JPS6276510A - On-load tap changer - Google Patents

Abstract

PURPOSE:To enable tap change-over at the time of a minute current load by connecting a nonlinear resistance in parallel to a thyristor switch and by stopping the ignition signal of the thyristor switch to make a thyristor switch not conductive at the time of a minute current load of the sensitivity level of a current detector or less. CONSTITUTION:A tap 3b supplies power to a load 7 through a contact 15 for conduction and if the load 7 is a minute current which is a too low level to be detected by a current sensor 5, the output of the current sensor 5 is zero. The output is sent to the detection circuit 13 of the current sensor and the detection circuit 13 of the current sensor judges that the tap change-over by the ignition of a thyristor in conduction impossible and opens a switch 14. This makes the ignition command signal of an ignition logic circuit 8 is not sent to an ignition circuit 9 and thyristors 1a-1d are made not conductive. Under these conditions, e.g., if a tap down command is given to a driving mechanism 16 from outside, the contact 15 for conduction changes over from the tap 3b to a tap 3c.

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]

FIG. 4 shows a conventional on-load tap switching device, and FIG. 5 shows output waveforms of current and voltage sensors.

In the figure, (la), (lb), (lc), (L+d
) are respectively thyristor elements, (2a) and (2b) are tap selectors, (3a) and (3b) are transformer taps,
(4) is the transformer winding, (5) is the current sensor that detects the current flowing to the load, (6) is the voltage sensor that detects the output voltage (Vp) of the transformer, and (7) is the power output from the transformer. The load to be supplied, (8) is a gate logic circuit, and (9) is each thyristor (la), (lb), (1c).

A firing circuit that gives a firing signal to a predetermined thyristor according to the firing command of the gate logic circuit (8) to the gate of (1d), a
n, Ql) are contacts for detecting rise and fall at the time of tap switching, respectively.

Here, the gate logic circuit (8) is connected to a contact (11, (b)) that detects the polarity of the output of the current sensor (5) and the voltage sensor (6), and the rise and fall at the time of tap switching. The thyristor to be fired is selected during tap switching and continuous energization, and a firing command is sent to the thyristor firing circuit (9).

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

Next, assume that the thyristors (1a) and (xb) 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), the tap lowering detection contact αη is turned on, and the sensor outputs of the current sensor (5) and voltage sensor (6) are reversed. When the polarity is determined, an ignition command is issued to the ignition circuit (9) based on the logic judgment of the ignition logic circuit (8), and the thyristors (la), (1b),
(lc) and (xa) may be ignited appropriately. For example, if the output vL of the voltage sensor (6) and the output 1L of the current sensor (5) have a relationship as shown in Figure 1lJE5, ■L is the detected winding voltage V, and the voltage between Vp and the tap is It is in phase with the voltage 7s. IL is a detected load current and is in phase with the load current IP. If the tap (3a) is selected at time t1, the thyristor (1a) is in a conductive state. The outputs of the current sensor (5) and voltage sensor (6) still have the same polarity VC. When a firing signal is given to the thyristor (IC) at this point, the tap (3111) → tap selector (
A circulating current flows in the order of 2b) → thyristor (lc) → thyristor (1a) → tap selector (2a) → tap (3a), and the current in thyristor (1a) becomes zero. At this time,
When a reverse voltage is applied to the thyristor (la), the thyristor (1a) becomes non-conductive. On the other hand, thyristor (IC)
continues to be conductive, supplying power to the load (7) instead of the thyristor (1a). After that, if the ignition signal is continuously applied to the thyristors (lc) and (la), the load current is continuously transferred from the tap (3b) through the thyristor (IC) or (1d) to the load (7).
). Let's assume that a tap switching operation is attempted from tap (3a) to tap (3b) at time t2, that is, when the outputs of current sensor (5) and voltage sensor (6) have the same polarity. It will look like this: At this time, the thyristor (1a) connected to the tap (3a) is operating. Here the thyristor (1c)
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, if the tap cannot be changed, the result is K.

Also, when a firing signal is given to the thyristor (1d), the tap (3a) → tap selector (
2a) → Thyristor (1a) → Thyristor (1d) → Tap selector (2'b) → Tap (3b), a short-circuit current flows between the taps, an excessive current several tens of times the rated current flows, and the transformer There is a risk of burning out the winding (4).

In addition, when raising the tap from tap (3b) to tap (3a), tap increase detection contact α0 is turned on and the sensor outputs of current sensor (5) and voltage sensor (6) are of the same polarity. Based on the logic judgment of the ignition logic circuit (8), an ignition command is issued to the ignition circuit (9), and the thyristor (x
a), (xb), (1c), and (1a) may be ignited appropriately. At this time, when the current sensor (5) and voltage sensor (6) are outputting different polarities, the tap (3a
) Even if the thyristors (la) and (lb) connected to the taps are fired, tap switching will not be possible or a short-circuit accident will occur between the taps, as described above. That is, in conventional tap changers, 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 could not be given.

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

[Failure to solve the problem]

The on-load tap switching device according to the present invention connects a non-linear resistor in parallel with a thyristor switch, detects the presence or absence of a current sensor output, and when the sensor output is present, the firing command of the firing logic circuit is turned on as is. 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. Switches the tap by passing the load circuit current through the resistor.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, (1) to (2) are the same as the conventional one.

