Electrical Machine-I Sessional (EEE2106)
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Questions and Answers

What is the rated power of the single-phase induction motor?

  • 1 kW (correct)
  • 0.5 kW
  • 2 kW
  • 3 kW

Which of the following describes the armature resistance of the 2 kW DC machine?

  • 2.00 Ω
  • 1.68 Ω (correct)
  • 2.50 Ω
  • 1.25 Ω

What is the service factor of the 4 1/2 kW DC generator/motor?

  • 1.5
  • 1.0
  • 1.15 (correct)
  • 1.75

How many phases does the 3-phase induction motor operate on?

<p>Three-phase (D)</p> Signup and view all the answers

What is the full-load current of the synchronous generator rated at 4 KVA?

<p>19.2 A (B)</p> Signup and view all the answers

What is the field current for the 4 1/2 kW DC machine?

<p>1.0 A (B)</p> Signup and view all the answers

What is the total voltage rated for the synchronous motor?

<p>220 V (A)</p> Signup and view all the answers

What occurs when coils are connected in subtractive polarity?

<p>The voltmeter reading will be zero. (C)</p> Signup and view all the answers

What is the turns ratio for the provided data where the primary voltage is 100V and the secondary voltage is 50V?

<p>0.5 (C)</p> Signup and view all the answers

What is the formula to determine primary resistance R1?

<p>R1 = V1 / I1 (B)</p> Signup and view all the answers

If the secondary voltage V2 is 300V with additive polarity, what can be concluded about terminals X1 and X3?

<p>They have the same polarity. (C)</p> Signup and view all the answers

In the provided data table, what is the equivalent resistance referred to the primary side when the secondary side resistance is R2?

<p>Equivalent resistance = R2 / (N2/N1) (D)</p> Signup and view all the answers

Which resistance value corresponds to the highest voltage input of 200V in the table?

<p>244.1 (C)</p> Signup and view all the answers

What impact does increasing the primary voltage have on the secondary current, assuming a constant turns ratio?

<p>It decreases the secondary current. (A)</p> Signup and view all the answers

What is the relationship between primary current I1 and secondary current I2 based on the data provided?

<p>I1 is inversely proportional to I2. (B)</p> Signup and view all the answers

What is the formula for calculating the efficiency of a system?

<p>Efficiency = (Output - Losses) × 100 / Input (D)</p> Signup and view all the answers

What does a high percentage of regulation in a transformer indicate?

<p>Significant voltage change with load variations (A)</p> Signup and view all the answers

When conducting a short circuit test, what does R01 and X01 refer to?

<p>Resistance and reactance on the high tension side (A)</p> Signup and view all the answers

What is indicated by the efficiency of 90% in the calculation provided?

<p>The losses account for 10% of the input power (D)</p> Signup and view all the answers

Which module is NOT listed as part of the apparatus for the experiment?

<p>AC Power Meter (C)</p> Signup and view all the answers

What is the effect of internal resistance and reactance on transformer regulation?

<p>They cause a decrease in voltage at the load with an increase in load (D)</p> Signup and view all the answers

Which of the following describes the term 'load' in the context of a transformer regulation experiment?

<p>The demand for power that the transformer must meet (C)</p> Signup and view all the answers

What do the variable knobs K3 and K4 control in the experiment setup?

<p>The input voltage levels (A)</p> Signup and view all the answers

What is the first step to start the procedure for the experiment?

<p>Keep all the Loads at OFF position. (B)</p> Signup and view all the answers

Which of the following is NOT a condition for two transformers to operate in parallel?

<p>The relative polarities on the primary and secondary sides should be opposite. (A)</p> Signup and view all the answers

What should be noted when all Loads are turned ON?

<p>The readings on the AC Voltmeter, Ammeter, and Wattmeter Module. (C)</p> Signup and view all the answers

What is representing the load in an R-C load scenario?

