Phasor Diagram Basics in Magnetizing Flux

Questions and Answers

What characterizes the no-load current in a transformer?

It flows through the secondary winding primarily.

It is made up of reactive and active components. (correct)

It consists solely of active power component.

It is only present when a load is connected.

What does the reactive component of no-load current do?

Creates heat through resistance.

Supplies power to the load.

Eliminates losses in the transformer.

Consumes energy to produce magnetic flux. (correct)

Which factor affects eddy current losses in a transformer?

Core temperature.

Core thickness and conductivity. (correct)

Hysteresis loop width.

Core material properties.

What differentiates hysteresis loss from eddy current loss?

Hysteresis loss arises from the material properties of the core. Signup and view all the answers

How can eddy current losses be reduced in transformer cores?

Laminating the core. Signup and view all the answers

What component of no-load current is responsible for iron losses in a transformer?

Active component. Signup and view all the answers

In transformer operation, what happens when the secondary circuit is open circuited?

The combined magnetic field strength decreases. Signup and view all the answers

What type of materials are best used to reduce hysteresis losses?

Low-hysteresis materials like silicon steel. Signup and view all the answers

What is primarily assessed during a standard visual inspection of a transformer?

Presence of manufacturer's labels Signup and view all the answers

What do open circuit tests on a transformer primarily evaluate?

Input power and core losses Signup and view all the answers

During an open circuit test, what is kept open?

High voltage side Signup and view all the answers

Which measurement indicates the input power during the open circuit test?

Wattmeter reading Signup and view all the answers

What does the shunt branch impedance in an open circuit test refer to?

Input impedance of the transformer Signup and view all the answers

What key factor influences the voltmeter reading in an open circuit test?

Rated voltage on the LV side Signup and view all the answers

If an open circuit test shows a no load power factor of 0.12, what does this imply?

High core loss in the transformer Signup and view all the answers

How is the estimated core loss of a transformer calculated during the open circuit test?

By measuring total input power and subtracting copper losses Signup and view all the answers

What is the phase relationship between the induced emf in the primary winding and the magnetic flux?

Lags by 90 degrees Signup and view all the answers

Which component is drawn in phase with the applied voltage V1 in the phasor diagram?

Working current Iw Signup and view all the answers

What is the turns ratio (TR) when a transformer has 1500 turns on the primary coil and 500 turns on the secondary coil?

3:1 Signup and view all the answers

Which of the following tests is NOT performed at the factory for transformer testing?

Periodic tests Signup and view all the answers

What is the purpose of conducting an open circuit test on a transformer?

To measure core losses of the transformer Signup and view all the answers

Which instruments are connected during the open circuit test on the high voltage side of the transformer?

Volt meter, Wattmeter, and Ammeter Signup and view all the answers

What is the purpose of routine tests conducted on transformers?

To confirm operational performance Signup and view all the answers

Why is the primary copper loss generally neglected in transformer analysis?

It is minimal compared to secondary losses Signup and view all the answers

What does the wattmeter reading indicate during the short circuit test?

Copper losses only Signup and view all the answers

Why can core losses be neglected during the short circuit test?

The applied voltage is quite small compared to rated voltage Signup and view all the answers

Which testing procedure might be conducted at the consumer site?

Pre-commissioning tests Signup and view all the answers

What does the equivalent resistance of a transformer represent in the context of the tests?

The copper losses at full load Signup and view all the answers

What angle is referred to as the no-load power factor angle in a phasor diagram?

The angle between I0 and V1 Signup and view all the answers

What is the primary outcome of the open circuit test in terms of numerical data?

The core loss of the transformer Signup and view all the answers

What does a low voltage of around 5-10% applied to the high voltage side during the open circuit test help achieve?

Minimize core losses during measurement Signup and view all the answers

Which parameter is NOT typically determined from the short circuit test of a transformer?

Efficiency of the transformer Signup and view all the answers

What is the primary purpose of the resistance test on electrical transformers?

