Final answer:
The sending end voltage per phase is calculated based on the total power, line-to-line voltage, power factor, and line parameters such as resistance and reactance.
Step-by-step explanation:
The student asks to determine the sending end voltage per phase for a three-phase transmission line with given load, voltage, power factor, resistance, and reactance values. To find this, you would use the formula for the sending end voltage, which takes into account the load voltage, the current through the line, the resistance and reactance of the line, and the power factor angle. Since we know the total power (P = 5000 kW), the line-to-line voltage (V = 25 kV), the power factor (0.85 lagging), and the line parameters (R = 4 ohms and X = 6 ohms per phase), the current can be calculated using the formula I = P / (sqrt(3) * V * PF). The power factor angle (phi) is derived from the power factor (PF) by the formula cos(phi) = PF. After calculating the current and the power factor angle, the sending end voltage per phase (Vs) can be found using the formula Vs = V + I * (R + jX) * e^(j * phi), where V is the receiving end voltage per phase, R is the resistance, X is the reactance, j is the imaginary unit, and phi is the power factor angle.