How to use fiber optic grating sensors to monitor the core temperature of dry-type transformers-INNO

Temperatuurregelaar voor droge transformator van Shenzhen Metro Line 4

In het slimme netwerk, power transformers have become indispensable equipment. The operation of transformers directly affects people’s production and life. In order to better detect the status of transformers, it is necessary to perform controllable detection on transformers. The lifespan of a transformer mainly depends on its insulation capacity. In the actual operation of transformers, the temperature of the transformer affects its insulation capacity, so the lifespan of the transformer is inferred by detecting the temperature of the transformer. During transformer operation, the core temperature can directly reflect the internal temperature, so there is an urgent need for a detection method that can accurately detect the core temperature.

Nu, there are three main methods for detecting the temperature of iron cores: thermal simulation measurement method, indirect calculation measurement method, and direct measurement method. The use of thermal simulation measurement method to measure winding temperature is widely used due to its simplicity, but the simulation process and temperature rise process have significant errors, resulting in inaccurate prediction results that cannot accurately reflect the winding temperature. The indirect calculation method for measuring winding temperature simplifies the thermal characteristic distribution of transformers, and the calculation is simple and has a certain degree of accuracy. Echter, the calculation results may be affected by the hot spots in the windings. The direct measurement method can accurately reflect the trend of temperature changes inside the transformer by directly measuring the winding temperature. Direct measurement methods mainly include electrical signal sensor testing, infrared temperature measurement testing, and fiber optic temperature measurement testing.

The electrical signal sensor measurement method is used to directly measure the internal temperature of transformers, but the electrical signal sensor has a short lifespan and is greatly affected by electromagnetic interference, and the test results cannot accurately reflect the internal temperature. The infrared temperature measurement method uses infrared testing, but it is susceptible to electromagnetic interference and cannot transmit the test results in a timely manner, waardoor het onmogelijk wordt om een real-time monitoringfunctie te realiseren. De glasvezeltemperatuurmeetmethode wordt veel gebruikt vanwege de hoge meetnauwkeurigheid. Echter, wanneer deze methode wordt toegepast op de temperatuurmeting van transformatoren, glasvezelsensoren kunnen alleen op basis van ervaring worden geplaatst, resulterend in problemen zoals een klein aantal temperatuurmeetpunten en een ongelijkmatige verdeling van temperatuurmeetpunten.

In dit artikel wordt een methode voor het monitoren van de kerntemperatuur van een transformatorspoel voorgesteld op basis van glasvezel optische roostersensoren om de problemen van een beperkt aantal temperatuurmeetpunten aan te pakken, ongelijkmatige verdeling van testpunten, en het onvermogen om meetresultaten in realtime te verzenden bij de huidige directe meetmethoden. This method can improve the current level of internal temperature detection in transformers, increase the service life of transformers, and reduce the failure rate of transformers.

1. Principles of grating sensors
Fiber Grating Sensor is a wavelength modulated fiber optic sensor that obtains sensing information by modulating the fiber Bragg wavelength with external physical parameters. Fiber optic grating sensors have advantages such as anti electromagnetic interference, good electrical insulation performance, klein formaat, en laag transmissieverlies.

Fiber Bragg gratings have thermal optical and thermal expansion effects, which will directly affect the temperature characteristics of fiber Bragg gratings. When the thermal optical effect occurs in the fiber optic grating, the effective refractive index of the corresponding grating will change. Als de roosterperiode verandert, het geeft aan dat het glasvezelrooster een thermisch uitzettingseffect heeft ondergaan. Als de temperatuur en de Bragg-golflengte veranderen, het geeft aan dat zowel het thermische optische effect als het thermische uitzettingseffect worden gegenereerd op het glasvezelrooster.

Fiber Bragg Grating kan niet alleen de temperatuur meten, maar ook spanning. De rekeigenschappen van vezel-Bragg-roosters worden voornamelijk beïnvloed door elastische en elasto-optische effecten. Het elastische effect heeft een aanzienlijke invloed op de roosterperiode van vezel-Bragg-roosters, terwijl het elastische optische effect de effectieve brekingsindex van vezel-Bragg-roostersensoren verandert.

2 Ontwerpmethoden
Het ijzeren kerntemperatuurbewakingssysteem is gebaseerd op glasvezelroostersensoren is hoofdzakelijk verdeeld in sensor-ingebedde transformatoren, temperatuurdetectiesystemen, en sensortransmissiesystemen.

2.1 Temperatuurdetectiesysteem
Traditionele temperatuurdetectie kent problemen zoals problemen bij het meten van de temperatuur, beperkte meetpunten, en zwak anti-interferentievermogen van testmethoden. Daarom, deze studie stelt een methode voor om glasvezelroostersensoren in transformatorkernen in te bedden, het verzamelen van temperatuurgegevens via glasvezelroostersensoren en het verzenden van de verzamelde signalen. Vanwege het kleine formaat en het sterke anti-interferentievermogen van glasvezelroostersensoren, ze kunnen normaal werken in omgevingen met hoge temperaturen en hoge druk, zodat ze volledig in transformatoren kunnen worden ingebed. Ten eerste, het glasvezelrooster wordt voorgerekt met behulp van een glasvezelvoorrekgereedschap, en vervolgens wordt de bediende vezel verguld. Vanwege de temperatuur- en rekkarakteristieken van glasvezelroostersensoren, in order to improve the measurement accuracy of fiber optic grating sensors, it is necessary to reduce the influence of strain characteristics and improve the thermal expansion coefficient to enhance sensitivity. Due to the high thermal expansion coefficient of aluminum alloy, the measurement performance of fiber optic grating sensors can be improved by combining them with the aluminum alloy substrate of the iron core through rigid welding technology. Use tools to perform slotting work on the back of the iron core, with a moderate size that does not affect the normal operation of the iron core. During the process of wrapping copper flat wire with paper, a guiding device is used to guide the optical fiber into the small groove opened by the copper flat wire, while reserving the fiber tail fiber for leading out sensing signals.

2.2 Sensor transmission system
This study adopts wavelength division multiplexing technology and space division multiplexing technology. Wavelength division multiplexing technology is the transmission of two or more signals through different channels on a single optical fiber, without affecting each other. This transmission method allows optical fibers to transmit more information. Space division multiplexing technology combines multiple optical fibers to form multiple channels, each of which is independent of each other, and the signal is transmitted on the corresponding channel. By adopting wavelength division multiplexing technology and space division multiplexing technology, limited optical fibers can be maximally transmitted information, effectively solving the problem of fewer internal temperature measurement points in transformers. Ten eerste, detection data is collected through fiber optic grating sensors, and then transmitted to a demodulator. The demodulator converts the wavelength signal into a digital signal, and the computer receives the signal and displays real-time detection results.

To solve the problem of difficult temperature measurement and few temperature measurement points in transformers, this paper proposes a temperature monitoring method for transformer coil iron core based on fiber optic grating sensors. Embed the fiber optic grating sensor into the transformer core, and use space division multiplexing and wavelength division multiplexing methods to transmit the sensor information to the demodulator. The demodulator converts the wavelength signal into digital information and transmits it to the computer to achieve real-time monitoring function. The simulation results show that compared with the ESSM measurement method, ITM measurement method, and FOTM temperature measurement method, the FGCTM measurement method proposed in this paper can effectively improve the detection accuracy of internal temperature in transformers. Due to its advantages such as small size, sterke weerstand tegen elektromagnetische interferentie, and good insulation, fiber optic grating sensors can continuously achieve real-time temperature monitoring of high sealing and high-voltage equipment, making them suitable for other temperature detection applications.