Calculation Size of NGR/ Neutral Earthing Transformer (NGR/NET)

Generator Details:Generator Voltage (VL) (L-L) 11 KV

Maximum Over Voltage 14.3 KV

Frequency 50 Hz

Generator Transformer Details:Transformer Primary Voltage 11 KV

Transformer Secondary Voltage 6.6 KV

Capacitance Per Phase:Generator Winding Capacitance / Phase 0.22

Generator Connection Capacitance / Phase 0.001

Generator Transformer Capacitance / Phase 0.006

Generator Transformer Connection Capacitance / Phase 0

Transformer Cable Capacitance / Phase 0.0003

Surge Arrestor Capacitance / Phase 0.25

Other Capacitance / Phase

Total Zero Sequence Capacitance (C): 0.47730

Total Zero Sequence Capacitance Reactance to Ground (Xc): 6672.35 Ω/Phase

Neutral Earthing Transformer Size:Primary Voltage of the Grounding Transformer (Vp) 11 KV

Secondary Voltage of the Grounding Transformer (Vs) 6.9 Volt

Turns Ratio of the Grounding Transformer (N) 1594.20

Neutral Earthing Transformer % Reactance (X%) 4% 0.04

Neutral Earthing Transformer Reactance in PU (Xpu) 0.04 PU

Neutral Earthing Transformer Base KV (Bv) 0.24 KV

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Calculation Size of NGR/ Neutral Earthing Transformer (NGR/NET)

:Calculate Size of NGR/Neutral Earthing Transformer:Phase to Neutral Voltage (Vp1) 6.35 KV

% of Force field condition for Neutral Earthing Transformer 30% 1.3

Phase to Neutral Voltage under Force Field Condition (Vf) 8.26 KV

Capacitive charging current/phase (Ic) 1.24 Amp

Total Capacitive charging current (It) 3.71 Amp

Rating of Neutral Earthing Transformer (Pr) 40.83 KVA

Neutral Earthing Transformer overloading factor 2.6

Size of Neutral Earthing Transformer (P) 16 KVA

Residual Capacitive reactance (Xct) 2224.12 Ω

Required Resistance value at secondary side (Rsec) 0.001 Ω

Required Grounding Resistor value at primary side (Rp) 2224.12 Ω

Neutral Earthing Transformer Secondary Current 2276.15 Amp

Neutral Earthing Transformer Secondary Resistor Current (for 30 Seconds) 7693.38 Amp

Neutral Earthing Transformer Reactance Base(Base X): 3.67 Ω

Neutral Earthing Transformer Reactance (X) 0.15 Ω

Neutral Earthing Transformer X/R Ratio 167.63

Fault current through Neutral (single line to ground fault) (If) 2.86 Amp

:Results:Rating of Neutral Earthing Transformer (P) 16 KVAShort time Rating of Neutral Earthing Transformer 41 KVA

Ratio of Neutral Earthing Transformer 11000 /6,9 Volt

Neutral Earthing Transformer Secondary Current 2276.15 Amp

Required Grounding Resistor value at primary side (Rp) 2224.12 Ω

Required Resistance at secondary side (Rsec) 0.00 ΩNeutral Earthing Transformer Secondary Resistor Current (for 30 Seconds) 7693.38 Amp

VL/1.732

Vf=Vp1x 1,3

Ic=Vf / Xc

It=3xIc

Pr=VpxIt

P=Pr/ 2,6

Xct=Xc / 3

Rsec=Xct / (NxN)

Rp=Xct

X=Xpu x Base X

If=Vp1/Rp