List of Experiments. Exp. # Experiment Title Page #

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1 List of Experiments Exp. # Experiment Title Page # -- Safety Rules 02 1 Study of High Lab in the University 03 2 To Calibrate a Sphere-Gap using its Breakdown Strength against Gap Settings 07 3 To Calibrate a Rod-Gap using its Breakdown Strength against Gap Settings 10 4 To Calibrate a Cone-Shaped Gap using its Breakdown Strength against Gap Settings 13 5 To Calibrate Flat-Surface Gap using its Breakdown Strength against Gap Settings 16 6 To Calibrate Cone-Flat Surface Gap using its Breakdown Strength against Gap Settings 19 7 To Find Out The 50% Critical Impulse Flash-Over s on the 11kv Pin-Type Insulator with Positive & Negative Impulses 22 8 Study of Relationship between String Efficiency & the No. of Insulators (Units) used in a String Insulator 25 9 Study of Relationship between String Efficiency & the No. of Insulators (Units) used in a String Insulator with Guard Ring To Compare the Flashover s Wet and Dry for a Typical Outdoor Insulator To Measure the Ground Resistance 36 University of Engineering & Technology, Lahore. Page 1

2 Experiment # 7 To Find out the 50% Critical Impulse Flash-Over s on the 11KV Pin-type Insulator with Positive & Negative Impulse Control Panel Charging Unit Impulse Generator Insulator 0 CRO Apparatus: Test Specimen (11 kv Insulator) Impulse Generator Charging Unit Control Board 50% Critical Impulse Flash-Over : The 50% critical flashover voltage is the crest value of the impulse wave that under specified conditions causes flashover on 50 percent of the applications. University of Engineering & Technology, Lahore. Page 22

3 Procedure: The Impulse Generator shall first be adjusted to deliver a negative 1.2/50 µs waveform. It is applied on to the insulator until the flashover occurs. When the flash over occurs then it is tested for the voltage below it. If it again flashes, voltage is decreased to check. If it does not flashes then voltage is increased until it flashes. This process is repeated for one subsequent voltage value, where there is a 50% chance of Flashover. All this process is repeated for the positive waveform as well. Observations & Calculations: Barometric Pressure (b): Room temperature (t): Correction Factor (K): mm of Hg o C ( b/760 ) * ( 293 / (273 + t )) = Type of Insulator: 11KV Pin type (i) Type of Impulse Applied: Negative No of Readings KV Flash or Not (F/N) University of Engineering & Technology, Lahore. Page 23

4 50% Critical Impulse Flash Over = x K = KV (ii) Type of Impulse Applied: Positive No of Readings KV Flash or Not (F/N) 50% Critical Impulse Flash Over = x K = KV Comments: Teacher s Initials: Date: University of Engineering & Technology, Lahore. Page 24

5 Experiment # 8 Study of relationship between String Efficiency & the no of Insulators (units) used in a String Insulator. A B C Water Resistance D V3 E V4 230V IVR 0-460V V 0-150KV V 0 0 Apparatus: Insulator string 1. 3 units 2. 4 units 3. 5 units Electrostatic Voltmeter 150 kv Testing Transformer with Control & Protection Gear Procedure: The circuit arrangement of the experiment is shown in fig. A specific voltage is applied across the string. of each unit is measured with respect to ground using an electrostatic type Voltmeter. Thus voltage distribution across each unit can be found out. Protective resistance is inserted to protect the secondary of high Testing Transformer University of Engineering & Technology, Lahore. Page 25

6 in the case of short circuit during breakdown. Three different readings are taken by changing the no. of insulators from 3 to 5. String Efficiency is calculated for each string. Observations & Calculations: (i) 3 Insulators applied on the string = V = KV Across Insulator A B C Equation - V - Efficiency = across string n x across unit near power conductor = % (ii) 4 Insulators applied on the string = V = KV V3 University of Engineering & Technology, Lahore. Page 26

7 Across Insulator A B C D Equation - V3 - V - V3 Efficiency = across string n x across unit near power conductor = % (iii) 5 Insulators applied on the string = V = KV V4 V3 Across Insulator A B C D E Equation - V3 - V4 - V3 V - V4 University of Engineering & Technology, Lahore. Page 27

8 Efficiency = across string n x across unit near power conductor = % Comments: Teacher s Initials: Date: University of Engineering & Technology, Lahore. Page 28

