1) How many cycles of the 7th harmonic do you expect to see during a single cycl
ID: 2291377 • Letter: 1
Question
1) How many cycles of the 7th harmonic do you expect to see during a single cycle of fundamental current? 2) How do harmonics cause transfomer temperature to increase? 3) If fundamental current is 185 amps, then what is the percent of total harmonic current distortion for the following current spectrum? 15 = 65. 17-25. 111-12. I 13-8 4) How do harmonics impact the sizing of power transformers? 5) What is the resonant frequency for a circuit containing inductance of 1mH (0.001H) and capacitance of 575uF (0.000575F)? 6) What frequency is the11th harmonic if fundamental frequency is 60Hz? 7) Under typical condition, might the magnitude of 11th harmonic current be greater than the magnitude of 7th harmonic current? 8) What is the maximum allowable harmonic voltage distortion for a 480V system according to IEEE-519? 9) What is the available short circuit MVA for a 3-phase transformer rated 1000kVA, 5.75% impedance, 480Vu? 10) At what frequency does XL -XC for the following component values [C 1 151uF, L-35uH] and what are the values of XL and Xc at this frequency?
Explanation / Answer
1.) 7 cycles of 7th harmonic in a single cycle of fundamental current is expected.
As For 50 Hz fundamental , 7 th harmonic will be 7 x 50 = 350Hz
Time period is inverse of frequecy.
So,
Tfundamental = 1/50 = 0.02 s
T7th harmonic = 1/350 = 2.857 x !0-3 s
No. of 7 th harmonic cycle in 1 fundamental cycle = Tfundamental/ T7th harmonic
= 0.02 / ( 2.857 x 10-3)
= 7.
So, 7 cycles of 7th harmonic in a single cycle of fundamental current is expected.
2) Increase in harmonics causes extra losses in windings and thus resulting in increase of transformer temperatue.
Winding losses are done in the form of heat.
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