High Voltage Engineering S.R.C.O.E, LONIKAND PUNE Page 1 PRACTICAL WORK BOOK For Academic Session 20_ _ HIGH VOLTAGE ENGINEERING (Elective-III) (403149) 2008 pattern For B.E. (Electrical Engineering) Department of Electrical Engineering (University of Pune)
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High Voltage Engineering
S.R.C.O.E, LONIKAND PUNE Page 1
PRACTICAL WORK BOOK For Academic Session 20_ _
HIGH VOLTAGE ENGINEERING
(Elective-III) (403149) 2008 pattern
For
B.E. (Electrical Engineering)
Department of Electrical Engineering
(University of Pune)
High Voltage Engineering
S.R.C.O.E, LONIKAND PUNE Page 2
SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND (096)
DEPT. : ELECTRICAL ENGG. HIGH VOLTAGE ENGINEERING (403149) SEM. : II (BE)
TITLE: LIST OF EXPERIMENTS
Minimum eight experiments
1. Measurement of breakdown strength of solid insulating materials.
2. Breakdown of air under uniform and non-uniform field.
3. Measurement of breakdown strength of liquid insulating materials.
4. Effect of gap length on liquid insulating material.
5. Breakdown of composite dielectric material.
6. Study of impulse generator.
7. High voltage withstand test on cables/safety gloves/shoes as per IS.
8. Surface flashover on the surface of polymer insulator materials.
9. Horn gap arrangement as surge diverter.
10. Measurement audible and visible corona inception and extinction voltage.
11. Surface flashover on corrugated porcelain insulator materials.
12. Sphere gap voltmeter.
13. Development of tracks and trees on polymeric insulation.
14. Measurement of breakdown strength of gaseous dielectrics.
15. Study of output voltage waveform of multistage voltage doubler circuit on CRO.
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SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND (096)
DEPT. : ELECTRICAL ENGG. HIGH VOLTAGE ENGINEERING (403149) SEM. : II (BE)
TITLE: SAFETY PRECAUTION IN HV LAB
All electrical test laboratories shall adequately take care of safety aspects on following points
and ensure compliance with suitable display, training, guidance etc.
a. The laboratories are expected to comply with the safety requirements of electrical shocks:
through use of Earth Leakage Circuit Breaker (ELCB) or any other device and damage to
personnel by use of Safety Helmet as per IS 2925, Gloves as per IS: 13774, Safety shoes
as per IS 12254 & IS 2071 Part 1, Insulated tools as per IS 13772, Earthing rods as per IS
3043, Fire hazards as per SP 30 and Rubber mats as per IS: 5424.
b. Back up controller where necessary shall be provided in order to control the
environmental chambers in case of malfunction of original controller for environmental
chambers.
c. A danger notice board with a sign of skull and bones shall be displayed in Electrical
testing area with voltages above 400 Volts. SP 30 charts where required shall be
displayed.
d. Testing staff working in live electric supply environment shall have knowledge of risk
and hazards involved in testing Supply to vehicles and cranes shall have suitable trip
facility and the metal rails shall be electrically continuous and earthed.
e. Instructions for resuscitation of persons suffering from electrical shocks shall be
prominently displayed.
f. Switchboard shall have clear space around as specified by statutory authority.
g. Due care shall be taken where the equipment is likely to have emissions in test which may
endanger the operator/ equipment.
h. Fire buckets filled with clear and dry sand and water ready for immediate use for
extinguishing fires in addition to fire extinguishers for dealing with electric fires shall be
available.
i. Fire extinguishers of suitable type depending upon class of fire:
Class of Fire Suitable type of Extinguishers
Fires in Ordinary combustibles (Wood, rubber, plastic and the like) Gas expelled, Water
type and anti-freeze type extinguisher and water buckets.
Fires in flammable liquids (paints, grease, solvents & the like) and electrical circuits
Chemical extinguishers of carbon-dioxide & dry powder type, sand buckets and foam
type
Fires in gaseous substances under pressure including liquefied gases Chemical
extinguishers of carbon-dioxide and dry powder type
j. Availability of first aid kit.
k. Ensure minimum safe clearance in air between high voltage terminal and earth during
testing at different voltage levels of AC/ DC/ Impulse applications.
l. Ensure proper earthing of equipment before making physical contact.
m. Operation of equipment by only authorised personnel Use of safety interlocks.
n. Restrict entry with prominent display boards, of un-authorised persons during testing.
o. Where necessary, control desks shall have inter-locks and control shall be with the
authorised persons only.
p. In respect of testing Liquid dielectric, provision for body shower and eye-wash shower
with exclusive over head tank for these showers.
