Skip to main content

Lightning Phenomena

Lightning Phenomena

[caption id="attachment_1162" align="alignnone" width="3862"]Lightning Phenomena Lightning Phenomena[/caption]

Lightning has always been attracting mankind since the early times. Lightning is a natural electrical phenomenon consisting of a high current, short time discharge that neutralizes an accumulation of charge in the atmosphere. The discharge path can be between two different locations in a cloud, two clouds, a cloud and the earth (or any structure connected to the earth). The mechanisms by which such charge accumulations take place is not yet fully known but is related to the motions of large air masses that come across certain conditions of humidity, temperature, and pressure. When the electric held become excessive a breakdown or lightning flash takes place. As explained earlier, lightning strokes that terminate on or near to power lines create problems for power engineers. The real incentive to obtain additional knowledge about lightning came from the necessity of the electrical industry to protect against its effects. It has been proved that lightning is the greatest single cause of outages in the transmission sector. where the temperature is about -5°C and that the main positive charge center is located several kilometers higher up, where the temperature is usually below -20°C. Figure (4.2) shows such a cloud located above an overhead transmission line.

Fields of about 1000 V/m exist near the center of a single bipolar cloud in which charges of about 20 C are separated by a distance of about 3 km, and indicate the total potential difference between the main charge centers to be between 100 and 1000 MV. The energy dissipated in a lightning flash is therefore of the order of 1000 to 10,000 M]. Vertical separation of the positive and negative charge centers is about 2-5 km, and the charges involved are 10-3 0C. During an average lightning storm, a total of the order of kilo-coulombs of charge would be generated between the 0°C and the -40° C and the -40°C levels, in a volume of about 50km.

Read More

Popular posts from this blog

Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant.  The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated.  There is sometimes difficulty 1n locating the drainage face, sometimes thin previous seams that can act as good drainage face are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform. Read More Muller-Breslau principle

Price Guard Wire Method

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now

Negative Booster

Negative booster A negative booster is employed to conform to the regulation that the potential difference between any two points of the rail return shall not exceed 7 V. Two boosters, positive and negative, are used which are mechanically coupled together and driven by a DC motor. The positive booster is connected to the trolley wire (near the generating station) and the negative booster (separately excited) is connected to the track rail.  The 'positive booster' adds voltage to the line while the 'negative booster lowers the potential of the point it is connected to. As we go along the trolley wire away from the generating station/sub-station, the potential drop increases, and the voltage of the trolley wire falls. Since the current returns via the track rail points away from the generating station acquire high potentials. This potential is brought down by the negative boost provided by the negative booster. When the load is sufficiently far aw