JPH0336904A - Enclosed switchboard - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a closed switchboard, and particularly to suppressing switching surges of a vacuum circuit breaker housed inside the switchboard.

(Prior Art) As is well known, when a vacuum circuit breaker switches an inductive load current, a switching surge voltage is generated. These opening and closing surges are
There is a surge of several kHz associated with current interruption and a surge of several MHz associated with re-ignition.

CR suppressor is used to suppress these surges.

Lightning arresters, non-linear resistors, etc. have been used. However, all of these surge suppression devices are intended to suppress the voltage to ground, and are not intended to suppress surges of several MHz associated with re-ignition (however, by suppressing the voltage to ground, This has the effect of suppressing the peak value of several MHz surges caused by re-ignition. Journal of the Institute of Electrical Engineers of Japan,
Vol, 93. (See Nα8) On the other hand, since high-voltage motors and the like are connected to the end of the system, regulations regarding impulse withstand voltage have not been included in the standards. If a switching device that generates high-frequency surges, such as a vacuum circuit breaker, is connected to open/close such an electric motor, problems may arise in terms of insulation coordination with the electric motor.

That is, when a surge having a steep wavefront length enters the electric motor, a large voltage is shared by the coil at the eye part of the electric motor. In such a situation, the problem is not the disconnection between the coil and ground (main insulation), but the insulation between the turns inside the coil (interlayer insulation). In the case of AC voltage during constant operation, the voltage sharing between the coils is approximately equal, so only a small voltage is applied between the turns inside the coil, and therefore operation can be performed even with a low glabella insulation level. However, when a surge with a short wavefront length invades, the voltage shared by the coil at the sunrise portion increases. It is known that the shared voltage of this eye part becomes larger as the wavefront length becomes shorter. For example, when the wavefront length is 0.2. It is known that when a surge enters the solar cell, the ratio of the shared voltage at the sunrise portion becomes approximately 90%.

(Problems to be Solved by the Invention) As described above, the purpose of conventionally used surge suppression devices is to suppress surges that occur between the ground and the ground. But like electric motors.

When considering insulation coordination with equipment where there is a large imbalance in the voltage distribution of various parts in response to steep surges and where insulation deterioration is large, it is necessary to suppress the occurrence of steep surges themselves.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a closed switchboard that suppresses the steep surge that occurs when a vacuum circuit breaker is turned off.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a closed power distribution board that houses a vacuum circuit breaker and connects it to an inductive load or a capacitor bank via a cable, in which a ring is installed for each phase near the cable terminal processing section. A magnetic material is installed through the cable.

(Function) The wavefront length of the steep surge when the vacuum circuit breaker re-ignites is determined by the inductance around the vacuum circuit breaker and the surge impedance of the line. Also, the wavefront length at that time will be relaxed as the inductance around the vacuum circuit breaker increases.
By installing a ring-shaped magnetic material in the part of the vacuum circuit breaker where high-frequency surge current flows, the inductance around the vacuum circuit breaker above appears to increase, which alleviates the sudden rise in surge voltage during re-ignition. can do.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a side view showing one embodiment of the present invention.

In FIG. 1, a closed switchboard 10 includes a closed box 11, a vacuum circuit breaker 12 equipped with a vacuum valve 12a and an operating mechanism section (not shown), a main circuit disconnect section 13a on one side of the vacuum circuit breaker 12, and a main circuit disconnect section 13a on the power supply side. A bus bar 15 connected via the circuit conductor 14 and a current transformer 17 connected via the other main circuit conductor 13b and the load side main circuit conductor 16a are housed. A load side cable 19 is connected via the main circuit conductor 16b and the cable head 18, and a ferrite ring (hereinafter referred to as ferrite ring) 20 is inserted near the connection part of the load cable 19 with the cable head 18. Install.

The load side cable 19 has a core wire 21, as shown in FIG.
Insulating layer 22. The ground, 1i 123 and the jacket 24 are arranged coaxially. Ground layer 2 of this load side cable 19
Connect the ground lead wire 25 connected to ferrite ring 2 to
0 is passed through and connected to the ground bus bar 26 provided in the closed box 11. Here, for the ground lead wire 25, the jacket 24 is removed, the ground layer 23 is removed except for a part, and the remaining part is connected from the outside. After this connection, the insulating tape layer 27 is formed by repeatedly winding the insulating tape.

Next, the operation of the closed switchboard configured as described above will be explained. When the vacuum circuit breaker 12 interrupts the motor load, the third
Repeated re-ignition (multiple re-ignition) as shown in the figure may occur. This phenomenon occurs when the current is cut off immediately after the contacts in the vacuum valve open.

This occurs when the contacts in the valve are not sufficiently opened.

For this reason, the transient recovery voltage accompanying the current interruption exceeds the withstand voltage between the contacts, a discharge occurs between the contacts, and at this time the high frequency current flowing between the contacts is extinguished at its current zero point. These phenomena occur repeatedly and the voltage gradually increases. When the vicinity of the re-ignition point where this phenomenon occurs is enlarged, the result is normally as shown in FIG. That is, since the voltage changes rapidly at the moment of re-ignition, it is necessary to consider the line as a distributed constant.

In general on-site power distribution systems, the vacuum circuit breaker and the electric motor are usually connected with a salt cable.

