1.
The positive, negative and zero sequence reactance of a 15 MVA, 11 KV, three phase wye connected generator are 11%, 8% and 3% respectively. The neutral of the generator is grounded and the generator is excited to the rated voltage on open circuit. A line to ground fault occurs on phase ‘a’ of the generator. Calculate the fault current.
2.
An electric hoist makes 10 round trips per hour. For each trip, a load of 6 tons is raised in a hoist cage to a height of 200 ft in 11/2 min, and then the returns empty in 11/4 minutes. The cage weighs 0.5 ton and has a balanced weight of 3 tons. The efficiency of the hoist is 80%, and that of the driving motor is 88%. Calculate the electric energy required per round trip.
3.
The ABCD constant of the nominal pi circuit representation of a transmission line are: A=D=0.9 cis (0.3ᵒ), B=82.5 cis 76ᵒ, C=0.0005 cis 90ᵒ. What is the maximum power that can be transmitted over the line without making the system unstable if VS=VR=110KV.
4.
A string of four insulators has a self-capacitance equal to 5 times of pin to earth capacitance. Find the string efficiency. 64.86%
5.
The per unit reactance of a synchronous generator are Xd = 1.1, Xd’ = 0.24, Xd’’ = 0.15. the generator is operating without load at 5% above rated voltage then a three phase fault occurs at its terminal. If a generator is rated 500 MVA and 20 KV, determine sub-transient fault current?
6.
The incremental fuel cost for the two power plants are given by: dF1/dP1=0.01 P1 + 10 and dF2/dP2=0.2 P2 + 10. The system operates at $11.6 MWh for minimum fuel cost. Determine the power generated of each power plant.
7.
A generator with 1.0 p.u. reactance is connected to a synchronous motor of 0.2 p.u. reactance. If the motor drawing (0.8-j0.2) p.u. current at terminal voltage is 0.97<0ᵒ p.u., calculate the complex power delivered by the generator?
8.
A synchronous generator and a motor are rated 30,000 kva and 13.2 kv and are both have a sub-transient reactances of 20%. The line connecting them has a reactance of 10% referred to the machine ratings. The motor id=s drawing 20,000 kw at 0.8 power factor leading and a terminal voltage of 12.8 kv when a symmetrical three phase fault occurs at the motor terminals. What is the magnitude of the subtransient current?
9.
Convert 377 radian per second to rpm. 1000 radians per second = 9,549 RPM
10. The number of cycles in which a high speed circuit breaker can complete its operation is __________. 3-8 11. A 4 poles dc generator has simplex lap winding. If the armature current is 100 amperes, what is the current per path? 250 AMP 12. Walls, doors roofs and floors of transformer vault protected with automatic sprinklers carbon dioxide or halon shall be constructed that have adequate structural strength for the conditions with a minimum _______ fire rating. 3 HOURS 13. What is the minimum ampacity of all conductors from generator terminals to the first overcurrent device for a 240 volts, 125KVA 60 Hz generator. 14. The present estimate of solid coal reserves in the United States is about 1.5x109 tons, with an energy content of 940 watts-years/ton. If the power consumption growth rate is 3.38% per year, approximately how long will the coal reserve last? Assume that all energy will be supplied by coal and that the present peak power demand is 425 GW. 15. What is the minimum ampacity of conductor for a capacitor bank rated 50 kvar, 240 volts 3-phase. kVAR × 1000 Full-load current = ------------------------1.73 × Volts 16. The transients which are produced due to sudden but energetic, changes from one steady state of a circuit to another are called _________ transients. A. initiation C. relaxation B. TRANSITION D. subsidence 17. A 13.8 kV/440 V, 50 kVA single-phase transformer has a leakage reactance of 300 ohms referred to the 13.8 kV side. Determine the per unit value of the leakage reactance for the low-voltage base. 18. A 0-1 mA meter has a sensitivity of
1K ohm/volt meter 19. While describing the sheath of a cable, the abbreviation XLPE means ___________ polyethylene
Cross linked
20. Two capacitors of 0.1 µF, 250 V and 0.2 µF, 500 V are connected in series. What is the maximum voltage that can be applied across the combination?
