JPH09113544A - Current measuring system for substation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand the measurable large-current region without increasing the iron core cross sectional area of a bushing current transformer(CT) by measuring the current flowing in the bushing CT with a photo-sensor. SOLUTION: A solenoid type photo-CT 4 is installed near a bushing CT 2. The photo-CT 4 is constituted of a solenoid coil 5 and a photo-sensor 6, a solenoid coil 5 having the load resistance smaller than that of the rated load is connected to the secondary side of the bushing CT 2, and the photo-sensor 6 is fitted in it. The photo-sensor 6 converts the current flowing in the bushing CT 2 into a light signal and outputs it, and the light signal is sent to a photoelectric converter 8 via an optical cable 7 and extracted as an electrical signal. Only the solenoid coil 5 is connected to the secondary side of the bushing CT 2, and the load resistance of the bushing CT 2 can be reduced. The saturation of the bushing CR 2 hardly occurs in the large-current region, and a large current can be measured.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power plant, a switchyard,
The present invention relates to a current measuring system used in a substation or the like (hereinafter referred to as a substation or the like) to measure a current passing through a bushing and flowing in a line.

[0002]

2. Description of the Related Art Conventionally, a current measuring system using a bushing CT has been used to measure a current flowing through a bushing and a line in a substation or the like. In the current measurement system using the bushing CT, for example, as shown in FIG. 9, the auxiliary CT3 is connected to the secondary side of the bushing CT2 attached to the bushing 1, and the auxiliary CT3 is connected.
The secondary side is connected to a relay or meter.

Generally, the characteristics of a CT with an iron core at a large current are restricted by its burden resistance, and if the specifications other than the burden resistance are the same, the larger the burden resistance, the more the induced electromotive voltage will flow when a large current flows. There is a property that the magnetic flux density of the iron core quickly reaches saturation with an increase in the exciting current. In the conventional current measuring system as shown in FIG. 9, the impedance of the laying cable, the relay, the meter, etc. is limited, so that the burden resistance of the bushing CT2 is also limited, and a large DC transient current is included. In order to accurately measure the current value up to the current, it was necessary to increase the iron core cross-sectional area of the bushing CT2 and reduce the iron core magnetic flux density.

It is not necessary to accurately measure the transient current immediately after the accident when it is simply detected that an overcurrent has flowed in the line or when the accident detection time may be long, and this saturation phenomenon is a serious problem. Does not mean Therefore, in a busbar protection relay system of a substation with a capacity that does not impair the stability of the system in the unlikely event of an accident, a current measurement system as shown in FIG. 9 has been used. However, recently, it has been required to accurately detect the waveform of the short-circuit current immediately after the accident that flows in the line in order to disconnect the relevant accident bus line within a few cycles after the accident has occurred. The short-circuit current that flows in the line in case of an accident is increasing. Therefore, in order to meet these requirements with the conventional current measuring system, the core cross-sectional area of the bushing CT2 must be made very large.
There was a problem that the equipment cost was very high.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and can greatly expand the measurable large current region without increasing the iron core cross-sectional area of the bushing CT. It was made to provide a current measurement system for substations and the like.

[0006]

SUMMARY OF THE INVENTION The present invention, which has been made to solve the above-mentioned problems, is intended to connect a solenoid coil or a resistor having a smaller burden resistance than the rated load to the secondary side of a bushing CT. It is characterized in that an optical sensor is installed inside the device or in a portion capable of detecting a magnetic field or voltage generated in the resistor, and the current flowing through the bushing CT is measured by the optical sensor.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. FIG. 1 is a partial sectional view showing a basic embodiment of the present invention, and FIG. 2 is a circuit diagram thereof. In these figures, 1 is a bushing and 2 is a bushing CT. A solenoid type light CT4 is installed near the bushing CT2. The solenoid type optical CT4 is composed of a solenoid coil 5 and an optical sensor 6, and has a bushing CT2.
A solenoid coil 5 having a smaller burden resistance than the rated load (preferably the burden resistance is 20% or less of the rated load) is connected to the secondary side of the solenoid coil 5, and an optical sensor 6 is installed inside the solenoid coil 5. There is. The optical sensor 6 converts the current flowing through the bushing CT2 into an optical signal and outputs the optical signal. The optical signal is sent to the photoelectric converter 8 via the optical cable 7 and is taken out as an electric signal. The solenoid coil 5 and the optical sensor 6 are housed in a shield case 9. 10 is an airtight terminal.

