Electrical interview questions from power electronics. Electrical questions from semoconductor, power diodes, transistor, thristor, MOSFET and IGBTS, bridge. Why IGBT is very popular nowadays? Lower hate requirements Lower switching losses Smaller snubber circuit requirements What are the different methods to. Power Electronics Objective Questions 1. Questions & Answers on Diodes The P-N Junction Power Diode – Part 1 Power Diode – Part 2 Types of Power Diodes .
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POWER ELECTRONICS Interview Questions and Answers pdf free download mcqs objective type questions lab viva manual GATE CAT. + Power Electronics Interview Questions and Answers, Question1: What is holding current in SCR? Question2: What is latching current in SCR? Question3: . 50 TOP POWER ELECTRONICS Interview Questions and Answers pdf POWER ELECTRONICS Interview caite.info - Free download as PDF File .pdf), Text .
What are the main components used for isolating the Power Circuits, Power Semiconductor from the low-power circuit? Switching losses at turn-on and turn-off. Top 10 facts why you need a cover letter? It runs at dangerously high-speed on no load. An inverter in which the commutating elements are connected in series with the load is called a series inverter. Define Latching Current? Show related SlideShares at end.
Most of the time the last digit tells you how many zeros to write after the first two digits and these are read as Pico-Farads. The reason that 4ma is chosen instead of 0 mA is for fail safe operation. For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate psi, or full scale. Due to any problem in instrument i.
So if range is mA then we can differentiate whether it is due to broken wire or due to 0 psi. Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated. CT-current transformer. What Is Reverse Power Relay? Reverse Power flow relay are used in generating station's protection. A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid.
To stop the flow of power from grid to generator we use reverse power relay. It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load. Definition Of Power Electronics?
Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches. The main task of power electronics is to control and convert electrical power from one form to another.
AC to DC conversion: Rectifier is used for converting an AC voltage to a DC voltage. Rectifier applications: Variable speed dc drives, Battery chargers, DC power supplies and Power supply for a specific application like electroplating.
DC to AC conversion: Inverter circuit is used to convert DC voltage to an alternating voltage. Inverter applications: Emergency lighting systems, AC variable speed drives, Un-interrupted power supplies and Frequency converters.
AC to AC conversion: A cycloconverter converts an AC voltage to another AC voltage. Cycloconverter applications: It is rarely used. Can be used for controlling the speed of an AC traction motor.
In this region SCR exhibits the reverse blocking characteristics similar to diode. Forward conduction losses Loss due to leakage current during forward and reverse blocking Switching losses at turn on turn off Gate triggering loss. Load current waveform is also improved. Explain The Function Of Cyclo-converter? What Is An Inverter? Define Circuit Turn Off Time. It is defined as the time during which a reverse voltage is applied across the thyristor during its commutation process.
If the circuit turn off time is less than the thyristor turn off time the device may turn on at an undesired instant resulting in commutation failure. A dc Chopper is equivalent to the transformer in ac circuit. It is a static switch used to get the variable dc voltage from a constant dc voltage. Natural commutation Forced commutation. What Is Natural Commutation? The process of the current flowing through the thyristor goes through a natural zero and enable the thyristor to turn off is called as natural commutation.
What Is Forced Commutation? The process of the current flowing through the thyristor is forced to become zero by external circuitry is called as forced commutation. What Is Step Down Chopper? In step down chopper, the average output voltage is less than the input supply voltage. It is also known as Buck converter. What Is Step Up Chopper? In step up chopper, the average output voltage is more than the input supply voltage.
It is also known as Boost converter. What Is Voltage Commutation? The process of a charged capacitor momentarily reverse biases the conducting SCR and turns it off is called as voltage commutation. What Is Current Commutation? The process of a current pulse is made to flow in the reverse direction through the conducting SCR and thus made the net SCR current becomes zero, consequently turn off the SCR is called as current commutation.
The advantages of current commutated chopper is;. What Is Load Commutation? In load commutation, the load current flowing through the thyristor either becomes zero or is transferred to another device from the conducting SCR. To turn on these kind of devices single pulse of short duration is sufficient. Continuous gate voltage of entire on time is not required. It will avoid the hard triggering.
Lower hate requirements Lower switching losses Smaller snubber circuit requirements. Because the controlling parameter is gate-emitter voltage. Because the output drain current can be controlled by gate-source voltage. Because the output collector current can be controlled by base current. A thyristor can be turned off by making the current flowing through it to zero. Define Latching Current? The latching current is defined as the minimum value of anode current which it must attain during turn on process to maintain conduction when gate signal is removed.
Define Holding Current? The holding current is defined as the minimum value of anode current below which it must fall to for turning off the thyristor. What Is A Snubber Circuit? It consists of a series combination of a resistor and a capacitor in parallel with the thyristors.
Forward conduction losses Loss due to leakage current during forward and reverse blocking. Switching losses at turn-on and turn-off. Gate triggering loss. Define Hard-driving Or Over-driving? When gate current is several times higher than the minimum gate current required, a thyristor is said to be hard-fired or over-driven. Define Circuit Turn Off Time?
Circuit turn off time should be greater than the thyristor turn-off time for reliable turn-off, otherwise the device may turn-on at an undesired instant, a process called commutation failure. Elimination of commutation of commutating components in forced commutation, resulting in reduction in cost, weight and volume.
