How to use fluorescent fiber optic temperature measurement for switchgear

Principle and usage of fluorescent fiber optic temperature measurement for switchgear

Fluorescent fiber optic temperature measurement for switchgear is an advanced temperature monitoring technology based on the analysis of fluorescence afterglow.

Principle core: Fluorescent substances emit fluorescence energy upon excitation by light of a certain wavelength (excitation spectrum). After the incentive is removed, the persistence of fluorescence afterglow depends on factors such as the characteristics of the fluorescent substance and environmental temperature. This excited fluorescence usually decays exponentially, with the decay time constant being the fluorescence lifetime or fluorescence afterglow time (ns). The decay of fluorescence afterglow varies at different environmental temperatures. The detector can accurately measure the ambient temperature of the probe and provide monitoring and alarm by measuring the length of the fluorescence afterglow lifetime.

Sensor in the usage method: In the switchgear, use a fluorescent fiber optic temperature sensor to achieve temperature measurement. The probe size of this sensor is extremely small and can be directly installed on key components such as busbars, moving contacts, and stationary contacts in switchgear, thus achieving contact measurement. The tail fiber of the sensor is made of soft and sturdy specially designed optical fiber, which has the advantages of high transmission bandwidth, stable signal, anti electromagnetic interference, anti winding, high impact strength, and fast connection. The tail fiber sheath has the characteristics of high temperature resistance, aging resistance, corrosion resistance, insulation resistance, and non adhesion, and can adapt to harsh environments such as high voltage, high temperature, and strong electromagnetic fields.

Measurement and signal transmission: Fluorescent optical fibers (including sensing heads) convert the temperature information of the monitoring location of the temperature probe into optical signals and transmit them to the fiber optic temperature transmitter. The fiber optic temperature transmitter can convert multiple temperature information into digital signals in real time and transmit them to the backend communication software or display head (if configured). In this process, due to the characteristics of electrical insulation, intrinsic safety, and immunity to electromagnetic interference of optical fibers, even if there is significant electromagnetic interference such as electromagnetic radiation, surges, and electrical pulses inside the switchgear, it will not affect the accuracy of measurement and signal transmission.

Operation steps for fluorescent fiber optic temperature measurement in switchgear

1、 Selection and preparation of sensors

Choose the appropriate sensor: Select the appropriate fiber optic temperature sensor (such as a fluorescent fiber optic sensor) based on the temperature range and accuracy requirements that need to be monitored. Ensure that the selected sensors can meet the operating temperature range inside the switchgear. For example, if the normal operating temperature range inside the switchgear is between -20 ℃ and 150 ℃, then it is necessary to select sensor 19 that can accurately measure within this temperature range.

Check the integrity of the sensor: Before installation, it is necessary to check whether the probe, tail fiber, and other parts of the sensor are damaged. Ensure that the optical fiber is not broken and the probe is not damaged, so as not to affect the accuracy of the measurement.

2、 Install sensors

Determine installation location: Install key components inside the switchgear, such as busbars and dynamic and static contacts. These areas are prone to generating heat due to the passage of current and are key areas for temperature monitoring. For example, installing sensors near the connection points of the busbar and the contact points of the contacts can promptly monitor any abnormal temperature rise that may occur in these areas.

Installation method: Install the sensor probe directly on the measured point to achieve zero distance monitoring. Due to the small size of the sensor probe (such as a diameter of about 3mm), it can accurately locate the installation position. During the installation process, it is important to ensure that the sensor is securely fixed to prevent any looseness or displacement that may affect the measurement results.

3、 Connect and configure related devices

Connecting fiber optic: Connect the tail fiber of the sensor to the fiber optic temperature transmitter. When connecting, make sure the connection is firm, and the interface of the optical fiber should be clean and free of dust, debris, etc. to ensure good transmission of optical signals.

Configure transmitters and other devices (if any): If it is a multi-channel temperature monitoring system, it is necessary to configure the fiber optic temperature measurement transmitter, such as setting the sensor numbers, measurement ranges, and other parameters corresponding to each channel. If there is a matching fiber optic temperature measurement system header or upper computer software system, corresponding configuration is also required, such as setting communication parameters (such as RS485 baud rate, data bits, stop bits, etc.), alarm thresholds, etc.

