PRACTICAL WORK BOOKFor Academic Session 2009

ELECTRICAL MACHINES THEORY &DESIGN (EE-445)

ForBE (EE)

Name:Roll Number:Class:Batch:Department :

Department of Electrical EngineeringNED Universit y of Engineering & Technology, Karachi

TABLE OF CONTENTS

EXPERIMENT # TITLE Page

#

1 Determine the outputs of two D.C. machines from their physical dimensions

1

2 Develop a fact sheet to show how to obtain the most efficient motor at the lowest price

2

3 Study the types of Standard Explosion Protection Enclosures for electrical equipment

4

4 Design of Electrical Equipment for Hazardous Areas- Hazardous Area classification in North America

7

5 Design of Electrical Equipment for Hazardous Areas- Hazardous Area classification in Europe

9

6 Design of Electrical Equipment – Level of Ingress Protection (“IP rating”)

11

7 Design of Transformer–Methods of cooling of Transformers

13

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Experiment No. 1 TITLE: Determine the outputs of two D.C. machines from their physical dimensions. THEORY: The formula for calculation of output of DC machine is : Output = (π2 x Bav x ac x 10-3) D2 x L x n Where: Bav = specific magnetic loading; ac = specific current loading; D = diameter; L= Core length; n = speed PROCEDURE:

1. Measure the following dimensions of the two DC machines.

2. Take Bav= 0.6 Wb/m2 ; & δ = 5.0 A/mm2

CALCULATIONS & RESUTS

1. Derivation of relationship, ac = (δ x Sf x As x S)/ (π x D), starting from the basic definition of ac, i.e. ac = IZ Z / π D

2. Output of Machine A:

3. Output of Machine B:

Machine D (m) L (m) n (rps) No. of slots S

Slot space factor Sf

Area of slot As (mm)2

A B

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Experiment No. 2 TITLE: Develop a fact sheet to show how to obtain the most efficient motor at the lowest price THEORY Efficiency is an important factor to consider when buying or rewinding an electrical motor. Following are the frequently asked questions that help to make the correct decision. QUESTIONS

1. Why is improving motor efficiency important?

2. What is an energy-efficient motor?

3. What efficiency values should I use when comparing motor?

4. When should I consider buying an energy-efficient motor?

5. When is an energy-efficient motor cost effective? Give the relation ships for “ Annual Energy Saving” & Simple Payback”.

6. Should I rewind a failed motor?

7. What design factors should I consider when choosing a new motor?

ANSWERS

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CONCLUTIONS

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Experiment No. 3 TITLE: Study the types of Standard Explosion Protection Enclosures for electrical equipment. THEORY: Various types of enclosures for electrical machines and other electrical equipment are used to prevent electrical apparatus from igniting the surrounding atmosphere when energized. TYPES OF EXPLOSION PROTECTION: Define the following terms as per Standards:

1. Flameproof Enclosures- Ex protection type ‘d’

2. Increased Safety – Ex protection type ‘e’

3. Intrinsic Safety – Ex protection type ‘ i’

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4. Pressurized or Purged – Ex protection type ‘p’

5. Oil Immersion – Ex protection type ‘o’

6. Powder Filled – Ex protection type ‘q’

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7. Non-Sparking and Restricted Breathing – Ex protection type ‘n’

8. Special Protection – Ex protection type ‘S’

9.Moulded/Encapsulated – Ex protection type ‘m’

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Experiment No. 4

TITLE: Design of Electrical Equipment for Hazardous Areas- Hazardous Area classification in North America. THEORY: Hazardous areas are locations where the potential for fire or explosion exists because of gases, dust or easily ignitable fibers in the atmosphere. In North America, Hazardous Areas are separated by classes, divisions and groups to define the level of safety required for equipment installed in these locations. Classes define the general form of materials in the atmosphere. Divisions define the possibility of the presence of flammable materials. Groups classify the exact flammable nature of the material. CLASSIFICATIONS: Study and complete the following tables:

CLASSES

Class I

Class II

Class III

DIVISIONS Division 1

Division 2

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GROUPS

Group A

Group B

Group C

Group D

Group E

Group F

Group G

CONCLUSIONS:

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Experiment No. 5

TITLE: Design of Electrical Equipment for Hazardous Areas- Hazardous Area classification in Europe. THEORY: Hazardous areas are locations where the potential for fire or explosion exists because of gases, dust or easily ignitable fibers in the atmosphere. In Europe and countries outside North America, classification of hazardous area is different and is follows; Zones are used to define the probability of presence of flammable materials. Protection Types denote the level of safety for the device. (Ref. Experiment No. 3). Groups classify the exact flammable nature of the material. These groups are different than American groups. Temperature Identifications convey the maximum surface of the apparatus based on 40 oC ambient. CLASSIFICATIONS: Study and complete the following tables

ZONES ( degree of “risk”) Zone 0

Zone 1

Zone 2

Zone 10

Zone 11

Groups

Group I

Representative Gas:

Group II A

Representative Gas:

Group II B

Representative Gas:

Group II C

Representative Gas:

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TEMPERATURE CODES oF oC

T 1 T 2 T 3 T 4 T 5 T 6

CONCLUSIONS:

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Experiment No. 6 TITLE: Design of Electrical Equipment – Level of Ingress Protection (“IP rating”) THEORY: Three digits are used to denote the level of ingress protection (“IP rating”) that a piece of electrical equipment meets. (Third digit is commonly omitted) IP Ratings Complete the following tables. IP First number – protection against solid objects 0

1

2

3

4

5

6

IP Second number – Protection against liquids 0

1

2

3

4

5

6

7

8

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IP Third number – Protection against mechanical impacts 0

1

2

3

4

5

6

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Experiment No. 7 TITLE: Design of Transformer–Methods of cooling of Transformers THEORY:

There are a number of methods for cooling of transformers. The large number of methods used for dissipation of heat generated in transformers makes it necessary to use a concise standard designation for them.

Description of cooling methods:

1. Cooling Mediums (Coolants) Complete the following table:

Medium Air Gas Synthetic oil

Mineral Oil Solid Insulation

Water

Symbols

2. Circulation of cooling medium: Describe the two ways of circulation of coolants for dry type and oil immersed transformers and give the symbols.

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3. Transformer oil: Describe the functions of transformer oil:

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4. Important characteristics of transformer oil: Write the important characteristics: