Because of fault there is a unbalance condition in the three phase stator currents and because of these unbalance currents dual frequency currents starts flowing in rotor core. these dual frequency currents heats up rotor and harms rotor. due to same unbalance currents damage of stator also takes place.
Negative arrangement channel furnished with the over current relay is utilized for the insurance against unbalance loading. From the hypothesis of the symmetrical components, we realize that unbalanced three phase currents contains the negative sequence part. This negative sequence current reasons warming of the stator.The negative warming accompanies the resistance law so it is corresponding to the square of the current. The warming time consistent normally rely on the cooling framework utilized and is equivalent to I²t=k where I is the negative succession current and t is the time of flow in seconds and k is the constant generally lies between 3 and 20. Its general practice to utilize negative current transfers which matches with the above warming aspects of the generator. In this sort of assurance three Cts are joined with three stages and the yield from the secondaries of the Cts is sustained to the curl of over current transfer through negative succession channel. Negative succession circuit comprises of the resistors and capacitors and these are joined in such way that negative succession currents moves through the transfer loop. The hand-off might be set to work at any specific quality of the unbalance currents or the negative succession part current.
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