RE: transformer PPT
1Transformers.docx (Size: 21.13 KB / Downloads: 104)
They are used to change the amplitude of high frequency pulses by the turns ratio and to provide isolation betweencircuits.Its main parts are:-
Manufactured from laminations of CRGO(ColdRolled Grain Oriented)Silicon Steel. It gives very low specific loss at operating flux densities.
Windings:-They are made from paper insulated copperconductors which are transposed at regularintervalsthroughout the winding. It provides equal flux linkage andcurrent distribution between strands.
They use a maximum amount of conductormaterial to provide the required shape and physicalstrength, and use a minimum amount of insulatingmaterial to provide only the insulating function.
Pressure Relief Valve:-
Transformers are provided with pressure relief valve which operates in case of suddenpressure formation inside the transformer.
Transformers are provided withcooling bank. These are provided with fans and pumps.These fans and pumps automatically operate, dependingupon the settings of winding temperature .
Protective Relays .
A current transformer (CT) is used for the measurement of electric currents.
When current in a circuit is too high to directly apply to measuring instruments, a currenttransformer produces a reduced currentaccurately proportional to the current in thecircuit, which can be connected to measuringand recording instruments.
Voltage transformers (VT) are another type of instrumenttransformer, used for metering and protection in high- voltage circuits.
They are designed to present negligible load to the supply being measured and to have a precise voltage ratio toaccurately step down high voltages so that metering andprotective relay equipment can be operated at a lowerpotential.
V Ts are typically used for higher voltages (for example,765 k V
for power transmission), or where isolation isdesired between the meter and the measured circuit.
A relay is an electrically operated switch.
These are used to protect electrical circuits from overloador faults.
Relays find applications where it is necessary to control acircuit by a low-power signal, or where several circuitsmust be controlled by one signal.
When an electric current is passed through the coil, theresulting magnetic field attracts the armature.
The consequent movement of the movable contacts eithermakes or breaks a connection with a fixed contact.
If the set of contacts were closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts wereopen.
W hen the current to the coil is switched off, the armature isreturned by a force, approximately half as strong as themagnetic force, to its relaxed position.
This force is provided by a spring.
A circuit breaker is an automatically-operated electricalswitch.
It is designed to protect an electrical circuit from damagecaused by overload or short circuit.
Its basic function is to detect a fault condition, interruptthe continuity, and immediately discontinue electricalflow.
Operation of a C.B.
Circuit breakers for large currents or high voltages areusually arranged with pilot devices.
It senses a fault current and operate the trip openingmechanism.
The trip solenoid that releases the latch is usually energized by a separate battery.
Once a fault is detected, contacts within the circuit breakeropen to interrupt the circuit.
Some mechanically-stored energy (using something suchas springs or compressed air) contained within the breakeris used to separate the contacts.
Circuit breakers have solenoids to trip the mechanism, andelectric motors to restore energy to the springs.
The circuit breaker contacts carry the load current without excessive heating, and also withstand the heat of the arc produced when interrupting the circuit.
Contacts are made of copper or copper alloys, silveralloys, and other materials.
When a current is interrupted, an arc is generated.
This arc is contained, cooled, and extinguished in acontrolled way, so that the gap between the contacts canagain withstand the voltage in the circuit.
Once the fault condition has been cleared, the contacts areagain closed to restore power to the interrupted circuit.