hv manual for 2013

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EXPERIMENT NO: -

Aim: - Overview of lab equipments and safety Precautions

Theory:-

The high voltage laboratory consist of

(A) 420 kV Impulse Test

1) H.V. Test transformer

Technical specification:

Type: TEO 100/10

Rated primary voltage: (0-220 V)

Rated secondary voltage: (0-100kV)

Rated primary current: 22.75 A

Rated secondary current: 50Ma

Thermal rating: 5KVA- Continuous, 10KVA short time duty

2) Impulse Capacitor:


Type: CS 100

Rated dc and impulse voltage: 140 kV peak

Rated capacitance: 100Nf±10%

Rated test voltage: 160 kV peak

3) Load capacitor:


Type: CB 140

Rated dc and impulse voltage: 140 kV peak

Rated capacitance: 1200 pF± 10%

Rated test voltage: 160 kV

4) Measuring Resistor

Technical specification:Type: RM 280

Rated DC voltage: 140 kV peak

Rated resistor: 280 MΩ

Rated current cont: 0.5Ma

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5) Charging resistor:


Type: RL 2.5

Rated DC voltage: 140kV peak

Rated resistance: 2.5MΩ

6) Wave front resistor:

7) Wave tail resistor:

8) H.V.Silicon rectifier

9) Earthing switch

10) Sphere Gap

11) Drive for sphere Gap

12) Earthing Rod

13) Connecting Cup

14) Floor Pedestal

15) Connecting Rod

16) Sphere Bar

17) Support insulator

B) Horn gap apparatus (Make High voltage India)

Specification of transformer:-

Input voltage: 230 v, AC

Output voltage: 0-10Kv

Output current: 20Ma

Operation duty: Continuous

Type of cooling: Air-cooled

C) Digital cable fault locator 2000 A (P.E.Systems Pvt. Ltd. Bangalore)

D) ELTEL Cts-500 kit for Measurement of capacitance and Dissipation factor (Tan

δ) of Insulating material.

E) 25 KV High Voltage Tester

Specification:-Input: 0-230, AC, 50 C/S, single phase

Output: 0-25kV AC, Leakage current: 15mA, 30mA

Type of cooling: Air cooling. Timer: 0-30 hours.

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F) Oil Tester for testing of Transformer oil.

Safety Precautions:

Safety Rules for Moderate and High Voltages

High Voltage: All conductors on which high voltage may be present should be confined withingrounded or properly insulated enclosures. Instrumentation cabinets containing high voltage conductors

should have safety interlocks on access doors. If confinement of high voltage is not possible, then bare

conductors at high voltage must be enclosed within grounded safety enclosures with working interlocks.

Except by deliberate breach of the enclosure, contact with bare conductors at high voltage should be

impossible without tripping the interlock.

The proposed test area configuration requires written approval from the following:

• One-time approval by the Group Leader for two-person operation

• Annual approval by the Group Leader and Division Chief for one-person operation

• Case-by-case approval by the Group Leader and Division Chief for unattended operation

• One-time notification of Division and Laboratory safety officers for new systems

All interlocks should be tested during Division safety reviews. When the use of permanent enclosures

would be impossible or impractical, temporary setups are permitted contingent upon operation by two

people and obtaining the necessary approvals. The test area must be surrounded by a temporary

grounded safety fence or by ropes. Interlocks are strongly recommended, and the absence of interlocks

will require justification. The distance between the fence or rope and the exposed conductor must be 1 m

or greater. Climbing over ropes is strictly forbidden, and the voltage must be controlled by a switch

outside of the test area. Case-by-case written approval by the Group Leader and Division Chief is

required for this mode of operation.

Moderate Voltage: All permanent setups with bare conductors at moderate voltages (voltages

exceeding 120 V rms or dc, but not exceeding 1000 V rms or dc) must be EEEL Safety Rules for

Moderate and High Voltages

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surrounded by a safety fence or other barrier for one-person or unattended operation, with working

interlocks in place for unattended operation. The distance between the fence or rope and the exposed

conductor must be 1 m or greater. Climbing over ropes is strictly forbidden, and the voltage must be

controlled by a switch outside of the test area. Special confinement (fences or other barriers) is not

required for two-person operation, but is recommended.The proposed test area configuration requires written approval from the following:

• One-time approval by the Group Leader for one-person operation

• Annual approval by the Group Leader and Division Chief for unattended operation

• One-time notification of Division and Laboratory safety officers for new systems

The requirements for temporary setups with bare conductors at moderate voltages are the same as for

permanent setups, but with case-by-case approval for one-person or unattended modes of operation.

Permanent setups with covered or insulated conductors, and unexposed terminals, require one-time

approval from the Group Leader, and this approval is sufficient for unattended operation.

Signs and Warning Lights

DANGER HIGH VOLTAGE signs must be on display on all entrances to all test areas where bare

conductors are present at both moderate and high voltages. These signs should be in the vicinity of the

test area and on the outside of the door leading to the laboratory area.

A warning light, preferably flashing, must be on when high or moderate voltages are present, and

ideally should be activated by the energizing of the apparatus. The warning light must be clearly visible

from the area surrounding the test area. In special cases where such a light interferes with an experiment,

it can be omitted with special permission from the Group Leader and Division Chief.

In all cases where there is direct access from the outside hallway to the area where high or moderate

voltages are present, a warning light, DANGER HIGH VOLTAGE sign, a safety interlock (for high

voltages) and a locked door are required.

For unattended setups with bare conductors at high or moderate voltage, a warning sign with the

names of two contact persons and the dates of unattended operation must be posted on the door leading

to the high-voltage area. In addition, written notice of unattended testing of high or moderate voltage

with bare conductors must be sent to the NIST Fire Department (in Gaithersburg) or to the Engineering,

Safety, and Support Division (in Boulder) clearly stating the anticipated dates of operation. A warning

light on or near the door to the laboratory must be illuminated when high or moderate voltages with bare

conductors are present.

