JPS633534B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to power cable lines.

Metal sheathed single-core power cable lines generally employ a cross-bond system to reduce circulating current flowing through the sheath. As shown in Fig. 1, two wires are connected to each section sandwiched between two grounded normal junction boxes 2a and 2b provided for each metal sheath 1AS, 1BS, and 1CS of each phase cable 1A, 1B, and 1C. By providing one or more insulated junction boxes 3 and sequentially connecting the metal sheaths 1AS, 1BS, and 1CS of different phase cables before and after the insulated junction boxes using bonding wires 4, the metal sheath 1
The circulating voltage induced in AS to 1CS is canceled out, and the current flowing in metal sheaths 1AS, 1BS, and 1CS is suppressed.

However, in actual power transmission lines, it is difficult to make the spacing between each junction box and each cable the same due to topography and other reasons, and because the spacing between the junction boxes is different, the voltage induced in each metal sheath cannot be completely controlled. I can't cancel it. Therefore, in some cases it is a reality that rather large currents flow through the metal sheath and the sheath losses are still considerable.

In order to suppress this sheath current, there is an idea of inserting a reactor in the middle of the cross bond wire, but when high frequency waves such as lightning surges and switching surges come, abnormally high voltage is generated in this part. Therefore, in order to suppress this, a new anti-corrosion layer protection device must be installed on both sides of the reactor, which is quite expensive. On the other hand, as a protection circuit for the cable sheath anti-corrosion layer, there is an idea of connecting the arrester closely to both ends of the insulated junction box as shown in Figure 2, but in actual lines, due to space problems, the arrester is connected insulated. These protective devices cannot be installed closely to the box, and these protective devices must be installed using long lead wires. Therefore, if the voltage drop due to the inductance of this lead wire becomes very large, it may become impossible to protect the anti-corrosion layer.

The present invention was developed in view of the above circumstances, and its purpose is to greatly reduce the circulating current flowing through the metal sheath and protect the sheath anticorrosion layer from lightning surges, etc. The purpose is to provide a new power cable line.

That is, the gist of the present invention is to use a coaxial cable as a metal sheath cross bond wire, attach a reactor to the outer periphery of the coaxial cable, and attach a reactor to suppress the sheath current.
An arrester is attached to one end of the coaxial cable between the core wire and the sheath.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be specifically described below with reference to drawings showing embodiments.

Figure 3 shows an example of a cross bond, in which the core wires 51, 51', 51'' of the coaxial cables 5, 5', 5'' and the sheaths 52, 52',
This is done by connecting 52'' as shown in Figure 3.
That is, the sheath 52' of another coaxial cable 5' is connected to the metal sheath on one side of the insulated junction box via the core wire 51 of the coaxial cable 5, and the sheath 52' of the coaxial cable 5 is connected to the metal sheath on the other side. A core wire 51'' of another coaxial cable 5'' is connected through the cable. A reactor 7 is provided in the sheath of each coaxial cable 5, 5', 5'' to suppress cable sheath current. Core wires 51, 51', 5 of each coaxial cable 5, 5', 5''
1'' and the sheaths 52, 52', 52'', an arrester 6 is provided. Assuming that a lightning surge enters the cable 1A, the equivalent circuit at this time is shown in FIG. An induced voltage e is generated in the insulated junction box, and the core wire 51 and sheath 52 of the coaxial cable 5
Surge currents i are generated in directions opposite to each other. This surge voltage is the sum of the voltage between the terminals of the arrester 6 and the voltage drop of the coaxial cable, but the voltage between the arrester terminals is suppressed to the limit voltage, and the voltage drop of the coaxial cable is a low value because the surge impedance of the coaxial cable is small. Therefore, the voltage induced in the insulating junction box can be suppressed to a predetermined value or less. Although a surge current flows through the coaxial cable, the direction of the surge current is opposite between the core wire and the sheath, so no magnetic flux is generated outside the coaxial cable, and the reactor 7 installed outside this It will not work against surges. (No voltage is generated in the reactor.) Next, consider the metal sheath current at commercial frequency. The metal sheath current can be expressed as the sum of the zero-period current and the circulating current, most of which is the latter, and in order to suppress the metal sheath current, it is sufficient to reduce this circulating current component.

