How is the winding temperature of an oil immersed transformer measured?

The transformer winding temperature has an important effect on the properties of the insulating layer material. Excessive winding temperature will cause the brittleness rate of the insulating layer material to accelerate, and the dielectric strength can be reduced, which will endanger the reliable operation of the transformer. Therefore, the accurate measurement and real-time monitoring system of the transformer winding temperature is particularly important. Since the transformer winding is in a high potential, the immediate and accurate measurement of the winding temperature must get rid of the problems of the insulation layer and the interference signal. Although the existing scientific research clearly proposes the use of photoelectric sensors to accurately measure the winding temperature, due to its high cost and difficulty coefficient, indirect measurement of the winding temperature is generally used at this stage.

The basic principle of transformer winding temperature measurement:

Generally, the winding temperature measurement of oil-transformed power engineering transformers generally adopts the indirect measurement method based on the "thermal simulation" method. The oil-transformer winding temperature Tw can be equivalent to:

Tw=T0+k*△Two

In the formula, T0 is the high-level oil temperature of the transformer, △Two is the copper oil temperature difference, which is obtained by thermal simulation, and k is the thermal index, which is related to the transformer volume and winding structure.

The detection system is mainly composed of a temperature sensor package, a temperature measurement compensation loop, and a controller. Among them, the temperature measurement compensation circuit and the temperature controller are all in the temperature sensor package, and the temperature sensor package is immersed in the high-level oil of the transformer, which is used for magnetic induction of the high-level oil temperature. The controller consists of two parts: the temperature controller connected to the mechanical watch of the on-site winding temperature, the collected temperature value is reflected in the reading value of the temperature indicator plate; the Pt100 thermal resistance, whose resistance value changes with the temperature change, the collected temperature value It is used as a video surveillance system for sending electronic computer background management.

The transformer winding temperature measurement compensation loop is formed by an adjustable loop and a heating loop connected in series, leading to the secondary end of a dedicated current and voltage transformer. The current I of the secondary side of the current and voltage transformer is proportional to the winding load current. A part of the current I is separated by an adjustable loop, and the other flows through the heating loop, and the current flowing through the heating loop is recorded as Ih. When the winding passes through the load current, the heating resistor in the heating loop causes an additional temperature under the effect of the current Ih. Before the application of the winding temperature detection system, it must be calibrated, that is, the size of Ih is adjusted according to the resistance value in the adjustable loop, so that the temperature caused by the heating loop can simulate the copper oil temperature difference △Two, so that it can be indirectly accumulated by means of accumulation. Measure the winding temperature.