Description : what is firing angle?

**Answer** : Firing angle is time in electrical degrees from the instant the valve voltage is positive to the application of firing pulse to the valve (start of conduction). Also called delay angle.

Description : Define: i) Firing angle ii) Conduction angle

**Answer** : (i) Conduction Angle (β): Conduction angle is defined as the angle between the instant the SCR is triggered or turned on and the instant at which the SCR is turned off. Assuming that the SCR ... maximum average output voltage to the angle when the SCR is actually triggered or fired by gate pulse.

Description : When the firing angle a of a single-phase, fully controlled rectifier feeding constant direct current into a load is 30°, the displacement power factor of the rectifier is

**Answer** : When the firing angle a of a single-phase, fully controlled rectifier feeding constant direct current into a load is 30°, the displacement power factor of the rectifier is √3/2

Description : Thyristor can be protected from over voltages by using

**Answer** : Thyristor can be protected from over voltages by using Voltage clamping device

Description : What is the use of a thyristor in a circuit?

Description : what are the disadvantages of thyristor?

**Answer** : Disadvantages of thyristor The silicon controlled rectifier (SCR) is unidirectional devices, so it can control power only in DC power during positive half cycle of AC supply. Thus only DC power is ... cycle. It cannot be used at higher frequencies. The gate current cannot be negative

Description : Draw the structural diagram of GTO. Explain briefly the switching behavior of GTO with the help of appropriate voltage and current waveform.

**Answer** : Gate Turn Off Thyristor (GTO) Conventional Thyristor can be turned on with gate terminal but can not turn off from gate terminal. But in case of Gate Turn Off Thyristor (GTO), we can turn it on and off ... subdivided as storage period (Ts), fall period (Tp) and tail period (Tt).

Description : Leakage current flows through the thyristor in

**Answer** : Leakage current flows through the thyristor in Forward blocking mode and Reverse blocking mode.

Description : Why thyristor are not preferred for inverter?

Description : Is a SCR a thyristor?

**Answer** : Yes, SCR is a thyristor. Thyristor is the family and SCR is the member of that family but SCR is universally known as thyristor.

Description : How is a thyristor used to convert AC to DC?

**Answer** : Yes ,it is one of the main advantage using thristors as a switch in DC circuit ,it has a high current gain

Description : Explain thyristor gate drive circuit.

**Answer** : Thyristor Gate Drive Circuit: The thyristor can be turned on by pulse voltage signal at gate terminal and it does not require continuous drive signal like the transistor. The gate ... circuit provide required minimum gate voltage and gate current then the thyristor conducts properly.

Description : parallel operation of MOSFET can be done more easily as compared to thyristor. why?

**Answer** : Parallel operation of MOSFET can be done more easily as compared to thyristor because the resistance of MOSFET is increases with increase in temperature. MOSFET have the positive temperature coefficient. In ... the parallel operation of MOSFET can be done more easily as compared to the thyristor.

Description : write short notes on thyristor CSI .

**Answer** : Current-source inverter (CSI) is an inverter with a DC current input. Current source inverters are most commonly used in very high power AC motor drives.

**Answer** : By using some circuit the forward DC current of thyristor is forced to zero is called forced commutation.

**Answer** : Natural commutation is also called as line Communication. The turning off of thyristor due to AC supply is called natural commutation or line commutation. If the thyristor is connected to AC supply ... connected to positive and anode terminal get connected to negative, this turns off the thyristor.

Description : Explain the concept of lagging and leading phase angle by waveform.

**Answer** : i) Leading phase angle : When two ac quantities of same frequency do not attain their respective zero or peak values simultaneously, then the quantities are said to be out-of-phase quantities. The ... Similarly, in the second diagram, the voltage is said to be lagging the current by Φ.

**Answer** : If the current in a capacitor leads the voltage by 80°, the loss angle of the capacitor is 10°.

Description : thyristor can be turned off by?

**Answer** : Thyristor can be turned off by making anode potential equal to cathode potential or by making anode potential less than cathode potential.

Description : What will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value ?

