In that method the total resistance and capacitance of the medium transmission line is shown as half at the supply end and the other half at the receiving end. Also the total capacitance of the line is considered in the middle of the line in the consolidated state. This is called the nominal T method.
In the nominal T method, all the resistances and inductances of a line are divided into two equal parts and arranged along the length of the line at the sender and receiver ends and the total capacitance is assumed to be centered in the middle of the line.
That is, the total resistance of the line (\frac{R}{2} ) is calculated half at the supply end and half at the customer end and half of the total inductance (L) or inductive reactivity X_L of the line at the supply end and the other half at the customer end. In this method the total capacitance of the line or capacitive reactance X_C is considered in the middle of the line in the consolidated state. Notice the circuit below.
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As pictured above, We get;
V_R = Load voltage per phase,
I_R = Load current per phase,
R = Resistance of each phase,
X_L = Inductive Reactance per Phase,
C = Capacitance per phase,
Cosϕ_R = Power factor on the receiving end, (lagging)
V_S = Transmission edge voltage,
V_1 = Horizontal voltage of capacitor C.
The following vector is drawn based on the circuit shown above, where the voltage \overrightarrow{V_R} at the receiving end is marked as the reference vector.
In the nominal T method, From the figure above we get;
Voltage at the receiving end, \overrightarrow{V_R}\ =\ V_R\ +\ J0 V_R = V_R + J0
Load current, \overrightarrow{I_R}\ =\ I_R\ \left(\cos\phi_R\ -\ j\sin\phi_R\right) I_R = I_R (cosϕ_R − jsinϕ_R )
Horizontal voltage of capacitor C, \begin{array}{l}\overrightarrow{V_1}=\ \overrightarrow{V_R}\ +\ \overrightarrow{I_R}.\overrightarrow{\frac{Z}{2}}\\ \ =\ V_R\ +\ j0\ +\ I_R\ \left(\cos\phi_R-\ j\sin\phi_R\right)\end{array}
Capacitive current, \overrightarrow{I_C}\ =j\omega C\overrightarrow{V_1}\ \ \ =\ j2\pi fC\overrightarrow{V_1}
Current at the transmitting edge, \overrightarrow{I_S}\ =\overrightarrow{I_R}\ +\ \overrightarrow{I_C}
Transmission voltage, \overrightarrow{V_S}\ =\overrightarrow{V_1}\ +\ \overrightarrow{I_S}\ .\ \overrightarrow{\frac{Z}{2}}\ \ =\ \overrightarrow{V_1}\ +\ \overrightarrow{I_S}\ \left(\frac{R}{2}\ +j\frac{X_L}{2}\right)
Transmission power factor, \cosϕ_S=\cos(ϕ_1+ϕ_2)
Now,
ϕ_1=\overrightarrow{V_R} and \overrightarrow{V_S}
ϕ_2=\overrightarrow{I_S} and \overrightarrow{V_R}
So, ϕ_2=\tan^{-1}\ \ \ =\frac{In\ the\ X\ component\ of\ \overrightarrow{V_S\ }}{In\ the\ Y\ component\ of\overrightarrow{V_S}\ }
Voltage regulation in nominal T method
The no-load voltage must be calculated at the receiving end while maintaining the voltage at the transmitting end while conducting voltage regulation and in that case the circuit of the nominal T method will be as follows.
Now, for the nominal T method-
% Regulation =\frac{V_R\prime-V_R}{V_R}\ \times\ 100
The following formulas will apply to specific efficiencies –
% Efficiency (η) =\frac{power\ of\ receiving\ edge}{power\ of\ transmitting\ edge}\times\ 100
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