ChinSun Bushings with On-Line Monitoring Sensor

On-line monitoring and diagnostics of the bushing insulation is an important measure to evaluate the insulation state and to judge the potential failure probability of the bushing.


ChinSun’s bushing is a capacitance-graded type, in which a well-designed voltage grading structure is obtained by an arrangement of conductive or semi-conductive layers incorporated into the insulating material. This kind of capacitance-graded structure results in a number of coaxial capacitors in series to uniform voltage distribution radially and longitudinally. In fact, this structure is the internal insulation of the bushing (also known as the main insulation or simply called the capacitance core).


In bushing’s service life, the capacitance core may become damp or deteriorated because of defects in production or suffered overvoltage, overheating, mechanical forces etc., which will lead to insulation failure ultimately. It is really important to find out the deterioration before insulation failure occurs. That establishes a task to judge the condition of the main insulation in time. In practice, there are two aspects of this task.


First, we can judge whether the insulation material is damp or deteriorated by measuring the insulation resistance and dielectric dissipation factor. And second, we can estimate whether some capacitors in series have been punctured by measuring the general capacitance, and comparing the newly measured value with the earlier measured ones.


Traditional Preventive Test


Traditionally, in order to ensure their operation reliability, the substation equipments, including the bushings, are periodically tested during power-off maintenance. For bushings, the dielectric dissipation factor and capacitance of the bushing is measured with a Schering bridge under power-off condition. For OIP capacitance-graded bushing, oil samples need to be taken from inside the bushing and to be tested. By comparing the measured results with the factory records or previous measurement data, we can evaluate the insulation state, whether it can be adopted for further operation.


This kind of preventive test is carried out periodically on a regular schedule, which is difficult to reflect the latent failure of the internal insulation in time, and has some blindness. It also wastes a lot of manpower and material resources. Therefore, it cannot fully meet the requirements of safe, economical and stable operation of the power grid.


So, in the technological innovation, it is hoped to use remote on-line monitoring technology to guarantee the reliable operation of substation equipment, which may effectively avoid serious losses caused by equipment failure.


ChinSun Bushings with On-Line Monitoring Sensor


The on-line monitoring device of ChinSun bushing is installed at the operation site of the electrical equipment in the substation. Single set of monitoring device is needed for each group of bushings (three-phase), which can measure the bushing’s dielectric current, and then calculate and monitor the dielectric dissipation factor, capacitance and other insulation characteristic parameters on site. And through the communication bus, these results are digitally transmitted to the substation monitoring host. The monitoring host can control the working status of each monitoring device, read and process their measured data and abnormal information, save data to disk. It can communicate with the upper-grade backstage at any time, i.e. transmit data to it and/ or accept remote instructions from it.


Key Technologies of ChinSun Bushings On-line Monitoring


Signal sampling technology: The small current sensor used by ChinSun Bushings on-line monitoring system has a special design of active zero-flux and Thro-core structure. Long-term operation shows that the sensor has excellent temperature characteristics and strong electromagnetic compatibility. It can meet the equipment sampling accuracy under complex substation field interference.


Digital signal transmission technology: This transmission technology uses a distributed measurement structure, so that every single unit takes measurement at the same time. All the bushings in the substation are measured at the same time, which makes it easy to exclude the impact of external disturbance on the monitoring results.


Digital measurement technology: The monitoring device is responsible for measuring the dielectric current signal and the PT voltage signal. The two signal acquisition systems start synchronously. The A/D converted digital signals are processed by Fast Fourier Transformation (FFT). The fundamental vectors of the detected signals relative to the supply power can be obtained. And the insulation parameters such as capacitance and dielectric dissipation factor tanδ can be calculated.


Compared with traditional maintenance, ChinSun Bushings on-line monitoring technology have many advantages:


  1. No need for periodical power outage and maintenance without signs of equipment damage, which can save a lot of manpower and material resources.
  2. No need for live manual detection on high-voltage equipment, which can ensure personal safety.
  3. It also has the advantages of high measurement accuracy, excellent anti-EMI capability, and strong adaptability to extreme environments.
  4. It can detect potential faults in the insulation in time, so that it can effectively prevent insulation failures, and ensure the safe and reliable operation of the equipment.


How to improve the stability of substation operation? How to strengthen the personal safety and managing ability of maintenance personnel? These are important problems in smart grid construction, and also the focus considerations of ChinSun Bushings in developing to on-line monitoring technology. The condition-based maintenance gradually replaces the time-based maintenance, which is an inevitable trend in the developing process of power system. The ChinSun bushings that utilize on-line monitoring through remote control technology are more in line with the correct direction of future electrical system construction and will become the prospective mainstream products of the substation equipment.