clean degree. Lighting Fixture Type

Open

Closed

Reflectors

Clean Degree

Res. App.

Industrial App.

A

1.27

1.27

B

1.33

1.33

C

1.42

1.42

D

1.48

1.48

A

1.33

1.5

B

1.39

1.6

C

1.54

1.69

D

1.61

1.78

A

1.33

1.45

B

1.39

1.54

C

1.48

1.61

D

1.54

1.69

For an open lighting fixture in a computer lap room and under a clean room condition, clearance factor is 1.27

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Number of lamps / Lighting Fixture (n): 4 x 18

n=4

2 x 36

n=2

Spot light:

100

n=1

60

n=1

Utilization factor (Uf): 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 below: 1. Room index: 𝒌𝒓 =

𝑳. 𝑾 𝑯 (𝑳 + 𝑾) Hf

Where:

H2

Kr…Room index W…Room width L….Room length H…distance between the lighting fixture & working plan.

H1 = Ht – Hw ,

H1

Hw

H2 = Ht - (Hw + Hf)

 About work plan height we can consider below assumption:     

For home rooms except toilets & kitchens For Toilets For Kitchens For all offices For Markets & Shops

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Hw = 80 cm Hw = 40 cm. Hw = 120 cm. Hw = 80 cm. Hw = 20 cm

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2. Reflection factors: (𝛒𝐰 , 𝛒𝐜 , 𝛒𝐆.𝐅) Depending on wall, ceiling, ground colors and materials, Reflection factor can be determined by using the following tables:

Utilization factor can be one from the following tables by using both of Room index and Reflection factors.

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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 L

W=8m

W

H=4m Work plan = 85 cm The above data is for a Conference room, with a white colored ceiling, it’s 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: 𝜌𝐶 = 0.7, 𝜌𝑤 = 0.5, 𝜌𝐺 = 0.2 H = Ht – (Hs + Hw)

lighting fixture will be on false ceiling (Hw = 0.7 m)

H = 4 – (0.85 + 0.7) = 2.45 m 𝐿.𝑊

Kr = 𝐻(𝐿+𝑊) =

15 𝑥 8 2.45 (15+8)

H= 2.45 m Kr = 2.12

From tables: (Uf = 0.52) 𝐸.𝐴.𝐹

N = 𝑄.𝑛.𝑈 = 𝑓

500 𝑥 120 𝑥 1.33 3250 𝑥 2 𝑥 0.52

N = 23.6 units ≈ 24 units

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Arrangement of lighting fixture:

𝑵𝒘 = √

𝑵. 𝒘 𝑳

𝑵. 𝑳 𝑵𝑳 = √ 𝒘

The distance between each lighting fixture and the other is double the distances between the lighting fixture and the wall to avoid blind spots. So if we have a room like shown in figure with dimensions of 10 mt as length & 8 mt as width, and this room will have 24 units. 𝑁𝐿 = √

𝑁.𝐿

𝑁𝑤 = √

𝑤

= √

10𝑥24 8

= 5.47 ~ 6 𝑢𝑛𝑖𝑡𝑠

𝑁. 𝑤 8𝑥24 = √ = 4.3 ~ 4 𝑢𝑛𝑖𝑡𝑠 𝐿 10

X 2X 2X

2X

10 m 2X 2X

2X 2X 2X X y 2y 2y 8m

So best arrangement will be 4x6 units. 𝟏𝟎

12X = 10

X=

8Y = 8

Y=1

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𝟏𝟐

=

2y

𝟓

y

𝟔

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Control of lighting circuits: Lighting circuits can be controlled by lighting switches.

Lighting switches can be classified 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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Chapter Two 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:    

Road Way Classification. Area Classification. Street Width. Poles height.

Roadway Classifications:     

Freeway Expressway Arterial Local Alleys

Area Classifications:  Commercial (> 25000 vehicles per day)  Intermediate (>7000 & <25000 vehicles per day)  Residential (<7000 vehicles per day)

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Poles height and street width affect lighting 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<=H

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 heights of the luminaries.

W=1~1.5 H

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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

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.

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Types of lamps used in Street lighting  High pressure sodium lamps (Highway Streets): It is suitable for such kinds of lighting even in cloudy weather.

 Low pressure sodium lamps (Tunnels): This type of lamp is used in tunnels and closed public places. They also have relatively long life.