4、 Testing and Validation

Preliminary testing: Conduct preliminary testing after completing installation and configuration. It is possible to determine whether the sensor is working properly and whether the measured value is within a reasonable range by observing the temperature display value on the fiber optic temperature transmitter or display head (if any).

Comparison and verification with known temperature (optional): If possible, other measuring devices with known and accurate temperature (such as high-precision thermometers) can be used to measure the temperature near the sensor, and then compared with the measurement results of the fluorescent fiber temperature measurement system to verify the accuracy of the measurement. If the error is within the allowable range, it indicates that the system installation and configuration are correct; If the error is large, it is necessary to check whether there are any problems in the installation of sensors, equipment connection, and configuration.

How to correctly use the fluorescent fiber optic temperature measurement system for switchgear

1、 Daily monitoring

Real time data viewing: With the help of relevant equipment in the system (such as fiber optic temperature measurement system headers or upper computer software systems), real-time temperature data of various monitoring points in the switchgear can be viewed. For example, through the upper computer software system, monitoring data can be displayed in various forms such as status lights, curves, and tables on the monitoring interface, making it convenient for users to intuitively understand temperature changes.

Comparative analysis: Compare and analyze temperature data from different monitoring points. Under normal circumstances, there may be some temperature differences in different parts of the switchgear. However, if the temperature at a monitoring point is significantly higher than that of other similar parts, or the temperature rises abnormally fast, it may indicate that there are abnormal conditions in that part, such as increased contact resistance, component aging, etc.

2、 Exception handling

Set alarm threshold: Based on the normal operating temperature range of the switchgear and the safety requirements of the equipment, set the alarm threshold reasonably. When the temperature exceeds the set threshold, the system will issue an alarm, such as sound and light alarm, dry contact output, etc., to remind the operator to pay attention. For example, for the contact parts of certain switchgear, if the normal operating temperature is between 50 ℃ and 80 ℃, the alarm threshold can be set when the temperature reaches 90 ℃ to detect overheating in a timely manner.

Troubleshooting: When the system issues an alarm, it is necessary to conduct timely troubleshooting. Firstly, check the corresponding equipment components of the alarm monitoring point for obvious physical damage (such as contact burns, discoloration of the busbar, etc.), and then check whether the connection parts are loose and the contact is good. If the false alarm is caused by a malfunction of the sensor itself, it is necessary to check the connection and damage of the sensor.

3、 Data recording and analysis

Historical data recording: The system should have the function of recording historical temperature data, such as the upper computer software system being able to record the historical temperature information of each contact point in the past month. By analyzing these historical data, we can understand the temperature trend of the equipment and predict possible faults. For example, if the temperature of a monitoring point gradually increases over a period of time, although it has not yet reached the alarm threshold, this trend may indicate that the equipment is about to have problems and requires early maintenance.

Trend analysis: Analyze the long-term trend of temperature data, combined with the operating conditions of the switchgear (such as load size, operating time, etc.), to evaluate the health status of the equipment. For example, if the temperature of the switchgear increases significantly during high load operation, but returns to normal during low load, this may indicate that the equipment has insufficient heat dissipation capacity under high load and needs to consider improving heat dissipation conditions or upgrading the equipment.

Precautions for fluorescent fiber optic temperature measurement in switchgear

1、 Sensor related

Temperature range matching: When selecting sensors, it is important to ensure that they can adapt to the temperature range inside the switchgear. If the temperature range of the sensor is too small, when the temperature inside the switchgear is too high, it may cause damage to the sensor or inaccurate measurement; If the temperature range is too large, it may affect the accuracy of the measurement. For example, for some switchgear operating in high-temperature environments (such as those in the metallurgical industry), it is necessary to choose sensors that can withstand higher temperatures.