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Grounding Stick

Before touching a high-voltage circuit or before leaving it unattended and exposed, it must be de-

energized and grounded with a grounding stick. The grounding stick must be left on the high-voltage

terminal until the circuit is about to be re-energized. Grounding sticks must be available near entrances

to high-voltage areas. Automatic grounding arrangements or systems that employ audible warning tonesto remind personnel to ground the high-voltage equipment are strongly encouraged for two-person

operation, and are mandatory for one-person or unattended operation.

For systems with bare conductors at moderate voltages, the use of grounding stick is strongly

recommended, particularly if the setup contains energy-storage devices.

Modes of Operation

Two-person: Two-person operation is the normal mode of operation where high or moderated voltages

are present. Allowed exceptions are:

• When all potentially dangerous voltages are confined inside a grounded or insulated box, or where the

voltages are constrained in a shielded cable, or where the is no access to bare conductors

• When one-person or unattended operation setups have been designed and approved according to the

rules set out in this document and with appropriate approval.

• It is presumed that both individuals participating in two-person operation will follow basic high-

voltage safety procedures and will monitor each other’s actions to ensure safe behavior.

One-person: One-person operation of systems using high and moderate voltages with bare or

exposed conductors may be approved, after appropriate review and authorization, in order to provide for

the efficient use of staff for long-term applications where it is judged that safety would not be

compromised.

Unattended: It is recognized that in order to run efficient calibration services and maintain

appropriate delivery schedules, unattended operation of systems using high and moderate voltages may

be necessary. In such cases, unattended operation is permitted.

With appropriate review and authorization, for systems having no bare or exposed conductors, and

where required warning signs, lights, and barriers are present. Unattended operation of setups with bare

or exposed conductors at high and moderate voltages may be necessary under special circumstances,

such as for unusually long data-acquisition periods. This is meant to be a rare occurrence. Should this

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mode of operation be frequently employed, then the apparatus should be modified to enclose all

potentially dangerous voltages.

Circuit Breakers and Disconnects

Circuit breakers, disconnects or contactors used to energize a high-voltage source must be left in an

open position when the supply is not in use. Laboratories should always be left in a configuration that at

least two switches must be used to energize high-voltage circuits. Whenever possible a “return-to-zero- before energizing” interlock should be incorporated into the high-voltage supply.

Proper Circuit Design Recommendations

Draw the circuit and study it before wiring it for operation at high voltage.

Make sure all devices that require grounding are securely grounded.

Allow adequate clearances between high-voltage terminals and ground.

Solicit a second opinion before operation for the first time.

Transformers and Variacs

Make certain that one terminal of each transformer winding used to provide a separately derived system

(this excludes the winding connected to the power supply) as well as the transformer or variac case are

properly grounded. The common terminal of a variac should be connected to the supply neutral. Cascadetransformers and, in some cases, isolation transformers are exceptions.

Result: - High voltage lab equipment and safety precaution has been studied.

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EXPERIMENT NO: -

Aim: - To study high voltage equipments and high voltage laboratory

Theory: - Theory should covered

1) H.V.Transformer

2) Impulse generator 100kVac, 140kV dc,420kVImpulse,2.94kJ,3-stage

3) High voltage potential divider

4) Different types of electrodes with different sizes (sphere gap, rod gap and point

gap)

5) Rectifier circuit

6) Earthing switch7) Earthing rod

8) Control panel

9) Horn gap apparatus

10) Digital cable fault locator

11) Eltel-cts-500 kit.

12) 25 kv High voltage tester

13) Oil testing kit

14) Pin type insulator.

15) Suspension type insulator

Result: Hence studied the high voltage equipments and high voltage laboratory.

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EXPERIMENT NO: -

Aim: - To study different types of insulator and High voltage cable

Theory:-Types of Insulators

There are several types of insulators but the most commonly used are pin type, suspensiontype, strain insulator and shackle insulator.

1 Pin type Insulators

Fig.Pin Type Insulator

As the name suggests, the pin type insulator is secured to the cross-arm on the pole. There is

a groove on the upper end of the insulator for housing the conductor. The conductor passes

through this groove and is bound by the annealed wire of the same material as the conductor.

Pin type insulators are used for transmission and distribution of electric power at voltages up

to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky andhence uneconomical.

Pin Type Image

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2 Suspension Type

Suspension Type

For high voltages (>33 kV), it is a usual practice to use suspension type insulators shown in

Figure. consist of a number of porcelain discs connected in series by metal links in the form

of a string. The conductor is suspended at the bottom end of this string while the other end of

the string is secured to the cross-arm of the tower. Each unit or disc is designed for low

voltage, say 11 kV. The number of discs in series would obviously depend upon the working

voltage. For instance, if the working voltage is 66 kV, then six discs in series will be

provided on the string.

Suspension Type Image

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3 Strain Insulators

Strain Type Insulator

When there is a dead end of the line or there is corner or sharp curve, the line is subjected to

greater tension. In order to relieve the line of excessive tension, strain insulators are used.

For low voltage lines (< 11 kV), shackle insulators are used as strain insulators. However,

for high voltage transmission lines, strain insulator consists of an assembly of suspension

insulators as shown in Figure. The discs of strain insulators are used in the vertical plane.

When the tension in lines is exceedingly high, at long river spans, two or more strings are

used in parallel.

4 Shackle Insulators

Shackle Type Insulator

In early days, the shackle insulators were used as strain insulators. But now a days, they are

frequently used for low voltage distribution lines. Such insulators can be used either in a

horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt

or to the cross arm.

10

http://en.wikipedia.org/wiki/Strain_insulator


http://en.wikipedia.org/wiki/Transmission_line

http://en.wikipedia.org/wiki/Shackle


http://en.wikipedia.org/wiki/Transmission_line

http://en.wikipedia.org/wiki/Shackle

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Different Types of cables 1) Low voltage cables

2) Medium voltage cables3) High voltage cables

4) Extra high voltage cables

Result: Hence we studied the different types of insulators and cables

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EXPERIMENT NO: -

Aim: - Calibration of voltmeter by using sphere gap method.

