JPS64887B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cable insulated connection for power cable sheath circuit stranding, and more particularly to an AC cable insulated connection for an OF cable or a cross-linked polyethylene power cable having a metal shielding layer and an outer semiconducting layer. The present invention relates to a cable insulated connection part suitable for a laid line employing a cross-bond grounding method that reduces sheath circulating current flowing through the metal shielding layer of a power transmission system.

In AC power transmission systems, conventionally, in order to reduce sheath circulating current, the metal shielding layer of the cable has been cut off at certain lengths to provide cross-bond grounding.

By the way, conventionally, when cutting the edges of the metal shielding layer at the cable connection part, the external semiconducting layer was also removed, and considering that the electric field from the cable conductor side is likely to concentrate at the edge, the external semiconducting layer was removed. An insulating reinforcing layer was provided at the edge of the semiconductive layer and the metal shielding layer. For this reason, construction work required considerable cost and time.

Furthermore, conventionally, the insulated connection part of a cable has a structure that completely insulates the external semiconducting layer in consideration of abnormal situations, and has a structure that can withstand DC withstand voltage or impulse withstand voltage of several tens to hundreds of KV. It was common. However, normally only a voltage of several tens of volts is applied to an insulated connection part, and even in an abnormal situation, essentially no high voltage is applied to the insulated connection part if some kind of protection device operates well. Therefore, on the premise that high voltage is not applied at all times or during abnormal conditions, it may be possible to simplify the structure of the insulated connection portion.

Based on the above findings, there is a concept of cutting only the metal shielding layer and not cutting the outer semiconductive layer. (Utility Model No. 55-40965, Utility Model 55
(Refer to No. 112426) According to such a structure, since the outer semiconductive layer is not edged, the electric field will not be concentrated, so there is no need to intentionally provide an insulation reinforcing layer, and the construction work is simply a matter of forming the metal shielding layer. The process is as simple as removing a portion of the cable, greatly reducing installation time and making it as reliable as the cable itself.

However, while electric field concentration does not occur, if an abnormal surge voltage enters the cable system or a ground fault current flows into the sheath circuit due to a system fault, a large voltage will be generated in the external semiconducting layer. The semiconducting layer is burnt out or deteriorated, and
In the worst case, the insulating layer may also burn out or deteriorate, making it impossible to use it further.

The present invention has been made in view of the above-mentioned circumstances, and is intended to effectively solve the problem of burnout or deterioration of the external semiconducting layer due to the invasion of abnormal surge voltage and ground fault current during system faults, and to provide a long-lasting solution. The purpose of this invention is to provide a cable insulated connection part that can ensure stable insulation properties.

The cable insulated connection part of the present invention is formed for sheath twisting in order to cancel the external sheath circulating current in a three-phase AC power transmission cable system having an external semiconductive layer, and is made of metal with the external semiconductive layer connected. Only a portion of the shielding layer is removed, and a surge arrester and a saturable reactor are connected in parallel between the ends of both metal shielding layers.

An embodiment of the cable insulated connection part of the present invention will be described below with reference to FIGS. 1 to 3.

1 is a cable, 2 is a cable metal shielding layer (external sheath circuit), 3 is a jumper wire, 4 is an insulated connection part, 7 is an insulating layer of the cable, 8 is an external semiconducting layer,
9 is a metal shield electrode (insulated connection part electrode terminal). As shown in Fig. 1, in a cable system in which the sheath circuits of the cables 1 of the U, V, and W layers are twisted, each end of the cable metal shielding layer 2 of the insulated connection part 4 is connected to the outside. It is connected to the semiconducting layer 8 via a metal shield electrode 9, and a gearless arrester 5 and a saturable reactor 6 are connected between the metal shield electrodes 9,9. With such a protection device, the gear press arrester 5 operates against surge overvoltage, and the saturable reactor saturates and low voltage occurs against large commercial frequency currents caused by cable ground faults. This becomes a reactance and flows through the reactor, and no overvoltage is applied to this insulated connection.

During constant operation, a small sheath current flows, which increases the reactance of the reactor and generates a voltage of several tens of volts, but the gearless arrester 5 does not operate. In this manner, only the cable outer semiconducting layer exhibits stable characteristics for voltages of several tens of volts, and the structure shown in FIG. 3 can satisfy the requirements for an insulated connection. In this way, the cable conductor is shielded from the electric field, and insulation problems due to electric field distortion due to the insulated connection portion do not occur.

