JPH0528483B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an on-load tap switching device that is capable of switching taps even under a minute current load state.

[Conventional technology]

Figure 4 shows a conventional tap switching device under load.
FIG. 5 shows the output waveforms of the current and voltage sensors.
In the figure, 1a, 1b, 1c, 1d are thyristor elements, 2a, 2b are tap selectors,
3a and 3b are transformer taps, 4 is transformer winding,
5 is a current sensor that detects the current flowing through the load; 6
is a voltage sensor that detects the output voltage V _P of the transformer,
7 is a load supplied with power from a transformer, 8 is a gate logic circuit, and 9 is each thyristor 1a, 1b, 1
A firing circuit provides a firing signal to a predetermined thyristor according to a firing command from the gate logic circuit 8 to the gates c and 1d, and 10 and 11 are contacts for detecting rise and fall at the time of tap switching, respectively.

Here, the gate logic circuit 8 turns on when the taps are switched and when the current is continuously energized, based on the combination with the contacts 10 and 11 that detect the polarity of the outputs of the current sensor 5 and the voltage sensor 6, and the rise and fall when the taps are switched. It is configured to select the thyristor to be fired and send an firing command to the thyristor firing circuit 9.

Next, the operation will be explained. In Figure 4,
When a voltage is applied in the direction of the arrow in the figure and when a current flows, the sensor outputs of the current sensor 5 and the voltage sensor 6 are output in the positive direction, and in the opposite direction, they are output in the negative direction.

Next, it is assumed that the thyristors 1a and 1b are in a conductive state and the tap 3a is selected to supply power to the load 7. At this time, in order to lower the tap from tap 3a to tap 3b, tap lowering detection contact 11 is turned on and current sensor 5
When the respective sensor outputs of the voltage sensor 6 and the voltage sensor 6 have opposite polarities, a firing command is issued to the firing circuit 9 according to the logical judgment of the firing logic circuit 8, and the thyristors 1a, 1b, 1
c and 1d should be ignited appropriately. For example _, if the output V _L of the voltage sensor ₆ and the output i _L of the current sensor 5 have a relationship as shown in _FIG . It is in phase with the voltage V _S. i _L is the detected load current and is in phase with the load current i _P. If tap 3a is selected at time _tl , thyristor 1
a is in a conductive state. Further, the outputs of the current sensor 5 and the voltage sensor 6 have the same polarity. At this point, if a firing signal is given to thyristor 1c, the voltage between the taps will be
By V _S , tap 3b → tap selector 2b →
A circulating current flows from thyristor 1c to thyristor 1a to tap selector 2a to tap 3a, and the current in thyristor 1a becomes zero. At this time, as a reverse voltage is applied to the thyristor 1a, the thyristor 1a
becomes non-conductive. On the other hand, the thyristor 1c continues to be conductive and supplies power to the load 7 instead of the thyristor 1a. After this, thyristor 1
If the ignition signal is applied to thyristors 1c and 1d continuously, the load current will flow from tap 3b to thyristor 1c or 1d.
Through this, the load current can be continuously supplied to the load 7. Suppose that at time _t2 , that is, when the outputs of current sensor 5 and voltage sensor 6 have the same polarity,
If we consider a case where a tap switching operation is to be performed from tap 3a to tap 3b, the situation will be as follows.
At this time, thyristor 1 connected to tap 3a
a is working. Even if an ignition signal is applied to the thyristor 1c, the thyristor 1c does not become conductive because a reverse voltage is applied to the thyristor 1c due to the voltage between the taps. In other words, tap switching is not possible. Furthermore, when a firing signal is given to the thyristor 1d, a short-circuit current between the taps flows through the _{path of} tap 3a → tap selector 2a → thyristor 1a → thyristor 1d → tap selector 2b → tap 3b due to the tap-to-tap voltage V S, resulting in several tens of the rated current. An excessive current that doubles will flow and there is a risk of burning out the transformer winding 4.

When the tap is raised from the tap 3b to the tap 3a, when the tap rise detection contact 10 is turned on and the sensor outputs of the current sensor 5 and the voltage sensor 6 are of the same polarity, the ignition logic circuit 8 is activated. Depending on the judgment, a firing command may be issued to the firing circuit 9 to appropriately fire the thyristors 1a, 1b, 1c, and 1d. At this time, when the current sensor 5 and voltage sensor 6 are outputting outputs of different polarities, tap 3
Even if thyristors 1a and 1b connected to a are fired, tap switching cannot be performed as above, or
This will cause a short circuit accident between the taps. That is, in conventional tap switching devices, polarity detection of the voltage and current sensors is a necessary condition for properly firing the thyristor.