**Answer** : 90° will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value.

Description : What is the maximum value of torque angle in synchronous motor?

**Answer** : The maximum value of torque angle in synchronous motor is 90 degrees electrical.

Description : How to find total impedance Z, current I and Impedance angle ?

**Answer** : How to find total impedance Z, current I and Impedance angle ?

Description : Phase margin is the amount of angle to make the system (1) Oscillatory (2) Stable (3) Unstable (4) Exponential

**Answer** : Phase margin is the amount of angle to make the system Unstable

Description : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are (A) 0.5 pu ... pu, 0.5 pu (C) 0.707 pu, 0.707 pu (D) 0.5 pu, 0.5 pu

**Answer** : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are 0.866 pu, 0.5 pu

Description : Torque angle for the synchronous machine is the angle between (A) stator magnetic field and rotor magnetic field (B) stator magnetic field and net magnetic field in the air gap (C) rotor magnetic field and net magnetic field in the air gap (D) excitation voltage and impedance voltage drop

**Answer** : Torque angle for the synchronous machine is the angle between rotor magnetic field and net magnetic field in the air gap

Description : The product of apparent power and cosine of the phase angle between circuit voltage and current is?

**Answer** : In parllpar reasonans RLC circuit the current is

Description : The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.

**Answer** : The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of 45 degrees.

Description : Two waves of the same frequency have opposite phase when the phase angle between them is?

**Answer** : Two waves of the same frequency have opposite phase when the phase angle between them is 180°.

Description : Tangent of angle of friction is equal to?

**Answer** : Tangent of angle of friction is equal to coefficient of friction.

Description : Angle of friction is the?

**Answer** : Angle of friction is the angle between normal reaction and the resultant of normal reaction and the limiting friction.

**Answer** : The coupling angle or load angle of synchronous motor is defined as the angle between the rotor and the stator poles of opposite polarity.

Description : The synchronous motor will develop maximum power when the load angle is?

**Answer** : The synchronous motor will develop maximum power when the load angle is 900.

Description : Describe the working principle of Thyristor operated dimmer with the help of circuit diagram.

**Answer** : Thyristor operated dimmer: A popular thyristor operated dimmer circuit employ TRIAC-DIAC phase control for low AC power control. During each half-cycle, the capacitor charges through (R1+VR1). When the ... time constant {C (R1+VR1)}. Thus by reducing VR1 the lamp brightness can be increased.

**Answer** : No we cannot turn off normal thyristor using Gate.

**Answer** : Thyristor conducts when the anode voltage is greater than cathode and when the current provided to Gate.

**Answer** : Thyristor have three terminals anode, cathode and Gate.

**Answer** : Thyristor can only be turned on by small gate pulse but it cannot be turn off by using gate hence thyristor is called semi controlled device.

**Answer** : Thyristor can be turn on by positive gate pulse and the current will continue to flow through the device even when the gate voltage is low hence thyristor is called latching device.

Description : Thyristor Switched Capacitor (TSC)

**Answer** : Thyristor Switched Capacitor (TSC) TSC is a static compensator. TSC is use for compensating reactive power. Compensation is required for voltage regulation, increasing stability, ... compensating device like TCS phase angle between voltage and current can be maintain.

Description : A single-phase fully controlled thyristor bridge ac-dc converter is operating at a firing angle of 25o and an overlap angle of 10o with constant dc output current of 20 A. The fundamental power factor (displacement factor) at input ac mains is (A) 0.78 (B) 0.827 (C) 0.866 (D) 0.9

**Answer** : A single-phase fully controlled thyristor bridge ac-dc converter is operating at a firing angle of 25o and an overlap angle of 10o with constant dc output current of 20 A. The fundamental power factor (displacement factor) at input ac mains is 0.78

Description : A single phase fully controlled thyristor bridge ac -dc converter is operating at a firing angle of 25 degree and an overlap angle 10 degree with constant dc output current of 20A. The fundamental power factor (displacement factor) at input ac mains is : (A) 0.78 (B) 0.827 (C) 0.866 (0) 0.9