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The voltage arc length characteristics of a DC arc is given by V = 20 + 40L, where L = arc length in cm. The power source characteristics can be approximated by a straight line. Open circuit is 80 V and short circuit current 1000 Amps. The optimum arc length in mm
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- 0.5
- 1
- 5
- 10
Correct Option: C
Constant voltage Characteristics
V = 20 + 40 L ...(i)
Vocv = 80 V, Iscc = 1000 Amp.
| V = vocv − | .I | |
| 1scc |
| V = 80 − | I ....(ii) | |
| 1000 |
Vtransfermer = Varc
| 20 + 40L = 80 − | L | |
| 1000 |
| I = | (60 − 40L) | |
| 80 |
Power = V.I.
| For optimum Arc length | = 0 | |
| dL |
| (20 + 40L)(60 − 40L) | . | |
| 80 |
Hence L = 0.5 cm = 5mm