[Problem that the invention seeks to solve]

Conventional on-load tap switching devices are configured as described above, so when supplying power to a minute current load that cannot be detected by a current sensor, the output polarity of the current sensor cannot be determined and the appropriate input to the thyristor cannot be determined. There was a problem in that tap switching was not possible because an ignition signal was not given.

This invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide an on-load tap switching device using a thyristor that can perform tap switching even when the current in the load circuit is below the sensitivity level of the current sensor. shall be.

[Means for solving problems]

The on-load tap switching device according to the present invention connects a non-linear resistor in parallel with the thyristor switch, detects the presence or absence of the output of the current sensor, and when the sensor output is present, the ignition command from the ignition logic circuit is directly used to ignite the switch. A current sensor detection circuit is provided which prevents the firing command from the firing logic circuit from being sent to the firing circuit when there is no sensor output.

[Effect]

The on-load tap switching device according to the present invention stops the firing signal of the thyristor switch to make the thyristor switch non-conductive when the current in the load circuit is below the sensitivity level of the current sensor. Flow the load circuit current through the tap and switch the tap.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, numerals 1 to 11 are the same as the conventional one. A nonlinear resistor 12 is connected in parallel with the thyristors 1a and 1b, and has voltage-current characteristics as shown in FIG. 13 is a current sensor output detection circuit that detects the presence or absence of the output of the current sensor 5; 14 is a switch operated by the current sensor output detection circuit 13; it is closed when the current sensor 5 has an output; When there is nothing, it is open. 15 is a current-carrying contact, and 16 is a drive mechanism for communicating the current-carrying contact 15 with the tap selectors 2a, 2b. This drive mechanism 16 is
Current-carrying contact 15 and tap sensor 2a, 2b
The electrode distance (slide distance) of the voltage taps 3a and 3b that slides is A, and the voltage taps 3a and 3
The distance between the electrodes b and between the electrodes of the voltage taps 3b and 3c is C, respectively, and the spatial distance between the current-carrying contact 15 and the tap selector 2a or 2b is B, respectively.
The above components are arranged so that the formula A>B>C holds true.

Next, the operation will be explained. First, the voltage/current characteristics of the nonlinear resistor 12 will be explained with reference to FIG. In FIG. 2, V ₂ is a limiting voltage and is set to a value lower than the reverse withstand voltage of the thyristors 1a and 1b. V ₀ is the peak value of the tap-to-tap voltage V _S , and at this value, the current I ₀ flowing through the nonlinear resistor 12 is extremely small and can be considered as zero current. When voltage V ₁ is applied to nonlinear resistor 12 , it is assumed that the minimum current value I ₁ that can be detected by current sensor 5 flows through nonlinear resistor 12 . Due to this, the voltage V ₂ ,
The relationship between V ₀ and V ₁ is V ₀ < V ₁ < V ₂ , where the peak value of the voltage between taps V ₀ is the circuit voltage V _p
Since it is about 2 to 3% of the voltage V ₁ ,
The voltage V ₂ is considered to be about 6 to 7% of the circuit voltage V _p .

In FIG. 1, which has such a nonlinear resistance 12, if the tap 3b is supplying power to the load 7 via the current-carrying contact 15, the load 7 is a minute current load, and this load current is passed through the current sensor 5. If the current is at a low level that cannot be detected, the output of the current sensor 5 will be zero. The output of the current sensor 5 is sent to the current sensor detection circuit 13, and the current sensor detection circuit 13 determines that tap switching by normal thyristor firing is not possible, and opens the switch 14. As a result, the ignition command signal of the ignition logic circuit 8 is not sent to the ignition circuit 9. Therefore, thyristors 1a, 1b, 1
d becomes non-conductive.

In this state, when a tap-down command is given to the drive mechanism 16 from an external device (not shown), the drive mechanism 16 operates to switch the current-carrying contact 15 from the tap 3b to the tap 3c.

