JPS6256728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a busbar protection device that prevents malfunctions due to ground induced current of an indoor electric station flowing into a stopped line in a busbar system to which a plurality of power transmission lines are connected.

Currently, there are busbar protection devices for electrical stations that use voltage differential methods and ratio differential methods, but in either case, the total amount of current flow in and out of all feeders, bank circuits, etc. of the electrical station is If it is zero, it is assumed that no accident has occurred in the busbar protection section.
Furthermore, when the total sum of inflows and outflows exceeds a certain value, it is determined that an accident has occurred within the busbar protection section, and busbar protection is performed.

This principle will be briefly explained with reference to FIGS. 1 to 3. In FIGS. 1 to 3, BUS1 is a bus line, and feeders 1 to 3 and bank circuits 4 and 5 are connected to this bus line BUS1, respectively. Here, the bus bar protection section means the area below the current transformers CT1 to CT3 in the diagram for feeders 1 to 3, and the bank circuits 4 and 5.
In the figure, it is located above current transformers CT4 and CT5, and each line current taken out by these current transformers CT1 to CT5 is inputted to a bus protection device (not shown).

FIG. 1 shows a case where there is no accident, and the sum of currents flowing in and out of feeders 1 to 3 and bank circuits 4 and 5 is zero according to Kirchhoff's law.

Further, FIG. 2 shows an example of an accident outside the bus protection section in the feeder 1, in which the sum of the current inflow and outflow of each of the feeders 1 to 3 and the bank circuits 3 and 4 is zero, as in the case without an accident.

Furthermore, Figure 3 shows the case of an accident inside the busbar protection section, in which case feeders 1 to 3, bank circuit 5,
The total sum of the currents flowing in and out of each of the four currents has a finite value corresponding to the fault current at the bus fault section.

Therefore, in the busbar protection device, this value is sensed and all disconnectors (not shown) of the feeders 1 to 3 and bank circuits 4 and 5 are tripped to protect the busbar.

By the way, the power transmission system of the above-mentioned system generally has two lines installed side by side, and when a line is stopped, a grounding device for the line is always turned on as a safety measure. Therefore, if the grounding devices at both ends of the stopped line are turned on when one line is stopped, a closed circuit with the earth as the return path is formed. Therefore, when two circuits are installed together, the circuit receives induction from the healthy circuit, and a current (hereinafter referred to as ground induced current) flows through the stopped circuit. Figure 4 is a system diagram of such a power transmission system, showing feeders 1 and 2 shown in Figures 1 to 3 as two-line parallel systems; This indicates a state in which the machine is stopped. 6 is a grounding device provided at both ends of each line of the feeder 2, and 7 is a disconnector for disconnecting both ends of each line from the own electric station bus line BUS1 and the opposite electric station bus line BUS2. Further, I ₂ is the current flowing in the healthy line, and I ₀ is the ground induced current due to the current I ₂ flowing in the healthy line.

However, in the case of the power transmission form shown in Figure 4,
Since the grounding device 6 is within the busbar protection zone, the sum of the ground induced currents has a value equivalent to the ground induced current I ₀ even though there is no accident.
The value is sufficient to cause the busbar protection device to malfunction.
Furthermore, since this ground induced current I ₀ depends on the value of the normal line current, the value of this ground induced current cannot be ignored if it is specified that not only a large-capacity load line but also a nearby fault current passes through.

Therefore, in order to eliminate such a problem, if the line grounding device is installed outside the bus bar protection area, the current transformer will not sense the ground induced current _I0 , so there will be no problem.

However, when installing a switchgear indoors, generally a wall bushing cut out from the wall is used to lead the overhead wires, and a bushing-type current transformer is installed in which the current transformer is attached to the bushing. Install only the device on the line side of the current transformer (outside the bus protection area)
It cannot be installed in This is because bushing type current transformers are smaller and much cheaper than glass type current transformers, and they do not require insulation distance from other equipment, allowing for effective use of space. It is. In addition, gas-insulated switchgear has become widely used in recent years, and when using this gas-insulated switchgear, it is most economical to install the current transformer in the bushing, as in the indoor type switchgear. Not only that, but it goes without saying that when determining the overall equipment layout, economical design is possible when there are fewer restrictions on the relative positions of equipment.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to reduce the current flowing in a healthy line when the grounding device is within the bus protection zone in a bus system in which two or more power transmission lines are connected to the bus. An object of the present invention is to provide a busbar protection device that can prevent malfunctions due to ground induced current even if a ground induced current flows through a stopped line due to this.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 5 shows, as an example, a case where two parallel lines for the feeder 2 in FIG. 2 are connected to the bus line BUS1. That is, in FIG.
A current transformer CT6 is provided in the grounding circuit of the grounding device 6 connected to the inside of the busbar protection section of each line, and a ground-induced current is generated in the secondary circuit of the current transformer CT2 provided in the secondary line. The configuration is such that the connections are made so that the currents cancel each other out.

