Description : State why a transformer always have an efficiency of more than 90%.
Answer : As transformer is static device with no moving parts, the losses due to friction & windage are completely absent. Hence transformer has efficiency of more than 90%.
Answer : The efficiency of a power transformer is of the order of 98 percent.
Answer : An ideal transformer will have maximum efficiency at a load such that copper loss equal to iron loss.
Description : For a transformer, operating at constant load current, maximum efficiency will occur at?
Answer : For a transformer, operating at constant load current, maximum efficiency will occur at unity power factor.
Description : Step-down transformer converts high voltage and low current into: (A) How voltage and high current (B) High voltage and low current (C) Low voltage and high current (D) None of the above
Answer : Step-down transformer converts high voltage and low current into: Low voltage and high current
Description : Transformer efficiency
Answer : Transformer efficiency
Description : A transformer operates 24 hours day at full -load. It's full -load efficiency is : (A) equal all day efficiency (B) more than all -day efficiency (C) less than all -day efficiency (D) equal to maximum efficiency
Answer : A transformer operates 24 hours day at full -load. It's full -load efficiency is : equal all day efficiency
Answer : The efficiency of transformer is Greater than electrical Machine because there is no rotational losses in transformer and there is no air gap losses in transformer so losses is less in transformer compare to electrical machine so efficiency is higher in case of transformer.
Answer : Transformer efficiency is maximum when copper losses are equal to iron losses.
Description : The efficiency of two identical transformers under load conditions can be determined by?
Answer : The efficiency of two identical transformers under load conditions can be determined by back-to-back test.
Description : A heavy ladder resting on floor and against a vertical wall may not be in equilibrium, if?
Answer : A heavy ladder resting on floor and against a vertical wall may not be in equilibrium, if the floor and wall both are smooth surfaces.
Description : The secondary of a current transformer is always short-circuited under operating conditions because it?
Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.
Description : Define armature reaction in an alternator. Explain the effect of armature reaction at various P.F. of loads of alternator.
Answer : Armature Reaction: The effect of armature flux on main flux is called as armature reaction. Armature Reaction at Various Power Factors: When armature is loaded, the armature flux modifies ... lagging p.f. For capacitive loads the effect of flux is partly distorting and partly strengthening.
Description : If non-linear loads are connected to the power system, then (A) displacement power factor is same as the total power factor (B) displacement power factor is not equal to the total power ... factor is due to harmonic currents (D) total power factor is due to fundamental component of current
Answer : If non-linear loads are connected to the power system, then displacement power factor is not equal to the total power factor
Description : What is the difference between linear and nonlinear electrical loads?
Description : Why do non linear loads cause harmonics?
Description : "Efficiency of thermal power station is low". — Justify.
Answer : Justification: Efficiency of thermal power station is low":- Overall efficiency of T.P.P depends upon efficiency of boiler, turbine and alternator. The heat produced due to combustion of coal ... losses in thermal power plant is 71%, So efficiency of thermal power plant is less about 29%
Answer : In a transformer, routine efficiency depends upon load current and power factor of load.
Answer : The maximum efficiency of a distribution transformer is at 50% full load.
Answer : A transformer cannot raise or lower the voltage of a D.C. supply because Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero.
Answer : The magnetising current of a transformer is usually small because it has small air gap.
Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.
Description : Name two methods for measurement of low, medium and high resistance. Give one advantage and one limitation of V- I method.
Answer : Methods for measurement of low resistance: 1. Ammeter voltmeter method 2. Kelvin's bridge method 3. Ohm meter method 4. Potentiometer method 5. Digital/analog multi-meter ... must be infinity for perfectly accurate measurement which is not possible. 2. Connection errors.
Description : Name the method used to measure following resistances:- (i) Low resistance (ii) Medium resistance (iii) Insulation resistance (iv) Earth resistance.
Answer : Following are the methods used to measure resistances:- (i) Low resistance: 1.Voltmeter-Ammeter Method 2. Kelvin's Double bridge Method (ii) Medium resistance: 1.Voltmeter-Ammeter Method 2. ... of Charge Method (iv) Earth resistance : 1. Fall of Potential Method 2. Earth tester
Description : State the range for low and medium resistance.
Answer : Low resistances: less than 1 ohm. Medium resistances: 1 ohm to 0.1 Mega ohm.