When focusing on one vacuum circuit breaker that has a side-by-side configuration, a similar feeder is connected to the power supply side of the X-empty circuit breaker, and the surge impedance seen from the vacuum circuit breaker becomes extremely small. Furthermore, the vacuum circuit breaker and the bus bar of the closed switchboard in which it is housed have stray inductance. Further, a salt cable is connected to the load side of the vacuum circuit breaker, and its surge impedance is several tens of ohms. Furthermore, the surge impedance of the motor connected to the other end of the salt cable is generally approximately Ω. Taking the above into consideration, the equal-magnification circuit at the time of re-ignition is found as shown in Figure 5. In the figure, the power supply side is a stray capacitance 30 to ground, and the discharge of the contact is simulated by closing the switch 31. The inductance around the vacuum circuit breaker is the power supply side stray inductance (L) 2)
32. Load side stray inductance (L33) 3
3, and the salt cable is represented by the cable 34.Since the surge impedance of the motor is large compared to the surge impedance of the salt cable, it can be ignored in response to steep surges. Without consideration, one end of the cable 34 was left open.

In the equal-magnification circuit shown in the figure, when the switch 31 is closed, the voltage waveform generated between the stray inductance 33 and the connection point of the cable 34 to the ground is as shown in Fig. 6, assuming that the line length of the cable 34 is sufficiently long. become. The time constant J of the rising portion of this voltage waveform can be expressed by the following equation (O). Here, Zo represents the surge impedance of the cable 34.

O) As is clear from the formula, at the time of re-ignition J = (L3.+LJ / Zc...
...In order to alleviate the steep rise in (1), L
, 2°L3ff or Z. It is conceivable to make it smaller.

However, reducing Zo for the purpose of surge suppression is wasteful. Also, L12°L3. teeth,
Since it is determined based on the busbar shape and arrangement, it is difficult to change this in terms of the busbar configuration.

Therefore, by attaching the ferrite ring 20, which is a ferromagnetic material, to a part of the loop through which the high-frequency current flows during re-ignition, as in the above-mentioned configuration, the magnetic flux corresponding to the high-frequency current flowing in the circuit is transferred to the inside of the ferrite ring 20. The magnetic flux linkage between the high-frequency current and the magnetic flux inside the ferrite ring 20 is increased, and the inductance of this part is increased, so that the appearance is as shown in the upper diagram. By increasing the value of +L33, the time constant J of the rising portion can be increased.

According to this idea, the same effect can be expected even if the ferrite ring 20 is installed at any position in the current loop through which the high-frequency current flows. However, installing a structure having such an effect in a live part reduces the insulation distance between ground and phases. Therefore, as described above, in the present invention, the ferrite ring 20 is installed at the cable 19 as shown in FIG. The load side cable can be considered to have stray capacitance distributed over the entire cable between the core wire 21 and the ground layer 23, as shown in FIG. When the switch 31 is closed, the high frequency current 35 flowing through the core wire 21 returns through the ground layer 23 to the switch 31 side. Therefore, in this state, the magnetic flux outside the cable disappears due to the current flowing through the core wire 21 and the ground layer 23, and even if the ferrite ring 20 is placed outside, no significant increase in inductance can be expected.

Therefore, the ground lead wire 3 connected to the ground layer 23 at the terminal part
5 is pulled out through the ferrite ring 20, the ferrite ring 20 makes 1.5 reciprocations as shown in the figure, and a magnetic flux effective for the high frequency current 35 flowing in the circuit is generated within the ferrite ring 20.

Moreover, installing the ferrite ring 20 at the cable terminal section makes the area around the ferrite ring 20 at ground potential, so that the effect of reducing the insulation distance due to the installation of the ferrite ring 20 is reduced.

Therefore, by configuring as described above, the following effects can be obtained. That is, (1) It is possible to alleviate the steep rise voltage at the time of re-ignition.

■ This can be done by modifying a part of the closed switchboard, and it is also easy to adapt to the existing closed switchboard.

■ It is possible to coordinate the insulation between the layers of the motor coil and the re-ignition surge.

Note that in the above embodiment, the load is an electric motor.

It can also be applied to other transformers, capacitor banks, etc.

〔Effect of the invention〕

As explained above, according to the present invention, the rise time of the surge voltage that has a short rise time that occurs when the vacuum circuit breaker is tripped or re-strike is lengthened, and the opening/closing surge of the vacuum circuit breaker is caused to become inductive. It is possible to provide a closed switchboard that reduces a large share of the load on the glabellar insulator.

[Brief explanation of drawings]

FIG. 1 is a side view showing one embodiment of the present invention, and FIG. 2 is a side view showing one embodiment of the present invention.
FIG. 3 is a surge voltage waveform diagram during repeated re-ignition related to the present invention; FIG. 4 is a surge voltage waveform diagram showing an enlarged part of FIG. 3; FIG. 6 is an explanatory diagram showing the operation of the embodiment of the present invention, and FIG. 7 is an explanatory diagram showing the operation different from that in FIG. 6 of the embodiment of the present invention. It is.

Claims (1)

[Scope of Claim] In a closed switchboard that houses a vacuum circuit breaker and connects to an inductive load or a capacitor bank via a cable, in the vicinity of the terminal processing section of the cable. A closed switchboard characterized in that a ring-shaped magnetic body is installed for each phase by penetrating the cable.