THEORY RELATED VIVA Q&A
- What is ohm’s law?
Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant.
Ohm’s Law Equation:
V = IR
where ,
V is the voltage across the conductor,
I is the current flowing through the conductor
R is the resistance provided by the conductor to the flow of current.
- What is an Ideal Transformer
An ideal transformer is an imaginary transformer in which no losses occur at all. In other words, the transformer Input power is equal to the output power of the transformer i.e. they have 100% efficiency. It is just a theoretical transformer because there must be some losses in a real transformer.
Transformer input Power = Transformer Output Power.
PIN = POUT.
- What is an KCL & KVL ?
Kirchhoffs Current Law
It states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“.
Mathematically,
Algebraic sum of ALL the currents entering and leaving a node must be equal to zero, I(exiting) + I(entering) = 0
This idea by Kirchhoff is commonly known as the Conservation of Charge.
Kirchhoffs Voltage Law
It states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero.
Mathematically,
Algebraic sum of all voltages within the loop must be equal to zero.
IR + EMF = 0
This idea by Kirchhoff is known as the Conservation of Energy.
- What is a leading & lagging power factor & how can you improve it? State the methods of power factor correction?
The cosine of the angle between voltage & current is called the power factor. If the current leads the voltage, it causes a leading power factor. If the current lags voltage the power factor is lagging.
Most loads are inductive that causes a lagging power factor. Thus these following methods are used for p.f correction (to nullify the lagging current)
- Static Capacitor
The capacitor helps in providing a leading current that eliminates the lagging component of current & improves the power factor
- Synchronous Condenser
It is an over-excited synchronous motor with no load that also provides a leading power factor.
- Phase Advancer
Phase advancer is a simple AC exciter which is connected on the main shaft of the motor and operates with the motor’s rotor circuit for power factor improvement. Phase advancer is used to improve the power factor of induction motor in industries.
- What is a motor starter?
Motor Starter is a device that connects in series with the motor to decrease the starting current (that could damage the windings in normal conditions) and gradually increase current after starting the motor (in other words start or stop the motor) and provide overload protection.
- What is Superposition Theorem?
In a linear bilateral network containing more than one source, the current in any of the branches is equal to the sum of current which would flow through the same branches by considering each source by their internal resistance.
- What is Norton's Theorem?
Any two terminal linear bilateral networks containing independent voltage sources and current sources may be replaced by an equivalent current source in parallel with resistance.
- What is Thevenin's Theorem?
Any linear bilateral network consisting any no. Of sources and resisters can be converted into a series circuit consisting of voltage source in series with equivalent resistor.
- What is Transformer?
It is defined as an electrostatic device which can transfer energy from one winding to another winding through magnetic fields.
- What is motor?
Motor is an electronic mechanical device which convert electrical energy into mechanical energy.
Motor obey Fleming left hand rule and based on principle of Faraday's law of electromagnetic Induction.
- What is Generator?
Generator is an electronic mechanical device which convert mechanical energy into electrical energy.
Generator obey Fleming Right hand rule and based on principle of Faraday's law of electromagnetic Induction.
- What is Fleming's Left and Right Hand Rule?
Fleming’s Right Hand Rule states that if we arrange our thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the motion of conductor relative to the magnetic field, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the induced current.
- What is star and delta connection in 3-phase supply?
3 phase system can be connected in two different styles I.e. star or delta. In star connection, line to line current is equal to line to neutral current. But, line to line voltage is root 3 times the line to neutral voltage. In delta connection, voltage across each element is equal to line voltage.
- What do you mean by line voltage and line current in 3-Phase AC supply?
Line voltage is the voltage measured between any two lines in a three-phase circuit. Phase voltage is the voltage measured across a single component in a three-phase source or load. Line current is the current through any one line between a three-phase source and load.
- Why all the measuring instrument connected to low voltage side instead of High Voltage side in open circuit test?
If we connect all the instrument connected to the high voltage sides and a transfer operating in no load condition then it is very difficult to measure voltage and current value by given instrument that why all instrument are connected to LV side instead of HV side.
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