Transformer Winding Types

Here are the study notes for the text:

Transformer Winding Types

• Primary Winding: receives electrical power from the source, connected to the input voltage or power supply
• Secondary Winding: delivers electrical power to the load, connected to the load or device that requires electrical power
• Single-Phase Transformer Windings: one primary and one secondary winding, commonly used in residential and small commercial applications
• Three-Phase Transformer Windings: three primary windings and three secondary windings, widely used in industrial power distribution systems
• Auto-Transformer Windings: one winding serves as both primary and secondary, more compact and cost-effective than traditional transformers
• Winding Arrangements:
  • Concentric Winding: better insulation and compact design
  • Sandwich Winding: reduces leakage inductance
• HV (High Voltage) and LV (Low Voltage) Windings:
  • High-voltage winding: fewer turns, connected to higher voltage side
  • Low-voltage winding: more turns, connected to lower voltage side

Transformer Design

• Determine Transformer Specifications: identify application, voltage rating, current rating, frequency, and power rating
• Core Selection: choose core material based on magnetic properties and losses, determine core cross-sectional area
• Winding Design: decide on number of turns for primary and secondary windings, calculate cross-sectional area of conductors
• Voltage and Turns Ratio: determine turns ratio based on desired output voltage and primary voltage

No-Load Current Calculation

• Understand Transformer Basics: primary and secondary windings, magnetic core, and open-circuited secondary winding
• Determine Transformer Rating: rated voltage and frequency
• Use Transformer Core Specifications: core material and geometry
• Calculate Magnetizing Reactance (Xm): Xm = V/( I_(no-load) )
• Apply the Equivalent Circuit: phasor diagram represents relationship between voltage, current, and impedance
• Determine No-Load Current (I no-load): I_(no-load) = V/Xm
• Consider Core Losses: hysteresis and eddy current losses contribute to no-load current

Primary and Secondary Winding

• Primary Winding: coil of wire through which electrical power is initially supplied to the transformer
• Secondary Winding: coil of wire where electrical power is delivered or output from the transformer
• Magnetic Core: enhances magnetic coupling between primary and secondary windings, improving energy transfer efficiency
• Turns Ratio: ratio of number of turns in primary winding to number of turns in secondary winding, determines voltage transformation ratio

Transformer with Resistance and Leakage Reactance

• Leakage Flux: small part of flux that does not link with secondary winding, produces self-induced emf in each winding
• Leakage Reactance: inductive effect of leakage flux, equivalent to an inductive coil in series with each winding
• Representation: primary and secondary windings with resistance and leakage reactance

EMF Equation of a Transformer and Voltage Transformation Ratio

• Induced EMF per Turn: 4.44f Fm, where f is frequency and Fm is maximum flux
• RMS Value of Induced EMF in Whole Primary Winding (E1): E1 = 4.44f N1 Fm
• RMS Value of Induced EMF in Whole Secondary Winding (E2): E2 = 4.44f N2 Fm
• Voltage Transformation Ratio (K): E1/N1 = E2/N2 = K

Mechanical Forces in a Transformer

• Electromagnetic Forces: axial and radial forces caused by magnetic fields interacting with current
• Mechanical Stresses: short-circuit forces, thermal stresses, and fault currents
• Causes of Forces in a Transformer: load currents, fault currents, core saturation, and transformer inrush current

Cooling Methods for a Transformer

• Oil Immersed Cooling: transformer core and windings immersed in oil, which acts as both insulator and coolant
• Oil Natural Air Forced (ONAF) Cooling: combination of natural convection and forced air cooling
• Oil Forced Air (OFA) Cooling: fans enhance heat dissipation rate
• Oil Forced Water (OFW) Cooling: heat exchanger transfers heat from oil to water circuit
• Direct Air Cooling: windings and core exposed directly to air, fans enhance heat dissipation
• Fin Cooling: increased radiating surface area for better natural convection and forced cooling### Cooling System
• Transformers generate heat during operation, and an effective cooling system is crucial to maintain optimal operating temperatures and ensure reliability.
• Radiators or cooling fins are attached to the tank surface to increase the surface area for heat dissipation.
• Fans may be installed to enhance convective cooling.

Buchholz Relay

• A Buchholz relay is a protective device that detects and signals the presence of gas or oil flow caused by internal faults.
• It is often installed within the transformer tank.

Oil Conservator

• An oil conservator is a compartment attached to the tank that allows for oil expansion and contraction due to temperature variations.
• It helps maintain a constant oil level and minimizes the contact between oil and air, reducing oxidation.

Pressure Relief Devices

• Pressure relief devices, such as pressure relief valves, are installed to prevent excessive internal pressure in the tank.
• They release excess pressure in case of a fault or abnormal conditions.

Oil Filling and Draining

• The tank is equipped with fittings for filling and draining oil, facilitating maintenance and repairs.

Gaskets and Seals

• Gaskets and seals are used at joints and openings to maintain the tank's airtightness and prevent oil leakage.

Lifting Lugs and Mounting Points

• Lifting lugs are provided for the safe transportation and installation of the transformer.
• Mounting points may be included for securing the transformer to its foundation.

Painting and Coating

• The exterior of the tank is painted and coated to protect it from corrosion and environmental exposure.

Testing

• Transformer tanks undergo various tests, including pressure tests, vacuum tests, and leak tests, to ensure their integrity and reliability.

Calculating Cooling Tubes

• The calculation of cooling tubes for a transformer involves determining the heat dissipation requirements and sizing the cooling tubes accordingly.
• The most common methods for cooling transformers are oil cooling and air cooling.
• The steps involved in calculating cooling tubes for a transformer include:
  • Determining the total heat load generated by the transformer
  • Selecting the cooling method based on the transformer's design and application
  • Calculating the required cooling capacity
  • Selecting the appropriate cooling tubes
  • Calculating the required flow rates of oil or air through the cooling tubes
  • Verifying that the selected cooling tubes and system can effectively dissipate the calculated heat load
  • Considering environmental factors such as ambient temperature and altitude
  • Including safety margins in the calculations