Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2002-01-15
2002-12-17
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S082000, C363S090000
Reexamination Certificate
active
06496391
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a power supply unit that supplies power to a measuring instrument for measuring various data of plant equipment or a watching device at a site where various plants are located.
2. Background Art
In a large-scale plant using electrical equipment, such as electric motors or transformers, for example, various plant facilities, such as power plants or water treatment plants, and the like, it is essential to secure reliability of the plant and improve rate of operation. That is, in such a large-scale plant, data of the set-up electrical equipment is collected to serve as information concerning operation, and operating conditions are subject to watch to immediately cope with anything abnormal that has been detected.
For such purposes, it is a recent trend to introduce an equipment condition-watching device for watching the conditions of the equipment so that various data are measured from the electric-power equipment, electrical equipment and the like installed in the plant. The data are then observed, and conditions of the equipment are watched or analyzed on the basis of the contents thereof.
The equipment condition watching device for watching the conditions of the equipment is directed not only to machine/electrical equipment such as electric motors, electric generators, pumps, valves, and piping but also to calculators and printed boards built into the equipment and measuring instrument.
There have been conventionally two types of such equipment condition watching devices for watching the conditions of the equipment. One is a device that is located close to the electrical equipment to be watched. This device measures data of the equipment to be watched regularly or at arbitrary times, thereby watching the conditions of the equipment at the time of measurement in substitution for a patrol carried out by an operator in the plant (the device is hereinafter referred to as a detecting device). The other is a device that measures data of the equipment to be watched on line at all times via a plurality of the detecting devices, thereby watching the conditions at all times (the device is hereinafter referred to as a central control device). The detecting device and the central control device are both located, e.g., on the site of the same plant. However, several detecting devices are widely placed in a scattered manner in the so-called site, while the central control device is located in a centralized manner in the so-called control building or the like. Both of them are located within a relatively short distance from each other. As a result, in order to transmit the collected data, a method of transmission without construction of a power line such as radio system can be easily employed.
Now, in order to operate the detecting device, a power supply is necessary as a matter of course. However, most of the detecting devices usually belong to a category of so-called light electric appliances and are operated at an extremely low voltage and a very small current. On the other hand, there is a lot of electrical equipment to be watched which can be operated at a high voltage and a large current. Therefore, it is often the case that although the device to be watched is an electrical equipment, an appropriate power supply for the detecting device is not available at the site of installation.
As a matter of course, it may be said possible to obtain a low voltage from the electrical equipment to be watched by a well-known method such as using a voltage-reducing resistance or transformer. Actually, however, for the purpose of securing voltage endurance, cost effectiveness is exceedingly bad, and moreover it is difficult to prevent invasion of a surge voltage resulting in deficiency in practical use. Thus, to provide a power supply, it becomes necessary to lay a power supply cable additionally as a power supply for measurement, or to employ a battery; otherwise electric power must be generated at the site utilizing, e.g., a solar battery. However, in order to lay and connect the power supply cable to the detecting devices widely scattered in the plant, a large cost is required. Moreover, the battery may bring about the trouble of maintenance or replacement. As for the solar battery, battery life is restricted, and a place for installation is so restricted that the solar battery cannot be used in this field of art.
As a method to solve these problems, Japanese Patent Publication (unexamined) No. Hei. 6-58960 proposed a power supply unit.
FIG. 9
is a schematic diagram of a known power supply unit which is similar to that disclosed in the above-mentioned gazette and which obtains a power via a current transformer used as a power supply for watching a transmission line.
FIG. 10
is specific diagram of such a circuit. In
FIG. 9
, reference symbol A designates a power supply unit. Reference numeral
81
designates a power line such as a distribution line. Numeral
82
designates a current transformer taking a power supply power from the power line
81
in a non-contact manner. Numeral
83
designates an AC current control circuit. Numeral
84
designates a rectifier circuit. Numeral
85
designates a voltage detection/control circuit.
The power taken from the current transformer
82
needs to be supplied as a stable power supply. This power control means is comprised of the AC current control circuit
83
, the rectifier circuit
84
and the voltage detection/control circuit
85
in
FIG. 9
, and a circuitry thereof is specifically shown in FIG.
11
. In the drawing, a resistance
86
in the AC current control circuit
83
and a condenser
87
form a protective circuit for protection when an abnormal voltage such as surge is generated. Numeral
88
designates a triac. Numerals
89
a,
89
b
are phototransistors. The rectifier circuit
84
is a full-wave rectifier circuit, and an output thereof is connected to circuits such as constant voltage diode
90
and light-emitting diodes
91
a,
91
b
for protection against over voltage in the voltage detection/control circuit
85
. Thus, when a DC output from the rectifier circuit
84
exceeds an inverse voltage of the constant voltage diode
90
, a current flows through the light-emitting diodes
91
a,
91
b
to cause them to emit light. By means of these signals of light, the phototransistors
89
a,
89
b
are operated to feed a current through a gate of the triac
88
. By this current, an anode and a cathode are brought into short circuit causing an input of AC to be interrupted. However, the triac
88
will be recovered by means of zero cross point of AC and will supply power up to a next over voltage.
The conventional power supply unit is arranged as mentioned above so as to control Ac. Therefore, even if the primary current varies, any over voltage is not outputted. However, the voltage detection/control circuit
85
operates at the moment when a value of a voltage waveform reaches to a voltage V
90
of the constant voltage diode
90
, and the AC control circuit
83
operates so as to surpass the output voltage. Therefore, as shown in
FIG. 11
, as to the output waveform, duration of the waveform becomes smaller as the primary current augments. As a result, as shown in
FIG. 12
, an average value of the output voltage shows such a characteristic as to be lowered as the primary current augments, above a level of the operation of the triac. In
FIG. 11
, numeral
93
is a waveform of the output voltage of the transformer
82
when the primary current is small. Numeral
94
is a waveform of the output voltage of the transformer
82
when the primary current is large. Numeral
93
a
is a waveform of the output voltage after operating the triac
88
on the waveform
93
thereby interrupting the waveform. Numeral
94
a
is a wave form of the output voltage after operating the triac
88
on the waveform
94
thereby interrupting the waveform.
Therefore, the range of the primary current magnitude sufficient for obtaining a stable voltage output is narrow. Even when employing a circu
Hattori Takayuki
Ikeda Ikuo
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Vu Bao Q.
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