Protection of sensors: During installation and use, attention should be paid to protecting the probe and tail fiber of the sensor. Avoid mechanical impact and wear on the probe, and avoid excessive bending, pulling, etc. on the tail fiber. Because these situations may damage sensors or optical fibers, resulting in interruption of optical signal transmission or inaccurate measurements.

2、 Installation and wiring

Installation firmness: When installing sensors, it is necessary to ensure firmness and reliability, especially in environments such as switchgear where vibration may occur. If the sensor is not securely installed, it is prone to looseness and displacement, which can affect the accuracy of the measurement. For example, sensors installed on the busbar can be secured using appropriate fixtures or straps.

Wiring specifications: The wiring of optical fibers should be standardized to avoid contact between the fibers and sharp objects inside the switchgear, and to prevent the fibers from being scratched. At the same time, it is necessary to avoid excessive winding or sharp bending of optical fibers to ensure good transmission of optical signals. If it is a multi-channel fiber optic wiring, it should be properly labeled for easy differentiation and maintenance.

3、 System operation and maintenance

Regular inspection: The entire switch cabinet fluorescent fiber optic temperature measurement system should be regularly inspected, including sensors, fibers, transmitters, display heads (if any), and upper computer software systems. Check whether the sensor measurement is accurate, whether the fiber optic connection is good, whether the transmitter is working properly, and whether the software system has fault alarms. For example, a comprehensive inspection can be conducted once a month or every quarter.

Environmental factors: The impact of the environmental factors in which the switchgear is located on the temperature measurement system should be considered. If the switchgear is in a humid environment, attention should be paid to moisture prevention to prevent moisture from entering the sensors or optical fibers and affecting their performance. If in an environment with corrosive gases, sensors and fiber optic sheath materials with corresponding protective capabilities should be selected.

Examples and Techniques of Fluorescent Fiber Optic Temperature Measurement in Switchgear

1、 Example

Monitoring of a certain substation switchgear: A fluorescent fiber optic temperature measurement system was applied in the switchgear of a certain substation. There are multiple circuits in the switchgear of the substation, and fluorescent fiber temperature sensors are installed on the busbars and dynamic and static contacts of each circuit. Through real-time monitoring of the system, it was found that the temperature of a certain phase contact in one of the switchgear gradually increased over a period of time. Although it did not reach the alarm threshold, by comparing the temperature of other phase contacts in the same switchgear with historical data, it was found that the temperature increase trend was abnormal. The operator promptly inspected the switchgear and found that insufficient contact pressure of the contacts caused an increase in contact resistance, resulting in a rise in temperature. By adjusting the contact pressure of the contacts, the problem of abnormal temperature rise has been solved, avoiding possible equipment failures and power outages.

Factory workshop switchgear monitoring: Due to high load and frequent fluctuations, the switchgear in a certain factory workshop is prone to overheating. After installing the fluorescent fiber optic temperature measurement system, set the alarm threshold to a value determined based on the normal operating temperature and safety margin of the equipment. During a production process, the system triggered an alarm indicating that the temperature of the busbar in a certain switchgear exceeded the alarm threshold. The maintenance personnel immediately inspected the switchgear and found that one of the connecting bolts on the busbar was loose, causing an increase in contact resistance and heating of the busbar. After timely tightening of the bolts, the temperature returned to normal, ensuring normal production in the workshop.

2、 Skills

Multi sensor layout optimization: When arranging sensors inside the switchgear, the layout should be optimized based on the structure and current distribution of the switchgear. For example, for three-phase switchgear, sensors can be installed at key locations of each phase's busbar and dynamic and static contacts, and the density of sensors can be appropriately increased in areas where temperature hotspots are prone to occur (such as near connection points) to ensure comprehensive and accurate monitoring of the temperature distribution inside the switchgear.

Using historical data to predict maintenance: Fully utilize the historical temperature data recorded by the system, analyze the trend of temperature changes, predict potential equipment problems in advance, and develop a reasonable maintenance plan. For example, if it is found that the temperature of a monitoring point increases to a certain extent during the high temperature period every summer, the area can be inspected and maintained before the arrival of summer, such as cleaning the contacts, tightening the connecting bolts, etc., to prevent equipment failure caused by high temperature.

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