Transformer Components, Types, and Applications in Power Systems
1. Transformer Components
Transformers are based on electromagnetic induction. They consist of two coils (primary and secondary) wound on a soft iron or silicon iron core. Some transformers have a third winding with lower voltage than the secondary.
2. What is a Transformer?
An electrical transformer increases or decreases voltage in an alternating current (AC) circuit while maintaining frequency. Ideally, the input power equals the output power. Real transformers have minor losses.
3. What is an Autotransformer?
An autotransformer resembles a transformer but has only one winding with at least three connection points (taps). The source and load connect to two taps, with one tap common to both. Each tap corresponds to a different voltage.
4. Transformer Core Construction
Transformer cores are built with thin, insulated silicon steel sheets to reduce eddy current losses, which cause heating. Eddy currents are induced in the core by the alternating magnetic field.
5. Transformer Voltage Ratio
The voltage ratio between the primary and secondary windings depends on the number of turns in each winding. More turns in the secondary result in a higher secondary voltage.
6. Star vs. Delta Connection
A star-connected secondary has a voltage 1.73 times higher than a delta connection. Star-delta starting reduces motor starting current. Star connection also avoids third harmonic voltage problems.
7. Identifying High and Low Voltage Sides
The high voltage winding has more turns with smaller cross-section conductors, while the low voltage winding has fewer turns with larger cross-section conductors.
8. Purpose of a High Voltage Transmission System
High voltage transmission reduces current for a given power level, minimizing power loss due to resistance (Joule heating).
9. Bundle Conductors in Transmission Lines
Using multiple conductors per phase (bundle conductors) increases the effective radius, reduces the electric field gradient, minimizes corona effects, and lowers line reactance.
10. Skin Effect
Skin effect refers to the tendency of AC current to concentrate near the surface of a conductor, increasing effective resistance at higher frequencies.
11. Mitigating Skin Effect
Litz wire (multiple insulated strands) or hollow conductors increase the effective conduction area, reducing skin effect.
12. Corona Discharge
Corona is a luminous discharge caused by the ionization of the air surrounding a conductor when the electric field gradient exceeds a certain value.
13. Negative Effects of Corona
Corona causes energy loss, radio interference, equipment degradation, and the production of pollutants.
14. Purpose of Overhead Ground Wires
Overhead ground wires (shield wires) protect transmission lines from lightning strikes.
15. Benefits of Transmission Line Duplication
Duplicating transmission lines increases system flexibility, reliability, security of supply, reduces power loss, lowers voltage drops, and allows for higher currents.
16. Shape of High Voltage Insulators
The bell shape of high voltage insulators increases their resistance to puncture, compression, and surface discharge, and helps shed water and contaminants.
17. Counteracting Mechanical Resonance in Transmission Lines
Weights (dampers) are placed on transmission lines near towers to prevent wind-induced resonance and vibrations.
18. Causes of Surges in Transmission Systems
Surges can be caused by line switching, load rejection, faults, and lightning strikes.
19. High Voltage Switch
A high voltage switch operates above 1kV and is classified by purpose (section, power section, circuit breaker) and drive mechanism (manual, spring, oil, hydraulic, electric).
20. High Voltage Disconnector
A high voltage disconnector isolates equipment but cannot interrupt current or extinguish an arc.
21. Unitary or Compact Substation
A unitary substation combines the transformer and high/low voltage switchgear in a single unit, often installed near load centers to reduce losses and costs.
22. Motor Control Center
A motor control center houses motor control equipment, typically in modular cubicles containing circuit breakers, contactors, and relays.
23. Effects of Short Circuits
Short circuits cause thermal and electrodynamic stresses, potentially leading to conductor melting, arcing, fire, and equipment damage.
24. Incandescent Light Bulb Operation
Incandescent bulbs produce light by heating a filament with electric current (Joule heating), causing it to emit light.
25. Third Harmonic Generation in Transformers
Third harmonics are generated due to the non-linearity of the transformer core’s magnetic saturation curve, distorting the magnetizing current.
26. Combined Cycle Power Generation
Combined cycle plants utilize waste heat from a gas turbine to generate steam for a steam turbine, increasing overall efficiency.
27. Location Advantages of Thermal Plants
Thermal plants can be located near fuel sources (natural gas, coal, etc.), while hydroelectric plants require specific water resources.
28. Working Fluids in Hydro and Thermal Turbines
Thermal turbines use steam or gas, which undergo significant density changes. Hydro turbines use water, which maintains a relatively constant density.
29. Alternative to Traditional Substations
Gas-insulated switchgear (GIS) using sulfur hexafluoride (SF6) can be used in space-constrained areas.
30. Common Power System Faults
Common faults include short circuits, insulation failure, overheating, lightning strikes, and overvoltage.
31. Common Electrical System Instruments
Common instruments include ammeters, wattmeters, voltmeters, frequency meters, and ohmmeters.
32. Role and Operation of Fuses
Fuses protect circuits from overcurrent by melting and interrupting the current flow.
33. Nuclear Plants and Base Load Demand
Nuclear plants are typically used for base load demand because they operate most efficiently at a constant output.
34. Pelton Turbine Applications
Pelton turbines are used for high-head, low-flow hydropower applications, such as in mountainous regions or with small rivers and streams.