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Laporan Pratikum Generator Dc ShuntFull description
KARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAK…Full description
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dc generator
KARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTIK LUAR GENERATOR DC SHUNTKARAKTERISTI...
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Tutorial 3. DC Generator (Answer) 1) Sketch the main component of a dc generator. Answer
2) Show use of the Faraday’s law at generator. Give two samples the other application. Answer
3) Show a concept model of electro mechanical systems that occur in the generator. Answer
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4) Show the basic electrical machine difference between generator and motor. Answer
5) Explain why the brushes of a DC machine always placed at the neutral points? Answer Because no current flow through brush and can reduce loss at the brush. 6) Described the construction of a commutator. Answer
Mica
Carbon brush
7) Explain how the induced voltage of a separately excited DC generator affected if a. The speed increases? Answer
b. The exciting current reduced? Answer
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8) Explain how do we adjust the voltage of a shunt generator? Answer
9) The terminal voltage of shunt generator decreases with increasing load. Explain. Answer
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EET306 Electrical Machine 10) Explain why the output voltage of an over‐compound generator increases as the load increases. Answer
11) Explain the difference between shunt, compound, and differential compound generators a. As to construction b. As to electrical properties Answer
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EET306 Electrical Machine 12) A separate excited DC generator turning at 1400 r/min produces an induced voltage of 127V. The armature resistance is 2 Ohm and the machine delivers a current of 12 A. Calculate: (a). the terminal voltage [v] Answer V – E – IaRa = 127 – (12)(2) = 103 V (b). the heat dissipated in the armature [w] Answer P= Ia2 Ra = (12)2 (2) = 288 W (c). the breaking torque exerted by the armature [N‐m]. Answer T = 9.55 E x I / n = 9.55 x 127 x 12 / 1400 = 10.4 N‐m [ 103V; 288W; 10.4N‐m] 13) A separately excited DC generator produces a no‐load voltage of 115V. What happens if a. the speed is increases 20%? Answer n2 = (1+0.2)n1 E1 / E2 = n1 / n2 E2 = (n2 / n1) x E1 E2 = (1.2 n1 /n1) x 115 V = 138 V b. the direction of rotating is reversed? Answer The polarity of output terminal will reversed. c. the exciting current is increased by 10 percent? Answer E = cnф ‐Æ ф≈ If If2 = (1 +0.1) If1 E1 / E2 = If1 / If2 E2 = (If2 / If1) x E1 E2 = (1.1If1/ If1) x E1 E2 = 1.1 E1 So The induced voltage will be increases 10 % from first induction. d. the polarity of the field is reversed? Answer The polarity of the terminal output of generator will be reversed too. [ ENL= 138V]
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EET306 Electrical Machine 14) Each pole of a 100 kW, 250 V flat‐compound generator has a shunt field of 2000 turns and a series field of 7 turns If the total shunt – field resistance is 100 Ohm, calculate the mmf when the machine operates at rated voltage. a. at no‐load b. at full‐load [5000A; 7800A]
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EET306 Electrical Machine 15) Fig. 1 show the no‐load saturation curve of a separately excited DC generator when it revolves at 1500 r/min. Calculate the exciting current needed to generate 120 V at 1330 r/min. Answer [2A]
Fig. 1 Saturation curve of DC generator
16) Referring to Fig. 2, the induced voltage in coil D is momentarily 18 V, in the position shown. Calculate the voltage induced in coils A, B and C at the same instant. [A=18V; B = 18V; C = 18V]
Fig. 2
Answer
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17) Referring to Fig.3, calculate the voltage induced in coils A when the armature has rotated by 90o; by 120o. [20V; 18V]
Fig. 3 Answer
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EET306 Electrical Machine 18) Brush x is positive with respect to brush y in Fig. 3. Show the polarity of each of 12 coils. Does the polarity reverse when a coil turns through 180o? Answer
19) The generator of Fig 4 revolves at 960 r/min and the flux per pole is 20 mWb. Calculate the no‐ load armature voltage if each armature coil has 6 turns. [ 276.5V]
Fig. 4 Answer
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EET306 Electrical Machine 20) a. How many brush sets are needed for the generator in Fig. 4? b. If the machine delivers a total load current of 1800 A, calculate the current flowing in each armature coil. [12 brush sets; 150A] Answer
21) The voltage between brushes x and y is 240 V in the generator shown in Fig. 4. Why can we say that the voltage between segments 3 and 4 must be greater than 40 V? Answer
22) Referring to Fig. 2, determine the polarity of Exy when the armature turns counter clockwise. Answer
23) a. In Fig.4 determine the polarity of a E34 between comutator segments 3 and 4, knowing that the armature is turning clockwise. b. At the same instant, what is the polarity of segment 35 with respect to segment 34? Answer
24) A 4‐pole 250 kW, 750 V DC generator has a lap winding on the armature. Calculate a. the full‐load current of the generator b. the current carried by the armature coils. Answer
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25) A 240 kW, 500 V 1750 r/min separately excited DC generator has an overall efficiency of 94%. The shunt field resistance is 60 ohms and the rated current is 5A. The I2R loss in armature is 0.023 pu. Calculate a. the rated armature current b. the total losses in the machine c. the I2R losses in the machine d. the torque required to drive the generator at 1750 r/min. (The shunt field is powered by a separate source.) Answer
26) A 4‐pole DC generator delivers a current of 218 A. The average brush voltage drop on each of the four brush sets is found to be 0.6V. Calculate the total brush loss in the machine, neglecting friction loss. Answer
