Recent content by Pdave6

Davidbeach, Thank you. I was able to draw vectors and understand at least one cable reconnection configuration, which will give 60 degree shift. I did not attempt the other 2 combinations. But now I am convinced that it can be done and there are more than 1 ways to reconnect cables on primary...

Thanks Davidbeach. Vector realignment is a complex subject for me, especially when I have to swap terminals, but I will certainly try. Meanwhile it seems that I made a mistake in stating the problem. I am describing below more accurately. We have a 3 phase, 26.4 kV incoming from utility in the...

3 Phase Delta-Wye DYn1 transformer has primary terminal H1 connected to cable A, H2 to cable B, and H3 to cable C. The secondary terminal X1 is connected to cable a, X2 to b, X3 to c and X0 to cable n. The phase rotation is ABC on secondary. What external connection changes, on either...

Thank you all who have taken time to respond. This transformer was made by GE in USA hence it should be ANSI std. I have not read Ansi C57.12.10. I have no knowledge of IEC std either. As far as Off-Load tap changer is concerned, one has to physically climb on top of this transformer and...

Thank you JGHRIST. It seems that Fig 3 -Bushing arrangement, matches with what PRC wrote (Left side is H1 bushing, if you are on secondary bushings looking at high side bushings.) It seems that ANSI 57.12.10 may be defining it in a different way, but Fig 3 is very clear for H1 position. You...

PRC, Thank you.

I forgot to attach the transformer nameplate info. Here it is. Thanks.https://files.engineering.com/getfile.aspx?folder=30082b27-1062-4e8b-8c55-8e9c4f5aa42e&file=Transformer_nameplate_GE_3_winding.pdf

We have 3 phase 26.4kV Delta - 490 volt Delta and 490 volt Wye, 3 winding transformer which feed 12 pulse rectifier on 490 volt side, generating about 3 MW for Traction service. This oil filled transformer has nameplate but no markings at 26.4kV bushings for H1, H2 and H3. Similarly on secondary...

Thanks Stevenal. Now it makes sense. From your statement, I derive 1. "The 2nd, 5th, 8th, 11th........harmonics will rotate opposite to fundamental." This statement has tobe accepted as true because this is proved mathematically for distorted waveform. As you mentioned above these harmonics...

Thanks Stevenal and Electricpete. Both of you have tried to explain the idea further very nicely. I have understood from all above, that the original 120 degree phase shift for phase B wrt A, becomes 240 degree shift for 2nd Harmonic, (and original 240 degree phase shift for phase C wrt A...

Thanks Electricpete for very good explanation. It is interesting that motor may rotate (at least theoretically) at twice the speed, in the same direction, if frequency is doubled, i.e. from 60 hz to 120 hz. But the second harmonic ( which is also 120 hz)rotates in opposite direction. As you...

Question : Rotation Direction of Harmonics. Why some CW and some CCW in 3 phase induction motor? Assuming with A-B-C phasor sequence, a 3 phase induction motor field rotates clockwise. Assuming the motor has 4 poles, speed will be just under 1800 rpm clockwise for 60hz supply. If we decrease...

Please see fault record file created by Eaton's EDR-5000 relay, for Magnetizing Trip condition. You can see RMS and fundamental current values. I forgot to mention earlier that relay takes 32 samples per Cycle. (Applicable to earlier uploaded files.) Thanks...

Please see magnetizing current file, after B coil connection was corrected, with no trip. The neutral current instantaneous dropped from appro. 600+ amp to about 60A...

Thank you all for taking time to read and respond. 1. Trips were during magnetizing inrush which has unbalanced current flowing thru neutral. The load is balanced and after magnetizing there is zero or close to zero current expected in neutral. 2.I did not mention earlier that recently we had...