 Metal halide lamps.  Mercury lamps (Internal 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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The distribution lighting network consists of: - Lighting distribution box - Poles - Lighting luminaries - Cables

Design of the street lighting scheme:

𝐅 𝐱 𝐔. 𝐅 𝐱 𝐌. 𝐅 𝑬= 𝐒𝐱𝐖 Where: F: is lamp flux in lumens. U.F: is the utilization factor. 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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 Lamps Flux is taken from lamps catalogues : As example:

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 Utilization Factor can be calculated from below curve:

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Recommended Illuminance Values: Road Classification

Free Way

Express Way

Arterial

Local

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Area Classification

Illuminance Value

Commercial

21

Intermediate

17

Residential

12

Commercial

15

Intermediate

12

Residential

9

Commercial

12

Intermediate

9

Residential

6

Commercial

6

Intermediate

5

Residential

3

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Road Classification

Alleys

Side Walks

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Area Classification

Illuminance Value

Commercial

4

Intermediate

3

Residential

2

Commercial

3

Intermediate

6

Residential

2

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Chapter Three Elec. Outlets & Power Calculations

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Electric Outlets & Power Calculations Types of Electrical Outlets: 1. Normal Single & Duplex Sockets: This electrical outlet is single phase up to 10A or 16A, Used for light home loads like [TV, DVD… ETC]. These outlets have different shapes as shown below:

Normal Single Socket

Normal Double Socket

Normal Single Socket

Normal Single Socket

(Schuko plug)

(UPS Socket)

Normal Double Socket (Schuko Plug)

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2. Power sockets: This electrical outlet is single phases up to 32A, Used for heavy home loads like [Microwaves… ETC].

Power Single Socket

Power Industrial Socket

UPS Power Socket

3. Floor Boxes: These boxes are used to provide an electrical outlet in floors, especially when this outlet is far away from walls. These boxes have different shapes as below:

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4. Three Phase Industrial Sockets: These sockets used for industrial applications & have a ratings up to 125A.

5. Disconnect Switches: These devices have many other names like [Isolator Switch or Safty Switch] & Used for [FCUAHU-Pumps-Elevators-…..ETC] as isolator switch only. Also have different ratings as : 10 – 16 – 20 – 25 – 32 – 40 – 50 – 60 – 80 – 100 – 125 – 200 – 250 – 300 – 400 – 500 – 630 – 800 – 1000 – 1250 – 1600 – 2000 – 2500 – 3200A

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For all previous sockets types there are IP code for each socket which refer to protection degree against water & dust.

Sockets distribution: Socket distribution for a given room is dependent on the following factors: 1- Room application 2- Room furniture 3- 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.

Power & Current Calculations: 

Electrical Power Triangle:

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 Power Factor: It`s a percentage of used active power.

𝑷. 𝑭 =

𝑷 𝑺

Where: P ==== Active Power S==== Apparent Power For fluorescent lamps

PF = 0.45 ~ 0.6

For tungsten or halogen tungsten

PF = 1

For any machine if power factor not given we can assume it by 0.8.

 Power Factor correction: If power factor is very low, which is mean we have a large amount of losses so we must correct power factor value to reduce amount of losses by using capacitor banks or static var compensators.

Qcap = Qold – Qnew = P tanϴold – P tanϴnew

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Qcap = P [ tanϴold - tanϴnew]

𝑸𝒄𝒂𝒑 =

𝑽𝟐 𝑿𝒄

𝑿𝒄 =

,

𝟏 𝟐𝝅𝒇𝒄

𝑸𝒄𝒂𝒑 = 𝟐𝝅𝒇𝒄𝒗𝟐

𝑪=

𝑸𝒄𝒂𝒑 𝟐𝝅𝒇𝒗𝟐

F

Capacitor Bank should be protected by circuit breaker with current In: 𝑄𝑐𝑎𝑝 = V I

,

𝑰=

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𝑸𝒄𝒂𝒑 √𝟑𝑽

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Power Calculations: A. For lighting: -

Incident & Florescent lamps: Depend on lamp power

-

For chandeliers: S= 400≈500 VA

B. For Electrical Outlets: Electrical Outlet Normal Single Socket Normal Duplex Socket Power Socket Water Heater Hand Drier

Power [VA] 180 ~ 250 VA 360 ~ 500 VA From 1500 up to 5000 VA depend on Load 1500 VA For W.H below 80Lt. & 2000 VA For W.H up to 100 Lt. 1500 VA

 For current calculations: A. Single phase loads:

I (Amp) = 4.5 Skva B. 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.

