Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-09-28
2002-09-24
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C250S297000, C250S221000
Reexamination Certificate
active
06456095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monitor and a monitor system for monitoring overheating of the materials constituting the interior of a generator and the purity of gas in the interior of the generator.
2. Description of the Related Art
Since generators supply electric power which is important in a community, it is essential to prevent occurrence of accidents in them. For this purpose, there have been used apparatuses for monitoring the gas in generators and detecting occurrence of overheating by which the generators fail.
There have been proposed heretofore monitors for monitoring overheating in the interior of a generator in operation by “Immediate Detection of Overheating in Gas-Cooled Electrical Machines (C. C. Carson et al., IEEE Conference Paper, 71C, p154 (1971)), “The Ion Chamber Detector as a Monitor of Thermally Produced Particles” (G. F. Skala, J. de Recherches Atmospherique, April-September, p189 (1966)), and U.S. Pat. Nos. 3,427,880, 3,573,460, and 3,972,225.
These conventional monitors are roughly divided into a monitor unit and a unit for confirming overheating by supporting the monitor, and the monitor is further divided into two devices using different measuring principles.
The conventional monitors will successively be described below.
FIG. 8
is a view showing a basic arrangement of a conventional monitor described in, for example, “Immediate Detection of Overheating in Gas-cooled Electrical Machines” (C. C. Carson et al., IEEE Conference Paper, 71C, P154(1971)).
In
FIG. 8
, the conventional monitor
1
includes a main body vessel
2
having a pipe
3
connected thereto for introducing the cooling gas in the interior of a generator (not shown) into the vessel
2
, an &agr; ray source
4
for ionizing the cooling gas introduced into the main body vessel
2
, a pair of electrodes
6
and
7
disposed in the vicinity of the gas outlet
5
of the main body vessel
2
, an ammeter
8
for measuring the current flowing between the pair of electrodes
6
and
7
, and a power supply
9
for imposing a voltage between the pair of electrodes
6
and
7
.
Thorium is used as the &agr; ray source
4
. Further, hydrogen gas is used as the cooling gas.
Note that, while not shown, the current value measured with the ammeter
8
can be recorded on a recording sheet and the like.
Next, operation of the monitor
1
arranged as above will be described.
First, the monitor
1
is connected such that hydrogen gas as the cooling gas of the generator is introduced into the main body vessel
2
through the pipe
3
and the hydrogen gas discharged from the gas outlet
5
is returned into the interior of the generator.
Then, the cooling hydrogen gas in the interior of the generator is partly introduced into the main body vessel
2
through the pipe
3
. The hydrogen gas introduced into the main body vessel
2
is ionized by an &agr; ray irradiated from the &agr; ray source
4
. At that time, hydrogen is ionized, and ion pairs, that is, hydrogen ions having a positive charge and hydrogen ions having a negative charge are created. Then, the ionized hydrogen is partly attracted by and reaches the electrode
7
, a current is generated between the electrode
7
and the main body vessel
2
(electrode
6
), and the remaining hydrogen is discharged from the gas outlet
5
, passing between the electrodes
6
and
7
. The hydrogen gas discharged from the gas outlet
5
is returned in the interior of the generator.
When only hydrogen molecules exist in the cooling gas introduced into the main body vessel
2
, the ionized hydrogen easily reaches the electrode
7
and a large ion current is observed by the ammeter
8
because the mass of the hydrogen molecules is very small.
In contrast, when small particles exist in the cooling gas in the interior of the generator, the number of hydrogen ions which reach the electrode
7
is reduced because the hydrogen ion pairs created in the main body vessel
2
bond to the small particles again and lose their charge. Further, while the small particles are ionized at the same time in the main body vessel
2
, they do not almost reach the electrode
7
because it is difficult for the mass of the small particles to largely move. In short, when small particles exits in the cooling gas, the number of ions which reach the electrode
7
is reduced and current measured with the ammeter
8
is decreased.
Reduction of a current value caused by existence of small particles depends on Formula 1 as described in “The Ion Chamber Detector as a Monitor of Thermally Produced Particles (G. F. Skala, J. de Recherches Atmospherique, April-September, p189 (1966)).
−&Dgr;
I=Qe
(1
−Fc
)
rZ/
2&agr; (Formula 1)
where, −&Dgr;I is the reduction of a current value, Q is the flow rate of hydrogen gas, e is the elementary charge, Fc is the ratio of ionized small particles, r is the diameter of small particles, Z is the concentration of small particles in hydrogen gas, and &agr; shows a rebonding constant of ions.
In (Formula 1), since Q, e, Fc and a are constants, when a small particle having a large product of r (diameter) and Z (concentration) exists, a current value measured with the ammeter
8
is reduced by −&Dgr;I as compared with a case in which the small particle does not exist.
Then, the small particles which can be detected with the conventional monitor
1
are specifically small particles having a diameter of 0.001 &mgr;m to 0.1 &mgr;m.
Next, the steps by which the conventional monitor
1
detects overheating in the interior of the generator will be described.
First, the value of a current flowing between the pair of electrodes
6
and
7
is measured with the ammeter
8
in the ordinary operating state of the generator in which overheating is not caused at all in the interior thereof, and the current value is recorded as a current level when the generator operates normally. Usually, the current value is measured successively at all times and recorded on a recording sheet and the like.
When a current value being monitored is lowered at a certain time, it is determined that small particles exist based on the principle shown by the above-mentioned Formula 1. In contrast, it is known that the materials in the interior of the generator generate small particles at the beginning of overheating. Therefore, when it is detected that a current is reduced by a value larger than a certain amount, it is determined that overheating is caused in the interior of the generator and an alarm is issued.
As described above, the conventional monitor
1
is a device for detecting the existence of small particles by the reduction of an ion current and has an object monitoring overheating of the generator by the detection of the small particles. Then, the conventional monitor
1
has only a function for detecting small particles and does not have a function for specifying the materials constituting detected small particles.
Further, the conventional monitor described in U.S. Pat. No. 3,427,880 is a device for detecting the existence of small particles by generating vapor droplets including small particles in cooling gas as nuclei and optically measuring the number of droplets and has an object for monitoring overheating of a generator by the detection of the small particles. Then, the conventional monitor also has only a function for detecting small particles and does not have a function for specifying the materials constituting detected small particles.
As described above, it is difficult for the conventional monitor
1
to specify whether detected small particles are generated by overheating or generated by friction and the like other than the overheating. Thus, a monitor used for determining whether the material in the interior of a generator is overheated or not is proposed in U.S. Pat. No. 3,972,255, and the like.
FIG. 9
is a view showing a basic arrangement of the conventional monitor described in, for example, U.S. Pat. No. 3,972,225.
In
FIG. 9
, the conventional monitor
10
includes a monitor u
Sorita Tetsuji
Takashima Mitsuru
Le N.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Vincent Q.
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