Answer / mayur kavar

The transformer works on the principle of mutual induction between the primary and secondary windings. The induction is caused by the constantly varying magnetic flux that links the two windings. The flux density in the windings is directly proportional to the induced voltage and inversely proportional to the frequency and the number of turns in the winding.

Magnetic Flux α Voltage/Frequency

Overfluxing is a dangerous situation in which the magnetic flux density increases to extremely high levels. The high flux density can induce excessive eddy currents in the windings and in other conductive parts inside the transformers. The heat generated by these eddy currents can damage the windings and the insulation. The high flux density also causes magnetostriction inside the transformer core and produces noise. The powerful magnetostrictive forces can also cause damage. The winding temperatures may also increase due to the heat produced.

The magnetic flux density is dependent on the current flowing through the primary windings in a transformer. This current is dependent on the voltage applied across the windings and the winding impedance. The impedance is dependent on the frequency of the applied voltage. If the nominal voltage is applied at a reduced frequency, the low inductive reactance will cause a higher current to flow through the windings.

Overfluxing is usually encountered in Transformers which are directly connected to the generator. It usually occurs when the generator is being started or stopped. As the rpm of the generator and consequently the frequency of the power falls, the same system voltage induces a higher magnetic flux. Modern Automatic Voltage regulators are equipped with V/Hz limiters which limit the voltage in accordance with the frequency.

Overfluxing can be prevented by the use of a Overfluxing relay. An overfluxing is an adaptation of an overvoltage relay. The PT voltage is connected across a resistor and a capacitor in series. The voltage sensing relay is connected across the capacitor. The relay operates in the event of an overfluxing and isolates the transformer

Answer / k.prakashchandra

In brief . Flux = K V / f . If the voltage increases or frequency decreases flux will increase when the other factor remains the same . That's why you can not give excitation unless the gen picks up at least 90 % of the rated speed in case of generator

what happen when power factor of 2 parallely operated transformer become equle?

0 Answers   Flextronics,

---

which book to refer in electrical engineering for iocl exam & which book for general english.

0 Answers   L&T,

---

How can step up and step down process in power transformer

1 Answers   MSETCL Maharashtra State Electricity Transmission Co Ltd,

---

How to calculate energy stored in a capacitance

0 Answers  

---

How to calculate Maximum Demand from Energy meter Reading.

1 Answers   Etisalat,

---

---

why wound rotor is star-connected?

4 Answers  

---

Is there any type of starter for DC motor other than two point,Three point and Four point starters?

0 Answers  

---

Why the transformers are rating in KVA.?

5 Answers   ISMT,

---

what is a composite error in current transformers, why occurs & in which it will occur i.e, either metering ct/ protection ct

0 Answers  

---

How to size a transformer which will supply power to 550kW,690V motor starting with VFD?

1 Answers  

---

A cylindrical wire is compressed in length by 10%. The percentage decrease in the resistance will be?????

0 Answers  

---

quantizer means?

0 Answers  

---