Practical Assignment HVE

TABLE OF CONTENTS

TABLE OF CONTENTS.....................................................................................................................................................2

SUBMISSION FORM FOR PRACTICALS.........................................................................................................................3

1 IMPULSE TEST.................................................................................................................................4(a) Practical example of an impulse generator circuit......................................................................4 (b) A photo of a test impulse generator and description of it..........................................................5(c) The operation of a impulse generator.........................................................................................5 (d) Advantages and disadvantages of the impulse generator...........................................................5(e) A standard wave shape of a 1/50 micro second wave.................................................................6

(f) The BIL value For a 22kV voltage regulator..................................................................................6

2 TAN DELTA TESTING..................................................................................................................................7(a) A construction diagram of a Tan – Delta test circuit.....................................................................7(b) A photo of a tan – delta tester and description of it.....................................................................7(c) A picture of a typical tan –delta test set-up for a test...................................................................7(d) Description of the operation of a tan – delta generator...............................................................7(e) A diagram of a basic Schering Bridge.............................................................................................8(f) Formulation of the three important equations applicable to the Schering Bridge.......................8

3 VOLTAGE RATIO TEST ON A TRANSFORMER..............................................................................................9(a) Description of a typical layout diagram of a transformer to be tested..........................................9 (b) Construction diagram of a voltage ratio-meter tester....................................................................9(c) Calculate the transformer ratio for Delta-star transformer............................................................9 (d) A typical name plate of a three phase transformer.......................................................................10(e) A picture of a typical voltage ratio test set-up for a test...............................................................10

4. SAFETY........................................................................................................................................................11(a) Actions that you should take before starting any experiment. ....................................................11(b) The responsibility of safety when doing an experiment...............................................................11

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1. IMPULSE TEST:

a) A 3-stage Marx impulse generator in circuit ‘b’ connections.

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b) Test impulse generator

c) In order that equipment designed to be used on high voltage lines, and others, be able to withstand surges caused in them during operation, it is necessary to test these equipment with voltages of the form likely to be met in service.The apparatus which produces the required voltages is the impulse generator. In high voltage engineering, an impulse voltage is normally a unidirectional voltage which rises quickly without appreciable oscillations, to a peak value and then falls less rapidly to zero. A full impulse wave is one which develops its complete waveshape without flashover or puncture, whereas a chopped wave is one in which flash-over occurs causing the voltage to fall extremely rapidly. The rapid fall may have a very severe effect on power system equipment.

d) Advantages: The proposed generator is portable, thereby allowing tests to be made on devices that cannot be moved

from their location. Testing results obtained with the proposed impulse generator were satisfactory in terms of time and

wave forms compared to other commercial impulse generators and the standard impulse wave simulator.

low cost implementation - Commercial components and low-cost components were used in this design

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8. bell-type insulator

and it's comfortable size for use and ease of transport.

Disadvantages: designed limitation and built with insulation to only deliver up to 20kV impulse voltage waves.

e) A standard wave shape of a 1/50 micro second wave clearly indicating the values of t0, t1, t2 and t3

f)System voltage

kV(rms)System voltage BIL*

kV(rms) kV(peak)

22 150

SABS 1019 (1985) stipulates the standard insulation levels for distribution systems.

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2. TAN DELTA TESTING a) a) Insulator b) equivalent circuit c) vector diagram

tan IR/IC

b) PE-ACDF-1 - Automatic Capacitance & Tan-delta tester 12kV 200mA from ABB

c) Tan delta measurement on a grounded cable

d) Tan Delta is also known as the 'loss angle' or 'dissipation factor'. It is used to test the level of degradation in insulation materials of electrical machines and power cables. The winding insulation of an electrical machine, or a cable free from defects, will act as a perfect capacitor, that is, it will only store energy and not dissipate it.In an ideal capacitor, the voltage and current are out of phase by 90 degrees and the current flowing through the insulation is purely capacitive Ic. However, dielectric losses within the insulation due to deterioration or other factors, will result in the reduction of the resistance in the insulation. This will in turn increase the resistive current Ir. The phase angle between the current and voltage is now less than 90 degrees, and the extent to which this is less than 90 degrees gives the level of degradation in the insulation. So this 'loss angle' is required to be measured.