(1) 10 cm dia.

(2) 5 cm dia.

Apparatus: - Sphere gap, 10cm / 5cm dia, Control Panel, H.V. transformer (230V / 100kV,10kVA), Capacitor Divider (100 pf), Connecting wires etc.

Circuit diagram: -

Theory: - A uniform field spark gap will always have a spark over voltage within a known

tolerance under constant atmospheric conditions. Hence sphere gap can be used for the

measurement of the peak value of the voltage, if the gap distance is known. The voltage

to be measured is applied between the two spheres and the distance between them gives a

measure of spark over voltage. Irradiation of sphere gap is needed when measurements of

voltage

less than 50kV are made with sphere gaps of 10cm dia. or less. There are various factors

that

affects the spark over voltage of the sphere gap are, nearby earthed objects.

1) Atmospheric conditions & Humidity.

2) Irradiation, &

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FUSE

REGULATINGTRANSFORMER

230 V / 100kV

10kVA

HT SWITCH

V

230 VAC

SUPPLY V

Scale

100 pf 100 kV

230V

1OOkV

SPHERE GAP

VOLTAGE

DIVIDER

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3) Polarity and rise time of waveforms,etc.

Procedure: -

1) Make the connections as shown in the circuit diagram. Using spheres of same

diameter.2) Adjust the suitable distance between the electrical say 0.5 cm or 1 cm from control

panel.

3) Increase the voltage gradually from control panel till breakdown occur.4) Measure this breakdown / spark over voltage for a given gap.

5) Change the distance & increase the voltage gradually.

6) Repeat the same procedure for both the sphere set.7) Find the percentage error and plot the graph between distance and RMS BDV

(measured value)

Observation Table: -

Sr.no.

Distance between

the

spherein cm

Peak BDV at

20o and 76

cm of Hg(A)

ActualBDV

= kV

B=KA

RMS BDV(V2)

=B/ √2 kV

RMS Value of BDV as per

voltmeter

KV (V1)

V1-V2 V1-V2 / V1

*100 =

% Error

01

02

03

04

BDV: - Break Down Voltage

Relation between air density factor δ and correction factor K

δ 0.70 0.75 0.80 0.85 0.90 0.95 1.0 1.05 1.10 1.15K 0.72 0.77 0.82 0.86 0.91 0.95 1.0 1.05 1.09 1.12

δ = p /760 * (273+20 / 273+ t)

p & t: - are atmospheric pressure and temperature while performing the experiments i.e.

at roomtemperature

δ : - Air density factor

K: - correction factor

Result: - From this experiments we are able to get the various breakdown voltages for different gaps between the electrodes. It is observed that as distance between the spheres

increases, break down voltage also increases.

Graph: - 1) Plot the graph between distance and RMS BDV (measured value)

2) Plot the graph between distance and percentage error.

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Questions: - 1) Write in brief the effect of near by earthed object on the spark over

voltage of sphere gap.

2) Write in brief the effect of irradiation on the spark over voltage of sphere gap.

3) Explain the measurement of high voltage by capacitance voltage

divider method.

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EXPERIMENT NO: -

Aim: -Calibration of voltmeter by using Rod gap

Apparatus: - Transformer (230/100 kV, 10 kVA) Voltage Divider (100pf)Control Panel, connecting rods, connecting wires, etc.

Rod gap method:-

Circuit diagram: -

Theory: - A rod gap is also sometimes used for approximate measurement of peak values of power

frequency voltages and impulse voltages. The rods will be either square edged or circular in spacing varies from 2 to 200 cm. The spark over voltage, as in other gaps is affected by

humidity and air density. (The power frequency breaks down voltage for 1.27 cm square

rod in air at 250

C and a pressure of 760 torr with the vapour pressure of water of 15.5torr.

15

FUSE


230 V / 100kV

10kVA

HT SWITCH

V

230 V

AC

SUPPLY V

VOLTAGEDIVIDER

100 kV

100 pf

RODGAP

100kV

230 V

SCALE

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1) For Rod gap

Sr. No.

Distance between

rods in cm

B. D. V. RMS value of BDV V1 (from

voltmeter)

% error = V1-V2 /V1

*100

Standard

value(peak value in

kV) (A)

Peak value at

existingtemperatureB = KA .(kV)

RMS

value= B / √2

1

2

3

4

Relation between air density factor δ and correction factor K

δ 0.70 0.75 0.80 0.85 0.90 0.95 1.0 1.05 1.10 1.15

K 0.72 0.77 0.82 0.86 0.91 0.95 1.0 1.05 1.09 1.12

δ = p/760 * (273+20 / 273+ t)

p & t: - are the atmospheric pressure and temperature while doing the practical

δ: - Air density factor


Result: - From the experiment BDV for different spacing have been found out .It is observed as distance

between the electrodes increases BDV also increases.

Graph: - For Rod gap(i) Distance Vs RMS BDV

(ii) Distance Vs % Error.

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EXPERIMENT NO: -

Aim: - Determination of break down voltage of Pin type insulator

1) Under dry condition

2) Under wet condition

Apparatus: - 1) H. V. transformer, 230V / 100kV, 10 kVA2) 11kV pin type fixed on table and its bottom is earthed.

3) Connecting wires & rod.

4) Control panel etc.

