ATTENDANCE / PUNCTUALLTY 10%
DATA SHEET / EXPERIMENT 30%
SCHEMATIC / GRAPHS 20%
DISCUSSION / CONCLUSION 40%
TOTAL 100%
KE48101 ENGINEERING LAB 6
EXPERIMENT 1
AC ELECTRICAL BREAKDOWN TEST IN AIR
Name : 1.
Matric No :
Lab Group Number :
Lecturer Name :
Lab Instructor Name :
Report Type : Informal Report
Date of Experiment :
Date of Report Submission :
Experiment 1
Title: AC Electrical Breakdown Test in Air
Reference:
[1] Terco Manual
[2] Naidu M.S. and Kamaraju V. 2004. High Voltage Engineering 3rd Edition. Singapore:
McGraw-Hill Publishing Company Limited
Objectives:
1. To understand the requirements for the generation of AC high voltage
2. To analyze methods of measuring AC high voltage using:
o Primary voltage and Transformer Ratio
o Sphere Gap
o Capacitor divider and AC peak voltmeter
Equipment:
Component Description Specification Part Number Quantity
HV Test Transformer 5kVA, 100kV HV9105 1
Control Desk HV9103 1
Measuring Capacitor 100pF, 100kV HV9141 1
AC Peak Voltmeter 200kV HV9150 1
Connecting Rod HV9108 2
Connecting Cup HV9109 2
Floor Pedestal HV9110 1
Motorized Measuring Sphere Gap HV9133 1
Earthing/Grounding Rod HV9107 1
Spacer Bar HV9119 1
Safety Instructions:
Refer to the Safety and Report Manual
KE48101 Engineering Lab 6 (High Voltage) FKJ, UMS
Diagram:
Introduction:
Alternating voltages are required for a large number of high voltage tests and many
other industrial applications. The AC test system is a fundamental test system that is
present in any high voltage laboratory. The most common source of AC voltage is the
high voltage transformer which may be a single unit tank type transformer or a cascade.
High voltage tests via an AC system can be performed directly with the AC voltage or
used, with the proper extensions, for the generation of impulse and DC voltages.
AC voltages can be measured using different methods which include determination by
using the breakdown voltage, VB of a sphere gap; Measurement of the peak voltage, VP
with the peak voltmeter in conjunction with the AC Measuring Capacitor; Measurement
of VRMS using the primary input voltage and transformer ratio.
Procedure:
1. Observe all safety precautions as mentioned in the Lab Manual at all times.
2. Arrange for the AC test setup of Figure 1.
3. Verify the setup
4. Clear the test area, lock the fencing door and take all necessary precautions
5. Energize the high voltage setup
6. Set the measuring sphere gap spacing to 10cm from the control desk
7. Reset the AC peak voltmeter reading
KE48101 Engineering Lab 6 (High Voltage) FKJ, UMS
8. Raise the voltage of the transformer gradually
9. Observe the occurrence of a spark signifying the breakdown of air
10. Record the reading of the voltmeter, Vp (denoted as û on voltmeter) as the
breakdown voltage of the air at 10cm gap. Also record the reading of û/√2 of the
voltmeter. Finally, record the reading of ûRMS from the voltmeter. Take 2 set of
readings for each sphere gap distance to get the mean value.
11. Measure AC peak breakdown voltage only for spherical electrodes as a function
of the gap spacing, s. Use gap spacing of 20 and 30cm.
12. Record and tabulate readings accordingly.
13. When the experiment is complete, turn off the main switch of the control desk and
supply.
14. Observe all safety precautions when entering the test area. DO NOT TOUCH ANY
PART OF THE HIGH VOLTAGE SETUP!
15. Discharge all test equipment/parts using the grounding rod and attach the ground
rod to the transformer.
Note: The voltmeter provides readings for peak voltage, û. There is also the reading of
û/√2 and ûRMS. û/√2 is the arithmetic mean and does not refer to the true RMS. The
true RMS refers to ûRMS.
Results:
Arithmetic True RMS
Breakdown Breakdown Peak Breakdown Voltage
Readings
Voltage Voltage (û)
(û/√𝟐 ) (ûRMS)
Gap Spacing 10cm 10cm 10cm 20cm 30cm
1st
2nd
Average
KE48101 Engineering Lab 6 (High Voltage) FKJ, UMS
Discussion:
1) Record the peak breakdown voltages, û for the given gap spacing from the table of
peak breakdown voltages per sphere gap distance of the IEC 60052 or that given in
page 229 of reference 2. Record these values. Plot the graph of the values of û for
both methods versus increasing gap distances, s.
2) From the plotted graph, what can you say about the readings of û obtained via the
experimental and theoretical methods? Is there any difference in the readings?
3) If yes, why should there be a difference in the values of û?
4) Is there a difference between the values of ûRMS obtained through method 1 (from
the voltmeter) and û/√2 from method 2 (from the table in reference 2 or IEC
60052)? Explain the difference, if any, and describe the meaning of true RMS as
opposed to the arithmetical mean.
5) Is there any other method to obtain û/√2 ? Discuss one method and include the
relevant diagrams.
KE48101 Engineering Lab 6 (High Voltage) FKJ, UMS
