How does a power transformer work?

A: The core components include: 1) Magnetic Core: Usually made of silicon steel sheets, it provides a low-reluctance path for magnetic flux, minimizing magnetic losses. 2) Windings (Primary & Secondary): Conductive coils (typically copper or aluminum) that transfer energy—primary winding connects to the power source, secondary winding connects to the load. 3) Insulation Materials: Separate windings from each other and the core to prevent short circuits, using materials like enameled wire insulation and polyester film. 4) Tank & Cooling System: For oil-immersed transformers, the tank holds insulating oil that cools the windings and enhances insulation. 5) Bushings: Insulate and support the leads extending from the windings to the external circuit.

A: The turn ratio (N₁/N₂) is the ratio of the number of turns in the primary winding (N₁) to the secondary winding (N₂). It directly determines the voltage transformation ratio: V₁/V₂ = N₁/N₂ (where V₁ is the primary voltage, V₂ is the secondary voltage). A turn ratio greater than 1 means the transformer is a step-down transformer (reducing voltage), while a ratio less than 1 indicates a step-up transformer (increasing voltage). This ratio also inversely affects the current ratio (I₁/I₂ = N₂/N₁) to maintain power balance (excluding losses).

A: A step-up transformer increases voltage: its secondary winding has more turns than the primary (N₂ > N₁), so V₂ > V₁. It is primarily used in power plants to boost generator output voltage (e.g., from 10kV to 500kV) for long-distance transmission, reducing current and line losses. A step-down transformer decreases voltage: its secondary winding has fewer turns (N₂ < N₁), so V₂ < V₁. It is widely used in substations and households to reduce high transmission voltage to usable levels (e.g., 220V or 110V) for appliances and equipment.

A: Silicon steel sheets are used to minimize two key magnetic losses: hysteresis loss and eddy current loss. Hysteresis loss occurs due to the repeated magnetization and demagnetization of the core by alternating flux; adding silicon to steel reduces this loss. Eddy currents are induced, circulating currents in the core material, causing heating. Laminating the core into thin silicon steel sheets (insulated from each other) breaks the path of eddy currents, significantly reducing their magnitude and associated heat generation. Solid iron would have much higher eddy current losses, making the transformer inefficient and prone to overheating.

A: The main types are: 1) Oil-Immersed Transformer: Uses insulating oil as both coolant and insulator. The oil absorbs heat from windings and core, transferring it to the tank walls or radiators for dissipation. Suitable for large-capacity, high-voltage applications (e.g., grid substations). 2) Dry-Type Transformer: Uses air as the cooling medium, with windings insulated by resin or other dry materials. It is smaller, fire-safe, and suitable for indoor use (e.g., buildings, factories). 3) Gas-Insulated Transformer: Filled with sulfur hexafluoride (SF₆) gas for insulation and cooling, used in compact, high-voltage installations where space is limited.

A: Common winding faults include turn-to-turn short circuits, ground faults, phase-to-phase short circuits, and open circuits. Causes include: insulation damage during manufacturing/repair, overheating from overload or poor cooling, mechanical deformation from short-circuit shocks, moisture absorption, and insulation oil degradation. Identification signs include: increased oil temperature, unbalanced DC resistance between phases, abnormal buzzing or bubbling sounds in oil, and activation of gas or differential protection relays. For confirmation, technicians measure winding resistance and perform insulation tests.

A: Mild heating is normal, as transformers have inherent power losses (copper loss and iron loss) that convert to heat. Copper loss occurs due to resistance in windings when current flows, while iron loss comes from hysteresis and eddy currents in the core. However, excessive heating (e.g., tank surface too hot to touch) indicates abnormal conditions, such as overloading, poor cooling (clogged radiators, insufficient oil), winding short circuits, or core faults. Transformers are designed with temperature limits; exceeding these can accelerate insulation aging and shorten service life, so proper ventilation and cooling system maintenance are critical.