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21. A dc shunt motor draws an armature current of 98.16A at 120 V. What is the hp output of the motor if the armature effective resistance is 0.06 Ω? 22. A non-sinusoidal emf having the equation v = 141.4 sin (ωt-600) – 56.6 sin (3ωt – 300) + 35.4 sin (5ωt – 900) is impressed upon a circuit. If the current has the equation I = 28.3 sin (ωt – 300) + 17sin (3ωt – 900), calculate the power factor of the circuit. 23. A diesel power plant has an overall efficiency of 30%. If the calorific value of diesel is 18,000 BTU/1b and cost PHP 6.00 per liter, how much is the fuel cost of production per KWHR of energy? Take the density of diesel as 900 grams per liter. 24. Two single-phase transformers operate in parallel. Transformer 1 is rated 100 kVA with 4% reactance while transformer 2 rated 75 kVA with 3% reactance. The transformers have secondary voltages of 220 volts and same voltage ratio. If the common load is 125 kVA at 80% p.f. lagging, determine the kVA sharing of each transformer 25. In transformer, the purpose of breather is to:
Breathers are used to absorb the moisture content from the sucked air, while the transformer oil gets expanded due to heating. 26. The maximum power developed in a synchronous motor occurs at a coupling angle of: 90o 27. The dc armature winding resistance between terminals of a 750-kva, 4400volt, three-phase alternator is 0.9 ohm. Calculate the copper loss in the winding at full-load. 28. It is also known as the polar graph of intensities of illumination.
photometric diagram 29. What is the frequency range of the electrical equipment used to melt metals without the use of bunker fuel oil for induction heating? Frequencies used in induction melting vary from 50 cycles per second (mains frequency) to 10,000 cycles per second (high frequency).
30. In a series motor, what is the relation of the connection of motor field winding with respect to the motor armature?
Because of the low resistance in the windings, the series motor is able to draw a large current in starting. This starting current, in passing through both the field and armature windings, produces a high starting torque, which is the series motor's principal advantage 31. Resistance of 15 ohms R1 and 45 ohms R2 are connected in parallel across 48 volts storage battery. Calculate total resistance Rt.
32. A shunt dynamo and battery of accumulator connected in parallel the dynamo has an induced emf of 100V and the battery has an open circuit voltage of 110V the resistance of the dynamo is 0.4 ohms and the battery resistance is 0.5 ohms. What is the common terminal potential drop by each if the output current is 40A. 33. A negative feedback amplifier has 0.5% of output voltage feedback and anti phase with it. The gain of the amplifier then if 150. Calculate the amplifier gain without feedback. 34. A 500 KVA, single phase transformer 13.2/0.4 kv has core loss of 1800 watts, 4% reactance and 1% resistance. What is the efficiency of transformer full load at 85% pf? 35. For three single phase transformers, a 600hp 2,400 volts three phase 60 Hz motor with an efficiency of 90% and power factor of 90% supplied from 34,500 volts utility. For delta-delta connection, what is the primary and secondary voltage rating of each transformer? 36. A 50 kva single phase transformer of ordinary efficiency at 96% works at full load for 8 hours per day to burn a street lights. Determine the all-day efficiency if the copper loss is 60% of the full load losses. 37. A dc shunt motor runs at 900 rpm from a 460V supply when taking an armature current of 25 A. Calculate the speed at which it will run from a 230V supply when taking an armature current of 15 A. The resistance of the armature circuit is 0.8 ohm. Assume flux per pole at 230V have to decrease to 75% of its value at 460V. 38. A 3 phase, 8 pole generator is delta connected. The terminal voltage is 2400 volts while the line current is 500 amperes. If the machine is converted to wye, what is the tolerable line current? 39. A 50Hp, 440V, three phase 60 cycle induction motor has a power factor of 87.2 and efficiency of 90.6%. What is the power input Hp? 40. A delta connected motor with 6 leads. 20 Hp, 3-phase, 60 Hz, 230V, 1750 rpm, 54 amperes squirrel cage induction motor with starting current of 5 times its full load current with normal applied voltage and develops 1.5 times of its full load torque T. What is the starting current in amperes per phase of the motor when delta connected? 41. A 3-phase induction motor has 4 pole, star connected stator winding and