Circuit diagram: -

Theory: - It is one of the earliest designs used for supporting line conductor. The pin insulator is supported on the forged steel pins and bolds, which are skewed to the cross section of this

supporting structure. The conductor is lied to insulator on the grooves. In order to increase the

leakage path, one, two or three rain shades are so designed when these insulators are wet even

then sufficient dry space is provided by the inner shades. For higher voltages the thickness of thematerial required for the purpose of the insulation. But the practical way is to use more than one

insulator unit instead of increasing the thickness. Flashover distances when the insulators are dry

and wet are different. The flash over voltage when the insulator is wet is less. The rain shadesshould not disturb the voltage distribution. They are so designed that their surface is right angle

to electrostatic lines of forces or they must try to lie in the equipotential.The pin type insulator is reliable for voltage level upto 33 kV max. and they are never

used for voltage beyond 80 KV. Since the suspension insulator is more reliable and

cheaper. The modern practice is “not too used” the pin type insulator beyond 33 kV.

Procedure: -

1) Make the connection as shown in circuit diagram.

2) Increase the voltage across pin type insulator (Dry condition) gradually from control

17

FUSE


230 V / 100 kV 10

kVA

HT SWITCH

V

230 V

AC

SUPPLY V

VOLTAGEDIVIDER

100 pf

100 kV

PININSULAT

OR

100 kV

230 V

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panel till spark over gets.

3) Note down this spark over voltage.4) Repeat the process for Wet condition.

5) Compare the observed value with standard value & find out the percentage error.


Pin Type Insulator = WD-10 type

Flash over voltage – Dry condition = 62.5 kV RMSWet condition = 38 kV RMS

1) For Dry Condition: -

Sr. No. Std. Flash over

Voltage (V1)RMS KV

Measured flash over

voltage (V2) KVRMS voltmeter reading

% error

= (V1-V2/V1)*

100

Avg. error

2) For Wet Condition: -

Sr. No. Std. Flash over

Voltage (V1)

RMS KV

Measured flash over

voltage (V2) KV

RMS voltmeter reading

% error

= (V1-

V2/V1)*100

Avg. error

Result: - The flashover voltage across pin type insulator is found to be ______kV

in dry condition. And _________kV in wet condition.

Questions: -

1. Write the dimensions of the different types of pin insulator and their flashover voltage under dry and wet condition..

2. Compare the properties of porcelain and glass insulator

3. List the solid dielectrics used in practice.

4. Why breakdown voltage reduces in case of wet condition.

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EXPERIMENT NO: -

Aim: - To study phenomenon of arc in Horn gap

Apparatus:-Horn gap (make High voltage India)

Specification of transformer:-

Input voltage: 230 v, AC

Output voltage: 0-10Kv

Output current: 20mA

Operation duty: Continuous

Type of cooling: Air-cooled

Theory:-

This is the most ideal equipment for class demonstration to explain the

phenomenon of corona formation, due to high voltage sparking. This is self contained

and compact unit.

This equipment is known as Horn gap equipment because two high voltage

electrodes are of the shape of horn. There is specially designed high voltage transformer

with center tap grounded. The horns are connected to the high voltage outputs of the

transformer. For the safety of the operator the horns, which are at high voltage, are

covered with transparent cover.

A suitable push button is provided in the front panel of the equipment. The

equipment starts operating as soon as we press the button. The input supply is 230 v ac.

Operation:-

Provide 230 v, ac to the equipment with the help of power chord provided with

the equipment. Now press the push the button in the front panel to see the corona

formation.The equipment continues to operate as long as we press the push button.We

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see that the spark starts from button of the horn, where the gap is minimum but sufficient

to cause the break down due to the application of 20 kV. Now the gap goes on increasing

and hence the spark also moves up and the length of the spark of the horns. This spark is

nothing but corona formation.

How corona occurs? As we apply the high voltage to the horn gap. The spark over or

breakdown will occur at the point of minimum gap of the horns. The upper layer of the of

the air will get ionized and its density and resistance will decrease. So, the spark will

move up progressively as the phenomenon goes on repeating until the corona reaches the

peak of the horns.

Precautions:-

1. Keep processing the push button as long as you want to see the corona.

2. Never touch the horn as long as the equipment is connected to 230v input supply.

3. Don’t touch the horns without grounding them.

4. The equipment must be grounded.

Result:-

Hence studied the arc in Horn gap.

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EXPERIMENT NO: -

Aim: - To determine string efficiency of suspension type insulator.

Apparatus: - String of Suspension Type Insulator, Sphere Gap, HV transformers 230V/100 kV 10

kVA,

Control Panel, Connecting rods etc.

Circuit diagram: -

THEORY: - Suspension type insulator consists of number of porcelain discs connected in series

by metal links in the form of a string. The conductor is suspended at bottom end of the stringwhile the other end is secured to the cross arm of tower. Each disc is designed for low voltage

say 11KV. The number of discs in series would obviously depend on working voltage e.g. for

66KV, 6discs are required. The ratio of voltage across the whole string to the product of number

of discs & voltage across discs nearest to the conductor is known as string efficiency.

Voltage across string

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String efficiency = ______________________________________________________

n * voltage across disc to nearest conductor

Where n = number of discs.

String efficiency is an important consideration since it decides potential distribution

along string. The greater the stringη, more uniform is the voltage distribution. Although

it is impossible to achieve 100% string η, yet efforts should be made to improve it as

close as possible to this value. The inequality of voltage distribution increases which inincrease in no. of discs in the string. Therefore shorter string has more efficiency than

longer one. String efficiency can be increased by

1 1) Using longer cross-arm.

2 2)Grading the insulator 3) Using a grid ring.

PROCEDURE: -

1) Make the connections as shown in circuit diagram.2) Set the distance between 10cm diameter sphere to maximum value.

3) Apply a constant voltage to the string say for 7 discs,11KV*7=77KV

4) Now reduce the distance between the spheres till flashover occurs.

5) Note the corresponding distance between the spheres at flashover.6) Make supply off and make connections for second step, keep maximum distance between the

spheres7) Decrease the distance from control panel till flash over occurs. It gives the BDV for (n-1)

discs excepting the bottom discs.

8) Repeat the procedure for all discs.


