Electrical engineering formula sheet pdf

Please forward this error screen to 158. Please forward this error screen to 103. If the live wire touches the grounded case then the circuit is effectively shorted and fuse will electrical engineering formula sheet pdf blow.

When the fuse is blown then the dangerous voltages are away. To ensure that all exposed conductive parts do not reach a dangerous potential. To provide safe path to dissipate lightning and short circuit currents. To provide stable platform for operation of sensitive  electronic equipment i. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment . Earthing provides an alternative path around the electrical system to minimize damages in the System.

Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other. The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems. Cast iron plate of size 600 mm x600 mm x12 mm. Galvanized iron plate of size 600 mm x600 mm x6 mm. Plate  burred at the depth of 8 feet in the vertical position and GI strip of size 50 mmx6 mm bolted with the plate is brought up to the ground level.

4 feet from the bottom of the pit. Use 500 mm X 500 mm X 10 mm GI Plate or Bigger Size for more Contact of Earth and reduce Earth Resistance. Wood Coal Powder use as good conductor of electricity, anti corrosive, rust proves for GI Plate for long life. The purpose of coal and salt is to keep wet the soil permanently. The salt percolates and coal absorbs water keeping the soil wet. Care should always be taken by watering the earth pits in summer so that the pit soil will be wet.

Coal is made of carbon which is good conductor minimizing the earth resistant. Salt use as electrolyte to form conductivity between GI Plate Coal and Earth with humidity. 500 mm X 500 mm X 10 mm in the mid of mixture. Use Double GI Strip size 30 mm X 10 mm to connect GI Plate to System Earthling.

It will be better to use GI Pipe of size 2. Flange on the top of GI Pipe to cover GI Strip from EARTH PLATE to Top Flange. Maintain less than one Ohm Resistance from EARTH PIT conductor to a distance of 15 Meters around the EARTH PIT with another conductor dip on the Earth at least 500 mm deep. Check Voltage between Earth Pit conductors to Neutral of Mains Supply 220V AC 50 Hz it should be less than 2.

It is the resistance of the soil to the passage of electric current. It varies from soil to soil. It depends on the physical composition of the soil, moisture, dissolved salts, grain size and distribution, seasonal variation, current magnitude etc. In depends on the composition of soil, Moisture content, Dissolved salts, grain size and its distribution, seasonal variation, current magnitude.

Most of the soils are very poor conductors of electricity when they are completely dry. Soil resistivity is measured in ohm-meters or ohm-cm. Soil plays a significant role in determining the performance of electrode. Soil with low resistivity is highly corrosive. If soil is dry then soil resistivity value will be very high. If soil resistivity is high, earth resistance of electrode will also be high. The resistivity of a soil can be determined by the quantity of water held by the soil and resistivity of the water itself.

Conduction of electricity in soil is through water. And further increase of moisture level in soil will have little effect on soil resistivity. In many locations water table goes down in dry weather conditions. Therefore, it is essential to pour water in and around the earth pit to maintain moisture in dry weather conditions. Resistivity of soil depends on resistivity of water which in turn depends on the amount and nature of salts dissolved in it. Common salt is most effective in improving conductivity of soil.

But it corrodes metal and hence discouraged. Thus in dry whether resistivity will be very high and in monsoon months the resistivity will be low. 150 ohm-meter, whereas for rocky or gravel soils, the same may be well above 1000 ohm-meter. In a sloping landscape, or in a land with made up of soil, or areas which are hilly, rocky or sandy, water runs off and in dry weather conditions water table goes down very fast.

In such situation back fill compound will not be able to attract moisture, as the soil around the pit would be dry. The earth pits located in such areas must be watered at frequent intervals, particularly during dry weather conditions. Though back fill compound retains moisture under normal conditions, it gives off moisture during dry weather to the dry soil around the electrode, and in the process loses moisture over a period of time. Therefore, choose a site that is naturally not well drained. Increase or decrease of moisture content in soil determines decrease or increase of soil resistivity. Thus in dry weather resistivity will be very high and during rainy season the resistivity will be low. The thermal characteristics and the moisture content of the soil will determine if a current of a given magnitude and duration will cause significant drying and thus increase the effect of soil resistivity.