Partial discharge monitoring of transformer temperature and liquid level, complete guide, solution

Sensor de temperatura de fibra óptica, Sistema de vixilancia intelixente, Fabricante de fibra óptica distribuída en China

Transformer oil temperature monitoring
The Importance of Transformer Oil Temperature Monitoring
Transformer oil temperature is one of the key indicators reflecting the operating status of transformers. During the operation of transformers, internal electromagnetic losses and winding resistance losses are converted into heat, which can cause the oil temperature to rise. Excessive oil temperature may accelerate the aging of transformer oil, reduce its insulation performance, thereby affecting the normal operation of the transformer and even causing faults. Por exemplo, when the oil temperature exceeds the specified limit for a long time, the insulation components in the transformer oil will decompose, producing some gases that may cause an increase in internal pressure and pose a safety hazard. According to relevant standards, for oil immersed transformers with Class A insulation, the maximum allowable temperature is 105 ℃, and the allowable temperature rise is 65 ℃ when the ambient temperature is 40 ℃.

Method of oil temperature monitoring
Temperature measurement: The traditional method is to directly measure the temperature of transformer oil using a mercury thermometer or pressure thermometer. This method is simple and direct, but it requires manual periodic data reading and cannot achieve real-time continuous monitoring.
Fiber optic temperature measurement: Fiber optic temperature measurement technology is a relatively advanced method. It utilizes the temperature sensitive characteristics of optical fibers to place them in suitable positions inside transformers, and obtains oil temperature information by detecting changes in the optical signal in the fibers. This method has the advantages of high accuracy, forte capacidade anti-interferencia, and the ability to achieve distributed measurement, which can accurately monitor the distribution of transformer oil temperature in real time.
Fault diagnosis based on oil temperature monitoring
By monitoring the oil temperature of the transformer, preliminary diagnosis of some faults can be made. Por exemplo, if an abnormal increase in oil temperature is found, it may be due to the overload operation of the transformer, which increases internal losses and generates excessive heat; It is also possible that there is a malfunction in the cooling system, such as a clogged radiator or a faulty cooling fan, which prevents heat from dissipating in a timely manner; It may also be due to local overheating faults inside the transformer, such as winding short circuits. When the oil temperature change rate is abnormal, it may also indicate potential faults in the transformer, such as the appearance of new heat sources in the oil or changes in the heat dissipation channels.

Transformer oil level monitoring
The significance of oil level monitoring
The oil level of a transformer is an important indicator for determining the internal insulation status of the transformer. Transformer oil plays an important role in insulation, heat dissipation, and arc extinguishing in transformers. Excessive or insufficient oil level may lead to a decrease in the quality of the insulation medium, thereby affecting the normal operation of the transformer. If the oil level is too high, it may increase the internal pressure of the transformer, which can easily cause oil leakage and even lead to serious consequences such as oil tank rupture; If the oil level is too low, the heat dissipation effect of the transformer will be affected, and some windings may not receive sufficient insulation protection, increasing the risk of faults such as short circuits.

Method of oil level monitoring
Oil level monitoring: Common types include glass tube oil level gauges and pointer type oil level gauges. The glass tube oil level gauge can directly observe the level of oil, but its accuracy is relatively low; The pointer type oil level gauge converts the change in oil level into the rotation of the pointer through a mechanical structure, making it easy to read the oil level value. When reading the oil level gauge, it is necessary to pay attention to sufficient ambient light, stand in front of the oil level gauge, and accurately observe the scale line and oil level indication.
Sensor monitoring: Automatic monitoring of oil level can be achieved through the use of oil level sensors. Sensors convert changes in oil level into electrical signals, which can be transmitted and processed through a signal transmission and processing system to obtain real-time oil level information and set alarm values. When the oil level exceeds the normal range, an alarm can be issued in a timely manner.
Handling of abnormal oil level
When abnormal oil level is detected, it needs to be dealt with in a timely manner. If the oil level is too high, it is necessary to check whether there are other faults causing oil volume expansion, such as high oil temperature or whether there is excessive oil replenishment. If necessary, oil can be drained appropriately to lower the oil level; If the oil level is too low, the first thing to check is whether there is oil leakage. If there is a leakage point, it needs to be repaired in a timely manner, and then an appropriate amount of transformer oil should be added to the normal oil level.