PRACTICE SET IN EE
runs on a 220 volts 50 Hz supply. The rotor resistance 0.1 ohm and blocked rotor reactance 0.9 ohm. The ratio of rotor to stator turns is 2/3. Calculate the torque in N-m when running with 4% slip. 42. Three phase 3 wire 50 Hz transmission line delivers a load of 2500 KVA at 6000V at 0.8 pf lagging at a distance of 10km. Line has resistance of 0.3 ohm/km and reactance of 1.28 mH/Km determine the sending end voltage. 43. A three phase 60 Hz transmission line is to deliver 20,000 Kw at 66,000 volts at a distance of 30 miles. The load pf is 85 percent lagging, the line conductor are 3/0 AWG with resistance per mile of 0.326 ohm at 20 degrees Celsius and at 72 inch spacing and reactance per mile pf 0.742 ohm. Find the resistance per conductor. 44. A load at 75 percent lagging power factor 20,000 KW is to be delivered at 69,000 volts 60 Hz over a 20 mile three phase transmission line. The conductors are 3/0 AWG copper spaced 72 inches. Resistance is 0.326 ohm per mile, reactance 0.742 ohm per mile. Capacitance is nil. What is the percent voltage regulation? 45. A three phase 60 Hz transmission line delivers 750 KW at 95 percent leading power factor ant at delta voltage of 6900 volts all measured at the load end. The resistance per conductor is 4.3 ohms and the reactance per conductor is 2.6 ohms. Assuming both the source ant the load to be wye connected, determine the impedance of the load. 46. A 120 cm long conductor is carrying a current of 1.2 A and is situated at right angles to a field of flux density of 0.65T. Calculate the force on conductor. 47. State the force in pounds upon one side of a coil of 50 turns carrying a current of 20 A if the real length of the coil is 12 inch and the flux density is 25,000 lines per square inch. There are 4.448x10^5 dynes in a pound. The conductors are at right angles to the flux. 48. In a T network having Z1=3+j2, Z2=0-j1 and Z3=3+j4 ohms. Determine the Z11 parameter. 49. In a π network having Z1=4000+j0, Z2=5000+j0 and Z3=2000+j0 ohms. Determine the Y22 parameter. 50. Find the turn ratio of a transformer used to match a 14400 ohms load to a 400 ohms load. 51. Two 2-H coil are connected in series so that the mutual induction between them is 0.2-H. find the total inductance when they are connected to be series aiding. 52. A poles 4 lap wound, dc machine has 728 active conductors running at 1800 rpm. The flux per pole is 30 mWb. The armature current is 120A, what is the electromagnetic power developed in the armature in kW? 53. When one coil of magnetically coupled pair has a current of 5 amperes, the resulting flux Φ11 = 0.4 mWb and flux Φ12 = 0.8 mWb respectively. If the turns are N1 = 500 and N2 = 1500, find the mutual inductance. 54. The line currents in a delta connected load are Ia = 5 cis 0deg. Ib = 7.07 cis 225deg and Ic = 5 cis 90deg. Calculate the positive sequence components of current for phase a. 55. Power system has receiving current of 1.2 pu or current at the receiving end and 0.6 pu voltage at the receiving end and 0.5 pu receiving power. When the base current is 160 A and base voltage is 20 kV, what is ohmic value of the resistance of the load? 56. A resistance R and inductive reactance X are connected in parallel across 2.4 kV rms absorbs 288 kW at 0.8 power factor. Find the value of X in ohms. 57. A 4 pole 60 Hz synchronous generator has a rating of 200 MVA, 0.8 power factor lagging. The moment inertia of the rotor is 45,100 kg-m2. Find inertia constant H. 58. A 250 MW, 60 Hz turbine generator has a speed regulation of 5% based on its own rating. The generator frequency decreases from 60 Hz to a steady state value of 59.7 Hz. Determined the increase in the turbine power output. 59. Two generating unit of 250 MW and 400 MW have governor speed regulation of 6% and 6.4% respectively from no-load to full load. They are operating in parallel and share a load of 500 MW. Determined the load shared by each unit. 60. The moment of inertia of a 100 MVA, 2 pole, 60Hz generator is 50x103 kg-m2. Determined the angular momentum M for the machine.
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