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Online partial discharge measurement service
I. The need to perform online partial discharge measurement
The following article will analyze in detail partial discharge and the need to perform online partial discharge measurements.
In the management and operation of the power system with the criteria of ensuring high reliability, economical and efficient use of electricity, good power quality, and safe and continuous power supply to the loads, the use of appropriate monitoring systems and protection devices is one of the most important issues. Compared with protection methods in the power system, partial discharge analysis (PD) is one of the promising solutions for monitoring and detecting potential problems in the system before it occur. Thanks to the development of other technical fields such as telecommunications electronics, computer science, and signal processing, system protection is becoming more accessible, more effective, and highly sensitive. PD analysis is capable of detecting potential signs of failure in the system in the simplest way.
II. Definition of partial discharge measurement
Partial discharge (PD) is the phenomenon of local dielectric breakdown of a small part of a solid or liquid insulation system under the influence of high voltage. While corona discharge is usually detected by continuous and relatively stable glow or transient discharge in air, partial discharge phenomena in an insulation system may or may not be observed frequently by the eye, and the number of partial discharges in the insulation system is often less than that of natural corona discharge.
PD often appears in gaps, cracks inside solid dielectrics, at the interface between dielectrics and conductors in solid and liquid dielectrics, or air bubbles in liquid dielectrics. The discharge phenomenon is limited to a part of the insulation, it only locally bridges the gap between the electrodes. Partial discharges can also appear along the boundary between different insulating materials.
Partial discharges often occur in gas-filled gaps in the dielectric because the dielectric strength is weak in these locations. Therefore, electrical induction occurs in gaps higher than in other locations in the dielectric. If this induced voltage is higher than the corona inception voltage (CIV), then partial discharges begin to occur.
When partial discharges occur, they rapidly destroy the insulating material and eventually lead to discharges. Partial discharges can be prevented through the design and selection of insulating materials. In high voltage equipment standards, the quality of insulation is assessed by using PD detection equipment during the manufacturing process as well as periodic inspections of electrical equipment. PD prevention and detection are necessary to ensure long-term, safe, and reliable operation of electrical equipment in the electrical system.
Discharge of RMU medium voltage cabinet cable ends due to poor contact
Equivalent circuit of partial discharges
The dielectric combined with the void is described by an alternative diagram as a voltage divider capacitor in parallel with another capacitor. In this diagram C1 is the discharge capacitor, C2 is the series capacitor and C3 is the parallel capacitor.
To determine partial discharge, one can rely on the following methods:
- Method of analyzing the electrical signal created by partial discharge.
- Method of detecting ultrasonic pressure waves created by partial discharge.
Partial discharge
During PD testing, if the partial discharge is very small, it can still be detected immediately, partial discharge is very difficult to measure because of its small intensity and short duration. To determine the partial discharge phenomenon, it is necessary to use the signal conversion on the oscilloscope.
PD lasts for a short period of time and the number of times increases in nanoseconds. On an oscilloscope, the discharge appears as spikes or chaotic pulses. The unit of magnitude of PD is usually picocoulomb.
III. Effects of partial discharge in insulation systems
The effects of partial discharge in high-voltage cables and equipment are very serious and can lead to complete destruction of the insulation system or electrical equipment.
In addition, the effects of PD in solid dielectrics are the formation of many partial discharge branches leading to the appearance of discharge channels, a process called a discharge tree. The repeated discharge process will lead to mechanical damage and destruction of the chemical properties of the insulation material.
Damage is caused by the energy dissipated by high-energy charges and ions, ultraviolet light from discharges, ozone gas attacking the void walls, and decomposing as a chemical destruction process releasing gaseous powder at high pressure. Chemical modification of the dielectric also tends to increase the conductivity of the dielectric.
The increase in electrical stress in the gap region accelerates the breakdown process. Some inorganic dielectrics, including glasses, ceramics, and ceramics, are more resistant to partial discharge breakdown than organic and polymeric dielectrics.
For paper-insulated cables, repeated discharges will change the chemical properties of the paper layers, leading to a decrease in insulation strength and at some point forming local conductive carbonic trees. This will cause local heating of the insulation material and cause the cable to explode.
Therefore, online partial discharge measurement is extremely necessary for the electrical system of the enterprise.
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For more information about the online partial discharge measurement service, please contact:
OTECH JOINT STOCK COMPANY
- Hotline: 1800 9472
- Phone number: (+84) 28 6686 3565
- Email: service@otech.com.vn
- Address: 02 Street 15, Van Phuc 1 Residential Area, Hiep Binh Phuoc Ward, Thu Duc City, Ho Chi Minh City, Vietnam.
