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The earthing transformer creates a neutral point for a network. ZN connection is usually applied. Z connection provides linear and specified zero sequence impedance. YN+d can also be applied.
Importance of Neutral Grounding :-
There are many neutral grounding options available for both Low and Medium voltage power systems. The neutral points of transformers, generators and rotating machinery to the earth ground network provides a reference point of zero volts.
This protective measure offers many advantages over an ungrounded system, like:
- Reduced magnitude of transient over voltages
- Simplified ground fault location
- Improved system and equipment fault protection
- Reduced maintenance time and expense
- Greater safety for personnel
- Improved lightning protection
- Reduction in frequency of faults.
There are five methods for Neutral earthing:
- Unearthed Neutral System
- Solid Neutral Earthed System
- Resistance Neutral Earthing System (Low Resistance Earthing & High Resistance Earthing )
- Resonant Neutral Earthing System
- Earthing Transformer Earthing
- Total capacitive charging current (It).
- Neutral earthing transformer secondary current.
- Required grounding resistor value at primary side (Rp).
- Required resistance value at secondary side (Rsec).
- Neutral earthing transformer X/R Ratio
- Fault current through neutral – single line to ground fault (If)
- Rating of neutral earthing transformer (P).
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