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Yes, SCR is a unidirectional switch.

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Description : Explain three phase half wave controller or three phase unidirectional controller.

Answer : Three phase half wave controller or unidirectional controller:

Description : The device which allows reverse power flow and withstands highest switch frequency is (A) GTO (B) MOSFET (C) IGBT (D) Inverter grade SCR

Answer : The device which allows reverse power flow and withstands highest switch frequency is MOSFET

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

Description : What are the desirable characteristics of ideal switch?

Answer : Desirable characteristics of the ideal switch: It is desirable to have power switches characteristics closer to ideal switch. The ideal switch should have the following characteristics. Zero resistance when ... . 100% efficiency. Able to control power flow with zero power dissipation.

Answer : Because it has a higher switching frequency and heat tolerance.

Description : Explain triggering of SCR using opto-coupler. State its advantages. 

Answer : Triggering of SCR using opto-coupler:  A simple opto-coupler based triggering circuit for SCR is shown in the figure. An optocoupler or opto-isolator is a combination of light source ... is small size and light weight device. iii)Interfacing with logic circuits is easily possible.

Description : Draw the circuit diagram of battery charger using SCR and explain it’s working.

Answer : Battery charger circuit using SCR: The figure shows the battery charger circuit using SCR. A 12V discharged battery is connected in the circuit and switch SW is closed. The singlephase 230V ... not fired. In this way, after full charging, further charging is automatically stopped.

Description : Explain the thermal triggering method of SCR. Enlist different triggering methods of SCR.

Answer : Types of Triggering: 1) Forward voltage triggering 2) Thermal triggering (Temperature triggering) 3) Radiation triggering (Light triggering) 4) dv/dt triggering 5) Gate triggering ... generated leakage current increases. This current gets multiplied internally and thyristor is turned on. 

Description : Explain working of AC circuit breaker using SCR with circuit diagram.

Answer : AC Circuit Breaker:  The circuit configuration of static AC circuit breaker using SCR is shown in the figure. When switch S' is closed, the SCRs T1 and T2 are fired in positive ... to non-availability of gate current. Thus the maximum time delay for breaking the circuit is one half-cycle.

Description : Temperature controller using SCR

Answer : Temperature controller using SCR The temperature control circuit is used to regulate the temperature. Figure shows the temperature control circuit using thermostat as temperature detector and SCR as ... half-cycle and heater gets connected to source to produce heat and raise the temperature.

Description : Compare SCR and TRIAC

Answer : SCR TRIAC It is an unidirectional device. It is a bidirectional device. It is turned-on by only positive gate current. It can be turned-on by either ... applications including lamp dimmer, heating control, zero voltage switched AC relay, small AC motor control etc.

Description : Describe triggering of SCR using UJT relaxation oscillator. 

Answer : Triggering of SCR using UJT relaxation oscillator: 

Description : How GTO is advantages over SCR

Answer : i) It is turned-off by negative gate pulse. ii) No commutation circuit required, reducing the cost, size, weight and volume of the circuit. iii) As commutation choke is not used, the associated acoustic ... turn off time permits high switching frequency. v) It has higher di/dt rating at turn-off. 

Description : Draw a neat labelling V-I characteristics of SCR and explain the region

Answer : (i) Latching current: It is the minimum anode current required to maintain the SCR in the conduction state just after turn-on and the gate signal has been removed.  (ii) Holding current: It is the minimum anode current required to hold the conducting SCR in the ON state. 

Description : Draw construction of SCR using two transistor model. Explain its operation.

Answer : Two Transistor Model of SCR or Thyristor

Description : The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply frequency of A) 10 kHz B) 10 Hz C) 5 kHz D) 5 Hz 

Description : SCR is more utilized as compared to Triac because it is

Answer : SCR is more utilized as compared to Triac because it is available with higher ratings

Description : A 230 V, 50 Hz phase controlled single-phase full-controlled SCR bridge converter draws 15 A constant dc current. If the source inductance is 3 mH, the drop in dc output voltage is (A) 4.5 V (B) 6.75 V (C) 9 V (D) 13.5 V

Answer : A 230 V, 50 Hz phase controlled single-phase full-controlled SCR bridge converter draws 15 A constant dc current. If the source inductance is 3 mH, the drop in dc output voltage is 9 V

Description : In a 230 V, 50 Hz single-phase SCR bridge converter operating at a firing delay angle, α and with large R-L load, the input source current is (A) sinusoidal current (B) constant dc current (C) continuous rectangular pulses (D) alternating rectangular pulses

Answer : In a 230 V, 50 Hz single-phase SCR bridge converter operating at a firing delay angle, α and with large R-L load, the input source current is alternating rectangular pulses

Description : An SCR without any external connections is considered as (A) two diodes in series (B) three diodes in series (C) two n-p-n transistors in series (D) two p-n-p transistors in series

Answer : An SCR without any external connections is considered as three diodes in series

Description : Why SCR is called as thyristor?