 Electric lines 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.

A. For lighting lines: No more Each line

With wire 1500 VA

Than

2.5 mm2

Size

No more Than

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With wire 2000 VA Size

16 Amp MCB

B. For socket lines: Each line

With

3 mm2

With 20 Amp MCB

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C. For power socket lines: Each line

No more Than

1500 - 5000 VA

With wire

4 - 6 mm2

Size

With 25 - 32 A MCB

D. For hand drier: No more

Each unit takes a separate line

With wire 1500 VA

Than

4 mm2

Size

With 25 Amp MCB

E. For air conditioners: Each unit takes a separate line: 1, 2.25, 3 HP

4 mm2

25 Amp

4 - 5 HP

6 mm2

32 Amp

 Load schedules Project Name: Panel Name: Breaking cap.: Circuit Cable Type Number size R1 Lighting 2.5 mm2 Y1 Lighting 2.5 mm2 B1 Lighting 2.5 mm2 R2 Socket 3 mm2 Y2 Socket 3 mm2 B2 A.C 4 mm2 R3 Spare Y3 Spare B3 Spare

MCB: cable: size: MCCB 16A 16A 16A 20A 20A 25A 16A 20A 32A

Total connected load Eng.M.Tharwat

R 800

Three phase Y

B

Notes

600 990 1600 1800 1500

2400 2400 2490

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 Panel Boards Forms:  Form.1:

 Form.2a:

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 Form.2b:

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 Form.3b:

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 Form.4:

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 Load balancing: Given that the network is featuring a star connection. It’s important to achieve I1 ≈ I2 ≈ I3 to reach an IN of nearly equal zero.

R

I1 R

N

IN Y

Y

B

B

I2

I3

 Balance Check: For any panel board, there is a balance check for three phase loads due to reducing neutral current & unbalanced stresses on circuit breakers. Unbalance ratio can be calculated by:

𝑼𝒏𝒃𝒂𝒍𝒂𝒏𝒄𝒆 𝑹𝒂𝒕𝒊𝒐(%) =

𝑳𝒂𝒓𝒈𝒆𝒔𝒕 𝑷𝒉𝒂𝒔𝒆 𝑳𝒐𝒂𝒅 − 𝑺𝒎𝒂𝒍𝒍𝒆𝒔𝒕 𝑷𝒉𝒂𝒔𝒆 𝑳𝒐𝒂𝒅 𝒙𝟏𝟎𝟎 𝑳𝒂𝒓𝒈𝒆𝒔𝒕 𝑷𝒉𝒂𝒔𝒆 𝑳𝒐𝒂𝒅

Unbalance Ratio (%) mustn’t exceed a value of 5~10% of total three phase load. For above panel bard unbalance ration will be: 𝑼𝒏𝒃𝒂𝒍𝒂𝒏𝒄𝒆 𝑹𝒂𝒕𝒊𝒐(%) =

𝟐𝟒𝟗𝟎 − 𝟐𝟒𝟎𝟎 𝒙𝟏𝟎𝟎 𝟐𝟒𝟗𝟎

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

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 Demand factors: It`s the percentage of expected on line loads connected at the same time as a percentage of total loads type. For lighting ……….. ……………….... 0.7 ≈ 1 For all sockets……............................... 0.6 ≈ 0.9 For Air conditioners …………………..

1

For heaters and hand drier …………….

1

 Diversity factors: It`s the percentage of expected on line loads connected at the same time as a percentage of grand loads. These factors take values from 0.7 to 1.