Therefore, with such a configuration, even if one line of the feeder 2 is stopped and a ground induced current I ₀ flows through this stopped line due to the current flowing in the healthy line, the ground induced current I ₀ causes current transformer CT2 to Since the secondary current is canceled by the secondary current of current transformer CT6 provided in the ground circuit, that is, the secondary current of current transformer CT2
Since the next current circulates as shown in Ioc, the bus protection device does not sense the ground induced current. Also, if the grounding device is disconnected, no current flows in the grounding circuit, and current transformer CT2
It has no effect on the next output.
On the other hand, in a healthy line, the grounding device 6 is not turned on, so the primary current (ground induced current) of the current transformer CT6 does not flow. This prevents the protection device from malfunctioning due to the secondary output of the current transformer CT2 due to the grounding induced current even if the grounding device 6 is provided within the busbar protection section of each line.

Next, other embodiments of the present invention will be described.

Figure 6 shows that when the earthing device 6 is turned on, the disconnector 7 must be
By opening the circuit, the secondary current due to the ground induced current of the current transformer CT2 is prevented from being input to the bus protection device. That is, in FIG. 6, the contacts 8a, 8 that respond to the opening and closing of the disconnector 7
b are connected in series and parallel to the secondary circuit of the current transformer CT2 as shown in the figure.

Therefore, with such a configuration, in the stop line, when the disconnector 6 is opened, the contact 8a provided in series with the secondary circuit of the current transformer CT2 is opened, and the contact 8b provided in parallel is closed. Therefore, even if a ground induced current flows in the stopped line, the secondary current Ios of the current transformer CT2 due to this ground induced current only circulates in the closed circuit and does not enter the bus protection device. Further, when the disconnector 6 closes, the contact 8a closes,
Since contact 8b opens, current transformer CT2 2
The following outputs are applied to the protection device and it is in normal operating condition.

As a result, even if the grounding device 6 is provided within the protection section of each line, it is possible to prevent the protection device from malfunctioning due to ground induced current, as described above.

Figure 7 shows that an auxiliary current transformer CT7 for canceling is provided in the secondary circuit of the current transformer CT2.
is activated or deactivated depending on the opening/closing conditions of the disconnector 7 or the grounding device 6. That is, in Fig. 7, an auxiliary current transformer is connected to the secondary circuit of current transformer CT2.
The primary windings of the CT 7 are provided in series, and the secondary windings are provided in parallel, and both ends of the CT 7 are connected so as to be short-circuited by a contact 8a that opens when the circuit is opened.
Contact 8b, which closes when open, is connected to auxiliary current transformer CT7-2
It is connected in series to the next winding.

Therefore, with such a configuration, when the disconnector 7 is opened, the contact 8a is opened and the contact 8b is closed and the current transformer
A closed circuit is formed in which the secondary circuit of CT2 passes through the primary and secondary windings of the auxiliary current transformer CT7. The next current Ios circulates as shown in the figure and does not flow into the protection device. Also, when the disconnector 7 is turned on, the contact 8a closes, and the contact 8b
is open and auxiliary current transformer CT7 is connected to current transformer CT2.
Next, it is removed from the circuit, and this time the current transformer
The secondary current of CT2 flows into the protection device.

This makes it possible to prevent the protection device from malfunctioning due to ground induced current, as described above.

Although the case where the opening/closing conditions of the disconnector 7 are used has been described above, the same effects as described above can be obtained by combining the opening/closing conditions of the grounding device and other conditions.

Thus, as is clear from the above embodiments, even if the relative position of the grounding device 6 with respect to the current transformer CT2 is in a positional relationship that poses a problem of ground induced current, malfunction of the busbar protection device can be prevented. Can be done.

As described above, according to the present invention, in a bus system in which a plurality of power transmission lines are connected to a bus, an auxiliary device for detecting ground induced current in the grounding circuit of each grounding device corresponding to each line within the bus protection section. A current transformer is provided, and the secondary circuit of the auxiliary current transformer is connected to the secondary circuit of the current transformer corresponding to the line.
Since the connection is configured so that the secondary current is canceled out, even if the grounding induced current flows to the stopped line due to the current flowing to the healthy line when the grounding device is within the bus protection area, this grounding induced current will It is possible to provide a busbar protection device that has a simple configuration and can reliably prevent malfunctions.

[Brief explanation of the drawing]

Figures 1 to 3 are bus system configuration diagrams for explaining the operating principle of the bus protection device; Figure 4 is a system configuration diagram for explaining the power transmission form of the power transmission line connected to the power station bus; FIG. 5 is a system configuration diagram showing an input circuit in one embodiment of the busbar protection device according to the present invention, and FIGS. 6 and 7 are similar systems to FIG. 5 showing other embodiments of the essential parts of the present invention, respectively. FIG. BUS1...Bus line, 1-3...Feeder, 4,
5...Bank circuit, 6...Disconnector, 7...Grounding device, 8a, 8b...Contact, CT1 to CT6...Current transformer, CT7...Auxiliary current transformer.

Claims (1)

[Claims] 1. In a bus protection device that extracts the current flowing through multiple power transmission lines connected to the bus using a current transformer and inputs each of these currents to the bus protection device, A grounding device is installed at each line and is turned on when the line is stopped, and an auxiliary current transformer is provided in the grounding circuit of this grounding device to detect the ground induced current.
A bus protection device characterized in that the secondary circuit of the auxiliary current transformer is connected to the secondary circuit of the current transformer corresponding to the line so that the respective secondary currents cancel each other out.