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.

Answer : SCR turned off when the anode current falls below holding current.

Description : What is holding current and latching current in SCR? Draw the gate characteristics of an SCR and explain the characteristics. What are the different signals which can be used for turning on SCR by gate control? compare them.

Answer : (i) Holding Current: Holding current is defined as the minimum anode current required to maintain conducting SCR in the on-state.  (ii) Latching Current: Latching current is defined as the ... the on-state immediately after the SCR has been turned on and the gate signal has been removed.

Description : What is the use of SCR?

Answer : SCR are use in lamp dimming, power regulators, motor control, rectifications of high power AC, control of welding machines and also use as switch these are some uses of silicon controlled rectifier.

Description : Draw & explain touch plate switch using IC555.

Answer : It is construct form monostable multivibrator , when metal plates touch by finger then voltage at pin number 2 goes to below 1/3 Vcc then output of lower comparator becomes high hence flip flop set and ... then output of timer goes low and it low till up to the metal plates touch by finger .

Description : Give the function of fuse and switch.

Answer : Functions of fuse:  * To break the circuit under fault condition.  * To provide overcurrent protection to the circuit.  * To provide short circuit protection to the circuit.  * To provide ...  * To make the electric circuit manually.  * To break the electric circuit manually.

Description : State the function of : i) MCCB ii) ELCB iii) MCB iv) Switch. 

Answer : i) MCB: Provide short circuit protection & over load protection to electrical loads.  ii) ELCB: Provides protection by detecting the unsafe magnitudes leakage currents flowing to earth and disconnecting ... rating.  iv) Switch: Make and break the electrical connection to the load manually.

Description : Transfer switch

Answer : .embed-container { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; } .embed-container iframe, .embed-container object, .embed-container embed { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }

Description : How rating of main switch and cable is selected for Industrial Installation.

Answer : 1. Rating of Main Switch or Fuse Rating is decided in industrial installation: Rating of main switch or fuse is based up the starting current of motor. For calculating starting current is considered 2 ... take 1.5 times the rated current or full load current. & thus cable rating is decided.

Description : Earthing switch is used for?  (A) Measuring of safety voltage (B) Protection of equipment from ground faults (C) Discharging residual energies (D) All of the above 

Answer : Earthing switch is used for?  (A) Measuring of safety voltage (B) Protection of equipment from ground faults (C) Discharging residual energies (D) All of the above 

Description : A switch tail ring counter is made by using a single D-FF. The resulting circuit is (A) T-FF (B) D-FF (C) SR-FF (D) JK-FF

Answer : A switch tail ring counter is made by using a single D-FF. The resulting circuit is T-FF

Description : A closed switch has a resistance of?

Answer : A closed switch has a resistance of zero.

Answer : The switch board instruments should be mounted in vertical position.

Answer : If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then Electrolytic capacitor will, in all probability, suffer break down.

Answer : Centrifugal switch disconnects the auxiliary winding of the motor at about 70 to 80 percent of synchronous speed.

Answer : In a single phase motor the centrifugal switch disconnects auxiliary winding of the motor.

Answer : A centrifugal switch is used to disconnect starting winding when motor has picked up about 50 to 70 per cent of rated speed.

Answer : A thermal protection switch can protect against overload.

Description : What is the difference between a switch and a relay?

Answer : Switch is simply a mechanical contact mechanism and relay is a electromagnetic switch . Switch can be direct mechanically turn on and off but relay can be operated by energising coil .

Answer : BJT act as switch in saturation and  cutoff region ( ON state in saturation region and OFF state in cut-off region )

Description : Purpose of Selective Catalytic Reduction (SCR)

Answer : Purpose of Selective Catalytic Reduction (SCR) : 1. It reduces Nox 75% to 90% 2. Converts it in to molecular nitrogen and water vapor 3. It reduces HC emission up to 80% 4. It reduces PM emission 20 to 25%.

Description : An inductor is connected in series with SCR to protect it from A) Excessive high voltage B) Excessive high dv/dt C) Excessive high di/dt D) Excessive large forward current 

Answer : An inductor is connected in series with SCR to protect it from Excessive high di/dt

Description : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) ... proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

Answer : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ directly proportional to α and inversely proportional to Φ

Description : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in (A) voltage notching (B) harmonic distortion (C) voltage sag (D) voltage swell

Answer : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in voltage notching

Description : How do you test an SCR?

Description : Why is pulse train gating preferred over pulse gating? Explain with relevant circuit and waveforms, the pulse train gating of SCRs.

Description : It is an unidirectional device that blocks the current flow from cathode to anode   (A) SCR (B) PCR (C) VCR (D) DCR

Answer : It is an unidirectional device that blocks the current flow from cathode to anode SCR 

Answer : An SCR is a Uni-directional switch

Description : The conducting SCR turns-off when the on-state current is (A) below the latching current (B) below the holding current (C) equal to the reverse leakage current (D) zero 

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