δ = P/760 * (273+20 / 273+ t)

P & t: - are atmospheric pressure and temperature while performing the experiments

δ : - Air density factor


For 10 cm Diameter Sphere: -

Sr. No. Distance

between sphere

at which spark over takes place

in cm

Spark over KV

peak at 200 C &

760mm HG std.From

manufactures

table A

BDV peak at

room temp. &

pressure inKV

B= KA

RMS value

of BDV in

KV

=B/√2

String

efficiency

η

01

02

03

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Voltage across the string V1

String efficiency η = __________________________________________________________ = ________________

n * voltage across the disc nearer to conductor n* (V1 - V2)

Result: - It is found that voltage across the each disc is not uniform. & string efficiency of

suspension type insulator is found to _________ % .

Discussion: - 1) Why it is necessary to calculate string efficiency.

2 2) How string efficiency can be increase.

3) What is efficiency for pin type insulator?

3 4) It is necessary to calculate string efficiency in case of dc supply.

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EXPERIMENT NO: -

Aim: -Calibration of voltmeter by using Point gap

Apparatus: - Transformer (230/100 kV, 10 kVA) Voltage Divider (100pf)

Control Panel, connecting rods, connecting wires, etc

Point Gap Method:

Circuit diagram: -

Theory: - A point gap method is also used for measurement of a peak value of power frequency, voltageand impulse voltage. Standard point gap is constructed and arranged according to the rules specified by

standard. Performing to high voltage testing techniques and point gap should be thoroughly

studied. Complete arrangement consisting of two rods of equal length and cross section area with their operating gear. Insulating sphere supporting frames leads up to the point at which the volt is to be

measured. One point is perfectly connected directly to earth, while the other sphere is connected to high

voltage conductor leads coming from H. T. transformers.

24

FUSE

REGULATING

TRANSFORMER

230 V / 100kV

10kVA

HT SWITCH

V

230 VAC

SUPPLY V

VOLTAGEDIVIDER

100 pf

100 kV

POINTGAP

SCALE

100KV

230 V

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2) For Point Gap

Sr. No. Distance in cm BDV in kV (voltmeter)

01

02

0304

Procedure: - 1) Make the connections as shown in the circuit diagram. Using spheres of same diameter.2) Adjust the suitable distance between the electrical say 0.5 cm or 1 cm from control

panel.

3) Increase the voltage gradually from control panel till breakdown occur.4) Measure this breakdown / spark over voltage for a given gap.

5) Change the distance & increase the voltage gradually.

6) Repeat the same procedure for both the sphere set.

7) Find the percentage error and plot the graph between distance and RMS BDV

(measuredvalue)

Result: - From the experiment BDV for different spacing have been found out .It is observed as distance between the electrodes increases BDV also increases.

Graph: - For Point gap(i) Distance Vs RMS BDV

(ii) Distance Vs % Error.

Questions: -(1) Write the advantages of high voltage voltage measurement by electrostatic

voltmeter.(2) Explain the high voltage measurement by resistance voltage divider method.

(3) Discuss the electrostatic field in case of sphere, flat and pointed electrodes.

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EXPERIMENT NO: -

Aim: - Determination of fault by digital cable Fault Locator

Model 2000A.

Apparatus: - Digital cable fault locator Kit, with circuit, connecting wires etc.

Circuit diagram: -

A) Single phase to Earth fault

E N D1

E N D2

R

Y

B

N e u t r a l

v1

& I1

C l i p

v 2 & I 2

C l i p

v 1 2 C l i p

2 0 % 4 0 % 6 0 % 8 0 %

RF

L o o p

1 0 0 %

A) Two phase to Earth fault :

E N D1

E N D2

R

Y

B

N e u t r a l

v1

& I1

C l i p

v2

& I2

C l i p

v1 2

C l i p

2 0 % 4 0 % 6 0 % 8 0 %

RF

L o o p

RF

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B) Three Phase to Earth faultEND

1END

2

R

Y

B

Neutral

v 1 & I 1

Clip

v2

& I2

Clip

v12

Clip

20% 40% 60% 80%

RF

Loop

RF

RF

External wire

B) Phase to Phase fault :

E N D1

E N D2

R

Y

B

N e u t r a l

v1

& I1

C l i p

v2

& I2

C l i p

v1 2

C l i p

2 0 % 4 0 % 6 0 % 8 0 %L o o p

Theory: - Fault locator is an essential complement to distance protective relay for transmission lines andfault recorder. Fault location are installed along with distance protection scheme and fault

recorders,

fault locator measures and indicates accurately the distance between the substation and the pointof fault.

Fault locator is connected to the line secondary CTs & VTs of the line under normal conditions,

the faultlocator monitors three phase currents & the ground current, voltage input signals continuously.

The

operation of the fault locator is with following steps (1) Data collection, (2) Starting of faultlocator,

(3) Sorting of measured instantaneous values, (4) Filtering of measured signals, (5)

Determination of

type of fault, (6) Solution of fault equation, (7) Pre-location of results.

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The input analog signals are converted into digital signals in A/D converter and stored in

memoryfor every six cycles continuously. When a fault occurs, trip circuit from the protective relay

initiates the

fault locator’s calculation program. The pre-fault sample values & during fault sample values areused

for calculating the distance of the fault. The calculation of distance is based on the principle

relays. The

fault distance is shown as % of total line length on two digital front mounted LED display.

Various types of fault that occur in a power systems are

1) Shunt type fault

a) Single line to ground fault (LG)

b) Line to line ground fault (LL)c) Double line to ground fault (LLG)

2) Series type fault

a) Open conductor fault (one or two conductors are open)

Procedure: -

1) Connect all batteries i.e. 6V 10A & 12V, 3.8A.2) Switch ON the instrument.

3) Create a fault at (20% to 100%) in between appropriate phases.4) Connect stimulating Board according to diagram.

5) Keep Earth / open switch in earth position.