A:  The normal buzzing sound comes from magnetostriction—expansion and contraction of the silicon steel core as it is alternately magnetized. This sound is steady and uniform under normal operation. Abnormal buzzing (loud, irregular, or accompanied by rattling) indicates issues: loose core clamping bolts (amplifying vibration), overload (increased magnetic flux density), voltage fluctuations, or faulty windings. If the sound suddenly becomes louder or changes tone, it may signal an impending fault, requiring immediate inspection by maintenance personnel.

A:  Capacity selection is based on the total connected load and future expansion needs. The basic principle is to choose a transformer with a rated capacity slightly higher than the total calculated load to avoid overloading. Specifically, calculate the total apparent power (in kVA) of all connected devices, then add a 20-30% margin for load growth and non-linear loads (e.g., motors, electronic equipment). Oversized transformers waste energy (higher no-load losses), while undersized ones operate under overload, leading to overheating and premature failure. For industrial applications, factors like load diversity and peak demand are also considered.

A:  Single-phase transformers have two windings (primary and secondary) and are used in single-phase power systems (e.g., residential areas, small appliances), converting single-phase AC voltage. Three-phase transformers have three sets of primary and secondary windings, designed for three-phase power systems (e.g., factories, power grids). They are more efficient, compact, and cost-effective than three separate single-phase transformers for the same total capacity. Three-phase transformers are essential for large-scale power transmission and industrial equipment (e.g., motors, compressors) that require three-phase power.

A:  A qualified 110V to 220V transformer can be used continuously if operated within its rated capacity and under proper conditions (adequate ventilation, dry environment, no overloading). Normal service life is 5-10 years, depending on quality, usage, and maintenance. Factors affecting life: poor ventilation (causing overheating), frequent overloading, moisture or corrosive environments (damaging insulation), and poor-quality materials (e.g., aluminum windings prone to oxidation). To extend service life, avoid overloading, keep the transformer clean, and ensure proper heat dissipation.

A:  Copper loss (I²R loss) is the power lost as heat in windings due to electrical resistance; it increases with load current. Iron loss (core loss) is constant (regardless of load) and comes from hysteresis and eddy currents in the core. Reduction methods: Use high-conductivity copper windings (instead of aluminum) to lower resistance (reducing copper loss); use thin, grain-oriented silicon steel sheets for the core (reducing iron loss); optimize winding design to minimize current density; and ensure proper cooling to reduce temperature-related resistance increases. For no-load loss reduction, amorphous alloy cores are used in high-efficiency transformers.

A: Immediate actions: 1) Disconnect the transformer from the power supply by tripping all side circuit breakers and opening isolation switches. 2) Stop the cooling system (fans, oil pumps) to prevent fire spread. 3) If oil is burning on the tank top, open the lower emergency oil drain valve to lower the oil level (avoiding core exposure). Do NOT drain oil if the internal core/windings are on fire, as this can cause an explosion. 4) Extinguish the fire using dry powder, carbon dioxide, or foam fire extinguishers (do not use water). 5) Activate the fire alarm and notify the fire department. After the fire, inspect the transformer for structural damage before considering restarting.

A: Future trends focus on high efficiency, miniaturization, intelligence, and environmental friendliness. 1) High-Efficiency Materials: Use of amorphous alloy or nanocrystalline cores to reduce no-load losses. 2) Miniaturization: Adoption of high-frequency designs and advanced cooling technologies (e.g., liquid cooling) for a smaller size. 3) Intelligence: Integration of sensors and IoT technology for real-time monitoring of temperature, oil quality, and load status, enabling predictive maintenance. 4) Environmental Friendliness: Development of oil-free (dry-type) transformers and biodegradable insulating oil to reduce environmental impact. 5) High-Voltage Capacity: Design of ultra-high-voltage transformers (e.g., 1100kV) for long-distance, low-loss power transmission.