Clarification with Generator Neutral Earthing, Neutral Link and Neutral Out

CT for REF is kept before NL: What your REF stands for?

CT for EFR is kept after NL: Your EFR, does it stand for earth fault relay or emergency frequency relay?

And what is your NL stand for?

Neutral Link? Why do you need it & for what kind of testing?

Can we see a sketch of your system incorporating all these?

By the way are your seniors, members if this forum? If not, please invite them to this August forum.

REF - Restricted Earth Fault Relay

EFR - Earth Fault Relay

NL -Neutral Link

Testing Means - Insulation Reading Measurement - In such occasions, the earth connection may need to be disconnected.

Neutral isn't about getting balanced voltages, Guv. Neutral is about providing a route for the imbalance current on single-phase loads. At least, it was when I went to classes.

If the neutral is not strongly earthed, the phase voltage which is getting in between phase and neutral will be unbalanced. This is what I meant.

Anyway, please refer to my route doubt. Which connection is advisable (1) or (2) in the diagram? If my query is not clear, I am ready to give again clarifications.

To put your question precisely, you want to know whether neutral distribution should be before the REf CT or after the REf CT. Is it so?

Yes, there lies a point.

For REF protection to locate internal faults, we use 3 line CTs and one neutral CT. I have shown only the neutral CT with the diagram. It should sense the neutral current, which is the total of the three line currents. In a balanced condition, this neutral current must be zero. When some internal fault occur, an unbalancing will occur and the net current will cause the REF relay to trip. The neutral earthing path gives a return path for any earth faults/leakages, which causes a current ('Ie') to travel. Let actual neutral current be, In (without 'Ie'). So, total neutral current (to the generator side) will be 'It' = 'In' + 'Ie'. The REF sensing CT in the neutral path should read 'It' and not 'In'. Am I right? If so, the CT should be located to read 'It'. With connection (1) in the diagram the REF CT can not read 'It', instead only 'Ie' will be sensed. So, connection (2) is preferable. Please analyse.

I am a trainer with L & T and conducting protective relay training programme is my cup of tea. I have thoroughly analysed the prepositions and have made a presentation on the same. But, being a computer novice, I am unable to post them here directly. However, if you can send me your mail ID thro this forum's mailbox, I will be able to send you the presentation by mail.

After an alround search, I conclude here below the clarification which I asked. Neutral out need to be from the incoming side of NL, before which REF CT is to be included. All other details remain same, as I explained earlier.The final diagram shall be as follows.I welcome, any more doubt if there.

Dear EE65,

I know I am visitng this thread after long time, however , I am faced with similiar situation now. In case you can share your above mentioned presentation, it would be great help to me as well.my mail id is mailtodkp at gmail do com.

Best regards

dinesh