6) Keep V1/V2 voltage switch in V1 position.

7) Keep fault resistance selector in 1MΩ position.

8) Keep V1/V2 voltage range selector switch at 20V position.

9) Null display reading to zero.10) Press push to read V1 display.

11) Change V1/V2 switch to V2 position.

12) Press push to read V2 display.

Observation Table:

V1

Distance to fault from End 1, in case of LLL G fault = __________ x 100V1 + V2

Sr. No.

Type of

Fault

Fault

locationchosen in

% of totallength

Reading of voltmeter

V1

Reading of voltmeter

V2

Distance to fault

from End 1 =

2 V1

__________

x 100V1 + V2

Remarks

compareB & E

A B C D E

1. L to G fault

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2. L-L-G fault

3.L-L-L-Gfault

4.L-Lfault

Result: - All types of faults are located by digital cable fault locator.

Conclusion: - It is found that the calculation of distance is based on the principle of distance relay. Alsofault location chosen in a % of total length is nearly equal to the distance of fault from end

(calculated)

i.e. selected value of fault locations & calculated value of fault locations are found to be same.

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EXPERIMENT NO: -

Aim: - Measurement of capacitance and dissipation factor (Tan δ) of solid insulating material by

Eltel

CTS-500Kit.

Apparatus: - Eltel Tan Delta Set, Testing transformer, connecting wires, etc.

Theory: - Write about (Tan Delta) Dissipation factor. Its basic theory

Write about Shearing bridge used for measurement of Capacitance and Tan delta.

General description of the equipment:-

General description about ELTEL – CTS – 500 Model: - It is a,

• Self contained instrument designed for the accurate measurement of

capacitance and Tan delta of electrical insulation. The test set is

suitable for making two terminals or three terminal measurements on a

specimen that may be grounded or floating.• The test set operates at a frequency of 80KHZ with voltage at 500v.

• Equipment works on the principle of transformer ratio bridge type

circuit.

Operating Instructions:

1) Connect the ground test lead to station ground using the test lead provided.2) Set the selector switch to the required position.

3) Connect the instrument to the specimen to be tested.

4) Connect H & L cable of meter to High and Low voltage side transformer respectively

5) Guard connects to earth and transformer body to earth separately.6) Set detector phasing switch.

7) Set DF range 0 to 1%.8) Set Cap multiplier to .01 uF.

9) Set capacitance switch to 5 & capacitance dial to 000.

10) Turn bridge power Switch ON.11) If the detector swings to the right, turn the capacitance multiplier switch in counter

clockwise direction until the detector swings to the left.

12) Advance the Capacitance switch clockwise until the detector swings to the then turn

the switch back by one step.13) Adjust the multiturn Capacitance dial to bring the detector to zero position.

14) Turn the detector phasing switch to DF.15) Bring the detector to zero by the DF range switch and DF dial.16) Turn the detector phasing switch to C and adjust C to null position.

17) Repeat above three steps until no further adjustment is required.

Procedure: -

1) Clean the transformer after isolating from the system and other accessories.

2) Remove oil and dry it.

3) Short the HV & LV terminals.

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4) Short the Neutral to corresponding terminal.

5) For UST Place the selector switch at UST (Ungrounded Sample Test CHL) For UST - meansmeasurement of H – L.

6) Repeat the operating instruction (1 to 14).

7) For second set of observation – ie. For measurement of H – GND – keep selector switch at L – Guard. And repeat the operating instruction.

Observation: - UST = Ungrounded Specimen Test.

GST = Grounded Specimen Test

1) FOR CAPACITANCE: -

Sr. No. Mode Multiplier

A

Switch

B

Dial

C

Capacitance calculation =

A X (B + 0.C )

01 UST 0.001uf 7 561 .007561

02

Calculations: -

Capacitance = A X ( B+0.C)

= .001*7 + .001* .561= 0.007561 uF= 7561 PF= 75.61%

2) For dissipation factor (tan δ): -

Sr. No. Mode DissipationFactor (DF)

Range

DialD

% tan δ = Lower Scale +

0.D * (Difference of Scale)

01 UST 10-20 258

02

Result: - Capacitance and % tan δ between two winding are found to be as follows,

1) between H & L UST ----------, ----------%

2) between H & L Guard ---------, ---------%3) between L & H Guard ----------, ----------%

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Precautions: -

1) Transformer must be isolated from the supply and load.

2) Clean the transformer and transformer bushings.

3) Results will be better in the dry atmosphere.4) While shorting the HV & LV terminals sag is not allowed.

5) Person should kept away several feet the test object, otherwise it may affects on the results.

6) It should be noted that in the GST mode of testing, the full test voltage is present between the

shells of the UHF connector and the body of the unit. Take care as to not to come in contactwith these two simultaneously.

7) This instrument must always be connected to ground with the supplied leads and front panel

ground binding post prior to and during all measurements. The apparatus being tested must be cleaned and correctly grounded to avoid any possibility of lethal floating potential.

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EXPERIMENT NO: -

Aim: - Measurement of oil loss angle by loss angle meter.

Apparatus: - Oil Loss Angle Meter (Model MLO – 1D), Million Mega ohm Meter (Model LS – 3D),

Three Terminal Oil Test Cell, Heating Chamber etc.

Theory: - Explain the Schering Bridge

Procedure: -

A) Measurement of Dielectric Constant

Equipment: - Oil Loss Angle Meter, Three Terminal Oil Test Cell.

Before proceeding to make this test, clean the oil cell throughly. This may be ensured by testing

empty clean cell on Million Megohm Meter.

1) Connect the oil loss angle meter to 230V AC, 50 Hz power supply.2) Switch on the equipment.

3) Keep ‘OPERATE’ switch in ‘SET ZERO’ position.

4) Keep the voltage at zero.5) Mount the oil cell on insulated base plate and connect the empty cell to the oil loss angle

meter by the cable provided. The connection should be (a) Terminal HV connect to outer

case. (b) Terminal LV to inner case & (c) Guard terminal should be connect to middleterminal of oil test cell.