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SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND (096)
DEPT. : ELECTRICAL ENGG. HIGH VOLTAGE ENGINEERING (403149) SEM. : II (BE)
EXPERIMENT NO. : SRCOE/ELECT/BE/HVE/__ PAGE:__-__ Date :
EXPERIMENT TITLE: HIGH VOLTAGE LAB LAYOUT
AIM: To Study High Voltage Lab Layout
APPRATUS:
Sr. No Name of the Equipment Specification Quantity
1
2
3
4
THEORY:
A. General Requirements of HV lab:
1. Customs made according to the type of equipment, available space and accessories.
2. Ground level location is preferred and floor loading has to be considered while designing
the lab.
3. Lab should be free from dust, humidity, draught.
4. Windows should be located at ground level and should have provision for black out so
that arcing can be easily observed.
5. Control room should have good view of the lab.
6. Adequate access door should be provided to bring in the equipment and test specimen.
7. Proper safety and warning system must be provided.
8. Lab should have adequate and proper clearance. Proper spacing should be kept within the
equipment.
9. Area around the equipment should be suitably demarked.
B. Classification of HV lab:
1. Small Lab:
• Less than 10 kW/10 kVA / 10 kJ
• 300kV AC single equipment
• 500 to 600kV (cascaded)
• Less than 100 kV (Impulse generator)
• 200 to 400kV DC
2. Medium Size lab:
• Used in the industries for routine test
• 100 to l000kVA
• 20 to 100kJ
• 200 to 600kV
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3. Large size Lab:
• Used in the industries for routine test as well as type tests and also for research.
• Test transformer (1.5 to 2 MV)
• Impulse generator (5 to 6 MV)
• HVDC rectifier (1.2 to 1.5 MV)
4. Ultra high voltage lab:
• Used for basic design of experimental transmission.
C. Tests which can be carried out in the HV lab:
1. Withstand test
2. Flashover test
3. Pollution test
4. Partial discharge test
5. Tan measurement
6. Power frequency test
7. Impulse test:
• Switching
• Lightning
8. DC voltage test
9. Radio interference voltage (RIV) measurement
10. High current test
D. Equipment in HV lab:
1. HV generator (Transformer)
2. Oil testing kit
3. Impulse Generator
4. Testing facilities for RIV testing and partial discharge
5. Sphere gap for voltage measurement
6. Corona cage
E. Grounding of HV lab:
There are three types of grounding.
1. Idea) ground:
• Equipotential plane approximated by copper or galvanized iron sheet
• Very expensive.
2. Single Point Grounding
• Ear thing grid is grounded at single point.
3. Bus grounding:
• Grounding is done at several points in a lab.
• Least satisfactory
F. Design and Specification of grounding system:
• Metal sheet is embedded in a concrete floor.
• Generally copper conductors are used.
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• Grounding grid is a mesh of 1m x 1m and is connected to metal grids of RCC
construction of lab.
• Chicken mesh of 1cm x 1cm is used to reduce the electromagnetic interference.
G. Rating of SRCOE HVE Lab Equipments:
1 AC/DC high voltage generator/transformer:
• Input: AC- single phase 230 V, 50/60 Hz
• Output Voltage:
• AC: 0 to 100 k V, 50 Hz
• DC: 0 to 60kV
• Output current:
• AC: 100 mA, 50Hz
• DC: 20 mA
2. Horizontal sphere gap voltmeter:
• Model:
• Sphere Diameter 250mm
• Cap scale: 0-100mm
3. Corona Cage:
4. Porcelain Insulators: three disc (each of 11kV)
5. Oil testing kit with filler gauge
6. Horn gap apparatus:
H. Safety Precautions to be taken in HVE lab:
1. Exposed metal parts on equipment which are not in use but in proximity of live equipment
should be treated as live to electromagnetic induction and discharged before touching.
2. Capacitors which are not in use should be shorted.
3. Flashover can be noisy and source of electromagnetic interference.
4. Some equipment require permanent ear thing. These equipments must have connection
which requires mechanical assistance to remove from circuit.
5. Electronic devices which cause or are susceptible to electromagnetic interference should
not be used.
6. Any equipment to be energized must have all exposed metal connected to ground unless
that metal is not a part of circuit.
7. Keep the mobile phones switched off in HV lab.
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High Voltage Engineering
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SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND (096)
DEPT. : ELECTRICAL ENGG. HIGH VOLTAGE ENGINEERING (403149) SEM. : II (BE)
EXPERIMENT NO. : SRCOE/ELECT/BE/HVE/01 PAGE:__-__ Date :
EXPERIMENT TITLE: BREAKDOWN STRENGTH OF LIQUID DIELECTRICS
AIM: To study Breakdown Strength of Liquid Dielectrics.