 Circuit breaker capacity calculations: After conducting load and diversity factor calculations, now we consider C.B capacity calculations which are as follows:

IC.B =

𝑺(𝒍𝒂𝒓𝒈𝒆𝒔𝒕 𝒑𝒉𝒂𝒔𝒆) 𝟐𝟐𝟎

=

𝑺(𝒕𝒐𝒕𝒂𝒍 𝒍𝒐𝒂𝒅) 𝟑𝟖𝟎√𝟑

𝒙 𝟏. 𝟐𝟓 𝒙 𝟏. 𝟐𝟓

MCB

MCCB

ACB

Miniature Circuit Breaker

Molded Case Circuit Breaker

Air Circuit Breaker

Nominal Current

10 – 125 A

32 – 1600 A

1600 – 5000 A

Short Circuit Current

6 – 30 KA

10 – 80 KA

Up to 150 KA

Num.Poles

SP – DP – TP - FP

TP - FP

FP

Adjustment

Fixed

Fixed - Adjustable

Adjustable

Abbreviation

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Circuit breaker standard: 10 – 16 – 20 – 25 – 32 – 40 – 50 – 60 – 63 – 75 – 80 – 100 – 125 – 160 – 200 – 250 – 320 – 400 – 500 – 630 – 800 – 1000 – 1250 – 1600 – 2000 – 2500 – 3200 – 4000 – 5000 - 6300 Amp.

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:

[4x10]+10 mm CU/PVC

40A

380V,50HZ,Isc

32A

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20A

16A

32A

20A

X1

X1

X1

X1

X2

Spare

Spare

Spare

A.C

Socket

16A

X3 Lighting

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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 Letter

KVA/HP at starting

A B C D E F G H J K

1.6 3.29 3.72 4.25 5.3 5.95 6.1 6.7 7.55 8.495

Code Letter

KVA/HP at starting

L M N P R S T U V

9.495 10.595 11.845 13.25 14.995 16.995 18.995 21.195 22.4

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

Ist= 1.5 * 37.75 = 56.625 Amp

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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 Factor

Less than 5 5:10 More than 10

Group Drive Group Drive Group Drive

1 0.85 0.7

Design a panel board that feed 6 motors with below ratings: 2 motors 2 HP - 3 motors 3 HP - 2 motor 5 HP. [Assume that all motors have a code letter A] Motor 2 HP: In = 2 * 1.5 = 3A , Ist = 3 * 1.6 = 4.8A , Ic.b = 4.8 * 1.25= 6A (10A) Motor 3 HP: In = 3 * 1.5 = 4.5A , Ist = 4.5 * 1.6 = 7.2A , Ic.b = 7.2 * 1.25= 9A (10A) Motor 5 HP: In = 5 * 1.5 = 7.5A , Ist = 7.5 * 1.6 = 12A , Ic.b = 12 * 1.25= 15A (16A) For 6 motors & from above table : (D.F=0.85) Im.c.b = 12 + [0.85(7.5+(2*4.5) + (2*3)] = 31.13A (32A)

.

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Chapter Four Power 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 classified as following below: Operating & Meggered Voltages

600/1000

450/750

Copper

Aluminum

Insulation Material

PVC

XLPE

Number of cores

Single

Multi core

Armored [STA – SWA]

Non-Armored

Reduced Neutral

Non-Reduced Neutral

Conductor Type

Armored Neutral Size

There is a parameter which cables can be classified by, this parameter is insulation class.

Insulation Classes: Insulation Class A B F H

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Standing Temperature Up to 90 c Up to 110 c Up to 130 c Up to 180 c

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To select a cable for a certain load like below:

AC Source 380 V, 50HZ

ELECTRICAL LOAD

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 [DE rating Factors] must be taken in consideration.

DE rating factors [Grouping Factors]: DE rating factors are the factors that affect cables’ life time and their standing current and it’s dependent on cable laying methods. From Cables catalogue we can obtain the DE rating factors ratings

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Df = D1 x D2 x D3 x D4 x D5 x D6 x…..Dy

Icable =

𝑰𝑪.𝑩 𝑫𝒇

Voltage Drop: A long distance cable and its internal impedance may cause a voltage drop more than the allowed percentage. Voltage Drop Percentage mustn’t more than 5%.

