3rd Harmonics

I'm no expert in harmonics, but if you have balanced loads, the currents in the generator neutral point should sum to zero. Since that's the ideal case and not reality, some current will flow on the neutral. I think since the generator is connected in grounded wye, some harmonic current will make its way to your transformer primary, where they will circulate in the delta and generate additional heat.

Better wait for a person more familiar with harmonics to weigh in on the issue.

Currents flow in connections across different potentials.

Odd harmonics are neutral displacements.

The Generator Island has no neutral connection between Generator to Delta Transformer winding, however the connections (Busbars) have different capacitive reactances & this may result in neutral displacement potential, the impedances are very high & the current therefore negligible.

The two star & grounded 11kV windings are however connected in what is commonly known as a "multiple earth" situation & current will flow in the neutrals.

Only one point of neutral earth should be made at any one time on the parallel 11kV sytem.

Any harmonics on the system will be reflected in the generator supply. Because of the Delta /wye comnnection zero sequence currents will only circulate in the delta of the transformer and will not be seen by the Generator.

Any 2/3rd (0.6667) pitch generator offers a very high zero sequence impedance. As such there will not be any zero sequence voltage generated by the generator. So, there is no question of 3rd harmonic current flowing from generator to the transformer.

I appreciate all the great comments to my post! Sometimes, "school book" technology just doesn't add up to what's out in the real world. I will now be able to set my protective relays with more confidence. Thanks all.

Dear Hughes,

The 3rd HARMONICS will be eliminated owing to STAR CONNECTION OF THE GENERATOR.

IN THE OLDEN DAYS DESIGN OF ALTERNATORS, THE 5th HARMONICS INTENSITY OR MAGNITUDE IS REDUCED BY SHORT PITCHING of the WINDING/COIL of the ALTERNATOR.

7th HARMONICS WILL BE PRESENT.

DHAYANANDHAN.S,

INDIA.