Dry-type transformer temperature sensor and oil-immersed transformer temperature sensor

Transformers are the core equipment of the power system. Temperature monitoring directly affects the lifespan and operational safety of the equipment. The structures of dry-type transformers and oil-immersed transformers are different, and the requirements for Temperature Sensors are also completely different. Choosing the wrong sensor can lead to inaccurate data or even cause faults. This article will help you sort out the key points for selecting sensors for these two types of transformers, assisting you in making the right choice once and for all.

1. Dry Transformer Temperature Sensor

The windings and cores of a dry transformer are exposed to the air, and they dissipate heat through air convection. Temperature Sensors are usually installed in a buried manner within the three-phase windings and directly measure the hotspot temperature of the windings.

• Core Requirements
• High Precision: The insulation class of the dry-type transformer (Class B 130℃, Class F 155℃, Class H 180℃) determines the temperature limit, and the sensor error directly affects the insulation life. The Pt100 A-class sensor (±15℃ at 0℃) is the industry standard.

• High consistency:The three-phase windings operate independently. The data from the three sensors need to be compared and interchangeable. If the consistency is poor, there may be incorrect startup or shutdown of the fan or failure to trigger an alarm for overheating.

• Quick response:The air cooling is fast, and the winding temperature changes rapidly. The response time of the sensor should be ≤ 5 seconds.

Pictures of the temperature sensors produced by Weilian for temperature measurement of dry-type transformers, in sets of three or four.

1. Temperature Sensor for Oil-immersed Transformers

The windings and cores of the oil-immersed transformer are immersed in insulating oil, and heat is dissipated through the oil circulation. The sensor is installed on the top of the oil tank, with the probe inserted 10-20 cm below the oil surface.

• Core Requirements
• High Sealing Performance: The sensor comes into direct contact with the insulating oil. Poor sealing can lead to oil leakage, moisture absorption, and failure. An IP67 or higher protection level is a basic requirement.

• Resistant to oil corrosion:If the insulation oil (mineral oil or synthetic oil) comes into prolonged contact with the sensor materials, it may cause corrosion. Therefore, materials resistant to oil (such as 304/316L stainless steel, fluorine rubber seals) should be selected.
• Operating temperature range:It needs to cover the operating temperature range of -30℃ to 150℃.

Picture of the high-sealing temperature sensor produced by Weilian for temperature measurement of oil-immersed transformers.

1. Overview of Core Differences between Two Types of Sensors

Comparison Dimension Dry-type Transformer Oil-immersed Transformer

Core Requirements Precision, Consistency, Response Speed Sealing, Resistance to Oil Corrosion

Key Indicators A-Class Precision (±0.15℃) Protection Level IP67/IP68

Installation Position Embedded in winding Inserted below the oil surface in the oil tank

Major Pain Points Phase data inconsistency Leakage, Moisture-induced failure

Companion Instruments BWDK Series BWY / BWR Series

Maintenance Points Annual calibration, check contact Check sealing, verify oil level

1. One-Sentence Selection Guide

Dry-type Transformer: Select Pt100 A-Class Sensor, focus on precision and consistency - the three-phase data must match, and there should be no deviation after replacement.

Oil-immersed transformer: Select IP67/IP68 protection sensors, pay attention to sealing - the transformer must remain completely sealed when submerged in oil for a long time without any leakage to ensure safe operation.

Summary: The temperature monitoring of dry-type transformers and oil-immersed transformers focuses on different aspects due to their structural differences. The dry-type core focuses on "accuracy and consistency", while the oil-immersed core focuses on "sealing". Understanding the core differences between these two types of sensors is essential to equip transformers with a pair of reliable "eyes" to safeguard the safe and stable operation of the power system.