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A three phase 50 MVA, 11 kV generator is subjected to the various faults and the currents so obtained in each fault are: 2000 A for a three phase fault; 1800 A for a line-to-line fault and 2200 A for a line-to-ground fault. Find the sequence impedances of the generator. (AMIE Summer 2022, 10 marks) Case 1 Consider the conditions w.r.t. the three phase fault \(\begin{array}{l}{I_f} = {I_a} = {I_{a1}} = {E_{a1}}/{Z_1}\\2000 = 11000/(\sqrt 3 {Z_1})\\{Z_1} = 3.18\Omega \end{array}\) Case 2 Consider the conditions w.r.t. the LL fault \(\begin{array}{l}{I_{a1}} = [{E_{a1}}/({Z_1} + {Z_2})]\\{I_f} = {I_b} =  - {I_c} = \sqrt 3 {I_{a1}}\\ = \sqrt 3 {E_{a1}}/({Z_1} + {Z_2})\,or\\({Z_1} + {Z_2}) = \sqrt 3 (11000/\sqrt 3 )/1800\\{Z_2} = 2.936\Omega \end{array}\) Case 3 Consider the conditions w.r.t. a LG fault \(\begin{array}{l}{I_{a1}} = \frac{{{E_{a1}}}}{{({Z_1} + {Z_2} + {Z_0})}}\\{I_f} = 3{I_{a1}} = 3\frac{{{E_{a1}}}}{{({Z_1} + {Z_2} + {Z_0})}}\\({Z_1} + {Z_2} + {Z_0}) = 3\frac{{{E_{a1}}}}...

Answer the following in brief (2 marks each) Why Arcing ground should be avoided? Arcing ground is the surge, which is produced if the neutral is not connected to the earth. In a three phase line, each phase has a capacitance on earth. When the fault occurs on any of the phases, then the capacitive fault current flows into the ground. If the fault current exceeds 4 – 5 amperes, then it is sufficient to maintain the arc in the ionised path of the fault, even though the fault has cleared itself. The arc extinguishes and restrikes in a repeated regular manner. The phenomenon of intermitting arcing is called the arcing grounding. Overvoltage thus produced damages the healthy conductor at some other points of the system. What is the function of d.c. reactor? The reactor is suitable for reactive power compensation and harmonic control system.It can improve the power factor, filter the harmonics, suppress the voltage waveform distortion, change the quality of power network and ensure the safe...

 Answer all parts of the following (2 marks each) 1. The function of speed changer is (a) Change the speed of governor (b) Limit the speed of governor (c) Steady state power output of turbine* (d) All of the above Explanation: This part of the system is used to provide a constant power setting to the turbine in order to get a constant output under steady state condition. 2. 250 MW machine with an operating load of 125 MW. Let the change in load be 1% for 1% change in frequency (scheduled frequency = 50 Hz) then B is equal to (a) 0.05 pu MW/Hz (b) 0.01 pu MW/Hz* (c) 0.1 pu MW/Hz (d) None of the above Explanation: (∂P D /∂f) = 1.25 / 0.5 = 2.5 MW/Hz B = (∂P D /∂f)/Pr = 2.5/250 = 0.01 Pu MW/Hz 3. The change in real power P produces little effect on receiving end voltage because (a) The voltage drop associated with this change is in phase with reference voltage (b) The voltage drop associated with this change is in quadrature with reference voltage* (c) The voltage drop associated with...

Answer the following in brief (2 marks each): Differentiate between a protective relay and a fuse. Relay switches current flow on and off when energized/de energized. A fuse lets current flow until it reaches a pre designed limit. What is restructure power system? Power restructuring, a systematic running of modifying the rules and instructions that control the power market to impart consumers for the option of power producing, those are may be traders and allowing rivalry within the traders. Deregulation improves the stock rate and usage. What is Static frequency drop? It is given as Δf 0 = -M/[D + (1/R)] Hz where M = load increase R = regulation D = frequency dependency List the various sources of reactive power. Some of the static sources for the reactive power in the power system are:     Shunt capacitors.     Filter banks.     Underground cables.     Transmission lines when lightly loaded.     Fuel cells. ...

What arc the applications of Y-bus and Z-bus matrix? Y bus is bus admittance matrix which is used (generally) in Load flow analysis. This matrix helps in finding values of P, Q, |V| & delta. The elements of matrix are the admittances of transmission lines between buses. Z bus is bus impedance matrix which is used in Fault analysis. What is restructure power system? Power restructuring, a systematic running of modifying the rules and instructions that control the power market to impart consumers for the option of power producing, those are may be traders and allowing rivalry within the traders. Deregulation improves the stock rate and usage. Due to gain in the electric market, the power rates are likely to come down which welfare the consumers. What is off nominal transformer ratio? Transformers with voltage ratios different from the nominal (expected) voltage ratios of their associated network sections are identified as off-nominal transformers. The Off-nominal Turns Ratio indicate...