Electrical Engineering

EngrX: Some basic facts an Electrical Engineer should know..! 1. You need to know Ohm's law V=IR, current is proportional to the voltage applied. 2. Electric shock is caused by current and not voltage. 30mA of current is enough to cause ventricular fibrillation in your heart. 3. Megger  is the name of a company. (Many people term measuring of Insulation resistance as Megger) 4. 'Exd' type equipments (sometimes called explosion proof) do not prevent explosion. They just help to isolate an explosion in the interior of the equipment from spreading outside. 5. Test before Touch. This is a mantra that every electrical engineer should remember. You need to check that there is no voltage before touching any live part. It may have been fed from a different source. 6. Nowadays, domestic fan regulators do not work on potential divider concept and there is no power loss if you operate the fan at lower/higher speeds. 7. System earthing and body earthing are different. 8. All motors are treated in kW/MW, transformers in MVA/kVA and fuses in A. 9. 'k' in kW, kVA, kA, kV need to be in smaller case and not as in KW, KVA, KA, KV. 10. Incidents can happen anytime and one should wear appropriate safety gear before working on an electrical installation. 11. In electrical cables, size of the core determines the amount of current it can carry and the thickness of Insulation determines the voltage level it can work at. 12. Making capacity of a circuit breaker is approximately 2.5 times its breaking capacity. 13. In transformers, Dyn11 vector group will become Yd1 if you change its primary and secondary sides. 14. Neutral is solidly grounded in the 415V system at the user end to protect people from shock. 15. 230V, that we measure is the rms value and the actual peak AC voltage is √2 * 230V. 16. Every electrical engineer should know how to give basic first aid and CPR. CPR can bring a dead person to life. 17. Zero watt bulbs available in the market are not actually rated for zero watt. Their ratings vary from 5W to 20W.

Types of Relays: 1.Electronic Relay 2.Rectifier Bridge Relay 3.Transistor Relay 4.Hall Effect Relay 5.Gauss Effect Relay 6.Magnetic Amplifying Relay

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Electrical Power Transformer, Distribution Transformer and Instrument Transformer - Power transformers are generally used in transmission network for stepping up or down the voltage level. It operates mainly during high or peak loads and has maximum efficiency at or near full load. Distribution transformer steps down the voltage for distribution purpose to domestic or commercial users. It has good voltage regulation and operates 24 hrs a day with maximum efficiency at 50% of full load. Instrument transformers include C.T and P.T which are used to reduce high voltages and current to lesser values which can be measured by conventional instruments. Two Winding Transformer and Auto Transformer - Former is generally used where ratio between high voltage and low voltage is greater than 2. It is cost effective to use later where the ratio between high voltage and low voltage is less than 2. Outdoor Transformer and Indoor Transformer - Transformers that are designed for installing at outdoor are outdoor transformers and transformers designed for installing at indoor are indoor transformers. Oil Cooled and Dry Type Transformer - In oil cooled transformer the cooling medium is transformer oil whereas the dry type transformer is air cooled. Core type, Shell type and Berry type transformer - In core type transformer it has two vertical legs or limbs with two horizontal sections named yoke. Core is rectangular in shape with a common magnetic circuit. Cylindrical coils (HV and LV) are placed on both the limbs. Shell type transformer: It has a central limb and two outer limbs. Both HV, LV coils are placed on the central limb. Double magnetic circuit is present. Berry type transformer: The core looks like spokes of wheels. Tightly fitted metal sheet tanks are used for housing this type of transformer with transformer oil filled inside.

Types of Transformer Transformers can be categorized in different ways, depending upon their purpose, use, construction etc. The types of transformer are as follows, Step Up Transformer and Step Down Transformer - Generally used for stepping up and down the voltage level of power in transmission and distribution power system network. Three Phase Transformer and Single Phase Transformer - Former is generally used in three phase power system as it is cost effective than later. But when size matters, it is preferable to use a bank of three single phase transformer as it is easier to transport than one single three phase transformer unit.

Use of Power Transformer Generation of electrical power in low voltage level is very much cost effective. Theoretically, this low voltage level power can be transmitted to the receiving end. This low voltage power if transmitted results in greater line current which indeed causes more line lossesBut if the voltage level of a power is increased, the current of the power is reduced which causes reduction in ohmic or I2R losses in the system, reduction in cross sectional area of the conductor i.e. reduction in capital cost of the system and it also improves the voltage regulation of the system. Because of these, low level power must be stepped up for efficient electrical power transmission. This is done by step up transformer at the sending side of the power system network. As this high voltage power may not be distributed to the consumers directly, this must be stepped down to the desired level at the receiving end with the help of step down transformer. Electrical power transformer thus plays a vital role in power transmission.Two winding transformers are generally used where ratio of high voltage and low voltage is greater than 2. It is cost effective to use auto transformer where the ratio between high voltage and low voltage is less than 2. Again a single unit three phase transformer is more cost effective than a bank of three single phase transformers unit in a three phase system. But a single three phase transformer unit is a bit difficult to transport and have to be removed from service entirely if one of the phase winding breaks down.

Definition of Transformer A transformer is a static machine used for transforming power from one circuit to another without changing frequency. This is a very basic definition of transformer. Since there is no rotating or moving part so transformer is a static device. Transformer operates on ac supply. Transformer works on the principle of mutual induction.