Question

Q1. A poly phase directional relay, each element of which develops maximum torque when the current in its current coil leads the voltage across its voltage coil by 30°. By drawing phasor dia grams, show how the total electrical torque can be calculated. Assuming that the relay constant K, is 3.0, calculate the total elecetrical torque for the connection if the system currents and voltages as applied to the relay are: IA 40+j10; IB-20 -j25; Ic 5 j10 60 +j0: VBn 20+j50; VcN 50 - 125

Answer 1

"Given that rightarrow A poly phase directional relay therefore The current and voltage torque is given by T = KVI cos(theta - z) where k = ""Torque constant"" z = ""maximum torque angle"" theta = phase angle difference between line voltage and current Here k = 3 z = 30 degree Given I_A = 40 + j 10 V_AN = 60 + j 0 I_B = 20 - j 25 V_BN = -20 + j 50 I_C = -5 + j 10 V_CN for voltage is V_AN = 60 + j 0 V_AN = 60 angle 0 degree V for current is I_A = 40 + j 10 = > I_A = 53.33 angle -153.5 degree A theta = -153.5 degree z = 30 degree \r\n T = z times I_A = 3 times 60 times 53.33 cos(-173.5) = > T = -9537.69 Nm (because angle -153.5 degree A in math form) for voltage V_BN = -20 + j 50 = 6231 angle "