Transformer winding temperature monitoring
The Influence of Winding Temperature on Transformers
The temperature of transformer windings is one of the key factors affecting the internal insulation of transformers. The temperature of the winding directly limits the load size of the transformer. When the transformer is running, the current passing through the winding will generate heat, causing the temperature of the winding to rise. Excessive winding temperature will accelerate the aging of insulation materials and shorten the service life of transformers. Por exemplo, when the temperature of the winding exceeds the allowable value for a long time, the insulation material will gradually lose its insulation performance, which may lead to short-circuit faults between the windings and seriously affect the normal operation of the transformer.

Methods for monitoring winding temperature
Temperature measurement: Similar to oil temperature measurement, a thermometer can be used to measure the temperature of the winding. Porén, due to the fact that the winding is located inside the transformer, direct measurement is difficult. Polo tanto, indirect measurement methods are usually used, such as measuring oil temperature and estimating the winding temperature based on empirical formulas or specific temperature relationship curves.

Sistema de medición de temperatura de fibra óptica fluorescente: This is a more advanced and accurate method. Fiber optic cables can directly enter the interior of transformer windings and obtain temperature information at various points of the winding by detecting the state of backscattered light in the fiber optic cables. This method can directly measure the hot spot temperature of the winding in real time, with a temperature measurement accuracy of up to 1 grao, and is very suitable for online measurement of large transformer windings.

Winding temperature monitoring and transformer life evaluation
By long-term monitoring of winding temperature, the lifespan of transformers can be evaluated. According to relevant research, the lifespan of transformers is closely related to winding temperature, and for every 6 degrees increase in temperature, the relative aging rate may double. Por exemplo, for a transformer designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98 ℃, which corresponds to “operating at an ambient temperature of 20 ℃ and a hot spot temperature rise of 78K”. By monitoring the winding temperature, the load of the transformer can be reasonably controlled to avoid prolonged operation at high temperatures, thereby extending the service life of the transformer.

Transformer core temperature monitoring
The role of iron core in transformer and its temperature influence
The iron core of a transformer is an important link in the conversion of electricity, magnetism, and electricity, and is one of the most important components of a transformer. During the operation of transformers, heat is generated due to hysteresis and eddy current losses in the iron core, causing the temperature of the iron core to rise. Excessive temperature of the iron core can cause a series of problems, such as a decrease in insulation performance between the iron core laminations, which can easily lead to iron core short circuit faults. If the iron core or clamp is grounded at two or more points, it will form a closed circuit, generate circulating current, further cause local overheating, and even burn out the iron core, damage the winding insulation, and cause damage to the transformer.

Iron core temperature monitoring method
Direct measurement: Install sensores de temperatura de fibra óptica on the surface of the iron core to directly measure the temperature of the iron core. This method can accurately obtain temperature information of the iron core, but it needs to be installed during transformer manufacturing or maintenance, and the installation position of the sensor needs to be reasonably selected to ensure that it can reflect the true temperature situation of the iron core.

The hazards and prevention of abnormal iron core temperature
An abnormal increase in iron core temperature may cause various malfunctions. In addition to the insulation performance degradation and short-circuit faults mentioned above, it may also lead to a decrease in transformer efficiency and an increase in operating costs. In order to prevent abnormal temperature of the iron core, in addition to temperature monitoring, in the design and manufacturing process of transformers, it is necessary to ensure good stacking technology of the iron core, reduce vibration friction, and prevent conductive impurities from entering the interior of the iron core; During operation, regular maintenance checks should be conducted to promptly identify and address factors that may cause an increase in iron core temperature, such as poor grounding of the iron core.

Transformer insulation resistance monitoring
The relationship between insulation resistance and transformer insulation performance
Insulation resistance is one of the important indicators for measuring the insulation performance of transformers. The insulation system of transformers is mainly used to isolate components of different voltage levels, prevent current leakage and short circuit faults. The magnitude of insulation resistance reflects the ability of insulation materials to obstruct current. If the insulation resistance is too low, it indicates that the insulation material may be affected by moisture, aging, damage, etc., which will increase the risk of leakage and reduce the safety and reliability of the transformer. Por exemplo, in humid environments or after prolonged operation, the insulation resistance of transformers may decrease, affecting their normal operation.

