What is the role that capacitive voltage sensor plays in GIS transient studies?
Masafumi Yashima, Hideo Fujinami, Tadasu Takuma§
Central Research Institute of Electric Power Industry
A reliable technique is needed for accurate measurement of very fast transient overvoltages such as disconnector-induced surges occurring in GIS which have very steep front and high-frequency oscillation. Recently, capacitive voltage sensors with very short response times have been proposed for this purpose. However, few studies have been made on the dielectric properties of materials used for a low-voltage-side capacitor, as well as the frequency bandwidth of the measuring system.
In this paper a thin mica plate is proposed for a low-voltage-side capacitor which has a surface coated with silver on both sides. This material has been shown to have stable and high static capacitance up to a high-frequency range. A quantitative estimate also is given for the frequency bandwidth of the measuring system. Furthermore, a practical-scale sensor of this type has been developed which can successfully measure simulated disconnector-induced surges of several hundred kilovolts under similar conditions in GIS.
Full Paper can be bought from Wiley Interscience.
I am wondering if and how it can be used for online condition assessment...
Discussion welcomed.
Monday, December 1, 2008
Retrofit and Field Test of Large Power Transformers with Fiber Optic Partial Discharge Sensors(Project Notes)
A tow-year project initiated by EPRI in 2006 has focus attention on Extending the useful life of power transformer so as to increasing the life of the power transmission and distribution infrastructure.
Central of the project features with effective transformer diagnostics and condition assessment.
The project aims to process data from testing in-tank, fiber optic partial discharge sensors and developing better transformer tank penetration methods for sensor insertion.
The project includes:
1. Develop a method and then manufacture and test prototypes of a cost-effective penetrator mechanism and sensor system suitable for retrofit into transformers
2. Obtain proof-of-concept of internal fiber optic pd sensors in an operating transformer with known pd
3. Establish an initial database to characterize the pd signals to the type of fault.
Abstracted and Summarized from EPRI
Central of the project features with effective transformer diagnostics and condition assessment.
The project aims to process data from testing in-tank, fiber optic partial discharge sensors and developing better transformer tank penetration methods for sensor insertion.
The project includes:
1. Develop a method and then manufacture and test prototypes of a cost-effective penetrator mechanism and sensor system suitable for retrofit into transformers
2. Obtain proof-of-concept of internal fiber optic pd sensors in an operating transformer with known pd
3. Establish an initial database to characterize the pd signals to the type of fault.
Abstracted and Summarized from EPRI
SF6 Insulated equipment Online Safety Issue
Online safety diagnostics of SF6 insulated equipment (Notes)
SF6 Gas is widely used in electric power industry, the internal metal kernel, dust and moisture content, are major reasons that lead to GIS fault. When there is conductive material within equipment, partial discharge produces abnormal noise, vibration and discharges with small light, in the phenomena of decomposition of SF6 gases.
Partial Discharge (PD) rises big concern for GIS, GCB and GIT.
Major Techniques employed for PD.
1. measuring electromagnetic wave to locate and judge the pd level.
2. UHF measurement and location.
3. High-frequency earthy current testing.
4. Sound tranmission and vibration test.
5. Chemical method, to analyze composition of sf6 Gases (HF/SO2/SOF2)
Actually there exists no effective method that can fix the problem well. There are both benefits and defects. among the methods, UHF is most popular at the present, but it is still difficult to measure the pd level and the cost is relative high.
Two extra research that complements the method
1. GIS discharge model or function( within or outside GIS)
2. Discharge Data Process to identify faults.
Also there are research that employs ultrasonic fault detection method which seldom sees the application.
J.ZH
Simplified Notes from
IEEETM Central Source
SF6 Gas is widely used in electric power industry, the internal metal kernel, dust and moisture content, are major reasons that lead to GIS fault. When there is conductive material within equipment, partial discharge produces abnormal noise, vibration and discharges with small light, in the phenomena of decomposition of SF6 gases.
Partial Discharge (PD) rises big concern for GIS, GCB and GIT.
Major Techniques employed for PD.
1. measuring electromagnetic wave to locate and judge the pd level.
2. UHF measurement and location.
3. High-frequency earthy current testing.
4. Sound tranmission and vibration test.
5. Chemical method, to analyze composition of sf6 Gases (HF/SO2/SOF2)
Actually there exists no effective method that can fix the problem well. There are both benefits and defects. among the methods, UHF is most popular at the present, but it is still difficult to measure the pd level and the cost is relative high.
Two extra research that complements the method
1. GIS discharge model or function( within or outside GIS)
2. Discharge Data Process to identify faults.
Also there are research that employs ultrasonic fault detection method which seldom sees the application.
J.ZH
Simplified Notes from
IEEETM Central Source
The Role short circuit impedance plays in Power Transformer Assessment
Short Circuit Impedance (SCI) refers to equivalent impedance from one side of Power Transformer (PT) with another side being short-circuited.
The main part of SCI is inductive value, so sometimes it can approximates to leakage inductance.
When testing the SCI, allow one side (ofen secondary) winding be short-circuited, and applies test voltage from another side winding (ofen primary), and then measure the impedance using VA or PQ method.
SCI can be used for frequency response test, with the help of equivalent model, to analyze defect of PT, such as winding deformation, internal insulation and core characteristics.
To analyze the data
Three phase comparision of impedance, periodic comparison and historic comparison are methods usually used to comprehensively characterize structural information of PT.
Also from a point of view to assess PT operation conditions, SCI is an improtant factor that help make medium or long time maintenance decisions.
J.ZH
Notes of Pusala Technology
成都普莎拉科技有限公司
IEEETM Central Source
The main part of SCI is inductive value, so sometimes it can approximates to leakage inductance.
When testing the SCI, allow one side (ofen secondary) winding be short-circuited, and applies test voltage from another side winding (ofen primary), and then measure the impedance using VA or PQ method.
SCI can be used for frequency response test, with the help of equivalent model, to analyze defect of PT, such as winding deformation, internal insulation and core characteristics.
To analyze the data
Three phase comparision of impedance, periodic comparison and historic comparison are methods usually used to comprehensively characterize structural information of PT.
Also from a point of view to assess PT operation conditions, SCI is an improtant factor that help make medium or long time maintenance decisions.
J.ZH
Notes of Pusala Technology
成都普莎拉科技有限公司
IEEETM Central Source
How to enlarge leakage inductance for experiment
Leakage Inductance Issue
It is determined by structure of transformers, not easy for change. a possible way is adding inductance in series with the primary (high voltage side), so as to increase the voltage that applies on the transformers.
The principle behind this the series inductance be in series with equivalent capacitance, but it requires that the insulated voltage level of series inductance should be high enough.
Also increase the gap between winding and core, or between different windings can also enlarge leakage inductance.
Leakage inductance is supposed to be controlled in low value with consideration of applications. And in practice it is not easy to measure and assume, but most of the study and application consider that to be a constant value (due to what kind of use)
IEEETM Notes
It is determined by structure of transformers, not easy for change. a possible way is adding inductance in series with the primary (high voltage side), so as to increase the voltage that applies on the transformers.
The principle behind this the series inductance be in series with equivalent capacitance, but it requires that the insulated voltage level of series inductance should be high enough.
Also increase the gap between winding and core, or between different windings can also enlarge leakage inductance.
Leakage inductance is supposed to be controlled in low value with consideration of applications. And in practice it is not easy to measure and assume, but most of the study and application consider that to be a constant value (due to what kind of use)
IEEETM Notes
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