Transformer Thermometer
Transformer Thermometer
The thermometer is used to measure the temperature of transformer oil. These products are generally installed on the transformer to measure the high temperature of the oil. The high oil temperature is measured directly through a sensor installed on the tank cap.
The coil hot spot is assumed to be near the top of the coil where it is surrounded by oil. Therefore, this product measures the oil temperature, but the temperature difference between the coil and the surrounding oil must also be added to it.
The coil thermometer actually consists of an oil temperature measuring sensor and a thermal resistance (heater) wrapped around it. This heater is fed through a current transformer, with the sample current passing through the transformer, which leads to an increase in the temperature around the sensor.
Power transformers are vital components in a transmission system. The work to keep this equipment in dependable operating conditions depends a lot of its system to measure oil and winding temperature. It is known that high temperatures cause accelerated aging of the transformers and their inaccurate measurement limits transformer loading. However, so far, the application of digital temperature monitoring systems was strongly limited by the absence of reliability in the application of electronic devices directly in the big transformers, in general due to many cases of triggering with error and even failure in its electronic circuits. In this paper we present the solution based on modernization of the thermal protection, applying a micro-controlled of digital measurement system of the oil temperature of the oil and power transformer winding at the CTEEP.
With the modernization of the transformer thermal protection, it was to save in maintenance costs and improve the loading control of the transformer. The experience showed the feasibility of applying the digital technology in the existing and new transformers and helped to establish the minimum characteristics that these digital temperature measuring systems must have so they maintain the reliability level of the power transformers of the company.
Power transformers are the most important pieces of equipment in a substation, and its construction takes into consideration a life expectancy of 40 years. The accessories connected to it do not always have the same longevity.
This is why the maintenance process is a concern, so that it increases transformer operating reliability, and extends transformer service life, resulting, at the same time, in savings in the in the maintenance costs and in a shorter equipment downtime, which makes it a valuable activity in the substation asset management. And part of the work of maintenance team is to ensure that the accessories of the transformer continue working as they should, with measurement accuracy, or are kept in a condition of alarm and triggering that is reliable.
This work will present the solution that was adopted to make the monitoring of the power transformer park temperature at CTEEP feasible. It has an installed capacity of 43,223 MVA and an infrastructure formed by 12,249 transmission line km, 105 substations and over 500 550kV power transformers. The results of the modernization work of the thermal protection of power transformers replacing mechanical thermometers with a micro-controlled digital system to measure the temperature of the oil and winding and control the cooling system in the company transformers.
The most important components in the transformers are iron, copper, insulating oil and insulating materials. Of these, the most fragile one is the insulating material.
The main component of the several solid insulating materials used in high voltage transformers immersed in insulating liquid is cellulose. Among the solid insulating materials, the most commonly used one is paper.
Cellulose is an organic compound, with a molecule made of a long chain of glucose rings, or monomers. Each molecule of cellulose, when it is new, has from 1000 to 1400 glucose rings, connected to each other, as shown in Figure 1.
The most important components in the transformers are iron, copper, insulating oil and insulating materials. Of these, the most fragile one is the insulating material.
The main component of the several solid insulating materials used in high voltage transformers immersed in insulating liquid is cellulose. Among the solid insulating materials, the most commonly used one is paper.
Cellulose is an organic compound, with a molecule made of a long chain of glucose rings, or monomers. Each molecule of cellulose, when it is new, has from 1000 to 1400 glucose rings, connected to each other, as shown in Figure 1.
Extreme heat leads to cellulose fiber carbonization. However, moderate heat as normally happens in transformers, causes the individual monomers to break into the cellulose chain, forming a solid residue and liberating carbon dioxide and water. The degree of polymerization, as expected, is reduced, diminishing the mechanical resistance characteristics of cellulose.
As in a transformer, temperature is not distributed in an uniform way; in general, the analyses of heat effect on the deterioration of the cellulose must take into consideration the temperature of the hot spot, because this is the place where the greatest degradation will take place.
After knowing how temperature acts on the insulating material applied in the transformers, we will see how transformer temperature control is done..
