Because of fault there is an imbalance in the three phase stator currents and because of these irregularity flows, twofold frequency currents are impelled in the rotor center. This reasons the over warming of the rotor and therefore the rotor harm. Uneven stator currents likewise harm the stator. Negative sequence relay furnished with the over current relay is utilized for the assurance against unbalance stacking. From the hypothesis of the symmetrical parts, we realize that an unequal three phase currents hold the negative succession segment. This negative stage grouping current reasons warming of the stator. The negative warming takes after the safety law so it is corresponding to the square of the current. The warming time steady normally rely on the cooling framework utilized and is equivalent to I²t=k where I is the negative succession current and t is the present length of time in seconds and k is the steady normally 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 insurance three Cts are joined with three stages and the yield from the secondaries of the Cts is bolstered to the loop of over current transfer through negative sequence relay. Negative sequence relay comprises of the resistors and capacitors and these are joined in such way that negative arrangement momentums courses through the hand-off curl. The transfer might be set to work at any specific quality of the unbalance ebbs and flows or the negative arrangement segment current
1. Generator protection
http://www.cooperpower.com/Library/pdf/99066.pdf
2. Power system and protection
http://books.google.com/books?id=e0kdmbuWB0gC&pg=PA1&dq=generator+protectio
n&ei=I40fSLqaLKaiiwGIv_CKBg&sig=f8YRFoOQNFeheKHNB9u13v0ucSY#PPP1,M
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3. Protective theory relaying and application by Walter A. Elmore
4. Voltage regulators
http://en.wikipedia.org/wiki/Voltage_regulator
5 power engineering
http://en.wikipedia.org/wiki/Power_engineering
6. Google books of power system stability and control by Leonard L. Grigsby
nice post
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