Answer Posted / badshah

1.2 times that of 50 Hz Power. Frequency increases the
Speed & which in turn increases the power consumption
[P=(2*pi*N*T)/60 and N = 120f/Poles)]..so the ratio is
60/50. But the losses will be more, cause iron & hystersis
losses proportional to frequency squared. I think overall
efficiency may be reduced than when the motor is connected
50 Hz supply.

need to make a report. Need to choose a 3phase induction motor. Load conditions motor will operate in : Maximum Load: 30 Kw Speed: 2950 rpm Ambient temp: 20 cent Supply voltage: 440V Frequency: 50Hz need to look for the safety factor when choosing the motor, went through catalouge found a few, but dont know how to choose the safety factor allowing an extra load something above 30 KW to avoid any harm.

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we have a 2.5hp Starite electric motor water pump,the elec motor burned out,we need to replace starting capacitor(old capacitor specs erased),what microfarad rating capacitor do we need? 110-125V

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what is meant by loss of field in a DC motor? how a universal motor works?

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I am going to appear RRB Sr. Section Engineer Exam, Electrical. Can you send me previous year questions of RRB Electrical engineer. specially Section Engineer questions. my email id is likerahulworld@gmail.com

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1. A 380 / 220 V r.m.s. 3-phase 4-wire circuit carries loads of 8 + j8.1 ohm; 4 + j4.1 ohm; and 2 +j2.1 ohmin the three phases respectively. The length of the circuit is 100 m, and the resistivity of the phase conductors is 0.0005 Ω/m. The neutral conductor is of the same size as the phase conductors. a) Select a reference angle 0for the first phase. Then write down the three phase voltages in both polar format and complex number format. b) Make appropriate assumptions, and take temperature effects on resistance is insignificant. Calculate the currents in the three phases. (Note: Determine conductor resistance, and apply Kirchhoff’s Voltage Law) Based on the result, suggest a main switch rating for the circuit. c) Show your preferred direction of neutral current in a diagram, and then determine its value. (Note: Apply superposition principle, and Kirchhoff’s Current Law) Use its magnitude to show that in this circuit, the unbalanced load may increase the voltage drop in some of the phases. (Note: Also observe the common volt drip in neutral) State your assumptions, if there are any. d) Suddenly the neutral wire of the circuit is broken. Estimate the new currents in the first phase, i.e. Phase L1. State your assumptions, if there are any.

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