Size-of-NETCalculation1.6.14.xlsx

	C	E	F	H	J	K	M
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2	Calculation Size of Neutral Earthing Transformer (NET)
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5	Generator Details:			:Calculate Size of Neutral Earthing Transformer:
6	Generator Voltage (VL) (L-L)	11	KV	Phase to Neutral Voltage (Vp1)	6.35	KV	VL/1.732
7	Maximum Over Voltage	14.3	KV	% of Force field condition for Neutral Earthing Transformer	30%	130%
8	Frequency	50	Hz	Phase to Neutral Voltage under Force Field Condition (Vf)	8.26	KV	Vf=Vp1x 1.3
9	Generator Transformer Details:			Capacitive charging current/phase (Ic)	1.24	Amp	Ic=Vf / Xc
10	Transformer Primary Voltage	33	KV	Total Capacitive charging current (It)	3.71	Amp	It=3xIc
11	Transformer Secondary Voltage	11	KV	Rating of Neutral Earthing Transformer (Pr)	40.83	KVA	Pr=VpxIt
12	Capacitance Per Phase:			Neutral Earthing Transformer overloading factor	2.6
13	Generator Winding Capacitance / Phase	0.22	µ Farad	Size of Neutral Earthing Transformer (P)	16	KVA	P=Pr/ 2.6
14	Generator Connection Capacitance / Phase	0.001	µ Farad	Residual Capacitive reactance (Xct)	2224.12	Ω	Xct=Xc / 3
15	Generator Transformer Capacitance / Phase	0.006	µ Farad	Required Resistance value at secondary side (Rsec)	1.059	Ω	Rsec=Xct / (NxN)
16	Generator Transformer Connection Capacitance / Phase	0	µ Farad	Required Grounding Resistor value at primary side (Rp)	2224.12	Ω	Rp=Xct
17	Transformer Cabale Capacitance / Phase	0.0003	µ Farad	Neutral Earthing Transformer Secondary Current	65.44	Amp
18	Surge Arrestor Capacitance / Phase	0.25	µ Farad	Neutral Earthing Transformer Secondary Resistor Current (for 30 Seconds)	221.18	Amp
19	Other Capacitance / Phase		µ Farad	Neutral Earthing Transformer Reactance Base(Base X):	3.67	Ω
20	Total Zero Sequence Capacitance (C):	0.47730	µ Farad	Neutral Earthing Transformer Reactance (X)	0.15	Ω	X=Xpu x Base X
21	Total Zero Sequence Capacitance Reactance to Ground (Xc):	6672.35	Ω/Phase	Neutral Earthing Transformer X/R Ratio	0.14
22	Neutral Earthing Transformer Size:			Fault current through Neutral (single line to ground fault) (If)	2.86	Amp	If=Vp1/Rp
23	Primary Voltage of the Grounding Transformer (Vp)	11	KV	:Results:
24	Secondary Voltage of the Grounding Transformer (Vs)	240	Volt	Rating of Neutral Earthing Transformer (P)	16	KVA
25	Turns Ratio of the Grounding Transformer (N)	45.83		Short time Rating of Neutral Earthing Transformer	41	KVA
26	Neutral Earthing Transformer % Reactance (X%)	4%	4%	Ratio of Neutral Earthing Transformer	11000 /240	Volt
27	Neutral Earthing Transformer Reactance in PU (Xpu)	0.04	PU	Neutral Earthing Transformer Secondary Current	65.44	Amp
28	Neutral Earthing Transformer Base KV (Bv)	0.24	KV	Required Grounding Resistor value at primary side (Rp)	2224.12	Ω
29				Required Resistance at secondary side (Rsec)	1.06	Ω
30	Jignesh.Parmar, www.electricalnotes.wordpress.com, jiguparmar@yahoo.com			Neutral Earthing Transformer Secondary Resistor Current (for 30 Seconds)	221.18	Amp
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