<p>Combination of resistive and capacitive components. (A)</p> Signup and view all the answers

Which equipment is used to determine the R and X values on the secondary side?

<p>R-L-C meter. (A)</p> Signup and view all the answers

What does the term 'regulation' refer to in the context of transformer operation?

<p>The change in voltage from no load to full load. (C)</p> Signup and view all the answers

What is indicated if the mA deflects in the positive direction during the relative polarity test?

<p>H1 and X1 have the same mode of winding. (A)</p> Signup and view all the answers

What should be done after completing the readings with resistive load?

<p>Draw vector diagrams and calculate regulation. (A)</p> Signup and view all the answers

What happens to the phase voltage when an induction motor is started using a star-delta starter?

<p>It is reduced to 0.58 of normal voltage. (D)</p> Signup and view all the answers

Why is the star-delta starting method unsuitable for motors at voltages exceeding 3000 V?

<p>Excessive number of stator turns are needed for delta running. (B)</p> Signup and view all the answers

What is the starting torque behavior of an induction motor when using the star-delta starter?

<p>The starting torque is one-third of the short-circuit value. (C)</p> Signup and view all the answers

Under which condition is the star-delta starting method effective?

<p>When the application is light loaded during the start. (C)</p> Signup and view all the answers

What happens after the induction motor reaches its operational speed during star-delta starting?

<p>It is switched to delta configuration. (B)</p> Signup and view all the answers

What is one method of connecting three transformers for 3-phase circuits?

<p>Δ-Y connection (B)</p> Signup and view all the answers

In a three-phase transformer bank, which connection type allows for a phase shift of 30 degrees?

<p>Y-Δ connection (C)</p> Signup and view all the answers

Which component measures the current in the AC circuit during the experiment?

<p>AC Ammeter Module (D)</p> Signup and view all the answers

What type of curve is created by plotting torque against slip for an induction motor?

<p>Rectangular hyperbola (C)</p> Signup and view all the answers

Which of the following statements is true regarding the efficiency determination for each transformer combination?

<p>Efficiency is determined after measuring voltmeter and ammeter readings. (A)</p> Signup and view all the answers

What happens to the running torque as the slip increases in an induction motor?

<p>Running torque increases and reaches maximum at breakdown torque. (D)</p> Signup and view all the answers

Which equipment is NOT mentioned as part of the experiment setup for testing transformer connections?

<p>DC Voltmeter (C)</p> Signup and view all the answers

What should be done before applying voltage to the transformer setup?

<p>Connections should be verified by the lab teacher. (D)</p> Signup and view all the answers

Flashcards

DC Generator/Motor 2kW Rating

A direct current machine rated at 2 kW, operating at 250/250 volts, 8.0 amps, and 1450 RPM. It's wound compound, with field amps of 0.467A.

DC Generator/Motor 4.5kW Rating

A direct current machine rated at 4.5 kW. It operates at 250/250 volts, 18.0 amps, 1450 RPM, wound compound, with field amps of 1.0A.

Synchronous Machine (1500 RPM)

A constant-speed machine rated at 4 kVA, 0.8 power factor, 220/240 V, 3-phase, 19.2/9.6 A and a maximum field amp of 2.1 A .

Induction Motor (3 hp)

A 3-phase AC motor rated at 3 horsepower (hp), operating at 220/440 volts, 50 cycles, 1450 RPM, type M, frame 254U.

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Single Phase Induction Motor (DE1028)

A single-phase motor with a rating of 1 kW, operating at 220 volts, 6.6 amps, 2820 RPM, and 50Hz.

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Field Amps (DC Machines)

The amount of current flowing through the field windings of a DC motor or generator, directly impacting the magnetic field strength.

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Service Factor (Motors)

A rating that indicates the motor's ability to handle intermittent overloading.

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Line-to-Line Stator Terminal Resistance

Electrical resistance measured between any two phases in the stator of an AC motor or generator. Measures resistance in the stator.