Even if a cross bond is applied, circulating current flows on an actual line because the length of the cross bond section and the distance between the phases are different for each section, and the induced voltage △e due to this deviation is
This is because this occurs in each cross bond circuit.

The induced voltage due to the deviation of A, B, and C phases is △ea,
Naturally, if △eb and △ec are the sum of these (△
ea+△eb+△ec) becomes zero. Here, the impedance of the cross bond circuit is Zo, the inductance 2 of the reactor is L, and the frequency of the current is (ω-
2π), and each cross bond current is Ia, Ib, Ic, △ea=Zo・Ia+jωL(2Ia−Ib−Ic) △eb=Zo・Ib+jωL(2Ia−Ic−Ia) △ec=Zo・Ic+jωL(2Ic) −Ia−Ib), and by taking the sum of these, the sum of each current (Ia
+Ib+Ic) is found to be zero.

Considering this, the voltage drop in each phase △e
is Δe=(Zo+j3ωL)I, and it can be seen that the sheath current I is limited by the inductance L of the reactor.

In this embodiment, the reactors 7 are provided in all three phases, but the same effect can be obtained even if the reactors 7 are provided in only two of the three phases. The primary winding of reactor 7 is 1
It can be a book or multiple books.

According to the present invention, the following effects are achieved.

(1) Since the reactor can suppress the sheath current, the sheath loss can be significantly reduced.

(2) Since a coaxial cable is used for the cross bond wire, the reactor (installed outside the coaxial cable) will not operate against surge waves, so there is no need to install an arrester on the reactor.

(3) Since a coaxial cable is used for the cross bond wire, the voltage drop in this part can be ignored, and the surge voltage of the corrosion protection layer can be suppressed to the level of the arrester's limit voltage.

(4) Generally, when the sheath current is suppressed with a reactor, etc., when a large current such as a ground current flows, a high voltage is generated between the reactors, and the reactor must be an expensive saturable type. However, the present invention In the circuit configuration, the ground current is a zero-sequence component, so
As in the case of surge voltage, the reactor does not operate and no voltage is generated across the reactor. Therefore, it is not necessary to make the reactor a saturable type, and it is inexpensive.

(5) Since the arrester used in the present invention is not grounded, there is no need to provide a low resistance grounding part.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of a conventional power cable line, Fig. 2 is an explanatory diagram showing an example of a conventional arrester installation method, Fig. 3 is an explanatory diagram showing an example of the present invention, and Fig. 4 FIG. 2 is an explanatory diagram showing a portion of the equivalent circuit of the embodiment for surge voltage. 1A: Cable A phase, 1B: Cable B phase, 1
C: Cable C phase, 1 AS: Metal sheath A phase, 1
BS: Metal sheath B phase, 1CS: Metal sheath C phase,
2a, 2b: Ordinary junction box, 3: Insulated junction box, 4:
Cross bond wire, 5: Coaxial cable, 51:
Coaxial cable core wire, 52: coaxial cable sheath, 6: arrester, 7: rear star.

Claims (1)

[Claims] 1 Two wires each in the section sandwiched between two ordinary junction boxes for grounding of three metal sheathed single-core power cables.
In a power cable line in which two insulated junction boxes are provided, and the metal sheaths of the other phase cables are cross-bonded in sequence before and after each of these insulated junction boxes, the metal sheath on one side of the insulated junction box 3 is connected to the coaxial cable. 5 through the other coaxial cable 5'
The metal sheath on the other side is connected to the core wire 51'' of another coaxial cable 5'' via the sheath 52 of the coaxial cable 5, and the metal sheath on the other side is connected to the core wire 51'' of another coaxial cable 5''. , 5'' and the sheath, and a reactor 7 is provided around the outer periphery of the sheath of the coaxial cables 5, 5', 5''. cable line.