MGVCL Exam Paper (30-07-2021 Shift 3)
A DC shunt generator has an induced voltage of 220 V on open circuit. When the machine is on load the terminal voltage is 200 V. Find the load current if the field resistance is 100 Ω and armature resistance is 0.2 Ω.
Voltage equation for Dc shunt generator, Eb = V + Ia*Ra V = Ish*Rsh Ish = 200/100 = 2 A Eb = V + Ia*Ra 20 = Ia*Ra Ia = 20/0.2 = 100 A I = 100 - 2 = 98 A
1.6 inches = 1.6 inches x 1,000 mils per inch = 1,600 mils 0.25 inch = 0.25 inch x 1,000 mils per inch = 250 mils Area = 1,600 x 250 = 400,000 square mils
The ratio of full load current to short circuit current = 1/6 Xsc = j/(1/6) External reactance required = j*((1/6) - 0.06)) = j*0.106 pu Full load current = (40*1000)/(√3*15) = 1539.6 A Per unit reactance = j*0.106 = (I*Xr)/V j*0.15 = (1539.6*Xb)/((15/√3)*1000)) = 0.60 ohm
Dynamic voltage restoration (DVR) is a method of overcoming voltage sags and swells that occur in electrical power distribution. Devices used for DVR include static var devices, which are series compensation devices that use voltage source converters (VSC). The DVR is used to inject three phase voltage in series and in synchronism with the network voltages in order to compensate voltage disturbances with a benefit of active /reactive power control.
The speed regulation of a motor expresses how much its speed varies between no-load and full load. The synchronous motor runs at a constant speed whose magnitude is dependent on supply frequency and the number of poles. Since the speed of the motor is constant hence its speed regulation is zero. Under no-load conditions with normal excitation, armature current Ia drawn by a synchronous motor lags the applied voltage V by a small angle.
EXAMIANS