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Protection Riddle No.54 - Measuring of 7th voltage harmonic
Studious groups were commanded to harmonic affect on protective relay investigation in a power plant substation. Ali as youngest member of group should be gather field data and information. For evaluation of amount of 7th voltage harmonic , he should be done some measuring in secondary side of voltage transformers. He faced to several CVT in substation at various place, but he preferred to use of power generator VT as a dependable and confident signal source for his measurements.
How can you guess his reason for mentioned VT selection?

Author : Hamid - From: Iran
Sat, October 24th, 2009 - 10:36
In case of no load situation in secondary  side of step-up transformer , it's OK and does not present any problem . But , in case of loading , as the transformer is being operated in nonlinear zone ( knee point) , the magnetizing current and secondary side current will be nonsinusidal .In this case , the voltage in CVT of substation point will have 7th harmonics , but the CVT of Generator side does not show it.

Author : AMIR KHASHAYAR - From: Iran
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