JPS633533B2 - - 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. or more insulated junction boxes 3 are provided,
By sequentially connecting the metal sheaths 1AS, 1BS, and 1CS of the different-phase cables using bonding wires 4 before and after the insulated connection boxes 3a and 3b, the circulating voltage induced in the metal sheaths 1AS, 1BS, and 1CS is canceled. , metal sheath 1AS, 1BS, 1
The current flowing through CS 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 junction boxes is different, it is difficult to completely control the voltage induced in each metal sheath. I can't cancel it. The reality is therefore that in some cases quite large currents flow through the metal sheath and the sheath losses are still quite large. 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, an 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.

The present invention has been made in view of the above circumstances, and its purpose is to provide a power cable that can greatly reduce the circulating current flowing through the metal sheath and that does not generate abnormal voltage even in the event of lightning surges, etc. The purpose is to provide a railway line.

That is, the gist of the present invention is to use a coaxial cable as a cross bond wire of a metal sheath, and to attach a reactor to the outer periphery of the coaxial cable for suppressing the sheath current.

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

Figure 2 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 2.

That is, one end of one cable sheath 1AS is connected to the sheath 52' of another coaxial cable 5' via the core wire 51 of the coaxial cable 5, and the other end of one cable sheath 1AS is connected via the sheath 52 of the coaxial cable 5. Core 5 of the end and another coaxial cable 5″
1" are connected.Each coaxial cable 5,
A reactor 7 is provided in the sheaths 5' and 5'', and an arrester 6 is connected to the core wire. Let's now consider the case where a lightning surge hits the cable (for example, 1AS).

The equivalent circuit at this time is shown in FIG.

At this time, an induced voltage e is generated in the insulated junction box,
Currents are generated in the core wire 51 and sheath 52 of the coaxial cable by surges in opposite directions.

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 low because the surge impedance of the coaxial cable is small. The voltage induced in the insulated junction box can be suppressed to a predetermined value or higher.

Note that surge current flows through the coaxial cable, but since the direction of the surge current is opposite between the core wire and sheath, no magnetic flux is generated outside the coaxial cable, and the reactor 7 installed outside this This means that it will not work against large surges.

Next, consider the metal sheath current at commercial frequencies. The metal sheath current can be expressed as the sum of the zero-sequence 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.

Circulating current flows on an actual line with cross bonds because the cross bond section length and interphase distance 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. A,
The induced voltage due to the shift of B and C phases is △ea + △eb,
If △bc is the sum of these (△ea+
△eb+△ec) becomes zero. Here, if the impedance of the cross-bond circuit is Zo, the inductor 2 of the reactor is L, the frequency is (ω-2π), and each cross-bond current is Ia, Ib, Ic, then △ea=Zo・Ia+jωL(2Ia-Ib −Ic) △eb=Zo・Ib+jωL(2Ib−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 Δe in each phase becomes Δe=(Zo+j3ωL)I, and it can be seen that the sheath current 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 other than the coaxial cable) will not operate in the event of a surge, 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 sheath current is suppressed using a reactor, etc., when a large current such as ground current flows, a high voltage is generated between the reactors, and the reactor must be an expensive saturable type. In the circuit configuration, since the ground current is a zero-sequence component, the reactor does not operate as in the case of surge voltage,
No voltage is generated between the reactors. Therefore, it is not necessary to make the reactor a saturable type, and it is inexpensive.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a conventional cross-bond method, FIG. 2 is an explanatory diagram showing an embodiment of the present invention, and FIG. 3 is a portion of an equivalent circuit of the embodiment for surge voltage. FIG. 1A...Cable A phase, 1B...Cable B phase, 1
C...Cable C phase, 1AS...Metal sheath A phase, 1
BS...Metal sheath B phase, 1CS...Metal sheath C phase,
2a, 2b...Ordinary connection box, 3...Insulated connection box, 4...
Cross bond wire, 5, 5', 5''... coaxial cable, 51, 51', 51''... core wire of coaxial cable,
52, 52', 52''...Coaxial cable sheath, 6
...Arrester, 7...Reactor.

Claims (1)

[Claims] 1 Each of the three metal-sheathed single-core power cables has two wires in each section sandwiched between two ordinary junction boxes for grounding.
In a power cable line in which insulated junction boxes 3 are provided and metal sheaths of other phase cables are cross-bonded to each other in order before and after each insulated junction box, the metal sheath on one side of the insulated junction box 3 is connected to the coaxial cable 5. The metal sheath on the other side is connected to the core wire 51'' of the other coaxial cable 5'' through the sheath 52 of the coaxial cable 5. Arresters 6 are installed on the core wires of the coaxial cables 5, 5', 5''.
are connected, and the coaxial cables 5, 5',
A power cable line characterized in that a reactor 7 is provided on the outer periphery of a 5″ sheath.