Development Of Online Monitoring Device For Dielectric Loss Of High Voltage Bushing

High voltage power transformer is an essential voltage conversion equipment in the power systems,and bushing is an important component in the transformer structure,and its insulation fault is one of the main faults of the transformer.Once the bushing fails,it may lead to the shutdown or even serious burning of the transformer.Therefore,it is very important to detect the insulation performance of bushing to prevent the occurrence of transformer accidents.One of the important indexes to measure the insulation performance of capacitive bushing is dielectric loss factor.At present,the traditional off-line measurement method is mostly used to measure the dielectric loss.This kind of method uses manual power outage for maintenance,which costs a lot and takes a long time.It is difficult to find the defects of bushing in time,which is easy to cause the safety hazards.Therefore,for realizing real-time monitoring of the bushing insulation status and ensuring the secure and stable working of the bushing,it is of great importance to study the on-line monitoring of the dielectric loss of the bushing.In this paper,by analyzing the principle of relative dielectric loss measurement method,a distributed monitoring method based on single-phase AC voltage as reference voltage is proposed to measure the relative dielectric loss of high-voltage bushing.The monitoring method is analyzed theoretically based on harmonic analysis algorithm.Based on the monitoring method,the hardware of the monitoring device is developed,and the slave computer program and computer monitoring software are compiled.The monitoring device uses the passive zero flux through transformer to extract the current signal of the end screen of the bushing,and uses the bus potential transformer to obtain the reference voltage signal.The MCU is used as the control core,and the harmonic analysis method and quasi synchronous algorithm are used to process the collected data.The processed data is transmitted to the host computer through the optical fiber,and the host computer software realizes the functions of data operation,display and storage.Based on the above design,two acquisition units were made,and the experimental platform was built in the laboratory to carry out the confirmatory test.The results show that: when the reference voltage is used as the phase reference of the current signal,the phase of the current signal measured by a single acquisition unit is basically unchanged,and the phase difference between the current signals measured by two acquisition units is also constant.When the two acquisition units can not measure the current signal synchronously,the measurement result of the relative dielectric loss is almost not affected,and the error can be ignored,which shows that the monitoring method proposed in this paper is correct.The relative dielectric loss measured by the monitoring device is within ± 0.1%,which meets the requirements of the monitoring standard.Compared with the common transformer,the passive zero flux transformer is less affected by the excitation current,and can obtain the current signal of m A level stably.