Voltage drop calculations: 𝑽𝑭𝒂𝒄𝒕𝒐𝒓 𝒙𝑰𝑪.𝑩 𝒙𝑳 ]𝑿𝟏𝟎𝟎 𝟏𝟎𝟎𝟎𝑿𝟑𝟖𝟎

VD% = [ Where: VD% 𝑽𝑭𝒂𝒄𝒕𝒐𝒓 𝑰𝑪.𝑩 𝑳 Eng.M.Tharwat

Voltage Drop Percentage Voltage Drop Factor [Obtained from cables catalogues] Circuit Breaker Current Cables Length

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Chapter 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 companies. (2) Emergency as in hospitals. (3) Production as in factories…etc So 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 continuity: (A) (B)

Generators UPS

Difference between Generators and UPS: Generators are 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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Generators: Synchronous machines are used usually as generators. Synchronous Machines Components: 1. Stator. 2. Rotor:  Salient Pole Type.  Cylindrical Type. 3. Exciter. Concept of Operation:  The rotating magnetic field synchronous machine has the field-winding wound on the rotor, and the armature wound on the stator.  A dc current, creating a magnetic field that must be rotated at synchronous speed, energizes the rotating field-winding.  The rotating field winding can be energized through a set of slip rings and brushes (external excitation), or from a diode-bridge mounted on the rotor (selfexcited). The rectifier-bridge is fed from a shaft-mounted alternator, which is itself excited by the pilot exciter.  In externally fed fields, the source can be a shaft-driven dc generator, a separately excited dc generator, or a solid-state rectifier. Several variations to these arrangements exist.

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Uninterruptable Power Supply ”UPS”: An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails.

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ATS panels: Main source

ATS

G

Load

It’s a panel that consists of three switches one is connected to the main source, the second one is connected to the Generator and the third one is connected to the load through a controller “Microcontroller, PLC…Etc”

Distributers: It`s used in case of many transformers or generators & medium voltage loops.

G 1 3 2 UPS

L5

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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. S2 is bus coupler.

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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 discharging time 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.

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Chapter Six Short Circuit Current

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Short circuit current Due to large current passing through the network during faults, there are many effects of short circuit currents as following: 1. At fault location:  Damage Insulations for cables & bars.  Welding of conductors.  Fire & danger to life. 2. On fault circuit:  Electrodynamics forces result in deformation of bus bars & disconnect cables.  Temperature Rise in equipment 3. On other circuits:  Voltage Dip during the time.  Shut Down of a part of the network  Dynamic instability and /or the loss of machine synchronization.  Disturbances in control/monitoring circuits. So, the power systems should 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.

Thermal trip

Mag. trip

Ir

Im

Isc

Fig (A)

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Fig.A is a Circuit Breakers Characteristics, from a/m fig. :

Ir is normal breaker current that described as operation current. Im is a current that break trip become by magnetic part. Isc is a maximum short circuit current or maximum current that breaker can stand for a short trip time. There is another parameter that effect in breakers selection, this parameter is making current which defined as maximum current break can stand during making.

Short circuit current calculations: According to IEC60909. There are many ways to calculate short circuit current:  Symmetrical Components method. [Very complicated & N/A].  Impedance method. [Very simple & most common use in LV applications]

A. Impedance Method: IS.C =

𝑽𝑷𝒉 𝒁𝒔𝒄

𝒙 𝟏. 𝟎𝟓

Where: Vph is phase voltage Zsc is total Short Circuit impedance Multiplying value by 1.05 represent transformer terminal voltage with no load +5% To determine the impedances values for electrical equipments follow next paper.

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1/Up Stream Network: These values based on 400 volt, 50HZ network, so reactance given by:

Rup = Xup =

𝐕𝟐 𝐒𝐌𝐕𝐀 𝐕𝟐 𝐒𝐌𝐕𝐀

𝐱𝟎. 𝟏𝟓𝐱𝟏𝟎−𝟑 𝐱𝟎. 𝟗𝟖𝐱𝟏𝟎−𝟑

Voltage Rating (KV)

Power Rating

Resistance Value

Reactance Value

7.2 – 11 – 12 – 17.5 – 24 36 52 – 72.5

500 MVA

0.0481mΩ

0.314 mΩ

1000 MVA

0.0961mΩ

0.628mΩ

3000 MVA

0.288mΩ

1.884mΩ

2/Transformers: Short Circuit Voltage Short circuit voltage (Usc %) is the voltage that has to be applied to the primaries of a transformer, so that the nominal current flows through the secondary’s, when they are shorted. The Following Table gives the Usc% of the transformer: Transformer Apparent Power Sn [KVA]