9 Experiment # 9 Study of Relationship between String Efficiency & the No. of Insulators (units) used in a String Insulator with Guard Ring A B C Water Resistance D V3 E V4 230V IVR 0-460V V 0-150KV V 0 0 Apparatus: Insulator string 1. 3 units 2. 4 units 3. 5 units Electrostatic Voltmeter 150KV Testing Transformer with Control & Protection Gear Procedure: The circuit arrangement of the experiment is shown in fig. A specific voltage is applied across the string. of each unit is measured with respect to ground using an electrostatic type Voltmeter. Thus voltage distribution across each unit can be found out. Protective resistance is inserted to protect the secondary of high Testing Transformer in the case of short circuit during breakdown. Three different readings are taken by changing the no. of insulators from 3 to 5. String Efficiency is calculated for each string. University of Engineering & Technology, Lahore. Page 29

10 Observations & Calculations: (iv) 3 Insulators applied on the string = V = KV Across Insulator A B C Equation - V - Efficiency = across string n x across unit near power conductor = % (v) 4 Insulators applied on the string = V = KV V3 University of Engineering & Technology, Lahore. Page 30

11 Across Insulator A B C D Equation - V3 - V - V3 Efficiency = across string n x across unit near power conductor = % (vi) 5 Insulators applied on the string = V = KV V4 V3 Across Insulator A B C D E Equation - V3 - V4 - V3 V - V4 University of Engineering & Technology, Lahore. Page 31

12 Efficiency = across string n x across unit near power conductor = % Comments: Teacher s Initials: Date: University of Engineering & Technology, Lahore. Page 32

13 Experiment # 10 To Compare the Flashover s Wet and Dry for a Typical Outdoor Insulator. Water Resistance 230V V Insulator 0 0 Apparatus: Pin Type Insulator Water 150 kv Testing Transformer with control and protective gear Procedure: The purpose of this test is to show the two modes of flash over and to indicate the difference in the two flashover voltages. Precautions: Obtain the flashover voltage dry for the insulator, repeating tests several time in order to get a good average value. The dust on the insulator will lower the flash over value. University of Engineering & Technology, Lahore. Page 33

14 Theory: The flash over voltage of an insulator is considerably lower if its surfaces are wet. These wet surfaces form a conducting path and the effective insulated path for flashover is then shortened. Insulators are designed as that even under rain conditions, portions of the sheds remains dry and provide effective insulation. In the laboratory rain tests are often made by spraying water at an angle 45 o to the insulator subjected to voltage. Observations & Calculations: Barometric Pressure (b): Room temperature (t): Correction Factor (K): mm of Hg o C ( b/760 ) * ( 293 / (273 + t )) = Dry 1 min Power Frequency Withstand : Wet 1 min Power Frequency Withstand : Dry Power Frequency Flash Over : Wet Power Frequency Flash Over : kv kv kv kv Type of Test Dry Flash Over Wet Flash Over No. of Readings Average Corrected kv kv kv kv kv Dry 1 min Withstand or Not: Wet 1 min Withstand or Not: University of Engineering & Technology, Lahore. Page 34

15 Comments: Teacher s Initials: Date: University of Engineering & Technology, Lahore. Page 35

16 Experiment # 11 To measure the Ground Resistance Apparatus: Earth tester type 3235 Three electrodes Measurement leads Procedure: Make connection as shown above where E-P-C should be approximately in line. This three-point method involves passing a current into the electrode to be measured and measuring the voltage between the ground electrode (E) under test and a test potential electrode (P). A test current electrode (C) is driven into the earth to permit passage of current into the electrode to be tested. Potentials are measured with respect to the ground electrode under test which is assumed to be at zero potential. It is shown in the following figure University of Engineering & Technology, Lahore. Page 36

17 Precaution:. Make galvanometer balance by turning dial. For battery check, needle should be within blue belt. Theory: The purpose of electrical ground testing is to determine the effectiveness of the grounding medium with respect to true earth. The earth may provide the return path for fault currents, and for safety, all electrical equipment frames are connected to ground. The resistivity of the earth is usually negligible because there so much of it available to carry current. The limiting factor in electrical grounding systems is how well the grounding electrodes make contact with the earth, which is known as the ground rod interface. This interface resistance component, along with the resistance of the grounding conductors and the connections, must be measured by the ground test. In general, the lower the ground resistance, the safer the system is considered to be. There are different regulations which set forth the maximum allowable ground resistance, for example: the National Electrical Code specifies 25 ohms or less; MSHA (Mine Safety and Health Administration) is more stringent, requiring the ground to be 4 ohms or better (less resistance). University of Engineering & Technology, Lahore. Page 37

18 Observation Measured Ground Resistance = Ω Comments: Teacher s Initials: Date: University of Engineering & Technology, Lahore. Page 38

19 Students Feedback: Learning Outcomes: Suggestion for Improvement: University of Engineering & Technology, Lahore. Page 39