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This is a complete integrated Capacitance and Tan-Delta test set including inbuilt 12kV AC power source Measurement Bridge and a reference SF6 gas filled Standard Capacitor.

It is simple to use and easy to operate. It has a large backlit LCD display, and soft touch membrane buttons. The connections are simple and the set can be operated by inexperienced operators. The set is extremely light-weight and portable enough to be carried by a single person.

Equipped with a USB serial output port, users can download their test results on PCs, or can use the internal 99 test storage facility. Integrated thermal Printer also allows printing of results on site. The instruments are calibrated in our in-house test laboratory to give you results traceable to national standards.

If the angle is Delta, then the tangent of Delta can be calculated by dividing is 'opposite over adjacent', which is Ir/Ic.

e) Basic high voltage Schering bridge

f) (a) For the parallel circuit the dissipation factor is given by:

(b) for the series circuit:

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3. VOLTAGE RATIO TEST ON A TRANSFORMER :

a) Delta-star 3 phase transformer (/Y Connection)

This connection is generally employed where it is necessary to step up the voltage as for example, at the beginning of high tension transmission system. The connection is shown above. The neutral of the secondary is grounded for providing 3-phase 4-wire service. In recent years, this connection has gained considerable popularity because it can be used to serve both the 3-phase power equipment and single-phase lighting circuits.This connection is not open to the objection of a floating neutral and voltage distortion because the existence of a -connection allows a path for the third-harmonic currents. It would be observed that the primary and secondary line voltages and line currents are out of phase with each other by 30°. Because of this 30° shift, it is impossible to parallel such a bank with - 'or Y- Y bank of transformers even though the voltage ratios are correctly adjusted. The ratio of secondary to primary voltage is √3 times the transformation ratio of each transformer.

b)

c) kt = V1ph / V2ph

= 22000 / 400/√3= 31.75 step up

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d) Name Plate of a Transformer

e) I chose a simple typical setup for acquiring the voltage ratio, with the open circuit test.

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4. SAFETY

a) 1. There must be at least two (2) people in the laboratory/working area while working on live circuits.

2. Shoes must be worn at all times.

3. Remove all loose conductive jewelry and trinkets, including rings, which may come in contact with exposed circuits. (Do not wear long loose ties, scarves, or other loose clothing around

machines.)

4. Consider all circuits to be "hot" unless proven otherwise.

5. When making measurements, form the habit of using only one hand at a time. No part of a live circuit should be touched by the bare hand.

6. Keep the body, or any part of it, out of the circuit. Where interconnecting wires and cables are involved, they should be arranged so people will not trip over them.

7. Be as neat a possible. Keep the work area and workbench clear of items not used in the experiment.

8. Always check to see that the power switch is OFF before plugging into the outlet. Also, turn instrument or equipment OFF before unplugging from the outlet.

9. When unplugging a power cord, pull on the plug, not on the cable.

10. When disassembling a circuit, first remove the source of power.

11. "Cheater" cords and 3-to-2 prong adapters are prohibited unless an adequate separate ground lead is provided, the equipment or device is double insulated, or the laboratory ground return is known

to be floating.

12. No ungrounded electrical or electronic apparatus is to be used in the laboratory unless it is double insulated or battery operated.

13. Keep fluids, chemicals, and beat away from instruments and circuits.

14. Report any damages to equipment, hazards, and potential hazards to the laboratory instructor/safety representative or supervisor.

15. If in doubt about electrical safety, see the laboratory instructor/safety representative or supervisor. Regarding specific equipment, consult the instruction manual provided by the manufacturer of

the equipment. Information regarding safe use and possible- hazards should be studied carefully.

b) Employees/students - anyone doing electrical experiments or work need to understand the potential hazards and take proper precautions before working around something as dangerous as electricity. All employees/students must read and understand the information in that is contained in the safety policy of their respective work place or institution. Your personal laboratory/work place safety depends mostly on YOU. Employees/Students must adhere to written and verbal safety instructions/procedures throughout their career.

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Practical Assignment HVE

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