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Transformer Turns Ratio

The ratio of the number of turns in the secondary winding to the number of turns in the primary winding.

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Step-up Transformer

A transformer that increases the voltage from the primary to the secondary side.

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Step-down Transformer

A transformer that decreases the voltage from the primary to the secondary side.

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Transformer Polarity

The relative phase relationship between the voltage waveforms in the primary and secondary windings.

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Primary side voltage (V1)

The voltage applied to the primary winding of a transformer.

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Secondary side voltage (V2)

The voltage across the secondary winding of a transformer.

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Transformer resistance referred to the primary side

Equivalent resistance of the secondary winding calculated and treated as if it were part of the primary winding.

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Transformer Equivalent Resistance

A resistance measurement that takes into account the turns ratio of a transformer.

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Transformer Regulation

Transformer regulation is the change in voltage at the load of a transformer as the load current changes, holding the primary voltage constant. It indicates how well a transformer maintains a stable voltage output under varying load conditions.

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Transformer Efficiency

Transformer efficiency is the ratio of output power to input power, expressed as a percentage. It measures the transformer's ability to convert input power to output power.

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Short Circuit Test

A test on the transformer to determine the equivalent resistance and reactance referred to the high voltage (HT) side.

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Open Circuit Test

A test on the transformer under no-load condition.

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Regulation (Transformer)

The percentage change in the secondary voltage when load current varies, primary voltage is held constant.

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Equivalent Resistance (R01)

The internal resistance of the transformer referred to the high voltage side. Value obtained from the short circuit test.

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Equivalent Reactance (X01)

The internal reactance of the transformer referred to the high voltage side. Value obtained from the short circuit test.

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Load Variation

Change in magnitude or type of load connected to the transformer's output.

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Parallel Transformer Operation

Connecting multiple transformers together to share a load when a single transformer can't meet the demand.

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Parallel Transformer Conditions

Requirements for connecting transformers in parallel: identical primary/secondary voltages, same polarities, similar impedance ratios.

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Transformer Terminal Voltage

Voltage measured across the transformer terminals. Must be identical for parallel operation.

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Relative Polarity Test

Method to determine if transformer windings are connected with the same polarity; use DC current to check.

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R/X Ratio

Ratio of resistance to reactance in transformer windings. Ideally should be similar for good sharing of load between transformers.

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Transformer Impedance

Opposition of a transformer to current flow, impacts load sharing and stability.

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AC Voltmeter

Instrument used to measure alternating current voltage.

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Load Current

Current flowing through the load attached to the transformer.

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Star-Delta Starter

A type of motor starter that connects the stator winding of an induction motor in star configuration during starting and then switches to delta configuration once the motor reaches a certain speed.

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Starting Current and Torque

The amount of current drawn by the motor when it's initially turned on. This current produces the starting torque, which is the initial force used to get the motor rotating.

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Star Connection

A configuration where the stator windings of an induction motor are connected in a Y-shape. This results in reduced voltage across the windings during starting.

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Delta Connection

A configuration where the stator windings of an induction motor are connected in a triangle shape. This provides full voltage to the windings for normal operation.

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Application of Star-Delta Starter

It's used in applications where the motor needs a reduced starting current and torque, such as light-loaded machines like pumps and machine tools.

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3-Phase Transformer Banks

Groups of single-phase transformers connected to create a 3-phase power system. They allow for efficient transmission of power over long distances.

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Δ-Δ Connection

A 3-phase transformer bank connection where both primary and secondary windings are connected in a delta configuration. This connection provides good voltage regulation under unbalanced loads and is commonly used in distribution systems.

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Y-Y Connection

A 3-phase transformer bank connection where both primary and secondary windings are connected in a wye configuration. It's often used for high-voltage applications and offers good insulation for the windings.

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Y-Δ Connection

A 3-phase transformer bank connection where the primary winding is connected in a wye configuration and the secondary winding is connected in a delta configuration. It's a commonly used configuration for stepping down voltages in distribution systems.