To identify improper wiring and loose connections Signup and view all the answers

What does polarity testing in transformers ensure?

Windings are connected uniformly to avoid short circuits Signup and view all the answers

What is the main outcome of phase relation testing?

Calculation of angular displacement and phase sequence Signup and view all the answers

Why is oil testing a necessary procedure before energizing a transformer?

To verify the oil’s insulation and cooling properties Signup and view all the answers

Which of the following factors can be determined from an oil sample test?

Acid number and moisture content Signup and view all the answers

What is the primary benefit of conducting a visual inspection on transformers?

To identify potential problems that may not be detected otherwise Signup and view all the answers

What can be considered a significant risk if transformers are not tested for polarity?

Short circuits when transformers are paralleled Signup and view all the answers

How is the voltage relationship between primary and secondary windings verified during polarity testing?

By applying voltage between primary bushings and measuring secondary bushings Signup and view all the answers

Study Notes

Transformer No-Load Condition

When in no-load condition, the secondary winding is open-circuited, resulting in zero secondary current.
No-load current consists of two components:
- Reactive (Im): In quadrature with applied voltage, produces flux in the core without consuming power.
- Active (Iw): In phase with applied voltage, supplies iron losses and small primary copper loss.
No-load condition leads to a combined magnetic field that is weaker than the field from the primary winding alone.

Losses in Transformers

Eddy Losses:
- Caused by induced circulating currents.
- Result in electrical energy loss as heat due to core resistance.
- Dependent on magnetic field frequency, conductivity, and core thickness.
- Reduced by laminating cores or using high-resistivity materials.
Hysteresis Losses:
- Arise from magnetization and demagnetization of the core.
- Energy loss due to resistance of magnetic domains to realignment, dependent on material properties and flux density.
- Minimized using low-hysteresis materials, such as silicon steel.

Phasor Diagram Analysis

Magnetizing component (Im) creates magnetizing flux and is in phase with the flux.
Induced emf in primary and secondary lags the flux by 90 degrees.
Current (I0) lags behind the voltage vector (V1) by an angle φ0, defining the no-load power factor.
Active component (Iw) aligns with applied voltage (V1).
No-load current (I0) is the phasor sum of Im and Iw.

Transformer On-Load Condition

Transformer behavior changes during load, adjusting current distribution and magnetic fields.

Transformer Testing Procedures

Types of testing include:
- Factory tests: Type, Routine, Special tests.
- Site tests: Pre-commissioning, Periodic, Emergency tests.
Routine tests check for resistance differences and proper wiring in every manufactured unit.

Common Testing Procedures

Polarity Testing: Ensures all windings are connected in the same direction, vital for parallel operation.
Phase Relation Testing: Confirms correct phase relationships among transformers.
Oil Tests: Assess insulation and cooling properties through testing of oil quality (acid number, dielectric breakdown, moisture).
Visual Inspection: Simple but effective examination for physical damage, labels, and weld conditions.

Open Circuit Test

Conducted on the low voltage side with a voltmeter, wattmeter, and ammeter while keeping the high voltage side open.
Input power reflects core losses and copper loss under no-load conditions.
Used to determine core losses and parameters for the transformer's shunt branch equivalent circuit.

Short Circuit Test

Conducted on the high voltage side with low voltage applied to ffull load current in the transformer, while the low voltage side is short-circuited.
Allows assessment of copper losses by neglecting core losses due to minor applied voltage.
Results in determining copper losses at full load and parameters for the equivalent circuit analysis.

Transformer Example Problems

Calculate secondary voltage given a primary voltage of 240 V with 8 primary windings and 5 secondary windings.
Determine turns ratio for a transformer with 1500 primary turns and 500 secondary turns, using the formula TR = N1/N2.

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Description

This quiz covers the essential steps in drawing a phasor diagram for a circuit involving magnetizing flux and current relationships. It explores the phase differences between the magnetizing component, induced emf, and voltage, providing a foundational understanding for students of electrical engineering.