Calculate Size of Neutral Earthing Transformer [NET]

The Spradsheet provides calculations to determine the size and ratings of a neutral earthing transformer (NET) given specifications of a main transformer and requirements for the NET. It calculates that a 16 KVA NET with a turns ratio of 11,000/240 volts would be suitable. The NET would need a primary grounding resistor of 2224.12 ohms and a secondary resistor of 1.059 ohms to limit fault currents below 3 amps.

Reference: https://en.wikipedia.org/wiki/Grounding_transformer

Calculate Total Capacitive charging current (It).

Calculate Neutral Earthing Transformer  Secondary Current.

Calculate Required Grounding Resistor value at primary side (Rp).

Calculate Required Resistance value at secondary side (Rsec).

Calculate Neutral Earthing Transformer X/R Ratio

Calculate Fault current through Neutral (single line to ground fault) (If)

Calculate Rating of Neutral Earthing Transformer (P).

Title : calculate size of neutral earthing transformer

Type : Microsoft Excel Spreadsheet (xlsx)

Size : 48.0 KB 

FAQs:

What is the size of the neutral earthing conductor in a transformer?

Influence of the type of earthing system
The neutral conductor is protected against short-circuit. The size of the neutral conductor is at least equal to 16 mm2 in copper or 25 mm2 in aluminium.

How do you calculate the size of a neutral earthing resistor?

Once the current rating is determined, the Resistance or Ohmic Value of the resistor is calculated by dividing the Line to Neutral Voltage by the Current Rating. i.e. for a 4.16 kV System Neutral Grounding Resistor rated at 400 A. The line to Neutral Voltage will be 4.16 kV /√(3) = 2400 V.

How do you calculate the size of a transformer?

Guide to Transformer kVA Ratings
To calculate the kVA rating for a single-phase transformer, you’ll need to multiply the required input voltage (V) by the required current load in amperes (l) and then divide that number by 1,000: V * l / 1,000.