In the current measuring system of the present invention having such a configuration, since the solenoid coil 5 is only connected to the secondary side of the bushing CT2, the burden resistance of the bushing CT2 is shown in FIG. In addition, it can be set to about 2 / VA, which is about 1/50 of the conventional one. As a result, the bushing CT2 is less likely to be saturated up to a large current range, and the bushing CT2, which was conventionally able to measure only up to 20KA, does not change the cross-sectional area of the iron core at all and measures a large current up to about 100KA. Is possible. In the conventional current measurement system, the bushing CT2
In order to be able to measure a large current up to 100 KA by increasing the iron core cross-sectional area, the iron core cross-sectional area must be about 8 times that of the product of the present invention.

FIG. 3 is a partial sectional view showing a second embodiment of the present invention, and FIG. 4 is a circuit diagram thereof. In this case, a burden resistance type optical CT20 is used on the secondary side of the bushing CT2 instead of the solenoid type optical CT4 shown in FIGS. This burden resistance type optical CT20 is composed of a resistor 21 and an optical sensor 22 having a burden resistance smaller than a rated burden, and the light sensor 22 is attached to a portion capable of detecting a magnetic field or a voltage generated in the resistor 21. There is. Also in this case, since the low-load resistor 21 is only connected to the secondary side of the bushing CT2, the same excellent effects as described above can be obtained.

As described above, the burden resistance of the solenoid coil 5 and the resistor 21 used in the present invention is preferably 20% or less of the rated burden of the bushing CT2. The reason is as follows.

First, assume a bushing CT for a meter of the most common 275KV class with a rated current of 4000A, a rated overcurrent of 50KA, and a rated burden of 100VA. Generally CT for meters
Since the rated overcurrent constant is about 3 times, the CT for this meter saturates at -10% or more at 4000A x 3 = 12000A. When connecting a solenoid coil to this CT, the rated overcurrent is 50
Since KA / 12000A = 4.2, the rated overcurrent increase factor is 4.
If it is 2 or more, it can be used as a general relay. Fig. 10 is a graph in which the horizontal axis is the burden resistance R of the solenoid coil and the vertical axis is the rated overcurrent increase rate n. The burden resistance R at which the rated overcurrent increase rate is 4.2 is found on this graph. And becomes 4.7VA. This corresponds to 4.7% of the CT rated load of 100VA.

Similarly, the rated current of the 275KV class is 6000A.
Assuming a CT with a rated overcurrent of 50KA, the rated overcurrent increase factor is 2.9 in order to be used for general relays.
The load resistance R is 20 VA from the graph in Fig. 10.
This is equivalent to 20% of the CT rated load of 100VA. Rated current of CT of 275KV class is 2000, 3000, 400
Since it is defined as 0, 5000, and 6000A, it is preferable that the burden resistance of the solenoid coil 5 and the resistor 21 be 20% or less of the rated burden of the bushing CT2 in consideration of all of them. Since the burden resistance cannot be 0 VA in reality, it is actually preferable to set the range to 1 to 20%.

[0013]

EXAMPLE A specific application example of the current measuring system of the present invention will be described below. [Embodiment 1] FIG. 5 shows a case where the above-mentioned current measuring system is applied to a busbar protection relay system of a substation. A busbar protection relay 11 is connected to a photoelectric converter 8.
As described above, when the current measuring system of the present invention is used, the overcurrent waveform can be accurately measured up to a large current region, so that the busbar protection relay system that immediately disconnects the faulty busbar when overcurrent flows to the busbar is more appropriate. Can be operated. Moreover, since it is not necessary to increase the iron core cross-sectional area of the bushing CT2, there is an advantage that the existing bushing CT can be used as it is. The solenoid type optical CT shown in FIG.
Instead of 4, the burden resistance type optical CT20 shown in FIGS.
May be used.