APPRATUS:
Sr. No Name of the Equipment Specification
1 Auto transformer 5A, 230 V, 1 Phase 50 Hz AC.
2 Step up transformer 230V to 60/80/100 kV (centre tapped earth) ac.
3 Control panel
4 Oil test cup made of high impact transparent
5 Filler gauge 2.5mm
THEORY:
Liquid dielectrics are more useful as insulating materials than solid dielectrics or gases due to
some of its inherent properties. They are the mixtures of hydrocarbons and are weakly
polarized. They are 103
times denser than gases. The dielectric strength of gases is ideally
considered to be 10MV/cm, but practically it is of the order of 100kV/cm.
A liquid dielectric should withstand breakdown voltage without danger of sparking. It should
be free from moisture, products of oxidation, any fibrous impurity and other contaminants.
The presence of water in oil affects the electric strength of insulating oil and it decrease very
sharply if fibrous impurities are present in addition to water.
Liquid dielectrics are used mainly as impregnates in high voltage cables and capacitors, and
for filling up of transformers, circuit breakers, etc. It also acts as heat transfer agents in
transformers, and as arc-quenching media in circuit breakers. For the proper operation of
transformer, transformer oil is tested in HV laboratory using oil-testing kit. It’s ideal
breakdown strength is 15kV/mm. The procedure for testing of oil in HV laboratory is given
below:
CONSTRUCTION:
Al the components are housed in compact and rugged devices is mounted on the front slanted
panel.
H.T. transformer which is epoxy resin cast on which H.T. output terminals are provide on the
top plates. These H.T. electrodes are shaped suitable to accommodate the test cup easily. The
test cup capacity is of 500ml approxm. A transparent hood made of clear plastic / Acrylic
material is provide on the top of the test cup, so that when the tests is carried, the operator
will not come in the hood interlocking micro switch so that if by any change the hood lifted
from its position, the H.T. supply will be cut off automatically.
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PROCEDURE:
1. Adjust the gap between the electrodes to 2.5mm by the gauge provide with punch mark
for ‘GO’.
2. Fill the test vessel/ cup with the dielectric oil sample to be tested and place it on H.T.
electrodes. Close the hood properly, to operate the interlock microswitch, which acts as a
safety precaution for the operator.
3. Switch ‘ON’ the supply from mains, the corresponding lamp will glow.
4. Press ‘HT ON’ push button the contactor will operate and H.T. ‘ON’ lamp will glow. If
the contactor does not operate, it means that the variac brush arm is not at zero position or
the hood interlock is not closed. The zero interlocking of the variac is another safety
feature against switching on the unit directly at a higher voltage. This will be indicated by
voltmeter reading.
5. Keep increasing/ lower switch in lower position to bring the brush arm to zero position
and then again push the H.T. ‘ON’ push button.
6. Raise the voltage by putting the control switch on raise position. The voltage will increase
gradually in steps till breakdown of oil on the gap occurs i.e. oil sample test fails, the unit
will trip and the kV meter which has been provided with a pointer arresting mechanism
will read the breakdown voltage in kV. To lower down the voltage, put the control switch
on lower position before start of subsequent test.
7. Note down the readings for breakdown voltage, which is available on the digital meter.
8. Take 6 readings and discard the first one. Take average of remaining 5 readings as
breakdown voltage of oil.
9. Calculate the breakdown strength in kV/mm.
OBSERVATION TABLE:
Gap length between electrodes: ____________ mm.
Sr. no. Breakdown voltage Average breakdown voltage Remark
1. To be discarded
2.
3.
4.
5.
6.
Breakdown strength = average breakdown voltage (kV) / gap length (mm);
CONCLUSION:
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230V/100kV
AC
230V,
1ph
50Hz,
AC
supply
2.5mm
0 to 60kV
LV HV
Figure No.
230V/100kV
AC
230V,
1ph
50Hz,
AC
supply
2.5mm
0 to 50kVLV
HV
Figure No. Breakdown strength of liquid dielectric
High Voltage Engineering
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SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND (096)
DEPT. : ELECTRICAL ENGG. HIGH VOLTAGE ENGINEERING (403149) SEM. : II (BE)
EXPERIMENT NO. : SRCOE/ELECT/BE/HVE/02 PAGE:__-__ Date :
EXPERIMENT TITLE: EFFECT OF ELECTRODE CONFIGURATION
AIM: To Study Effect of Electrode Configuration on the Breakdown of Air Gap.