6) Now put ‘OPERATE’ switch in ‘HV ON’ position.

7) Gradually raise the voltage to about 300V.

8) With the help of ‘NULL’ control adjust the null meter to read 1.00.9) Put ‘OPERATE’ switch in ‘SET ZERO’ position.

10) Do not alter or disturb the voltage or control knob.

11) Pour required quantity of oil in the cell12) Now put ‘OPERATE’ switch in ‘HV ON’ position.

13) Null meter will show a different reading. This new reading directly shows the Dielectric

Constant of the sample under test.

B) Measurement of Dissipation Factor(Tan δ)

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Equipment: - Oil Loss Angle Meter, Three Terminal Oil Test Cell, Heating Chamber etc.

Tan δ for oils is normally measured at 900C as recommended by I. S. I., but for R& D purpose it can be

at any temperature upto 1500C.

1) Clean the Oil Cell thoroughly, this can be ensured by measuring resistance onMillion Megohm Meter which should by practically infinite.

2) Pour oil to be tested in the cell gradually, the oil enters the space cavity in

between the electrodes of cell through holes provided.

3) Keep Oil Cell in Heating Chamber.4) Connect Heating Chamber to 230V AC, 50 Hz supply.

5) Switch on the Heating Chamber. Pilot lamp will come on.

6) Switch on the Heater by a switch marked Heater ON/OFF. LED will glow indicating thatHeater is ON.

7) Connect the sensing probe to the Heating Chamber by means of connecting its 3 pin lunar

socket probe in the oil cell carefully.8) The meter on Heating Chamber will indicate the temperature of the oil in cell.

9) Connect Oil Loss Angle Meter to 230V AC, 50Hz power supply.

10) Keep the voltage Zero and ‘OPERATE’ switch in ‘SET ZERO’ position.11) Connect the Three Terminal Oil Cell to the instrument.

12) Slowly raised the voltage to create the desired stress level.13) When the temperature of oil cell in heating chamber reach to 900C, then heater supply will be

cut off automatically and heater ‘ON’ indication lamp will go off. The trip setting may bechanged if required by adjusting the ‘TRIP SET control.

14) Put ‘OPERATE’ switch in ‘HV ON’ position.

15) When the temperature is 900C, with the help of ‘NULL’ control adjust the null indicator toread 5.00.

16) Again put ‘OPERATE’ switch in SET ZERO. Set the zero on tan δ meter carefully with the

help of set zero control.

17)Put ‘OPERATE’ switch in ‘HV ON’ position and read the value of tan δ on the DP %

directly in percentage.

Result: - Hence measured value of dielectric constant ---------------.and Dissipation

Factor is ----------------------------------.

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EXPERIMENT NO: -

AIM: - To determine the breakdown voltage of Paper Insulator.

Apparatus: - 25 kV High voltage Paper Insulation Tester.

Specification:-Input: 0-230, AC, 50 C/S, single phase

Output: 0-25kV AC, Leakage current: 15mA, 30mA

Type of cooling: Air cooling. Timer: 0-30 hours.

Circuit Diagram:-

Theory:-

High voltage tester plays a vital role in the industry and research institutes. This tester

enables the operator to measure the high voltage withstand level at the required material. Particularly it

plays important role to measure the voltage withstand level between primary and secondary of the

distribution transformer, insulating material and electrical equipments.

Apparatus is an air-cooled single unit consisting of high voltage transformer and the

control. High voltage transformer is the key part of the equipment. This transformer has primary and

secondary windings, separated from each other with proper insulation. These coils are epoxy potted to

provide insulation. H.T is bought out through a bushing. Control panel is also a part of the equipment.

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Control pane has all the necessary meters, switches indicators etc, for easy operation. Zero interlock has

been provided in the test specimen. High voltage is always applied gradually to the test specimen.

Procedure:-

1. Connect H.T of the transformer to the test specimen and that specimen ground to the

control panel ground and mother ground.

2. Connect the control panel power card to the supply, 230 V, ac, 50c/s.

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3. Select the leakage current selector (15mAor 30mA) with the help of leakage current

selector switch.

4. Put the ‘mains on’ of the control panel then “mains on”, H.T off indicator will glow.

5. Bring the dimmer to zero position of zero interlocking, as result ‘Unit ready’ indicator

will glow.

6. Press the H.T. ON push button, HT on indicator will glow and H.T OFF indicator will

stop glowing. (H.T will not be “ON” till dimmer comes to zero position).

7. Increase the variable voltage to the required level, if you want timer immediately put

ON the timer otherwise leave it in bypass position.

8. If specimen withstands applied voltage at set time then equipment H.T. is OFF, we

conclude sample has passed the test. If equipment will trip before set time then we

conclude the sample failed(sample failed indicator will glow), if sample failed reset it

then dimmer bring to zero then press the H.T. on push button conduct the next test.

9. In case of emergency only the emergency push button, for releasing just rotate

clockwise, it comes up.

10. After testing put the Mains OFF, remove power card.

Precaution:-

1. Always put a proper fuse.

2. Nobody should go near the bushing when the test being conducted.

Observation Table:-

Sr.No. Thickness of the specimen(paper) in mm Time (sec) Breakdown Voltage

1. 0.5

2. 0.73 1.0

Results:-

The breakdown voltage of paper insulator is studied.

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EXPERIMENT NO: -

Aim: - To determine the breakdown strength of transformer oil

Apparatus: - Transformer oil tests kit, transformer oil.

Circuit diagram:-

Procedure:-

1. Study the enclose instructions on Transformer oil testing.

2. Switch on the test kit.

3. Slowly raise the voltage, and keep it at 30kV for one minute. At the end, record whether

the oil

sample with stood 30 kV for one minute. If it fails earlier, note the time it stood, 30kV. If

it fails at

a voltage lower than 30kV, record that voltage as breakdown voltage.

