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# Spreadsheet to calculate the size of neutral earthing transformer

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## Earthing transformer

When the system neutral may not available, earthing transformer may be used to obtain the neutral. The neutral point of transformer to the earth ground network provides a reference point of zero volts.

This spreadsheet calculates the following parameters of a neutral earthing transformer:

1. Total capacitive charging current (It).
2. Neutral earthing transformer secondary current.
3. Required grounding resistor value at primary side (Rp).
4. Required resistance value at secondary side (Rsec).
5. Neutral earthing transformer X/R Ratio
6. Fault current through neutral – single line to ground fault (If)
7. Rating of neutral earthing transformer (P).

It might be interesting to read technical article about all types of neutral earthing in power distribution: Part 1 and Part 2.

1. Robert Rajan
Aug 11, 2021

Excellent work on the NGT sizing calculator. Do you have Low resistance Neutral grounding resistor sizing spread sheet? If so please send the file to [email protected]

2. George Brown
Aug 05, 2020

Thank you, nice work!!

3. ERIC KWAME ANTWI
Jun 05, 2020

Please kindly check the work EARTHING, it should be EARTHLING for engineering pronounce

Thanks

Truly

4. RAMESH KUMAR KAPUR
Jun 04, 2020

Dear Mr. Jignesh,
From talk in your papers, it appears that you are talking sizing of Transformer for floating 3 phase system, but from spread sheet it appears, for single phase Grounding Transformer, for gounding 3 phase start connected Power Supply source with star point and star point of source grounded using 1 phase transformer with secondary Burdened via Resistance. Otherwise for floating system, it shall be 3 phase transformer or a 3 phase Reactor with impedence to limit phase to earth fault current to neutral. In case of 3 phase Transformer, it shall be Y-open delta (Say Y for floating system and open delta for , with Open Delta shorted via resistance to burden Primay in case of Earth Fault and Start of Primary solidly grounded. Your work sheet seems not correct, suggest review with Application of Earthing Transformer and fault current, giving system configuration in which you have designed the work sheet and details of Transformer connection etc. In all cases however, we can not size the Earthing Transformer on basis of charging system capacitance or giving short circuit path of Capacitive Current for 1 phase to earth fault. According to me it needs review.
Best regards
Ramesh Kapur

5. Edson Francisco Piloro
Apr 17, 2020

Good morning Mr jignesh, i van not download the sheet. Can you send to my e-mail please: [email protected]