Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-05-22
2002-09-17
Sherry, Michael J. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C219S069180, C702S189000
Reexamination Certificate
active
06452416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for measuring a partial discharge, and particularly to an apparatus for detecting a partial discharge when a high voltage rotating electric machine is out of operation or is in operation.
2. Description of the Related Art
In recent years, the size and number of a rotating electric machines are increasing with the increasing scale of plants in general industry, and thus, due to high reliability required for such an electric apparatus, it is necessary to perform maintenance and inspection in a reliable manner so as to prevent an abrupt accident, such as breakdown, from occurring.
Besides, with the greater part of many apparatuses manufactured in the high level economic growth period, 25 years or more have elapsed since their manufacture, and particularly in these electric apparatuses which have worked for a long period, a request for continuous monitoring during the operation becomes very high for the purpose of preventing an abrupt accident from occurring.
Moreover, the Electric Utility Industry Law in Japan or similar laws in other countries was revised on 1996 or will be revised in the future, so that regulations were or will be relieved so that an attempt at voluntary maintenance is strengthened, and an attempt to extend an interval between periodic inspections to a length of about 1.5 times the conventional interval has been carried out, so as to improve management efficiency. From such a point of view, it recently becomes more important to monitor an insulation state during the operation than in the past, and as a monitoring item, importance comes to be attached to a continuous monitoring technique of a partial discharge indicating insulation properties. In a rotating electric machine, when deterioration such as a crack or peeling occurs in an insulating layer of a stator winding by operational stress, a partial discharge is generated at the deteriorated portion by voltage during operation. The deteriorated state of insulation is comprehended by measuring the partial discharge. In general, since the partial discharge of the rotating electric machine or the like is buried in noise, it is necessary to distinguish the partial discharge from the noise so as to measure only the partial discharge. The noise during the operation is the greatest factor among others to make the measurement of the partial discharge difficult.
Many methods have been used for distinguishing a partial discharge from noise and measuring only the discharge of a deteriorated portion when insulation deterioration occurs.
For example, Japanese Patent laid-Open No. Hei. 3-12574 discloses that a partial discharge at the time of starting a rotating electric machine and a partial discharge at the time of a regular operation are respectively measured, and a difference between them is compared. Besides, there is disclosed an abnormality detecting method in which a command is issued so that a partial discharge during a starting period of a rotating electric machine is input to an appropriate device, which then measures the partial discharge quantity during this period and saves the result of this measurement. Then, the partial discharge at the time of the regular operation is measured, so that the saved partial discharge quantity at the time of starting and the partial discharge quantity at the time of the regular operation are compared with each other to find a difference therebetween.
Moreover, for example, Japanese Patent Laid-Open No. Hei. 1-116463 discloses a partial discharge measuring apparatus for a rotating electric machine, which is provided at a predetermined position of a lead for driving the rotating electric machine or outputting power generated thereby, so that a voltage wave and a current wave in a propagation wave of a partial discharge and noise propagating through the lead are detected to determine their polarities, whereby the travelling direction of the propagation wave in the lead is determined from a combination of the thus determined polarities of the voltage wave and current wave, and the partial discharge and the noise are discriminated from each other to detect only the partial discharge.
Besides, computer-aided methods are conventionally used as an insulation diagnosis method for detecting abnormality of insulation. Japanese Patent Laid-Open No. Hei. 3-238370 discloses such a partial discharge diagnosis method in which in the partial discharge measurement of gas insulation equipment, a neural network is made to previously learn a number of partial discharge waveform patterns and their generation factors, so that a partial discharge waveform detected from the gas insulation equipment is classified into a pattern, and a feature of the extracted partial discharge waveform is inputted to the neural network for analyzing a generation factor of the partial discharge.
Moreover, Japanese Patent Laid-Open No. Hei. 1-191071 discloses a monitoring method for a rotating electric machine, in which a high frequency electric quantity based on a discharge extracted from an electric power supply line of the rotating electric machine is attenuated, before measurement thereof, to a level suitable for detection by a detector through an attenuator in which the relation between an operation amount at the time of performing an attenuation operation of a high frequency electric quantity corresponding to a definite discharge quantity and an attenuated output is confirmed in advance, and then, actual measurement is made.
Besides, in the Electric Society Technical Report Second Part No. 402, there are reported insulation diagnosis methods for other various power plants in operation, or partial discharge measurement methods and apparatuses.
As a typical example of such conventional techniques,
FIG. 7
shows an example of insulation abnormality detection for a rotating electric machine, and the structure and operation of this conventional technique will be described with reference to FIG.
7
.
FIG. 7
is a structural view explaining an abnormality detecting method for a rotating electric machine disclosed in Japanese Patent Laid-Open No. Hei. 3-12574. In
FIG. 7
, reference numeral
1
designates a three-phase electric motor, and three-phase lines
3
are connected to windings U, V, and W of the respective phases of a stator
2
. Solid capacitors
4
having little loss at high frequencies are connected as coupling capacitors to the lines
3
. A detector
5
, a changeover switch
6
, a noise filter
7
, and a partial discharge measuring portion
8
are connected to the solid capacitors
4
. The partial discharge measuring portion
8
is constituted by a partial discharge measurement portion
9
for measuring a partial discharge at the time of starting the electric motor
1
and a partial discharge in a regular operation thereof, a discharge input time control portion
10
for controlling a partial discharge input time, and a discharge data storage portion
11
for storing discharge data.
A method of determining a deteriorated state by the thus structured conventional abnormality detecting method will be described. In the foregoing structure, it is assumed that there is a relation, as shown in
FIG. 8
, between the time from the start of the electric motor
1
to the regular operation and load current. From this relation, first, at the time of the start designated by reference numeral
11
, a partial discharge is measured by the partial discharge measuring portion
8
through the solid capacitors
4
. In this case, from
FIG. 8
, the start time
11
is as short as
12
seconds (even in a large machine, the time is 30 seconds), inputting of the partial discharge in the start period is instructed by the discharge input time control portion
10
, the partial discharge in this period is measured, and a measurement result is stored in the discharge data storage portion
11
, so that a partial discharge quantity at the start time is secured.
Next, the motor proceeds to a regular operation designated by reference numeral
1
Kaneda Yoshiharu
Tsurimoto Takao
Urakawa Nobuo
Leydig , Voit & Mayer, Ltd.
Nguyen Trung
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