Description : Which of the following is the least expensive protection for over current in low voltage system? (A) Rewireable fuse (B) Isolator (C) Oil Circuit breaker (D) Air break circuit breaker
Answer : Which of the following is the least expensive protection for over current in low voltage system? (A) Rewireable fuse (B) Isolator (C) Oil Circuit breaker (D) Air break circuit breaker
Description : In a 741 Op-Amp, there is 20 dB/decade fall-off starting at a relatively low frequency. This is due to the (A) applied load (B) internal compensation (C) impedance of the source (D) power dissipation in the chip
Answer : In a 741 Op-Amp, there is 20 dB/decade fall-off starting at a relatively low frequency. This is due to the internal compensation
Description : Accurate measurement of very low resistances is possible with (A) Megger (B) Wheatstone Bridge (C) Kelvin’s Double Bridge (D) Wagner’s Earthing Device
Answer : Accurate measurement of very low resistances is possible with Kelvin’s Double Bridge
Answer : Turbine used for low head is Kaplan turbine.
Description : At very low frequencies a series R-C circuit behaves as almost purely?
Answer : At very low frequencies a series R-C circuit behaves as almost purely capacitive.
Description : In an AC. circuit, a low value of kVAR compared with kW indicates?
Answer : In an AC. circuit, a low value of kVAR compared with kW indicates high power factor.
Answer : In a low power factor wattmeter the pressure coil is connected to the load side of the current coil.
Answer : A synchronous machine with low value of short-circuit ratio has lower stability limit.
Answer : The primary reason for low power factor is supply system is due to installation of induction motors.
Answer : A low utilization factor for a plant indicates that plant is used for stand by purpose.
Answer : To protect most of the electrical equipment handling low power, the types of relays used are thermocouple, electronic and bimetallic.
Description : What is the definition of extra low voltage?
Answer : Extra-low voltage (ELV) is an electricity supply voltage in a range which carries a low risk of dangerous electrical shock.
Description : What is the difference between a line voltage and low voltage control system?
Description : What is considered low voltage and high voltage?
Description : At which time power factor of the induction motor is low?
Answer : The power factor of the inducction motor is low at the time of starting as compare to while the induction motor is running.
Description : write short notes on Low-pass filter.
Answer : low-pass filter (1) filter exhibiting frequency selective characteristic that allows low-frequency components of an input signal to pass from filter input to output unattenuated all high-frequency components are ... the bandwidth of the filter. A filter whose impulse response is a low-pass signal.
Answer : MOSFET have high current losses due to High on state resistance. Hence MOSFET is used for low power applications.
Description : SEER: Seasonal Energy Efficiency Ratio (SEER)
Answer : SEER: Seasonal Energy Efficiency Ratio (SEER), is most commonly used to measure the efficiency of a central air conditioner. The higher the SEER, the more efficient the system OR It is the ... the ratio of total capacity to the total KW energy usage at specific humidity and temperature condition.
Description : Compare the salient features of LED and CFL based on: i] Lamp Efficiency ii] Life span
Answer : Parameter LED CFL Lamp Efficiency High (more than 70 lumen per watt) Comparatively less (50-60 lumen per watt) Life span (in working hours) 10000 3000
Description : Define PIV, TUF, ripple factor, efficiency of rectifier.
Answer : PIV: Peak Inverse Voltage (PIV) is defined as the maximum negative voltage which appears across non-conducting reverse biased diode. TUF : Transformer Utilization Factor (TUF) is defined as the ratio of DC output ... Efficiency of rectifier: η = DC output power/ AC input power = PLdc / Pac
Description : method for improving string efficiency
Answer : The Methods of Improving String Efficiency:- 1) By reducing value of ‘m’ or (‘k’) by using longer cross arm. 2) By Making of ‘m’ or (‘k’) equal to zero 3) By grading Insulator. 4) By Using guard ring.
Description : What is the efficiency of Class-B amplifier? A) 68.50% B) 78.50% C) 88.50% D) 98.50%
Answer : What is the efficiency of Class-B amplifier? A) 68.50% B) 78.50% C) 88.50% D) 98.50%
Description : The overall efficiency of Thermal Power Plant is equal to _______________ . (A) Regenerative Cycle Efficiency (B) Renkine Cycle Efficiency (C) Carnot cycle efficiency (D) None of the above
Answer : The overall efficiency of Thermal Power Plant is equal to Regenerative Cycle Efficiency.
Description : The rankine cycle efficiency of steam power plant is (1) 60-80% (3) 30-45% (2) 45-80% (4) 20-30%
Answer : The rankine cycle efficiency of steam power plant is 30-45%
Description : Transmission efficiency of a transmission line increases with the
Answer : Transmission efficiency of a transmission line increases with the increase in power factor and voltage