JPH0336698B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to reducing the insulation of a feeding substation that supplies current to electric cars in an AT feeding system AC electric railway.

Figure 1 shows the configuration of a single-phase feeding circuit in a conventional AT feeding system.

In the conventional AT feeding system, the feeding voltage at the substation is twice the voltage used by the electric car, and the voltage divided by the car winding transformer AT is sent to the electric car between the contact wire T and the rail R. The normal ground voltage of the feeder line is equal to the single electric voltage, and the insulation strength is half the feeder voltage.

However, in substations, the feeding side of the feeding transformer is non-grounded, so if AT is not connected before power feeding starts, a ground fault may occur on the substation feeding side. , the ground potential of the ground fault phase becomes 0 potential, and the potential of the healthy phase rises to twice the electric car voltage.

Therefore, on the substation premises feeding side, the electric car voltage is 2
Double the insulation strength is now required.

In contrast, the present invention relates to an AT feeding system using a three-winding transformer in which a secondary winding and a tertiary winding with equal voltages are connected in series and a neutral point is provided on the feeding side.

In other words, a reactor with a short-circuit device installed in parallel is inserted between the neutral point of the transformer and the rail to suppress the electric car current from flowing into the neutral point of the transformer, and also to prevent the AT from being connected. This provides an economical and highly reliable power feeding system by reducing the insulation strength on the feeding side of the substation to half of the conventional one, taking into account the possibility of a ground fault in the event of a ground fault.

The present invention will be explained below with reference to the drawings. Note that in the feeder circuit, the resistance component is very small compared to the reactance component, so in the following explanation, the resistance component will be ignored and only the reactance component will be considered.

Figure 2 is an equivalent circuit showing the separation reactance of a three-winding transformer.

Generally, the leakage reactance of a transformer with a large number of windings is measured from the voltage and current when one of the two windings, j, is short-circuited, the other winding is applied with voltage, and the other winding is open. The value converted to the reference voltage is displayed as X _ij .

Now, if we measure X _ij for the three-winding transformer with a winding ratio of 1:1:1 in Figure 2 and find the separation reactance of each winding, as is well known, becomes.

By the way, when using it for AT feeding,
Since the secondary winding and tertiary winding are connected in series and _the neutral point terminal _is taken out, X _{1 , N} ,
It is easier to understand if it is expressed as an equivalent circuit as X _F.
Since _{the winding} ratio of each winding is 1: ₁ :1, X _T +X _N =X ₁ +X _{2 X F} +X ₁₁ =X _{1 +} X ₃ holds true. Then, becomes.

Next, when AT is not connected, the voltage when the T phase or F phase has a ground fault on the feeding side of the substation premises,
Consider the current distribution in the simplest single-phase transformer with a neutral point.

In Figure 4, the T-N terminals are short-circuited and the U-V
When voltage V ₀ is applied to the terminal, the left and right windings are in series with respect to the primary winding, so windings 1 and 1'
The same current flows through and produces a magnetic field. In the left core leg, current flows through the winding 2 and cancels the magnetic field, but in the right core leg, the winding 3 is open, so the magnetic field is not canceled out, and the current flowing in the primary winding becomes an extremely small current.

As a result, the voltage in the secondary winding becomes almost 0, and the full voltage is applied to the tertiary winding, reducing the normal voltage from V ₀ to 2V _0.
rise to In other words, since the potential to the ground at the neutral point is 0, the potential of the healthy phase will rise to about twice the electric car voltage. It turns out that it cannot be reduced.

Therefore, the same consideration will be given to the transformer with the separate core leg shape and the winding arrangement shown in FIG. In this case, the upper and lower primary windings are connected in parallel, and independent currents flow through the windings 1 and 1' to generate a magnetic field. As for the upper core leg, winding 2 is short-circuited, so current flows and cancels the magnetic field, causing winding 1
A large current flows through the Winding 3 on the lower core leg
Since the winding 1' is open, the magnetic field is not canceled and only a small excitation current flows through the winding 1'.

As a result, the voltage in the tertiary winding is the same as before the short circuit.
V ₀ , and the potential of the healthy phase does not rise.

In this way, a three-winding transformer is a transformer in which the windings are arranged so that a magnetic field always cancels out against the primary winding, and the voltage of the healthy phase does not increase even if one phase is short-circuited. This transformer is in practical use and solves the problem of potential rise.

If the voltage and current capacity of the secondary winding of a three-winding transformer used for AT feeding are made equal, and the arrangement of the secondary and tertiary windings relative to the primary winding is approximately equal, the three-winding transformer can be The reactance is X ₁₂ ≒X ₁₃ X ₂₃ ≒X _{12 +}
From the formula, X _T ≒X ₁₂ , X _F ≒X ₁₃ , X _N ≒0 (5).