≤630

630<Sn≤1250

1250<Sn≤2500

2500<Sn≤6300

6300<Sn≤25000

Short Circuit Voltage Usc%

4

5

6

7

8

These values based on 400 volt, 50HZ, Transformers, so reactance given by:

Rtr = Xtr =

𝐖𝐜𝐱𝐕 𝟐 𝐒𝐊𝐕𝐀 𝐕𝟐 𝐒𝐊𝐕𝐀

𝐱𝟏𝟎−𝟑 , Wc is transformer copper losses

𝐱 𝐔𝐒.𝐂 𝐱 𝟏𝟎−𝟐

For simplification we can consider Rsc=0.2Xsc of transformer

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Power Rating

Usc%

Resistance Value

25 KVA

4

51.2mΩ

50 KVA

4

25.6mΩ

100 KVA

4

12.8mΩ

160 KVA

4

8mΩ

200 KVA

4

6.4mΩ

250 KVA

4

5.12mΩ

315 KVA

4

4.06mΩ

400 KVA

4

3.20mΩ

500 KVA

4

2.56mΩ

630 KVA

4

2.03mΩ

800 KVA

5

2mΩ

1000 KVA

5

1.6mΩ

1600 KVA

6

1.2mΩ

2000 KVA

6

0.96mΩ

4.8mΩ

2500 KVA

7

0.896mΩ

4.48mΩ

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Reactance Value 256 mΩ 128 mΩ 64 mΩ 40 mΩ 32 mΩ 25.6 mΩ 20.3 mΩ 16 mΩ 12.8 mΩ 10.16 mΩ 10 mΩ 8 mΩ 6 mΩ

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3/Circuit breaker:  RC.B is negligible  XC.B is negligible 4/Bus Way: ⍴𝐋  RB = mΩ 𝑺  XB = 0.15L mΩ

5/Cables: ⍴𝐋 mΩ 𝑺  XC = 0.08L mΩ [MultiCore Cables]  XC = 0.12L mΩ [Single Core Cables]

 RC =

Where:  ⍴ = 22.5 𝑓𝑜𝑟 𝑐𝑜𝑝𝑝𝑒𝑟  ⍴ = 36 𝑓𝑜𝑟 𝐴𝑙𝑢𝑚𝑖𝑛𝑢𝑚  S is cross section area of conductor per phase.

From a/m equations we can get the total short circuit impendence by: Rt =Rup + Rtr + Rb + Rc , Xt = Xup + Xtr + Xb + Xc 𝑍𝑠𝑐)𝑡 = √𝑅𝑡 2 + 𝑋𝑡 2 Short circuit current can be calculated by another method:

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“Up and Down Stream Tables”

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Chapter 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.

 The effect of the passage of Electric Current to the human body:

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To calculate maximum allowable current passing through human body: 𝐼=

116 √𝑡

𝑚𝐴

Earthing Systems terminology: According to IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT. The first letter indicates the connection between earth and the powersupply equipment (generator or transformer):  "T" — Direct connection of a point with earth.  "I" — No point is connected with earth (isolation), except perhaps via a high impedance. The second letter indicates the connection between earth and the electrical device being supplied:  "T" — Direct connection of a point with earth  "N" — Direct connection to neutral at the origin of installation, which is connected to the earth

TN networks: In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer. The conductor that connects the exposed metallic parts of the consumer's electrical installation is called protective earth.

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The conductor that connects to the star point in a threephase system, or that carries the return current in a singlephase system, is called neutral (N). Three variants of TN systems are distinguished:  TN−S: PE and N are separate conductors that are connected together only near the power source. This arrangement is a current standard for most residential and industrial electric systems particularly in Europe.  TN−C: A combined PEN conductor fulfils the functions of both a PE and an N conductor.  TN−C−S: Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, and separated in the service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of electric shock in the event of a broken PEN conductor - with a similar system in Australia and New Zealand being designated as multiple earthed neutral (MEN).

