Neutral Third Harmonic Undervoltage Requirement for Generator Protection

3rd Harmonic neutral voltage protection is the 100% stator earth fault protection. Conventional Stator earth fault protection can only protect around 90-95% of stator winidng in high reisitance grounding systems. The winding near to the neutral cannot be protected with this. For faults near to the neutral can be detected by this 3rd harmonic protection.

The 3rd harmonic is determined by the displcament voltage measured over two cycles by digital filtering.

Dear Mr. Johnson,

During our studies in electrical engineering class our Professors have taught that 3rd Harmonics is eliminated by STAR connection of the winding and 5th Harmonics is controlled by short-pitching of the windings.

The neutral is meant for carrying the un-balanced current flow.

The level of the Harmonics is Reciprocal of the series of Harmonics squared. i.e

for Example 7th Haronics will have a magnitude of 1/7^2= 1/49=0.0204 = 2.04 %

Of course Technology has developed fatastically to control the Harmonics, which are Harmful.

DHAYANANDHAN.S

IINDIA.