JPH019242Y2 - - Google Patents

Description

[Detailed explanation of the invention] Generally, double or triple wiring is used for wiring from the switchboard to the control panel for ease of construction when the current capacity of the electric line is large, such as 1000A.

For example, in the case of double wiring between bar terminal 1 on the switchboard side and bar terminal 2 on the control panel side as shown in the first diagram, leakage current can be controlled only by the zero-phase current transformer ZCT installed in one branch circuit. When trying to measure,
Because the load current is not shunted in a well-balanced manner due to differences in the resistance values of the parallel wiring, the unbalanced portion is measured.

This is why, in experiments, when the good load current is about 800 A, a zero-sequence component of about 10 to 15 A is detected in the zero-sequence current transformer ZCT.

In this invention, a zero-phase current transformer is installed in each branch circuit that is wired in parallel so that the load current is divided in the middle of the circuit, and a zero-phase current burden resistor is installed between these zero-phase current transformers. , a variable resistor that adjusts the phase of the output voltage of one zero-phase current transformer to be in phase with the phase of the output voltage of the other zero-phase current transformer, and a harmonic filter are connected, and each zero-phase By adjusting the phase difference in the output voltage due to variations in the current transformer and attenuating the harmonics, the unbalanced current from each branch circuit can be canceled out, making it possible to detect only the leakage current in the circuit. The purpose is to provide a measuring device.

Embodiments of the present invention will be described below based on FIGS. 2 to 7 of the drawings.
is a double-wired branch line in the middle of the three-phase line 3, ZCT ₁ and ZCT ₂ are zero-phase current transformers installed in each branch line 1 and 2, respectively, and R ₀ is a zero-phase current transformer ZCT ₁ ,
The zero-sequence current-bearing resistor is commonly connected between _{the secondary terminals of ZCT 2 , and R} Adjustment resistor, R is the other zero-phase current transformer
The phase resistor is connected in series with the resistor R ₀ between the secondary terminals of ZCT ₂ , C is the harmonic filter connected in parallel with the resistor R ₀ , Ia is the unbalanced load current, V ₀ indicates leakage current output.

FIG. 3 shows a simplified equivalent circuit of each of the zero-phase current transformers ZCT ₁ and ZCT ₂ .

Here, there would be no problem if the above two zero-phase current transformers ZCT ₁ and ZCT ₂ could be manufactured to be exactly the same, that is, XL ₁ = XL ₂ , but since this is not possible in actual manufacturing, XL ₁ ≠XL ₂ .

The output voltage V ₂ of the zero-phase current transformer ZCT ₂ is V ₂ =R ₀ Ia/n/1+R ₀ +Rx/j×L ₂ .

The vector locus _{of V 2} when the phase adjustment _{resistor R}

The trajectory of the output voltage V ₁ of the zero-phase current transformer ZCT ₁ is as shown in FIG.

In Fig. 5, the leakage current output V ₀ is V ₀ = V ₂ − _{V 1}
It is.

By increasing the phase adjustment resistor Rx, the vector of V ₂ moves in the direction of the arrow on a semicircle with a diameter of OP, and V ₀ =0 at a certain location.

When a leakage current occurs in the electrical circuit 3, the output V ₀ due to the leakage current is vectored to each zero-phase current transformer ZCT ₁ ,
It becomes the sum of the outputs of ZCT ₂ and can be detected.

However, in reality, since the iron cores of each zero-phase current transformer ZCT ₁ and ZCT ₂ are made of magnetic material, harmonic components remain in their secondary outputs and ΔV ₀ is generated.

Therefore, in the present invention, a harmonic filter C is connected to attenuate the harmonic component and improve the selectivity of the zero-sequence current of the fundamental wave.

With the above configuration, the unbalanced currents from the respective branch circuits 1 and 2 are canceled out, and only the leakage current of the circuit 3 can be detected.

FIG _. 6 shows another embodiment of the present invention. To explain it, _a zero-phase Connect the current burden resistors R ₁ and R ₂ respectively, and connect these resistors in series.
The phase adjustment resistor Rx is connected in series with the resistor R ₁ between the secondary terminals of one zero-phase current transformer ZCT ₁ , and the output voltage V ₂ of the other zero-phase current transformer ZCT ₂ is The resistor Rx is adjusted so as to correspond to the output voltage V ₁ of the current transformer ZCT ₁ , that is, to correspond to the intersection point P' of the extension of OP and the circle of OCD, as explained in the vector diagram of Fig. 7.
is adjusted so that the output voltage V ₂ is reduced to an output voltage V' ₂ equal to the output voltage V ₁ by the intermediate tap 4 provided on the resistor R ₂ , and the resistors R ₁ ,
R ₂ and a harmonic filter C are provided in parallel to detect the output V ₀ due to leakage current.

Since the present invention is constructed as described above, it has the advantage of being able to easily detect only the leakage current in the circuit by canceling out the unbalanced current from the double or triple-wired branch circuit in the middle of the circuit.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of double wiring in the middle of a three-phase circuit, Figure 2 is a circuit diagram of the leakage current measuring device according to the present invention, and Figure 3 is a diagram of each zero-phase current transformer in the device. Equivalent circuit diagram, Figure 4 is a diagram showing the vector trajectory when the phase adjustment resistance of the output voltage of zero-phase current transformer ZCT ₂ is variable, and Figure 5 is a diagram showing each output voltage of zero-phase current transformer ZCT ₁ and ZCT ₂ . FIG. 6 is a circuit diagram of a modified embodiment of the present invention, and FIG. 7 is a diagram showing the relationship between each output vector in the same embodiment. 1, 2...Diversion line, 3...Three-phase line, ZCT ₁ ,
ZCT ₂ ... Zero-phase current transformer, R ₀ ... Resistor for zero-phase current burden, Rx... Resistor for phase adjustment, R... Resistor for phase,
R ₁ , R ₂ ... Resistor for zero-phase current burden, 4 ... Intermediate tap, C ... Harmonic filter.

Claims (1)

[Scope of utility model registration request] Between the secondary terminals of the zero-phase current transformers installed in each branch circuit that is wired in parallel so that the load current is divided in the middle of the circuit, a zero-phase current burden resistor and one zero-phase current transformer are installed. A device for measuring leakage current in parallel wiring, which consists of a harmonic filter and a variable resistor that adjusts the phase of the output voltage of one zero-phase current transformer to be in phase with the phase of the output voltage of the other zero-phase current transformer.