Podcast Beta
Questions and Answers
What is the required maximum flux in the core of a transformer with a primary voltage of 3,000 V and a flux density of 1.2 Wb/m2?
For the 25-kVA transformer with a 2000/200 V rating, what is the efficiency at half full load if the iron loss is 350 W and the copper loss is 400 W?
In a transformer delivering 400 kVA at a power factor of 0.8 lagging, what is the percentage voltage drop if the percentage resistance is 2.5% and percentage reactance is 5%?
How many turns would the primary have if a single-phase transformer operates at a primary voltage of 1500 V with 250 turns on the secondary winding?
Signup and view all the answers
What defines the term 'absolute permeability'?
Signup and view all the answers
What is the no-load current drawn by the primary if the iron loss is 2 watt/kg and the density of iron is 7.8 gram/cm3?
Signup and view all the answers
In an A.C. circuit, what is the relationship between current and power in a purely inductive circuit?
Signup and view all the answers
Which characteristic is associated with series resonance?
Signup and view all the answers
What is the primary function of armature reaction in an alternator?
Signup and view all the answers
What is the effect of a high power factor on voltage regulation in alternators?
Signup and view all the answers
What is one of the primary purposes of conducting open circuit and short circuit tests on an alternator?
Signup and view all the answers
What is the significance of voltage regulation in a transformer?
Signup and view all the answers
In a star-connected three-phase transformer, how is the percent regulation calculated for varying power factors?
Signup and view all the answers
Study Notes
Magnetic Fields & Permeability
- Permeability is a material's ability to support the formation of a magnetic field within itself.
- Absolute permeability is the measure of the permeability of a vacuum.
- Relative permeability is the ratio of a material's permeability to the permeability of a vacuum.
Magnetic Circuit Basics
- Flux (Φ) refers to the total magnetic field lines passing through a given area.
- MMF (Magnetomotive Force) is the force that creates a magnetic field, measured in Ampere-Turns (AT).
- Reluctance (S) is the opposition to magnetic flux, analogous to resistance in an electrical circuit.
- The relationship between these is analogous to Ohm's Law in electrical circuits: Φ = MMF / S
AC Circuits
- Resistive circuit - Current and voltage are in phase. Power is P = I²R.
- Inductive circuit - Current lags behind voltage by 90 degrees. Power is P = I²XL.
- Capacitive circuit - Current leads voltage by 90 degrees. Power is P = I²XC.
Series Circuits
- R-L circuit - Voltage leads the current.
- R-C circuit - Voltage lags behind the current.
- R-L-C circuit - Impedance depends on the values of R, L, and C, and the frequency of the AC supply.
Resonance
- Series Resonance occurs when the inductive and capacitive reactances in a circuit are equal and opposite.
-
Properties of series resonance:
- The impedance of the circuit is minimum.
- The current in the circuit is maximum.
- The voltage across the inductor and capacitor are equal and opposite.
Transformers
- Working Principle: Based on the principle of electromagnetic induction.
- Construction: Consists of a core made of laminated iron, with two windings: primary & secondary.
- Operation - Voltage is induced in the secondary winding due to the changing magnetic flux in the core.
- No-load operation: Primary winding draws a small current (magnetizing current), creating a magnetic field.
- On-load operation: Secondary winding's current affects the magnetic field, leading to a voltage drop on the primary side.
- Equivalent circuit: Represents the transformer's behavior using resistance, reactance, and a magnetizing branch.
Alternators
- Working Principle: Based on Faraday's law of electromagnetic induction.
- Construction: Consists of a stator (stationary part) and a rotor (rotating part).
- Operation: Rotor's magnetic field cuts the stator windings, inducing an alternating voltage.
Alternator Types
- Salient pole alternators: Have large, prominent poles, suitable for low speeds.
- Non-salient pole alternators: Have smooth rotor, suitable for high speeds.
Armature Windings
- Full-pitch windings: Each coil spans 180 electrical degrees, resulting in a sinusoidal EMF waveform.
- Fractional-pitch windings: Each coil spans less than 180 electrical degrees, resulting in a less sinusoidal waveform.
Armature Reaction
- The armature current's magnetic field interacts with the rotor's magnetic field, creating an effect called armature reaction.
-
Effects of power factor (PF) on armature reaction:
- Lagging PF: Armature reaction weakens the main field.
- Leading PF: Armature reaction strengthens the main field.
Transformer and Alternator Testing
- Open Circuit (OC) Test: Measures the transformer's core losses.
- Short Circuit (SC) Test: Measures the transformer's copper losses.
Voltage Regulation
- Definition: The change in voltage at full load compared to no-load.
-
Methods of voltage regulation:
- Field excitation adjustment
- Voltage regulators
Hunting
- Definition: An undesired oscillation in speed and torque caused by load fluctuations or system instability.
-
Prevention:
- Improved damping mechanisms
- Automatic voltage regulators
Three-Phase Transformers
-
Connection Types:
- Star (Y) connection
- Delta (Δ) connection
Parallel Operation of Transformers
- Necessity: To handle increased load demands.
-
Conditions for parallel operation: Same voltage rating
- Same phase angle
- Same polarity
Transformer Efficiency
- Definition: Output power divided by input power.
- Factors affecting efficiency:
- Core losses
- Copper losses
Transformer Voltage Regulation
- Definition: The change in voltage at full load compared to no-load.
- Calculation: VR = (VNL - VFL) / VFL * 100%
Vector Grouping
- Purpose: To enable parallel operation of transformers by ensuring phase compatibility.
-
Types:
- Star-Star (Yy0)
- Delta-Delta (Dd0)
- Star-Delta (Yd11)
Transformer Maintenance
-
Yearly/Half-yearly:
- Inspection of insulation
- Oil testing and replacement
- Cleaning and inspection of cooling system
Effect of Excitation Change
- Increased excitation: Increases the magnetic field strength, leading to increased voltage and current.
- Decreased excitation: Decreases the magnetic field strength, leading to decreased voltage and current.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your understanding of key concepts related to magnetic fields, permeability, and AC circuits. This quiz covers topics like magnetic flux, MMF, and the behavior of resistive, inductive, and capacitive circuits. Challenge your knowledge and reinforce your learning!
