High voltage engineeringNeed for future………………

Design, Planning and Layout of high voltage laboratory

• Test facilities provided in high voltage lab

• Activity and study in high voltage lab

• Classification of high voltage lab

Our main aim to study is:

Why to study these topics?????

• In this industrial developing world the need of power is increasing exponentially thus to transfer high power at long distance is necessary

• So the transmission at h.v is possible which is up to 720 kv and 1000kv

• So extensively study is made on high voltage d.c. testing at 400 kv

• Thus to perform tests and research the lab providing high voltage is needed

• Transformers

• Lighting arrester

• Isolator and C.B

• Different type of insulators

• Cables

• Capacitors

• Line hardware and accessories

• Other equipment like reactors

.

Test facilities provided in high voltage lab

Activities and studies in high voltage laboratory

• Main is testing on equipment

• Other than it is research

• So research include

i. Breakdown strength of different material like solid ,liquid and gas.

ii. Electrical interference of transmission line

iii. High voltage power system’s insulation

iv. High current phenomena such as electrics arc and plasma physics

classifications

Type of h.v. lab

Small lab

Medium lab

Large lab

• Equipment rating :< 10kva/10KW

• Impulse equip.:< 10KJ energy

Voltage rating

• Size for room may be 15mx10mx8m

• Sometimes 5m x 8m only

size

• Mostly used by colleges and universities..

Used by

Small size lab

Medium size lab: an industrial lab

In industrial laboratories not much emphasis is generally given for undertaking research work and little flexibility may be available for incorporating new equipments

Other test equipment like the impulse current generator for testing surge diverters and d.c. test facilities for testing cables and capacitors can also be made available .

impulse generator rating:More than 10 to 20 KJ

Planning of such lab includeGround transport Handling equipment like cranes Rationalization of test procedure by

making instrument easily accessible Extension facility for future

Main function is to do routine testVoltage rating: 200 kv to 600 KV KVA rating: 100 to 1000

Large size lab

Used for testing and research work

It contains facilities like • One or more h.v. test halls,• Corona and pollution test chambers,• Outdoor test area for tests on large sized

equipment, transmission lines and towers etc.,

• Controlled atmospheric test rooms/chambers,

• Computer facilities, library etc. with good office facilities, and Provision for overnight tests and stay.

The building and equipment include the

workshop, material handling equipment

like cranes, ladders, air cushion platforms etc. and large control and

electric supply facilities (up to few KVA or

MVA).

such a laboratory will include a director or manager, few group

leaders, and section heads separately for

research, testing, measurements,

electronics and computer facilities

The cost of such

laboratories will be several

millions of rupees

HIGH VOLTAGE LAB

SIZE AND RATINGS OF LARGE SIZE HIGH VOLTAGE LAB

Withstand Voltages, Test Voltages and

the Rating of Equipment in High

Voltage Laboratories

Voltage and Power Ratings of Test

Equipment

Size and Dimensions of the

Equipment In High Voltage

Laboratories

Layout of High Voltage

Laboratories

Large size high voltage lab

Withstand Voltages, Test Voltages and the Ratingof Equipment in High Voltage Lab

• Generally up to 230 KV design it does not pose any problem but above 400 KV it is to be handle with care

• For research and development work, the voltage levels needed are usually about 1.3 times the maximum test voltage needed. Hence, the laboratories intended for different system voltages should have the test voltages

Voltage and Power rating of test equipment

1. D.C. Testing Equipment

2.Power frequency testing equipment

3.Impulse generators

4. Other hv testing equipment

D.C. Testing EquipmentIt can be performed with cascaded rectifier.

When testing polluted insulation intense care must be taken

It require currents of 50 to 200 mA, but strong pre-discharge streamers of 0.5 to 1.0 A of milliseconds duration may occur.

Hence, the generator must have adequate internal reactance in order to maintain the test voltage without too high a voltage drop.

Power Frequency testing equipment

The flashover voltage of an insulator in air or oil or in some fluid depends on the capacitance of the supply system, due to the fact that a voltage drop may

not maintain the pre-discharges before breakdown.

Hence, a minimum of 1000 pF or more in parallel with the energized insulator is needed to determine the real flashover or puncture voltage, and the generator has to supply at least 1A

in the case of clean and 5 A in the case of polluted insulator at test voltage on short circuit.