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4. Then raise the voltage till such time there is a break down, and record the breakdown

voltage. All

the time take care not to exceed the maximum voltage of 60kV.

5. Remove the suspended particles due to breakdown with the help of glass tube provided.

6. Wait for 5 minutes.

7. Repeat steps 3 to 6, five times given a total of six observations.8. Switch off the test kit.

Observation Table:-

Sr.

No.

Oil Sample

Distance between electrodes in

(mm)

Breakdown voltage in

(kV)

1. Transformer oil 1mm2. Transformer oil 2mm

3 Transformer oil 3mm



Result: - The break down voltage of given sample of transformer oil is ---------------------- kV.

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EXPERIMENT NO: -

AIM: To study Impulse Generator

Apparatus: Impulse Generator, Control Panel, CRO

Specification: 100 kV AC, 140kV DC, 420 kv Impulse, 3-Stage

Theory:

Multistage Impulse Generator Circuits

• The difficulties encountered with the requirement of very large size of spheres for the switching of

higher voltages, the increase of the physical size of other circuit elements, the problems in obtaininghigh dc voltage for charging C1 and, last but not the least, the requirement of corona free structure and

leads makes the single stage circuit inconvenient for producing higher voltages.

• In order to overcome these difficulties, in 1923 Marx suggested an arrangement where a number of

condensers are charged in parallel over high ohmic resistances and then discharged in series through

spark gaps.

A multistage impulse generator, proposed originally by Goodlet, is shown in Fig . It adopts the

efficient circuit discussed earlier.

Fig. Multistage impulse generator with wave tail and front resistors in each stage. R' 2:stage wave tail

resistors, R'1: stage wave front resistors, R"1 : External wave front resistor, R': Charging resistors

• The charging resistors R' are always large compared with the stage resistors R' 1and R’2, R’2 is made

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as small as is necessary for the required wave tail. Adding the external front resistor R" 1 helps todamp oscillations causal by the inductance and capacitance of the connecting leads between the

generator and the load, if these leads are long.

• It may be readily seen that this circuit can be reduced to the single-stage impulse generator circuit

shown in Fig. When the generator is fired, or in other words, the stage spark gaps have flash over in

sequence, the stage capacitors C1' come in series in the complete circuit. Hence the total discharge

capacitance C1 can be determined as:

and the effective wave front resistance R 1 can be calculated as,

and the effective wave tail resistance R2 is given as

where n is the number of stages.

• For this circuit, the wave front resistors R' 1 do not contribute to the discharge process of the main

capacitors C'l The current through R' 2 does not flow through R' 1 and hence does not reduce the initial

generator output voltage, the wave front magnitude of the voltage.

In a multistage impulse generator; it is desired that triggering or flashover takes place first at the stage

No. 1 and then in sequence at the higher number stages. Hence, the gap distance setting requirementis such that the gap distance set at stage one is smallest and the gap distances in higher stages are in

increasing order by a small difference.

There are three ways of triggering an impulse generator;

1. Fix the gap distance between the spheres and increase the stage applied dc voltage till the

flashover occurs.

2. Set the gap distance between the spheres large enough apply a desired voltage across them

and then reduce the gap distance till flashover takes place.

3. Fix both, the desired stage voltage and corresponding gap distance within prescribed limits

Fig. Then apply the trigger pulse to the trigatron on the first stage.

Result: Hence studied the Impulse generator

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EXPERIMENT NO: -

Aim: - Study of break-down voltage for different combination of electrodes.1) Sphere 10 cm dia & Sphere 5cm dia.

2) Sphere 10 cm & rod.

3) Sphere 10 cm dia & Point.

Apparatus: - Sphere, Rod, & Point electrode, control unit, HV transformer 10KVA, 230V/100KV,

Capacitor Voltage Divider, Connecting wires etc.

Theory: - The sphere gap between two spheres is a classical example of weakly non uniform field, the

degree of non-uniformity increases with increase in the ratio in the distance ‘S’ between the

electrodes to their diameter D. the sphere gap happen to be commonly acknowledged means

in the inter-national practice for the measurement of amplitudes of direct ac & impulse

voltages. Volt- Second characteristics of a sphere gap over a large internal of time is a

horizontal straight line & consequently the breakdown voltage of the gap does not depend

upon the duration of application of voltage & on the low of its variation with time.

Out of all the gaps having a weak non uniform field the sphere gap can be prepared mast

easily & is has least dimensions. In case of a gap between two planes each plane will require

to have rounded off edges & for the value discharge distance, diameter of the plane electrode

will have to be a few times larger than the diameter of sphere.

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Procedure: -

1) Place the two spheres of diameter 10cm & 5cm. respectively are shown in

circuit diagram.2) Set the distance between them at 0.5cm.

4 3) Increase the voltage with the help of tap changing transformer.

5 4) Observe the voltage at which breakdown takes place.

6 5) Now increase the gap between the two spheres in steps of 0.5cm & observe the

7 breakdown voltage.

8 6) Take 5 set of readings.

9 7) Now replace the 5cm sphere with

10 i) A rod electrode

11 ii) A point electrode & Repeat from step1.


1) For sphere 10cm & 5cm diameter

Sr. No. Gap between the electrode (cm) BDV RMS

01

02

03

2) For sphere 10cm & Rod electrode


0102

03

3) For sphere 10cm & Point electrode


01

02

03

Result: - The flashover voltage for the various combination of electrodes have been observed by varying the distance between them & graph of breakdown voltage Vs distance between

electrodes for these combinations have been plotted.

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Conclusion: - It is known that as the surface area between the two electrodes is reduced the electric

field between than becomes non- linear in nature. Thus for the sphere gap the surface

area is maximum and hence the graph revels maximum linearity. As the surface areadecreases from rod gap to point gap graph becomes more non-linear.

hv manual for 2013

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