Quais os principais componentes de um transformador de potência?

Transformers: Understanding Power Transformers

Introduction to Transformers

• A transformer functions to either elevate or reduce electrical voltage within power systems, playing a crucial role in generation, transmission, and distribution of electricity.

• The most recognized type is the distribution transformer, typically powered at high voltage (13.8 kV) with a secondary single-phase output of 220 or 127 volts.

Components of an Oil-Insulated Transformer

• Key components include:

• Magnetic core with windings (specifically a three-phase winding).

• Insulating oil filling the tank.

• High and low voltage bushings, tap changer, radiators, fans for cooling, expansion tank, gas relay, and oil sampling valve.

Bushing Functionality

• Bushings connect the electrical network to the energized parts inside the transformer tank.

• High voltage bushings are made from porcelain or polymer insulators and contain conductors insulated by materials like resin or oil-soaked paper.

Magnetic Core Design

• The metallic core is laminated to minimize eddy currents caused by electromagnetic induction; solid cores would lead to excessive heat loss.

• Laminated cores enhance efficiency by reducing losses; they can be either enveloping (where windings wrap around the core) or surrounded (core encases windings).

Core Efficiency and Material Properties

• Enveloping cores are cheaper but less efficient due to greater magnetic dispersion compared to surrounding cores used for higher voltages (>69 kV).

• The primary goal of a magnetic core is to concentrate magnetic fields; silicon steel has high relative permeability (~5,500), significantly enhancing field concentration compared to air.

Tap Changer Mechanism

• The tap changer adjusts the turns ratio of the transformer allowing regulation of secondary voltage based on system demand.

Importance of Insulating Oil

• Insulating oil serves dual purposes: it insulates energized coils from other components and aids in cooling.

• Regular physical and chemical analysis of insulating oil is essential for detecting moisture and flammable gases like acetylene and methane that indicate potential faults.

Cooling Mechanisms in Transformers

• Transformers generate heat due to Joule effect in windings and losses in the magnetic core; effective cooling methods are vital.

• Common cooling methods include natural air cooling, forced air cooling using fans, and forced oil circulation through radiators.

Refrigeration Systems in Power Transformers

Types of Refrigeration Methods

• Forced air cooling is utilized through radiators, enhancing efficiency with forced oil circulation via a pump.

• Heat exchangers are employed to circulate transformer oil alongside water or refrigerant liquids for improved cooling.

Expansion Tank Functionality

• The expansion tank allows the insulating oil's volume to expand and contract as it heats and cools, connected to the main transformer tank.

• A silica gel desiccator within the expansion tank removes moisture from the air, minimizing contamination of the oil by water.

Protection Mechanisms

• The Buchholz relay (or gas relay), detects internal short circuits by identifying gas bubbles that rise during faults, triggering a trip to disconnect the transformer.

• An important safety feature includes a pressure relief valve that opens under excessive pressure, preventing damage to the transformer.

Monitoring and Safety Features

• Temperature measurements of both winding and oil are crucial; they help prevent overheating during overload conditions.

• Two-stage temperature monitoring alerts operators before reaching critical limits, allowing time for corrective action.

Structural Considerations in Transformer Design

Fire Safety Measures

• High-power substations separate transformers with firewalls to prevent fire spread between units.

Oil Retention Systems

• Oil retention basins are designed to contain leaks and protect against environmental contamination, applicable in both small and large transformers.

Transformers: Oil vs. Dry Types

Characteristics of HVDC Transformers

• HVDC transformers have unique structures including extended bushings for connections to thyristor valve rooms used in AC/DC conversion processes.

Overview of Dry-Type Transformers