High Neutral Current

One of the possibilities is a shorted turn on G#1's windings, causing one of the phases' voltages to dip relative to neutral. What are these voltages?

Hi PWSlack,

From 400 VLL at 0A voltage drop to 398 VLL, these are same voltage drop on G#2. We already test for single load 100% kW and neutral current only 10A. What is shorten turn on winding ?.

Another possibility is that the load on one or two of the three phases is almost all capacitance on G#1.

It's a bit difficult to see from here, though.

Hi PWS,

But when I used with other generator and couple with sane engine, using the same component and power line - neutral current not more than 15A.

as you have said that alternator has re winded, has the winding is done for damaged phase or complete winding has changed chances for this problem are

unequal turns for 3 phases

improper neutral grounding

change in winding sequance

Use a power analyzer or oscillioscope and check the waveform of voltage,current, frequency in phases and neutral whether there are harmonics.

I think the generator # 2 is wrong rewind so the sum of currents the two generators operating in parallel is out of normal phases genrating high neutral currents.

For exmple, with measured current values, suppose the current "A" (912 Amps) at zero degrees, the current "B" (936 Amps) with a -145 degrees and current "C" (915 Amps) wit a -205 degrees lag, result in a neutral current of 700 Amps.

Is recommended the measurement of the angles of phase of line voltages on the generator # 2.

Dear Gentlemen,

Thanks for your great explanation. This G#2 generator rewind by local workshop and conclution is not far from rewinding the generator, and best thing is to repair it to stamford dealer.

Thank you

To Pak Yudha

Sorry I just flight back from Poso to inspection, Testing and Supervising the Hydro Power Plant 3x65 MW, New Construction.

Your G#1 when solo running is ok . its look Good, Balance voltage and current during in Load operation, but when synchronize your G#1 get high current.

Your G#1 Generator seem loaded high current circulation from the system due to wrong installation of static CT on this Generator.

Please check the connection for the static CT , its should be on the "V" phase, and should be same stator lead outgoing cables with refer to G#2.

I understand that your G#1 was rewound, but the rewound servicer was wrong connection of the CT. may be they have missing data where is should installed this CT

As you know that the stator out going may have 6 or 9 or 12 outgoing cables, Static CT should be installed at phase "V" and should have same lead with the G#2

Reversing or wrong connection this CT can create high circulating current from G#2 to G#1, that why your G#1 was loaded at the Neutral point, this phenomena's is similar with the reverse power.

Secondary CT connected to AVR with polarity code 'K - L", please do not reverse this terminal, and when generator connected in parallel with the other Generator, make sure that the K-L termination at the AVR is open not to be shorted.

Your G#1 Stator winding is OK !!, the problems is wrong current distribution during in synchronize due to reversing of CT polarity or wrong installation on the Stator Outgoing Lead

The static CT is use to control load power sharing during in synchronize

Following is figure may can help you as reference

Hi Pak Siswanto,

Thank you for your input, We missed to check that & we'll check it again.

Regards,

LS

Sir , Thanks about this point,

But I want to know why is the location of CCCT affect the neutral current??

THX