Shear Pin

Shear Pin is a safety device which breaks in case of mechanical overload, and prevents further damage to machinery, it is sacrificed to protect or prevent damage to bigger and more critical component of machinery. Its mechanical analogous to electrical fuse.

In a hydro power plant this pin is used to couple lever and lever handle, if the two loses synchronism between each other due two some mechanical fault the pin breaks, and air pressure decreases.

Resistance and its Unit

Resistnace
Is is the peoperty of substnace by virtue of which it opposes the flow of electrons(electricity) through  it. Metals,acid and salt solutions are good conductors of electricity. Amongst metals Silver, Copper and Aluminium ae very good conductors of electricity. this is due to presence of a large number of free or loosely -atttached electrons in their atoms. These Vagrant electrons assume a directed motion on the application of an electric potential difference. These electrons while flowing pass through the molecules or the atoms of the conductor, collide and other atoms and electons, thereby producing heat.

Those substance which offer relatively greater diffculty or hindrance to the passage of these electrons are said to be poor conductors of electricity like bakelite, mica dry wood etc.They are also called as insulators

Unit
The practical unit of resistance is ohm. A conduator is said to have a resistance of one ohm if it permitsone ampere current to flow through it when one volt is imptressed across its terminals.

Energy Efficiency of Power and Distribution Transformers

Power Transformer:- these are used at the sending and receiving end of a long, high voltage transmission line for stepping up or stepping down the voltage,they are manipulated to operate almost at or near their rated capacity (KVA rating). In view of this a power transformer is designed to have maximum efficiency at or near full load.(rated KVA). Hence choice of transformer should be based on full load efficiency.

Distribution Transformers are the one which are installed at consumer premises, where they are use to step down the voltage. The secondary winding of distribution transformers are directly connected to consumer terminals. The load on this transformer varies wide range during 24 hours day due to varying requirement ranging from zero to a maximum of its rated capacity. Note the primary of distribution transformer is constantly energized therefore core losses occur continuously.So  these transformer are designed to have minimum core losses, but for reduced core loss the maximum efficiency may occur at about one-half of its rated capacity. therefore choice of distribution transformer must be calculated as follows
Energy efficiency of a transformer is defined as the ratio of total energy output for a certain period to the total energy input for the same period

Relationship between Magnetism and Electricity

Whenever current flows through a conductor magnetic field is produced in the area surrounding the conductor (this phenomena was discovered by scientist Orested). So concluded that whenever the electrons are in motion magnetic field is produced vice versa is also true whenever magnetic field is in motion with respect to a given conductor electrons start flowing in that conductor, hence the current comes into existence (as proved by Faraday) . 

This phenomena whereby an e.m.f  and hence current is induced in any conductor which is cut across of is cut by magnetic flux is known as electromagnetic Induction.

Electromagnetic Induction is the basic phenomena on which every electrical machine works whether DC or AC including Transformers.

* intersecting fact

While the production of magnetic field due to flow of electrons was accidental discovery.

It took nine long years for Faraday to convert magnetic energy into electrical energy and all through these he use to carry magnets in his pockets so as to constantly remind him of the problem.

Rating of Transformers (why KVA and not KW)

Transformers have a name plate fixed on them on which rated output, rated voltages, the rated frequency, cooling method are recorded. The interesting fact is that its output rating is expressed in KVA (kilovolts ampere)rather then KW (kilowatt). This is due to the fact that the  transformer rated output is limited by heating and hence losses in the transformer. The two type of losses in a  transformer are core loss and ohmic losses.These  losses depend on transformer voltage and current and are almost unaffected by the load pf, therefore transformer rated output is expressed in VA or in KVA and not in KW

Transformers Noise

Transformers usually with ferromagnetic core produce a constant hum which leads to noise which can be very annoying especially in residential areas.The major cause of this noise is a phenomena called as magnetostriction. When the ferromagnetic core of transformers is magnetize, the core length along the alternating flux decreases and increases alternatively, with an alternative decrease and increase of its cross section. this phenomena of small change in the core dimensions is known as magnetostriction, alternatively the ferromagnetic core vibrates and humming is produced. this humming is further transfered to oil, transformer tank and then surroundings. The level of sound will increase with core flux density.

Transformers

The transformer is a device that transfers electrical energy from one circuit to another circuit through the medium of magnetic field and without change in the frequency. The electrical circuit which receives energy from the supply mains is called primary winding and the other circuit which delivers electric energy to the load is called the secondary winding.

This device is a electromagnetic energy conversion device. The electrical energy present in the primary winding is changed into magnetic energy and this magnetic energy is again converted back to electrical energy in  secondary circuit. The two circuits primary and secondary are magnetically coupled. Energy is transfered by this magnetic coupling between two cicuits  and no mechanical device is utilized therefore efficiency of transformers is as high as 98%.

Step Up Transformers: If the secondary windings has more number of turns then primary winding then the secondary voltage is higher then the primary voltage and the transformer is called as step up transformer.

Step Down Transformers: If the number of turns in the secondary side is less than the primary side then the voltage in secondary side is  lower then the primary voltage and the transformer is called as step down transformer.

There is  a third kind of transformer where number of windings in primary is equal to the number of windings in secondary these transformers are used for isolation purpose.