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TT network: In a TT (Terra-Terra) earthing system, the protective earth connection for the consumer is provided by a local earth electrode, (sometimes referred to as the Terra-Firma connection) and there is another independently installed at the generator. There is no 'earth wire' between the two. The fault loop impedance is higher, and unless the electrode impedance is very low indeed, a TT installation should always have an RCD (GFCI) as its first isolator. The big advantage of the TT earthing system is the reduced conducted interference from other users' connected equipment. TT has always been preferable for special applications like telecommunication sites that benefit from the interference-free earthing. Also, TT does not have the risk of a broken neutral. In locations where power is distributed overhead and TT is used, installation earth conductors are not at risk of becoming live should any overhead distribution conductor be fractured by, say, a fallen tree or branch. In pre-RCD era, the TT earthing system was unattractive for general use because of the difficulty of arranging reliable automatic disconnection (ADS) in the case of a live-to-PE short circuit (in comparison with TN systems, where the same breaker or fuse will operate for either L-N or L-PE faults). But as residual current devices mitigate this disadvantage, the TT earthing system has become much more attractive providing that all AC power circuits are RCD-protected. Eng.M.Tharwat

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In some countries (such as the UK) is recommended for situations where an low impedance equipotential zone is impractical to maintain by bonding, where there is significant outdoor wiring, such as supplies to mobile homes and some agricultural settings, or where a high fault currents could pose other dangers, such as at fuel depots or marinas. The TT earthing system is used throughout Japan, with RCD units in most industrial settings. This can impose added requirements on variable frequency drives and switched-mode power supplies which often have substantial filters passing high frequency noise to the ground conductor.

IT network: In an IT network, the electrical distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems, an insulation monitoring device is used to monitor the impedance.

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Soil Resistivity Measurements: Use the following items: 1. Earthing Megger. 2. Four Rods 60cm with diameter 13 mm. 3. Four Flexible Cables. Put four rods as shown in figure with equal distances & depth of 30cm. Connect earthing megger to make points C1& C2 as a current points & points P1 & P2 as a potential points.

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Then the earthing megger will give R value & we can get soil resistivity (ρ): ρ=2πAR

Where: A is a distance between electrodes in m

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. It

Re….. Earthing Resistance. I1

The sole purpose of any earthing system is to protect humans from (I 1)

I2

So for I1<<< I2 or (I1 ≅ zero) So it’s required Re <<< Rh For power systems: Rearthing = 2 ≅ 4 Ω For light current systems: Rearthing = 0.5 Ω

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It I1

I2

Rh

Re

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Earthing Systems Resistance Calculation:  Resistance of one vertical electrode is given by: 𝑅=

𝜌 2𝜋𝐿

8𝐿

[log ( 𝑑 ) − 1]

Where: R : is resistance of single rod in ohms. L : is rod length in meter. d : is rod diameter in meter. ρ: is soil resistivity in ohm meter.

 Total Resistance of (n) rods: This value depends on rods arrangement: 1. Vertical parallel rods arranged as hollow square: 1 + 𝑎𝜆 ) 𝑛 𝜌 𝑎= 2𝜋𝑅𝑆

𝑅𝑛 = 𝑅 (

Where: R: is resistance of single rod in ohms. S: is the distance between rods in meters. ρ: is soil resistivity in ohms meter. λ: is a factor given by below table. n: is number of rods.

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2. Vertical Parallel rods arranged as straight line: 1 + 𝑎𝜆 ) 𝑛 𝜌 𝑎= 2𝜋𝑅𝑆

𝑅𝑛 = 𝑅 (

Where: R: is resistance of single rod in ohms. S: is the distance between rods in meters. ρ: is soil resistivity in ohms meter. λ: is a factor given by below table. n: is number of rods.

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3. Three rods at the vertices of an equilateral triangle: 𝑅𝑛 =

1 8𝐿 {2 [log ( ) − 1] − 1 + 2𝐿𝑆} 3 𝑑

Where: S: is the distance between rods in meters. L: is rod length in meter. d: is rod diameter in meter.

Earthing System Measurements: Connect earth megger as below; the distances between rods are according to manufacture of earth megger regulations:

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Standards for electrical equipment’s& fixtures:

1. IP Code:

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2. IK Code:

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Refrences:  Egyptian Code.  IEC Code.  NEC Code.  BS – Earthing System Design.  ‫ جيالني‬/‫التمديدات الكهربية – د‬  Internet Articles

For any questions or notes: Eng.Mohammed Tharwat  Mob: 01066614891

F.B:  Official Page : https://www.facebook.com/courses.m.tharwat/?ref=bookmarks  Official Group: https://www.facebook.com/groups/1434852616764325/

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With my best wishes …… Eng.M.Tharwat

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