That is, since the saturable reactor 6 has a sufficiently large reactance at the voltage across both ends during normal operation, almost no current flows through the saturable reactor 6, and the sheath circulating current can be significantly reduced. However, if a voltage higher than a certain limit is applied to the saturable reactor 6 due to a ground fault, etc., it will suddenly become saturated and the reactance will become low. Therefore, it is necessary to bypass the large current by, for example, grounding the intermediate tap of the saturable reactor 6. I can do it.

As described above, the cable insulated connection portion of this embodiment is configured, and a conventional completely insulated type insulated connection portion is not required. That is, make an insulated connection,
The structure is simple because only the length of the metal electrode needs to be removed, the reliability of the insulation is increased, and the construction time can be shortened. Further, the disturbance of the electric field distribution as shown in FIG. 4 can be prevented as shown in FIG.

In addition, problems caused by intrusion of abnormal surge voltage and ground fault current in the event of a system fault can also be resolved.

In addition, in FIG. 4, 14 is a conductor, and 15 is an electric force line. Furthermore, the shape of the metal shield electrode 9 may be any shape, although in the above embodiment the conductor is wound three times. Furthermore, the edge cutting portion 4 of the metal shielding layer 2
Needless to say, the distance depends on the voltage generated during constant operation.

Figure 6 shows another example, in which the impedance of the cable shielding layer is high and the charging current flows in the length direction, making the shielding effect incomplete, or the voltage of several tens of volts between the electrodes increases long-term stability. When the cable shielding layer is damaged, this is compensated for by providing a reinforcing shielding layer 10 made of a semiconducting layer that is the same as or different from the cable shielding layer, and has the same effect as the above embodiment.

FIG. 7 shows still another embodiment, in which when the current density around the metal shield electrode 9 becomes high and unstable, the metal shield electrode 9 is covered with an electrode reinforcing shielding layer 11 to stabilize the current density. This embodiment has the same effects as the embodiment shown in FIG.

Note that the cloth gear press arrester and the saturable reactor are omitted in FIGS. 6 and 7.

In this way, the outer semiconducting layer 8 may be reinforced with a semiconducting layer of the same or different quality near the edge cutout 4, and furthermore, the metal shielding layer 8 may be reinforced with a semiconducting layer of the same or different quality. If there is a risk of deterioration due to an increase in the current density at the end of the edge cut portion 4 of the layer 2, the shape of the electrode should be changed to an appropriate shape, or
It is effective to reinforce the electrode part with a semiconductive layer.

As described above, the cable insulated connection part of the present invention has a simple structure that prevents disturbances in the electric field and improves the reliability of insulation. Therefore, it is possible to effectively prevent the burnout or deterioration of the outer semiconducting layer and the accompanying burnout or deterioration of the cable insulation layer, which is a major drawback when the outer semiconducting layer is left in place. As a result, stable insulation properties can be ensured over a long period of time, and its industrial value is extremely large.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram of a three-phase AC power transmission cable system using an embodiment of the cable insulated connection part of the present invention, Fig. 2 is a detailed view of part A in Fig. 1, and Fig. 3 is a detailed view of part A in Fig.
FIG. 4 is an explanatory diagram of the potential distribution of the conventional insulated connection part; FIG. 5 is an explanatory diagram of the potential distribution of FIG. 3;
FIG. 7 is a sectional view of the same portion as FIG. 3 of another embodiment of the cable insulated connection portion of the present invention. 1: cable, 2: cable metal shielding layer, 4:
Insulating connection part (edge cutting part), 8: gear press arrester, 6: saturable reactor, 8: outer semiconducting layer, 9: metal shield electrode, 10: reinforcing shield layer.

Claims (1)

[Claims] 1. In an insulated connection part of a cable for sheath twisting that has an outer semiconductive layer and is used to cancel a sheath circulating current, the metal shielding layer is partially cut and removed leaving the outer semiconductive layer. A cable insulation connection part characterized in that a gear press arrester and a saturable reactor are connected in parallel between the ends of the removed metal shielding layer. 2. The cable insulated connection portion according to claim 1, wherein a reinforcing shielding layer is provided on the external semiconductive layer.