Technology Behind Lightning

LIGHTNING

IN THE time it takes to blink, there are 10 flashes of fork lightning in the Earth's atmosphere. Each bolt travels at around a third of the speed of light, reaches temperatures as hot as the sun's corona, and carries about 10,000 times as much current as a household circuit. No wonder lightning triggers more than a third of North America's power cuts each year, and kills hundreds of people worldwide.

History of lightning experiments

The sheer electrical power of lightning has had researchers baffled. In 1752, Benjamin Franklin flew a kite into a storm cloud and showed that it became electrically charged.

Test equipments available in standard laboratories

*Impulse generator
*Air gaps

Experimental line

An experimental transmission line of 720 m length, divided into central

suspension span of 360 m, and two dead end spans of 180 m each. There is a

facility to vary the conductor to tower clearance, conductor to conductor

clearance and conductor to ground clearance. This facilitates the study of radio

noise, audible noise, corona loss etc.

Mock-up tower

The purpose of the mock-up tower is to study the air gap clearance at

transmission towers under switching surge stress. The arrangement comprises

two conductor bundles strung between two dead end towers 80 m apart with a

mock-up tower located in between.

Pollution test chamber

The pollution test chamber is perhaps one of the largest in the world with a

diameter of 24 m and a height of 27 m. Salt fog test can be conducted for

insulators, bushings etc., up to 1000 kV class.

Cascade Transformer

The cascade transformer, comprising two units rated 800 kV each (total rating is

9600 KVA) is used for energizing the experimental line, pollution chamber and

testing equipment. The equipment has an extension unit, which can generate

oscillating switching surge impulse of up to 2000 kV peak.

Impulse Generator

The impulse generator is used for switching impulse and lightning impulse tests

on air gaps and equipment insulation. The impulse generator rating is 5 MV, 500

kJ with 25 stages and a height of 23 m.

Electrical Interference and Audible Noise measurement facilities

The laboratory has the state of art facilities to measure the Radio & TV Noise

from AC/DC overhead power lines and sub-stations as per ANSI / IEEE Std. 430-

1986, ANSI / IEEE Std. 302-1981 and CISPR-18 up to 1000 MHz range. The

facility comprises of two EMI test receivers ESHS-10 & ESVS-10, Loop antenna,

Rod antenna, Bi-conical antenna and Log periodic antenna of Rohde & Schwarz,

Germany make. The precision impulse sound level meter CEL-414/3C make:

Lucas CEL Instruments Ltd., UK, covers the audible noise measurement.

Frequency Response Analyser.

Tests

Impulse test of transformer

Insulator strings/solid core/hollow porcelain/long rod

bushing/insulating materials. System voltage upto 800 kV.

• Impulse voltage withstand/flashover tests- lighting & switching

Isolator / CB / AB switches upto 800 kV system voltage

* Lightning & switching impulse test (Dry & Wet )

Power / distribution transformers ( upto 100 MVA)

* Lightning & switching impulse test

CT / VT / CVT / Bushing / Grading capacitor / Arrester Housing and Power

connector and other equipment upto 800 kV system voltages

* Lightning & switching impulse test (Dry & Wet, + / - ve Polarities)

Coupling capacitors / grounding capacitive reactors / RVT.

* Lightning & switching impulse test (Dry & Wet, + / - ve Polarities)

8. Chopped impulse test (fast transient test) on CT / PT up to 800 kV.