The output of testing transformer will be given by•p = 2ΠfC x V² x 10e-19 KVA

Transformer self capacitance ana capa. Of various high voltage e.g. bushing is used to measure load capac.

• The maximum charging voltage of an impulse voltage generator is given by the stage voltage multiplied by the number of stages. The peak value of the impulse voltage V5 for a standard 1.2/50 ^s wave is

•

V d.c. = Charging voltage,

• n = number of stages in the generator,

• CL = load capacitance, and

• Cg = generator capacitance.

Impulse Generators

• In order to test transformers which have large capacitance, a minimum of 30,000 to 40,000 pF of generator capacitance is needed.

• A simple calculation will show that a minimum of 135 KJ is required for a 3 MV impulse generator, if the IEC specification for impulse wave shape is to be maintained.

• The minimum energy rating of a 6 MV impulse generator will be about 600 kJ.

• From this it may be concluded that the energy rating in kilojoules may be approximated to be equal to 0.1 times the voltage rating in kV.

• There is no problem to pile up a large size capacitance in the form of a number of capacitors and to charge them in parallel and discharge them in series to give the requited peak of the standard impulse wave.

• But many difficulties exist in reducing the internal inductance of the circuit to a minimum to obtain a steep front and to avoid oscillations. As an example, a 4 MV impulse generator test circuit has a length equal to 0.1 times the voltage rating (kv)

• Hence, a very careful design and a very careful consideration of the test circuit only can give the optimum test conditions which are not far from theoretical specifications

IMPULSE GENERATOR

Other High Voltage Testing Equipment

Usually, the other testing equipment that will be available is, 1. impulse current generators for testing lightning arresters,2. test facilities for measuring RIV and partial discharges, 3. sphere gaps for measurement and calibration purposes, and 4. high voltage Schering bridge for dielectric testing. Usually, the impulse current generators are rated between 100 to 250 kA with an energy rating of 50 to 100 kJ.

This is more than adequate for testing with lightning stroke currents.

Partial discharge and RIV measurements require testing transformers free from internal discharges. The detection equipment should be capable of detecting 0.01 PC of charge in at lest object capacitance of 100 pF and 2 to 3 PC

Thus , test transformers should have internal discharges of the same order at the specified voltage value.

it is possible to design a.c testing transformers with necessary shielding, etc. with internal discharges less than 5 pC at 50OkV.

Where sphere gaps are used, it is important to bestow thought regarding the proper size and space requirements. Proper attention must be given to type and magnitude of the voltage to be measured, range of operation keeping in view that the sparking distance is less than 0.5 times the diameter of the spheres, and space requirements as specified in IS: 1876-1961 and other specifications

Control panel of high voltage testing instrument

Size and Dimensions of the Equipment In High Voltage lab• Mainly two type of lab:

1. indoor type & 2.outdoor type

• indoor type has the advantage of 1. protection of testing equipment against variable weather conditions, 2. simplicity in design and control of the test equipment, 3. provision of observation facilities during testing.

• outdoor laboratories have the advantage of1. less cost due to the absence of building cost and 2. the planned facility 3. layout cost

• But it has disadvantages 1. absence of lifting and supporting facilities, 2.climatic conditions which may restrict or impede testing 3.reproducibility of results not being guaranteed due to uncontrolled atmospheric conditions, and 4.artificial and wet test studies which are difficult due to wind variation, etc.

• When high voltage laboratories are planned as indoor laboratories, the following figures fix the dimensions of the laboratories:

1. Size of the test equipment for a.c., d.c., or impulse generators

2. Distances or clearances between the test object and ground during test conditions and also between all the high voltage terminals and earthed or grounded surroundings such as walls, roofs of buildings, and other test equipment not energized.

Layout of high voltage lab

• It is based on type of equipment to be tested , available space ,other accessories needed for the tests……

• EARTHING and SAFETY is foremost consideration ……

Lab

build

ing

High voltage lab in India

Impulse Tests on Transformers

Impulse Voltage Generator 600 kV , 18 kJ

Automatic HV and PD measuring systems for testing of bushings for SF6 switchgears

Complete High Voltage Test Systems

Complete High Voltage Test Systems

Specific test systems for different applications, like

• surge arresters

• switchgears

THANK YOU

DONE BY: NIDHI MARU