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
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,
Rod antenna, Bi-conical antenna and Log periodic antenna of Rohde & Schwarz,
Lucas CEL Instruments Ltd.,
Frequency Response Analyser.
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.