[Embodiment 2] FIG. 6 is a diagram in which a busbar protection relay 11, a device relay 12 and a meter relay 13 are connected to the photoelectric converter 8 of the current measuring system of the present invention. Also in this example, there is an advantage that the overcurrent waveform can be accurately measured up to a large current region as in the first embodiment. Further, in the conventional system, each relay needs a bushing CT, and it is necessary to connect each bushing CT and the relay with a cable. According to this embodiment, the number of cables is reduced. There is an advantage that it can be 1/3.

[Embodiment 3] FIG.
The bushing CT2 to which the meter relay 13 is connected is replaced with the current measuring system of the present invention, and the busbar protection relay 11 and the meter relay 13 are connected to the photoelectric converter 8. In the example of FIG. 5, the device relay 12 is connected to the bushing CT of the conventional current measurement system. According to this example, it is possible to construct a busbar protection relay system by using the bushing CT for the existing meter relay 13.

[Embodiment 4] FIG. 8 shows an example in which the current measuring system of the present invention is incorporated in an existing circuit in which the device relay 12 is connected to the bushing CT2. In this case, the bushing C connected to the device relay 12
The solenoid coil 5 is connected in series to the circuit on the secondary side of T2, and the optical sensor 6 is provided in the magnetic field generator or voltage generator inside the solenoid coil 5. A meter relay 13 is connected to the photoelectric converter 8 connected to the optical sensor 6. In addition, instead of this meter relay 13, a busbar protection relay 11
Can also be connected. As described above, since the burden resistance of the solenoid coil 5 is extremely small, even if it is connected to the circuit of the existing equipment relay 12, it has almost no adverse effect. According to this example, since the existing bushing CT2 can be used, the installation space can be reduced. In any of the embodiments, the solenoid type light C
Although T4 is shown, the burden resistance type light C shown in FIGS.
It goes without saying that T20 may be used.

[0017]

As described above, according to the current measuring system for a substation or the like of the present invention, the secondary side of the bushing CT is connected with a solenoid coil or a resistor that bears a much lower load than the rated load. Since an optical sensor is installed inside the solenoid coil or at a portion where the magnetic field or voltage generated in the resistor can be detected and the current flowing through the bushing CT is measured by the optical sensor, the iron core cross-sectional area of the bushing CT is large. It is possible to greatly expand the measurable large current region without changing. Further, since the burden resistance of the solenoid coil and the resistor is extremely small, there is an advantage that it can be incorporated into an existing current measuring circuit.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a basic embodiment of the present invention.

FIG. 2 is a circuit diagram of FIG.

FIG. 3 is a partial cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a circuit diagram of FIG.

FIG. 5 is a circuit diagram of the first embodiment.

FIG. 6 is a circuit diagram of a second embodiment.

FIG. 7 is a circuit diagram of a third embodiment.

FIG. 8 is a circuit diagram of a fourth embodiment.

FIG. 9 is a circuit diagram showing a conventional current measurement system.

FIG. 10 is a graph showing the relationship between the burden resistance R of the solenoid coil and the rated overcurrent increase rate n.

[Explanation of symbols]

1 bushing, 2 bushing CT, 3 auxiliary CT,
4 solenoid type optical CT, 5 solenoid coils, 6
Optical sensor, 7 optical cable, 8 photoelectric converter, 9 shield case, 10 airtight terminal, 11 busbar protection relay, 12
Equipment relay, 13 meter relay, 20 burden resistance type optical CT, 21 resistor, 22 optical sensor

Claims (1)

[Claims] 1. An optical sensor is connected to a secondary side of a bushing CT, which is connected to a solenoid coil or resistor having a load resistance smaller than a rated load, and a magnetic field or voltage generated in the solenoid coil or in the resistor can be detected. Is installed and measures the current flowing through the bushing CT with an optical sensor.