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Δ-Y Connection

A 3-phase transformer bank connection where the primary winding is connected in a delta configuration and the secondary winding is connected in a wye configuration. It's a common connection for stepping up voltages in power systems.

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Torque Equation

A mathematical expression that describes the relationship between the torque produced by an induction motor, the slip, and the motor's parameters. It's essential for understanding how torque changes with motor speed.

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Breakdown Torque (Tb)

The maximum torque that an induction motor can produce before it stalls. It's crucial for determining the motor's load-carrying capacity.

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Slip

The difference between synchronous speed (speed of the rotating magnetic field) and the actual rotor speed of an induction motor. It's a key factor in determining torque and power output.

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Study Notes

Electrical Machine-I Sessional (EEE2106)

  • Experiment 1: Polarity test and voltage/current relationship between transformer primary and secondary.

    • Transformer theory: A device that transfers electrical energy from one circuit to another without changing frequency.

    • Types: Step-up (primary voltage > secondary voltage) and step-down (opposite).

    • Polarity: Determined through testing, additive or subtractive.

    • Voltage and current relationship: E₁/N₁ = E₂/N₂ and I₁/N₂ = I₂/N₁ (where E and I are voltage and current, and N are turns).

  • Experiment 2: Open-circuit and short-circuit tests of a single-phase transformer.

    • Purpose: To determine the transformer's core loss and copper loss.

    • Core loss (iron loss): Measured by open-circuit test with rated voltage but no load to isolate core loss.

    • Copper loss (constant loss): Measured by short-circuit test with reduced voltage.

    • Efficiency calculation: Output power/input power.

  • Experiment 3: Transformer regulation under different power factors.

    • Purpose: To determine voltage change with varying load conditions (different power factors).

    • Regulation calculation: % Regulation = (Vnl - Vfl) / Vfl * 100 (where Vnl is no-load voltage, Vfl is full-load voltage).

  • Experiment 4: Parallel operation of transformers.

    • Purpose: Connecting two or more transformers to share the load capacity exceeding the capacity of a single transformer efficiently.

    • Conditions: Primary and secondary voltages must be identical, and polarities must be the same.

  • Experiment 5: Construction of three-phase transformers.

    • Using three single-phase transformers to build a three-phase transformer.

    • Relation between line and phase voltages/currents is explained.

    • Concepts of balanced/unbalanced loads are explored.

  • Experiment 6: Efficiency of three-phase transformers.

    • Determines the ratio of output power to input power.

  • Experiment 7: Speed-torque characteristic curve of a three-phase induction motor.

    • Purpose: To study the motor's performance curve for various operating conditions.

    • The graphical correlation of motor speed versus torque is noted.

  • Experiment 8: Blocked Rotor and No-load tests on three-phase induction motors.

  • Experiment 9: Study of a single-phase induction motor.

    • Self-starting mechanism through the usage of auxiliary windings in the stator windings.

  • Experiment 10: Circuit parameter measurement & efficiency calculation of single-phase induction motors.

  • Experiment 11: Capacitor value determination for maximum starting torque in split-phase induction motors.

    • Factors explored by varying capacitor value in the auxiliary winding.

  • Experiment 12: Starting an induction motor using a star-delta starter.

    • Purpose: A method for reducing starting current and preventing potential damage to the motor.

Other topics

  • DC Machines:

    • DC generators convert mechanical energy into electrical energy.
    • DC motors convert electrical energy into mechanical energy.

  • Synchronous Machines:

    • Constant-speed machines, used in power generation.

  • Induction Motors:

    • AC motors used for various applications, have adjustable speeds

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Description

This quiz focuses on key concepts and experiments related to transformers, including polarity tests and efficiency calculations. It covers the electrical characteristics of both step-up and step-down transformers, as well as open-circuit and short-circuit tests to determine losses. Test your understanding of these essential electrical engineering principles.

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