Electricity: power supply or regulation systems – For reactive power control – Using impedance
Reexamination Certificate
2000-03-10
2002-05-21
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
For reactive power control
Using impedance
C323S207000
Reexamination Certificate
active
06392390
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a synchronous switching apparatus for use with a multiple phase power system that controls the opening and closing timing of a power switch to suppress the occurrence of exciting inrush currents and surge voltages, which are hard on system equipment such as transformer, shunt reactor, power-transmission lines and capacitor banks.
BACKGROUND ART
In the closing and opening of a power switch, many methods for suppressing transient phenomena that are hard on system equipment have been proposed. For example, “Development of a gas-blast circuit breaker for 1000 kV GIS,” included in The 1994 Electric Society National Symposium Proceedings, pages 1453-1455, describes power switching equipment (circuit breaker) in which as means for suppressing surge voltages generated in system equipment such as transformer and shunt reactor, a resistor on the order of 500 to 1000 ohms is inserted before closing the switching equipment.
FIG. 7
shows the case in which a shunt reactor is energized by using this resistor insertion technique. In
FIG. 7
, (
1
a
), (
1
b
), and (
1
c
) are switching devices provided for R, S and T phases, respectively; (
2
a
), (
2
b
), and (
2
c
) are switching devices for closing or opening the switching device for the R, S and T phases, respectively; (
8
a
), (
8
b
) and (
8
c
) are switches for inserting resistors (
7
a
), (
7
b
) and (
7
c
), respectively, which are connected in parallel with the switching devices for the R, S and T phases, respectively; (
9
a
), (
9
b
) and (
9
c
) are reactor banks to be inserted; (
5
a
), (
5
b
) and (
5
c
) are measuring transformers used for measuring the source voltage of each of the R, S and T phases, respectively; and (
4
) is a control device for issuing closing commands to each switching device (
1
) and each switch (
8
).
When the switching devices of the conventional resistor insertion technique configured in this way are used to energize the reactor banks (
9
), first, the control device (
4
) issues a closing command to each of the switches (
8
a
), (
8
b
) and (
8
c
), and source voltage are applied to the reactor banks (
9
) through the resistors (
7
a
), (
7
b
) and (
7
c
). The currents caused by transient surge voltages upon inserting the resistors are rapidly damped by the resistors. Therefore, a voltage of small amplitude and having the same frequency as the source voltage is applied to the reactor banks (
9
). Subsequently, the control device(
4
) issues closing commands to each of switching mechanism (
2
a
), (
2
b
) and (
2
c
). Then, when the switching equipment is closed, transient phenomena can be suppressed and exciting inrush currents flowing into the reactor banks (
9
) can be also suppressed, because a voltage of the same phase as that of the source voltage has already been applied to the reactor banks (
9
) through the resistors.
However, this method has problems in that the switching equipment is not only comparatively expensive but also large because the method requires that the resistor elements and the switches for inserting the resistors having the capacity needed for each piece of equipment, must be provided inside the switching equipment.
Further, in the case of energizing transmission lines, it is impossible to suppress surges with the inserting resisters if the lines are long. Therefore, when energizing system equipment such as transformer and shunt reactor, in principle, the occurrence of transient exciting inrush currents and surge voltages can be suppressed by energizing at the peak value (an electrical phase angle of 90 degrees) of the source voltage. This is discussed by CIGRE et al. and disclosed in “Controlled Switching”, ELECTRA. NO. 164, (1995) and ELECTRA. NO. 165, (1995).
FIG. 8
shows an operating sequence when a transformer is energized using this synchronous switching apparatus. In
FIG. 8
, (
1
a
), (
1
b
) and (
1
b
) are switching devices provided for the R, S and T phases, respectively; (
2
a
), (
2
b
) and (
2
c
) are switching mechanisms for closing or opening the switching devices for the R, S and T phases, respectively; (
3
) is a transformer to be energized; (
5
a
), (
5
b
) and (
5
c
) are measuring transformers used for measuring the respective source voltage of the R, S and T phases; (
40
) is a phase control device for issuing closing commands to the switch mechanism (
2
) of each switching device (
1
).
When the transformer (
3
) is energized using the synchronous switching apparatus configured in this way, first the transformers (
5
a
), (
5
b
) and (
5
c
) used for measuring the respective source voltage of the R. S and T phases detect the zero points of the respective source voltage of the R. S and T phases. The phase control device(
40
) estimates “a pole-closing time Tc” which is the time until an electrical phase angle of a certain ideal angular phase is reached based on the operating time of the switching mechanism as determined from the temperature, operating voltages and past operating history as shown in
FIG. 9
, and then adjusts “the delay time Td” for outputting a closing signal such that closing may be established at a closing time Ta corresponding to the target electrical phase angle of each of the R, S and T phases, and provides a closing command to each of the switching mechanism (
2
a
), (
2
b
) and (
2
c
). By closing the switching equipment for the transformer (
3
) at the predetermined closing time according to this command, in principle, transient phenomena can be suppressed.
Further, “Development of a gas-blast circuit breaker for 1000 kV GIS”, included in The 1994 Electric Society National Symposium Proceedings, pp. 1453-1455, illustrates a power switch (circuit breaker)” that suppresses surge voltages generated in system equipment, such as power-transmission lines and capacitor banks, by inserting a resistor on the order of 500 to 1000 ohms before closing the switching equipment, as shown in FIG.
10
.
FIG. 10
shows the case of energizing capacitor banks using the switching equipment according to this resistor insertion technique. In this figure, similar reference characters are used to refer to portions that are identical or correspond to those in FIG.
7
. In
FIG. 10
, (
9
a
1
), (
9
b
1
) and (
9
c
1
) show capacitor banks to be energized.
By using the conventional switching devices according to the resistor insertion technique configured as above, when the capacitor banks (
9
a
1
), (
9
b
1
) and (
9
c
1
) are energized, first the control device (
4
) issues a closing command to each of the switches (
8
a
), (
8
b
) and (
8
c
), and source voltage are applied to the capacitor banks (
9
a
1
), (
9
b
1
) and (
9
c
1
) through the resistors (
7
a
), (
7
b
) and (
7
c
).
A current occurring due to a transient surge voltage upon inserting the resistor(s) is rapidly damped by the resistor(s). Therefore, a voltage having a small amplitude and with the same frequency as the source voltage is applied to the capacitor banks (
9
a
1
), (
9
b
1
) and (
9
c
1
). Subsequently, the control device (
4
) issues a closing command to each of the switch mechanism (
2
a
),. (
2
b
) and (
2
c
). Then, when the switching equipment is closed, transient phenomena can be suppressed and exciting inrush currents flowing into the capacitor banks (
9
a
1
), (
9
b
1
) and (
9
c
1
) can also be suppressed because a voltage which is in phase with the source voltage has already been applied to the capacitor banks (
9
a
1
), (
9
b
1
) and (
9
c
1
) through the resistors.
However, this method has problems in that the switching equipment is not only comparatively expensive but also has a large size because this method requires that the resistor elements and switches for inserting the resistors having the capacity needed for each piece of equipment, must be provided inside the switching equipment. Further, in the case of energizing transmission lines, it is impossible to suppress surges by inserting resisters for long transmission lines.
Therefore, when energizing system equipment such as transmission lines and capacitor b
Hidaka Mikio
Ito Hiroki
Kohyama Haruhiko
Laxton Gary L.
Sughrue & Mion, PLLC
Wong Peter S.
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