Guide to Selecting Transformer Oil Level and Temperature Controllers: A Comparison of Mechanical and Electronic Solutions

• Oil level thermostat: Designed specifically for measuring and controlling the oil temperature at the top of oil-immersed transformers. It features a mechanical temperature-sensing mechanism that provides independent temperature indication without requiring an external power source. Equipped with multiple sets of adjustable electrical contacts, it provides alarm and trip protection in the event of temperature exceeding set limits.
• Three Key Factors in Product Selection: The temperature measurement range must match the transformer’s operating oil temperature range; the number of electrical contacts is determined based on the control circuit requirements; the mounting interface must match the dimensions of the transformer’s temperature sensor socket and the length of the capillary tube
• For use with a winding thermostat: Oil-immersed temperature sensors monitor the overall thermal condition of the transformer, while winding temperature sensors monitor the maximum temperature of the internal windings. The two complement each other; for critical transformers, it is recommended to install both.

1. Core Functions of the Oil Temperature Controller

The oil-immersed temperature controller measures oil temperature via a temperature-sensing element immersed in the top layer of oil in the transformer tank. When the internal temperature-sensing medium expands due to heat, the resulting pressure is transmitted through a capillary tube, driving the pointer to rotate and indicate the temperature. This mechanical temperature-measuring principle does not rely on a power source and can accurately indicate the transformer oil temperature even in the event of a complete power outage at the substation.

In addition to temperature indication, the oil temperature controller uses a cam mechanism on the pointer shaft to drive a microswitch, thereby generating an electrical signal when the temperature reaches a preset value. Configurable control points include: the start and stop temperatures for the cooling fan or oil pump, the over-temperature alarm temperature, and the over-temperature trip temperature. All temperature thresholds can be freely adjusted within a specified range.

2. Key information to confirm when selecting a model

2.1 Temperature Measurement Range

The normal operating oil temperature ranges vary depending on the transformer’s capacity and voltage rating. When selecting a model, ensure that the temperature controller’s measurement range covers the entire oil temperature range from startup at the lowest ambient temperature to full-load operation. The measurement range should not be too narrow (which could cause the pointer to hit the bottom of the scale and damage the mechanism if the limit is exceeded) nor too wide (which would reduce the accuracy of readings within the normal range).

2.2 Number and Types of Electrical Contacts

The number of contacts depends on the design requirements of the control circuit. Select 2 sets of contacts if only an over-temperature alarm is required; select 4 sets if an alarm and trip are required; and select 6 sets if an alarm, trip, and fan control are required. The contact type (normally open or normally closed) must match the control circuit design. When selecting a model, it is recommended to reserve 1–2 additional sets of contacts beyond current actual requirements to allow for potential future functional expansion.

2.3 Installation Interface Parameters

The parameters that need to be confirmed include: the thread size of the sensor housing (to ensure the sensor can be fully screwed in and sealed), the length of the capillary tube from the top of the transformer to the thermostat’s mounting location (custom lengths are required if the standard length is insufficient), and the type of mounting bracket for the thermostat.

3. Comparison of Oil Surface Thermostats and Electronic Temperature Transmitters

4. Frequently Asked Questions FAQ

4.1 Q: Which should I choose, mechanical or electronic?

Answer: The two are not mutually exclusive. Mechanical temperature controllers are used for local temperature indication and basic protection; they are highly reliable and do not require a power supply. Electronic transmitters are used to transmit temperature signals remotely to a monitoring system. For transformers that require remote monitoring, both mechanical temperature controllers and electronic transmitters can be installed simultaneously, each performing its specific function.

4.2 Q: Is it a waste to choose too many contacts?

A: It’s not a waste. It’s much better to have extra spares on hand than to find yourself short when you need them later. Once a thermostat is installed and operational, retrofitting it with additional contacts later on is far more complicated than simply purchasing a few extra sets of contacts during the initial purchase.

4.3 Q: What are the requirements for capillary routing?

Answer: Avoid sharp bends (the bend radius should be at least five times the diameter of the capillary tube), avoid contact with vibration sources, and avoid external mechanical compression. The capillary tube route should be as short and straight as possible and should be properly supported and protected by a protective sleeve.

Disclaimer: The content of this article is for technical exchanges and reference only, and does not constitute any form of procurement commitment or contract offer. Product technical parameters, configuration programs and prices are subject to the actual signed contracts and technical agreements.

Need advice on selecting a transformer oil temperature controller? Please contact Innotongda for product information and a quote. Service Hotline: 13959168359 (also on WeChat).