Answered Questions

  • 3Phase rectified to single phase

    If I got a 380v 3-phase supply and I want to rectify it with thyristors to single phase how much voltage will I get ?What is the relationship?thanks


    • May 15th, 2012

    The dc output of the full wave rectifier is average value the amplitude of the sine wave. In short multiply the r.m.s value of the ac input voltage by its form factor (1.11 in case of pure sine wave) ...

  • Induction Motor Power Factor

    A 3-phase induction motor running on 500v at full load draw 40A current at 0.85 pf Lagging if 85 micro Farad capacitor connected across its terminal than what would be a New Power Factor?


    • May 1st, 2012

    You didn't specify the capacitors connection is delta or star
    assuming (delta)
    Xc = 37.462 ;
    reactive power drawn by capacitor = 6684.49 VAR
    active power drawn by motor = 34641 watt
    old power factor = .85 lag
    new power factor = .91 lag


    • Feb 18th, 2012

    --> Find the reactance offered by capacitor i.e 37.46 ohm. so leading current drawn by capacitor is 9.095A @90 deg lead. --> Current drawn by the motor is 40A @ 31.788 deg lag. --> Resultant current ...

  • Why there is series of resistors connected to pressure coil of watt meter?

    soomnath paul

    • Feb 2nd, 2013

    High resistance is connected in order to make the voltage appeared across the pressure coil in phase with the applied one.

  • Induction Motor selection

    Could you explain that how to select an induction motor for a specific mechanical load(inertia). is there any formula or calculation then please give me. i shell be very thankful to all of you.

  • Calculation of Electrical Cable size

    Will u please give the formula, for selection of cable sizing (both Copper and Aluminium) depend upon the electrical loads...


    • Mar 24th, 2014



    • May 3rd, 2012

    It depends on a lot of factors like current density for mm^2 temperature is the cable on cable trays or buried or inclosed in PVC is that a 3 phase cable multicore or what and also depends on the voltage but in general making a current density 2 A/mm^2 for copper for simple applications is good.

  • Induction Stove

    As all we know,induction stove works on the principle of electromagnetic induction.Thus an emf is induced in the vessel and eddy current flows through the vessel.Since the vessel is made of ferromagnetic material (high resistivity) larger amount of heat (H=I^2 R)is generated.What will happen if a human body comes into contact with this high resistive vessel??? Won't the human body resistance be parallel...


    • May 15th, 2012

    Human body under dry condition has much higher resistivity compared ferromagnetic material.

  • Three Phase Transformers

    A 3phase wye/delta transformeris rated 225kV/24kV, 400MVA and has a series reactance of 13.3ohms as referred to its high voltage side. The transformer is supplying a load of 325MVA at 0.9 pf lagging at a voltage of 24kV(line to line)on its low voltage side. It is supplied from a feeder whose impedances are (0.15+j1.5)ohms connected to its high voltage terminals. For these conditions calculatea> The...

  • Phase Conversion

    List various methods to convert 1 phase to 3 phase.


    • Sep 8th, 2010

    This conversion is done by using mainly two methods. They are:1. Convert 1-ph ac to dc by using power electronic converter then convert that dc to 3-ph ac using power electronic inverter using PWM...

  • Distribution Tower

    What types of tower & pole is used in power system distribution?

  • Electrical Machine Operation

    In a 50hz electrical machine what happens when we use more than or less than 50hz?

  • OC/SC Test On Low Voltage Side

    Why OC test is carried out on low voltage side of transformer?

  • Transformer Voltage Regulation

    Which of the following test are to be conducted for the determination of voltage regulation of a transformer.a. Load Testb. Short Circuit Testc. OC Testd. Retardation Test.


    • Oct 9th, 2017

    B. Short Circuit Test


    • Oct 9th, 2017

    SC Test Only... But also need to know about PF of the Load as V.R. of transformer depends on PF of Load

  • DC Voltage Control

    How we can step-up or step-down the DC voltage directly?


    • May 23rd, 2012

    A chopper is nothing but a thyristor/SCR/transistor circuit which operates with the principle of PWM (Pulse Width Modulation). If you need to boost DC voltage with chopper, additional circuits includi...

    sai charan

    • May 20th, 2012

    this can be done by using chopper.chopper is a dc equivalent of a.c transformer to which d.c input which is to be stepped up is applied at input terminals and output is taken from output terminals whi...

  • Circuit Breaker

    Explain what are Single and 2 Pole circuit breaker?


    • May 1st, 2012

    Yes and single pole means that circuit switch two poles / two wires (eg; live and neutral)
    3 poles used to switch 3 phase systems
    4 poles used to switch 3 phase + neutral wire
    5 poles used to switch 3 phase + neutral + ground wire

  • Q-point in transistor?

    What is the purpose of Q-point in transistor?


    • Nov 9th, 2015

    It is a DC operating point between saturation and cutoff. It must be selected in a way that it does not go into saturation or cutoff.


    • Oct 24th, 2015

    It is more important for a transistor because according to this value, it may operate as an amplifier or a switch and most importantly the point should not vary with temperature hence we normally prefer voltage divider bias.