By the way, when determining the current distribution when AT is connected to a three-winding transformer, in the equivalent circuit shown in Figure 6, V ₀ −V _AT =X _T I _T −2X _AT I _F +X _N I _N V ₀ − V _AT = -X _N I _N +2X _AT I _F +X _F I _F ...(6) Since I _L = I _T + I _F and I _N = I _T - I _F , erase the voltage and set the load to a constant current. Considering the source, becomes.

The reactance of equation (7) is X _N ≒ 0 from equation (5), and practically 4X _AT ≒ X _T ≒ X _F , so at the neutral point, I ₁₁ ≒ 1/3I _L ... It can be seen that a current of about (8) flows, and the utilization rate of the transformer's winding capacity becomes extremely poor.

FIG. 7 shows an embodiment of the present invention in which a reactor for current suppression is inserted at the neutral point.

Figure 8 is an equivalent circuit of Figure 7, where the reactance of the current-suppressing reactor is X _G , and the current distribution on the feeding side is calculated by replacing X _N in equation (7) with X ₁₁ +X _G. becomes.

In this case, if we define the unbalance rate of current in the feeding side winding of the transformer as α=I _T −I _F /I _T +I _F ……(10), then α=4X _AT −X _T +X _F /4 (X _AT +X _N +X _G ) +X _T +X _F ...
…(11) becomes. For example, if the feeding voltage is 60KV, the single-phase capacity is 50MVA, and the feeder transformer has a % reactance of 6%, and the reactance of AT is X _AT = 0, 5Ω, find the value of α by varying X _G. 9th
It will look like the figure.

That is, by inserting X _G , the unbalance of the current on the feeding side of the transformer can be reduced, and the utilization rate of the winding capacity of the transformer can be improved.

If a current suppression reactor is inserted into the neutral point of the transformer, the current imbalance on the feeding side of the transformer can be controlled as explained above, but in Fig. 7, the feeding side disconnector 52F is opened. If a ground fault occurs on the feeding side of the substation, a larger voltage will be generated at both ends of the reactor than normal, so a shunt gap G is installed in parallel with the reactor to prevent discharge at the ground fault. to prevent a significant voltage rise from occurring across the actuator.

In addition, it is also possible to provide a side path switch in conjunction with 52F in parallel with the reactor.

As explained above, according to the present invention, the current flowing to the neutral point of the feeding transformer is suppressed, and the insulation strength of the electrical equipment on the feeding side of the substation is increased compared to the conventional one.
By being able to reduce the power consumption to half that of the AT feeding system, it is possible to provide an economical and highly reliable power feeding system.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the conventional AT feeding system, Figure 2 is an equivalent circuit diagram showing the separation reactance of a three-winding transformer, and Figure 3 is a three-winding transformer showing the separation reactance on the feeding side. Fig. 4 is a winding arrangement diagram for a single-phase transformer with a neutral point, Fig. 5 is a winding arrangement diagram for a separate core leg three-winding transformer, and Fig. 6 is a winding arrangement diagram for a single-phase transformer with a neutral point. Figure 7 is an equivalent circuit diagram of an AT feeding system with reduced insulation strength using a three-winding transformer, which suppresses the neutral point current of the present invention and reduces insulation strength on the substation feeding side.
A circuit diagram of an example of the AT feeding system, Fig. 8 is an equivalent circuit diagram of Fig. 7, and Fig. 9 shows the relationship between the reactance of the current suppression reactor and the current imbalance rate of the transformer feeding side winding. FIG. T _r ... Feeding transformer, AT, AT ₁ and AT ₂ ...
Autotransformer, 1, 1' _{, 2 and 3...Transformer windings, V0...Power supply voltage, V AT ...} Voltage applied to AT,
X ₁ , X ₂ and X ₃ and X _T , X _F and X _N ... Separation reactance of the feeding transformer, X _G ... Reactance of the current suppression reactor, X _AT ... Reactance of the autotransformer, I _T , I _F and I _N ... Current on the feeding side of the feeding transformer, I _L ... Load current, α ... Unbalance rate of current in the feeding side winding of the transformer, 52F... Feeding current Disconnector, G...Side gap, SD...Discharger, U, V...Transformer primary winding terminal, T...
Contact wire, F...feeder, N...neutral point of transformer, R...rail.

Claims (1)

[Claims] 1. In a feeding transformer in the autotransformer feeding system (hereinafter referred to as AT feeding system), a three-winding transformer is used, a neutral point is provided on the feeding side winding, and a short circuit device is installed in parallel. By inserting a reactor between the neutral point and the rail, the electric car current flowing into the neutral point of the transformer is suppressed, and the insulation strength of the electrical equipment on the substation feeding side is reduced. Insulation reduction method for AT feeding system substations.