Reduction in acoustic noise and electromagnetic noise due to elimination of commutation chokes. Faster turn-off, permitting high switching frequencies. Improved efficiency of the converters. It converts fixed ac voltage into variable dc voltage. Steel rolling mills, printing press, textile mills and paper mills employing dc motor drives.
Input power factor is improved. Load current waveform is improved and thus the load performance is better. The delay angle is defined as the angle between the zero crossing of the input voltage and the instant the thyristor is fired. SCRs are subjected to a peak-inverse voltage of 2Vm in a fully controlled bridge rectifier. Hence for same voltage and current ratings of SCrs, power handled by mid-point configuration is about In mid-point converter, each secondary winding should be able to supply the load power.
As such, the transformer rating in mid-point converter is double the load rating. The commutation period when outgoing and incoming thyristors are conducting is known as overlap period. The angular period, when both devices share conduction is known as the commutation angle or overlap angle.
UJT firing circuit. The cosine wave crossing pulse timing control. Digital firing schemes. The input power factor is defined as the ratio of the total mean input power to the total RMS input volt-amperes.
Commutation is made simple. Distortion on the ac side is reduced due to the reduction in lower order harmonics. Inductance reduced in series is considerably reduced. Here the current flowing through the thyristor goes through a natural zero and enable the thyristor to turn off. A dc chopper is a high speed static switch used to obtain variable dc voltage from a constant dc voltage. Battery operated vehicles Traction motor control in electric traction Trolley cars Marine hoists Mine haulers Electric braking.
In a step- down chopper or Buck converter, the average output voltage is less than the input voltage. In a step- up chopper or Boost converter, the average output voltage is more than the input voltage. Average output voltage for step down chopper. What Is Meant By Duty-cycle? Duty cycle is defined as the ratio of the on time of the chopper to the total time period of the chopper.
What Is Meant By Trc? Constant frequency control Variable frequency control. In frequency modulation control, the chopping frequency f or the chopping period T is varied. Here two controls are possible. In this control method, the on time Ton is varied but chopping frequency is kept constant.
Voltage commutated chopper. Current commutated chopper. Load commutated chopper. In this process, a charged capacitor momentarily reverse biases the conducting thyristor and turn it off. In this process, a current pulse is made to flow in the reverse direction through the conducting thyristor and when the net thyristor current becomes zero, it is turned off.
In this process, the load current flowing through the thyristor either becomes zero or is transferred to another device from the conducting thyristor. The capacitor always remains charged with the correct polarity. Commutation is reliable as load current is less than the peak commutation current ICP.
The auxiliary thyristor TA is naturally commutated as its current passes through zero value. Commutating inductor is not required. It is capable of commutating any amount of load current. It can work at high frequencies in the order of kHz. Regenerative braking occurs when the motor speed exceeds the synchronous speed. In this case, the induction motor would run as the induction generator is converting the mechanical power into electrical power, which is delivered back to the electrical system.
This method of braking is known as regenerative braking. To improve input power factor To make the load current continuous. Chopper converts fixed dc voltage into variable dc voltage.
An inverter fed trapezoidal permanent magnet AC motor drive operating in self-controlled mode is called brushless dc motor. In medium and small size synchronous motors dc field can be produced by permanent magnets. According to construction 1. Surface mounted PMSM 2. Sinusoidally excited 2.
Trapezoidally excited. It acts as a protected cover for the whole machine and provides mechanical support for poles. It carries the magnetic flux produced by the poles. Circuit Breaker is one which makes or breaks the circuit. What is the difference between Isolator and Circuit Breaker? Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits.
But circuit breaker is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit, overload etc. What is the difference between earth resistance and earth electrode resistance? Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should recourse to its definition: Earth Resistance is the resistance existing between the electrically accessible part of a buried electrode and another point of the earth, which is far away.
The resistance of the electrode has the following components: A the resistance of the metal and that of the connection to it. B the contact resistance of the surrounding earth to the electrode. What is use of lockout relay in ht voltage? A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at one central location. This relay is powered by the same electrical source as the control power and is operated by a key lock switch.
The relay itself may have up to 24 contact points within the unit itself. This allows the control power for multiple machines to be locked out by the turn of a single key switch. What is the power factor of an alternator at no load?
At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor.
How to determine capacitor tolerance codes? In electronic circuits, the capacitor tolerance can be determined by a code that appears on the casing.
The code is a letter that often follows a three-digit number such as Z.
The first two are the 1st and 2nd significant digits and the third is a multiplier code. Most of the time the last digit tells you how many zeros to write after the first two digits and these are read as Pico-Farads. The reason that 4ma is chosen instead of 0 mA is for fail safe operation.
For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate psi, or full scale. Due to any problem in instrument i. So if range is mA then we can differentiate whether it is due to broken wire or due to 0 psi.
Two bulbs of w and 40w respectively connected in series across a v supply which bulb will glow bright and why? What is meant by knee point voltage? Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated. CT-current transformer. What is reverse power relay? Reverse Power flow relay are used in generating station's protection. A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid.
To stop the flow of power from grid to generator we use reverse power relay. What are the advantage of free wheeling diode in a Full Wave rectifier? It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load. Get daily job alert, placement paper and GK updates every day on your email. Register Now to benefit from our unlimited fresher focussed services! Contribute Placement Papers. Free Job Alert.