Measurement method for insulation resistance
Power outage measurement: This is the most commonly used measurement method. Before measurement, the transformer must be powered off, and there must be obvious disconnection points for each coil outlet. The surrounding area of the transformer must be clean, without grounding objects or operators. When measuring, use a shaking table that meets the voltage level requirements. For transformers with neutral grounding, the neutral point knife switch should be opened before measurement and restored to its original position after measurement. Both before and after measurement, discharge to ground is required. Por exemplo, a 1000-2500V megohmmeter can be used to measure the insulation resistance of distribution transformers. The measurement results and the oil temperature at the time of measurement should be recorded in the transformer file for comparative analysis.
Online monitoring technology: With the development of technology, some online monitoring technologies for insulation resistance have also emerged. These technologies can detect the decreasing trend of insulation performance in a timely manner by monitoring the changes in insulation resistance in real-time during the operation of transformers. Porén, online monitoring technology is relatively complex and costly, but for some important transformers, online monitoring can provide more timely fault warnings.
Analysis and Application of Insulation Resistance Measurement Results
The measured insulation resistance value needs to be analyzed. Generally speaking, the insulation resistance should be compared with the previous test results. If there is a significant change compared to the previous results, such as a sudden drop to 50% or lower of the initial value, further inspection or maintenance of the transformer may be necessary. Meanwhile, the insulation resistance of transformers of different voltage levels and types also has a certain reference range, which can be judged according to relevant standards. Por exemplo, the insulation resistance of oil immersed power transformers has a corresponding allowable range. By comparing the measured value with the allowable value, the insulation condition of the transformer can be evaluated.

Partial discharge monitoring of transformers
The concept and hazards of partial discharge
Partial discharge refers to the discharge phenomenon that occurs in a localized area of the insulation system of a transformer. When there are air gaps, impurities, or uneven insulation inside the insulation of a transformer, discharge may occur in these local areas under the action of an electric field. Partial discharge is not only a precursor to equipment insulation aging, but also an important cause of insulation aging and ultimately insulation breakdown. During partial discharge, phenomena such as electrical pulses, electromagnetic radiation, and ultrasonic waves may cause local overheating and the generation of characteristic oil and gas in transformers, leading to gradual damage to insulation materials and reduced insulation performance. Ultimately, this may cause short-circuit faults in transformers, affecting their normal operation and service life.

Methods for partial discharge monitoring
Ultrasonic testing method: When partial discharge occurs inside the transformer, ultrasonic signals will be generated. By installing ultrasonic sensors outside the transformer, these signals can be detected. This method has the advantages of non invasiveness and insensitivity to environmental interference, but its sensitivity to detecting some weak partial discharge signals may be relatively low.
Pulse current method: Partial discharge generates high-frequency pulse current. By using radio frequency current sensors to detect these pulse currents, partial discharge monitoring can be achieved. This method can directly measure the current signal generated by partial discharge, with high sensitivity, but is easily affected by external electromagnetic interference.
Ultra high frequency (UHF) detection method: Partial discharge occurring in transformer oil and oil/insulation paper has a wide frequency spectrum, which can excite ultra-high frequency electromagnetic wave signals of hundreds or even thousands of megahertz. The signal is obtained through sensors installed at the window opening of the transformer box to achieve partial discharge detection. The ultra-high frequency method has strong anti-interference ability, can locate local discharge sources, identify different insulation defects, has high sensitivity, and can perform long-term online monitoring of partial discharge in transformers and GIS. It is currently a relatively mature method for measuring partial discharge.
The significance of partial discharge monitoring
By monitoring partial discharge of transformers, potential problems in the insulation system of transformers can be detected in a timely manner. During the operation of transformers, if partial discharge is detected early, corresponding measures can be taken, such as adjusting operating parameters, repairing or replacing insulation components, to avoid further development of partial discharge and serious faults such as insulation breakdown. At the same time, analyzing the monitoring data of partial discharge can also provide insights into the health status of transformer insulation, and provide a basis for the maintenance and management of transformers.