Here, the tap switching operation is shown in Figures 3-a to 3-3.
This will be explained using figure e. Figure 3-a shows tap 3.
b shows the state before tap switching, in which current is being supplied to the load 7 through the current-carrying contact 15.
In the state shown in FIG. 3-a, the drive mechanism 16 operates in response to an external tap-down command, and the drive mechanism 16
are tap selectors 2a, 2b and current-carrying contact 1
5 to operate as shown in FIG. 3-e. In this way, the current-carrying contact 15 taps 3.
In the process of transition from tap 3c to tap 3c, as shown in Figure 3-b, the tap selector 2a and the current-carrying contact 15 come into contact with the tap 3b, and the tap selector 2b comes into contact with the tap 3c, so the load current is not energized until this state. It flows through contact 15.
Further, the tap selectors 2a, 2b and the current-carrying contact 15 are driven, as shown in FIG.
b are in contact with the taps 3c, respectively. As a result, a circuit voltage V _p is applied to the parallel circuit of each thyristor 1a, 1b and 1c, 1d, but due to the voltage-current characteristics of the nonlinear resistor 12 described above, the nonlinear resistor A voltage less than or equal to the voltage value V ₁ is applied at most to supply electric power to the minute current load 7 . At this time, the voltage applied to the nonlinear resistor 12 is at most about 3 to 4 of the total circuit voltage _Vp .
%, it is considered that the influence on the load 7 due to the voltage drop applied to the nonlinear resistor 12 can be almost ignored. By this, the circuit voltage V _p
and a minute load current is supplied to the load 7. This state continues until the current-carrying contact 15 separates from the tap 3b and comes into contact with the tap 3c.

Tap selector 2 from the state shown in Figure 3-c.
When a, 2b and the current-carrying contact 15 are driven,
As shown in FIG. 3-d, the current-carrying contact 15 comes into contact with the tap 3c. At this time, a circuit short-circuits the voltage V _S between the taps of the current-carrying contacts 15 through the nonlinear resistor 12. As a result, the voltage applied to the nonlinear resistor 12 becomes V ₀ at most, and I ₀ flows depending on the voltage-current characteristic of the nonlinear resistor 12 . As mentioned above, this value is extremely small and can be considered as zero current, and the load current flows from the tap 3c to the load 7 through the current-carrying contact 15. After this, the tap selectors 2a, 2b and the current-carrying contact 15 are further driven, and as shown in FIG.
stops working. In this state, each tap selector 2a, 2b is stopped without contacting any of the taps 3b, 3c.

The above operation has been described for switching to a lower voltage tap, but switching to a higher level tap is also performed in the same manner as described above.

In the above embodiment, a case was explained in which a nonlinear resistor was connected in parallel with one of the thyristor switches each having a pair of thyristors connected in antiparallel, but the nonlinear resistor was connected in parallel with the other thyristor switch or both thyristor switches. Even if connected, the same effects as in the above embodiment can be expected.

〔Effect of the invention〕

As described above, according to the present invention, a nonlinear resistor is connected in parallel with the thyristor switch, and when a minute current load is below the sensitivity level of the current detector, the ignition signal of the thyristor switch is stopped and the thyristor switch is disabled. Since the structure is conductive, tap switching is possible even with a minute current load.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an on-load tap switching device according to an embodiment of the present invention, FIG. 2 is a voltage-current characteristic diagram of a nonlinear resistor, and FIG. 3 is an operational diagram of tap switching.
Figure 4 is a configuration diagram of a conventional tap switching device under load.
FIG. 5 is a diagram showing the phase relationship between the outputs of a conventional voltage sensor and a current sensor. In the figure, 1a to 1d are thyristor elements, 2
a to 2c are tap selectors, 3a to 3c are taps, 4 is a transformer winding, 5 is a current detector, 6 is a voltage sensor, 8 is a gate logic circuit, 9 is an ignition circuit, 1
0 is a tap switching rise detection contact, 11 is a tap switching fall detection contact, 12 is a nonlinear resistor, 13 is a current sensor output detection circuit, 14 is a switch, 15 is a current-carrying contact, 16 is a drive mechanism, and 17 is a minute current load. . Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A thyristor switch with thyristors connected in antiparallel is connected to multiple taps of a transformer with different voltages, and a tap selector section with a nonlinear resistor connected in parallel with the thyristor switch detects the load current. Equipped with a current detector and a voltage detector that detects the voltage on the load side, when the load current exceeds the sensitivity level of the current detector, the current and voltage detected by the current detector and voltage detector at the time of tap switching are In a device that performs tap switching by igniting a predetermined thyristor based on the logic judgment of the ignition logic circuit based on the respective polarities of A tap switching device under load, characterized in that the tap is switched by making the tap non-conductive and allowing the current of the load circuit to flow through the nonlinear resistor.