Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
1998-02-03
2001-11-06
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S522000, C324S547000
Reexamination Certificate
active
06313640
ABSTRACT:
BACKGROUND
This invention relates to a system and method for diagnosing and measuring partial discharge. More particularly, this invention relates to a system and method for diagnosing and measuring partial discharge on-line in a power transmission system and for diagnosing and measuring partial discharge off-line in a high voltage device.
Power transmission systems often suffer from partial discharges due, for example, to faults in the insulation in a high voltage device in the system, loose terminal connections, floating particles, discharges from the transmission lines, etc. These discharges typically result from an electrical stress which locally exceeds a critical value of the dielectric system within the high voltage device. The discharge is considered to be “partial” because it does not bridge the entire dielectric system, causing an undesirable power arc, but merely discharges a small volume of the dielectric system.
Though a partial discharge has a small energy content, it can cause progressive deterioration of the insulation in the high voltage device. If the discharge is continuous, eventually it will be destructive to at least the part of the dielectric system affected by the discharge. Also, the partial discharge can spread and destroy the entire high voltage device. Therefore, it is important to detect partial discharge and determine its source.
Techniques have been proposed to diagnose and measure partial discharge to prevent destruction of the high voltage device. Conventionally, partial discharge is not measured while the high voltage device is installed, i.e., in service, in the power transmission system, due to noise produced by the surrounding equipment and transmitted by the transmission line. Instead, the high voltage device is typically taken off-line, i.e., disconnected from the transmission line, and powered by a motor and generator connected through a regulating transformer.
A conventional test arrangement for measuring partial discharge is illustrated in FIG.
1
. The conventional test arrangement includes a Motor
170
, a High Frequency Generator Set
160
, a Regulating Transformer
110
, and Reactors
120
. The Regulating Transformer
110
and the Reactors
120
are typically contained in a Mobile Trailer
100
, and the High Frequency Generator Set
160
and the Motor
170
are typically housed in a Mobile Trailer
150
. In preparation for the conventional test, a high voltage device, e.g., a Power Transformer
300
, is taken off-line, i.e. the high voltage transmission line supplying power to the Power Transformer
300
is disconnected. The Power Transformer
300
is connected to the Regulating Transformer
110
via the Reactors
120
and transmission lines
180
. During the test, the Power Transformer
300
is powered by the Motor
170
and the High Frequency Generator Set
160
, via the Regulating Transformer
110
, the Reactors
120
, and the transmission lines
180
. The High Frequency Generator Set
160
typically operates between approximately 240 and 400 Hz, and the Motor
170
is typically a diesel motor or a motor powered by an external power source (not shown). An output at a bushing tap of the Power Transformer
300
is detected by a Measurement System
190
. The Measurement System
190
measures the level of the output, and an operator determines whether or not partial discharge is occurring at that bushing tap or terminal of the Power Transformer
300
, based on the measured level.
The Measurement System
190
is typically only capable of measuring the level of an output from a bushing tap of the Power Transformer
300
during a single phase at a time. To measure the level of output during a different phase, the Measurement System
190
must be manually switched.
The conventional test arrangement depicted in
FIG. 1
requires a few days and several trained operators to set up, perform measurements, and disconnect. During the time of the test, the Power Transformer
300
is unavailable for power transmission. Since a high voltage device, such as the Power Transformer
300
, is a key part of an overall power transmission system, the conventional arrangement for measuring partial discharge can cause power supply interruption, particularly for large high voltage devices. In addition, the conventional arrangement requires bulky equipment. Thus, the conventional test arrangement is expensive, inefficient, and inconvenient.
There is thus a need for a method and system for diagnosing and measuring partial discharge which overcomes the drawbacks of the prior art.
SUMMARY
It is therefore an object of the invention to provide a method and system for diagnosing and measuring partial discharge on-line in a power transmission system. It is a further object of the present invention to provide a method and system for determining the type of partial discharge in a convenient and inexpensive manner. It is yet a further object of the present invention to provide a method and a system for diagnosing and measuring partial discharge off-line in a high voltage device, in an efficient manner.
According to a first embodiment, a method and system are provided for diagnosing and measuring partial discharge on-line in a power transmission system. A first detector detects pulses corresponding to partial discharge transmitted via a transmission line in the power transmission system. A second detector detects pulses corresponding to partial discharge output from at least one bushing tap of a high voltage device connected to the transmission line. The first and second pulses are added and/or subtracted, and a diagnostic and measurement system analyzes the results to determine whether or not the high voltage device and/or an external source produces partial discharge, to determine the type of such discharge, and to measure the level of the partial discharge. The diagnostic and measurement system simultaneously analyzes multiple phases of the outputs of the high voltage device, while the high voltage device is energized.
According to a second embodiment, a method and system are provided for diagnosing and measuring partial discharge off-line in a high voltage device. An output from at least one bushing tap of the high voltage device is split into AC and high frequency components. The AC component and the high frequency component are synchronized in a diagnostic and measurement system. The diagnostic and measurement system performs simultaneous analysis of multiple phases of the output of the high voltage device to determine whether the high voltage device produces partial discharge, to determine the type of partial discharge, and to measure the level of the partial discharge.
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Morris, III Arthur Sherman
Nasrallah Chaoukat Nabih
ABB Power T & D Company Inc.
Burns Doane , Swecker, Mathis LLP
Metjahic Safet
Nguyen Vincent Q.
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