Design Specifications for Oil-Immersed Transformers

　　I. Basic Requirements and Standards Compliance

　　Design Standards

　　Transformer design must comply with GB 1094 series standards (e.g., GB 1094.1-2013 Power Transformers – Part 1: General) and GB/T 6451, covering core parameters such as rated capacity, voltage levels, insulation levels, temperature rise limits, and short-circuit withstand capability.

　　Performance Parameters

　　Rated Voltage Range: 10 kV to 1000 kV, with common voltage levels including 35 kV, 110 kV, and 220 kV.

　　Rated Capacity: Ranging from tens of kVA to several million kVA, customized according to application scenarios and power demands.

　　Loss Requirements: No-load losses are related to the iron core, while load losses are associated with the windings and oil-immersed medium, both of which must meet national energy efficiency standards.

　　II. Core Component Design Specifications

　　Iron Core Design

　　Material: High-permeability cold-rolled silicon steel sheets or amorphous alloy strips are used to reduce hysteresis and eddy current losses.

　　Structure: Full-step lap joints, hole-free binding, and channel steel-type clamping structures ensure mechanical strength and electromagnetic performance.

　　Winding Design

　　Material: Copper wires or copper foils are used, with enameled copper conductors being of high quality.

　　Insulation: High-strength insulating materials are employed to ensure stability under high-temperature and high-voltage conditions.

　　Connections: Leads and conductive plates must be insulated, with conductor connections using phosphor bronze welding (tin soldering is prohibited).

　　Oil Tank Design

　　Structure: Welded from high-quality steel plates, with internal oil channels for oil circulation and heat dissipation.

　　Sealing: Corrugated oil tanks must have an expansion coefficient ≥1.3 times, and oil drain valves must adopt a double-seal structure to ensure no leakage.

　　Strength: Mechanical strength tests must comply with GB/T 6451 requirements, with no deformation under operating pressure.

　　III. Safety Protection and Monitoring Devices

　　Buchholz Relay

　　Transformers with a capacity of 800 kVA and above should be equipped with a Buchholz relay. The contact capacity shall be ≥66 VA at AC 220 V or ≥15 W for DC inductive loads.

　　Operating Conditions: The relay trips when gas accumulation reaches 250 mL–300 mL or when the oil flow rate is within the set range.

　　Pressure Protection Device

　　Sealed transformers must be equipped with a pressure protection device to ensure no operation under the highest ambient temperature and allowed load, and normal operation under no-load conditions.

　　Oil Temperature Measurement Device

　　Transformers with a capacity of 1000 kVA and above must be equipped with an outdoor temperature measurement device. The contact capacity shall be ≥50 VA at AC 220 V or ≥15 W for DC inductive loads.

　　The temperature measurement tube socket shall be installed on the top of the oil tank, extending 120 mm ± 10 mm into the oil for easy observation and accurate measurement in compliance with standards.

　　IV. Cooling System Design

　　Cooling Methods

　　Self-Cooling: Suitable for small- to medium-capacity transformers, utilizing natural heat dissipation from the oil tank.

　　Forced Oil Circulation Cooling: Suitable for large-capacity transformers, improving heat dissipation efficiency through external coolers that force oil circulation.

　　Cooler Control

　　The operating cooler can be manually or automatically started/stopped. It shall automatically start when the top oil temperature or load reaches the specified value.

　　In case of failure, the standby cooler shall automatically start. The control box shall be powered by two independent circuits with automatic switching in case of failure.

　　V. Installation and Maintenance Specifications

　　Installation Requirements

　　The foundation rails must be level, with the rail gauge matching the wheel specifications. Transformers equipped with Buchholz relays shall have a 1%–1.5% upward slope on the top cover along the airflow direction.

　　Flange connections shall use oil-resistant sealing gaskets, with rubber gasket compression ≤1/3 of its thickness to ensure sealing.

　　Maintenance Requirements

　　Oil Quality Testing: Regularly test indicators such as the acid value and dielectric loss of the insulating oil. Replace the oil if it exceeds standards.

　　Bushing Inspection: Ensure that the bushing creepage distance and anti-pollution capability meet requirements, and that the temperature rise at the connection of the terminal block does not exceed specified values.