@ is a nonlinear resistor connected in parallel with the thyristors (la) and (lb), and has voltage-current characteristics as shown in FIG. (to) is a current sensor output detection circuit that detects the presence or absence of the output of the current sensor (5), and q→ is a switch operated by the current sensor output detection circuit α1, when the output of the current sensor (5) is present. is closed and the current sensor (
It is open when the output heat is 5). (G) is the current-carrying contact, αQ is the current-carrying contact (G) and the tap selector (2
This is a drive mechanism that connects a) and (21)). This drive mechanism αQ changes the electrode distance (slide distance) between the voltage taps (za) and (3b) where the energizing contact (to) and the tap selectors (2a) and (2b) slide between the A1 voltage tap (3a) and ( The distance between the electrodes in 3b) and between the electrodes in voltage taps (3b) and (3C) are set to 0, respectively.
1 energizing contact OQ and tap selector (2a) or (
Letting the spatial distance of 2b) be B, A) B:
> The above components are arranged so that the formula C holds true. αη is a minute current load.

Next, the operation f will be explained. First, the voltage/current characteristics of the nonlinear resistance @ will be explained with reference to FIG.

In Figure 2, (Vz) is the limiting voltage and the thyristor (l
a) It is set to a value lower than the reverse withstand voltage of (lb). (Vo) is the peak value of the inter-tap voltage (Vs), and the current (Io) flowing through the nonlinear resistor (2) at this value is extremely small and can be considered as zero current. Voltage (Vl)
is applied to the nonlinear resistor 4, the minimum current value (L) that can be detected by the current sensor (5) flows through the nonlinear resistor (2).As a result, the voltage (V2), (
Between (VO) and (V+), (VO) < (Vl) <
(V2), where the peak value of the voltage between taps (Vo) is about 2 to 8% of the circuit voltage (Vp), so 8 to 4% of the voltage (Vr), and the voltage (■2 ) is considered to be about 6 to 7% of the circuit voltage (Vp).

In FIG. 1 with such a non-linear resistance port, the tap (8b) connects the load (7) via the current carrying contact cps.
Assuming that the load (7) is a minute current load, and this load current is at a low level that cannot be detected by the current sensor (5), the current sensor (5)
The output of the button becomes zero. The output of this current sensor (5) is sent to the current sensor detection circuit port, and the current sensor detection circuit determines that tap switching by normal thyristor firing is not possible, and opens switch 4. As a result, the ignition command signal of the ignition logic circuit (8) is transmitted to the ignition circuit (9).
Not sent to. Therefore, thyristor (la);
(lb) and (ld) become non-conductive.

In this state, when a tap lowering command is given to the drive mechanism σQ from the outside (not shown), the drive mechanism OQ operates (thus, the current-carrying contact (to) switches from the tap (8b) to the tap (3C). It is operated.

Here, the tap switching operation will be explained with reference to Figs. aa to 8-e. Figure 8-a shows the state before tap switching, where the tap (8b) is supplying current to the load (7) through the current-carrying contact (4).

In the state shown in Fig. 8-a, tap lowering command 1 is issued from the outside.
This causes the drive mechanism αQ to operate, driving the drive mechanism αG beam selectors (2a), (2b) and the energizing contact μs to operate as shown in FIG. 8-e.

In this way (in the process of the current-carrying contact 4 transitioning from the tap (8b) to the tap (8C), as shown in Figure 8-b, the tap selector (2a) and the current-carrying contact (4)
is in contact with the tap (8b) and the tap selector (2b) is in contact with the tap (8C), so that the load current flows through the current carrying contact (to) until this state. Further, the driven tap selectors (2a), (2b) and the current-carrying contact 4 are connected to the current-carrying contact (4) as shown in Fig. 8-C.
moves away from tap (8b), tap selector (2a) taps (8b), and tap selector (2b) taps (
8C) respectively. This (ζ, therefore, each thyristor (1a), (xb) and Dc), Dd) A circuit voltage (Vp) is applied to the CD parallel circuit, but due to the voltage-current characteristics of the nonlinear resistor (b) mentioned above, In response to a minute load current, a voltage that is at most a voltage value (Vl) or less is applied to the nonlinear resistor, and power is supplied to the minute current load (7). At this time, the voltage applied to the nonlinear resistor (2) is at most about 8 to 4% of the total circuit voltage (Vp), so the voltage drop applied to the nonlinear resistor (4) has no effect on the load (7). It can be considered that it can be ignored for the most part. As a result, the circuit voltage (Vp) and minute load current are supplied to the load α. In this state, current-carrying contact 4 is tapped (8
b) until it leaves and contacts the tap (lc).

Tap selector (2a) further from the state of FIG. 8-C.

(2b) and when the current-carrying contact 4 is driven, the 8th-d
As shown in the figure, the current-carrying contact αQ contacts the tap (8C). At this time, the current-carrying contact (to) becomes a circuit that short-circuits the inter-tap voltage (Vs) through the nonlinear resistor. As a result, the voltage applied to the nonlinear resistor is (Vo) at most, and the voltage-current characteristics of the nonlinear resistor (2) result in a voltage of 1. flows. As mentioned above, this value is extremely small and can be considered as zero current, and the load current flows from the tap (8C) through the current-carrying contact μs to the load α force. After this, tap selector (2a), (2b
) and the current-carrying contact OQ are driven, and as shown in FIG. 8-e, the tap (3C) and the current-carrying contact μs come into contact to complete the tap-down switching operation and the drive mechanism σQ stops operating. In this state, each tap selector (2a)
, (2b) are stopped in a state where they are not in contact with any of the taps (8b) and (8c).

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

In the above practical example, each pair of thyristors is connected in anti-parallel (parallel with one of the connected thyristor switches (this is explained in detail when a non-linear resistor is connected).
Even if the non-linear resistor is connected in parallel with the other thyristor switch or both thyristor switches, the same effect as in the above embodiment can be expected.

〔Effect of the invention〕

As described above, according to the present invention, a non-linear 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 activated. Since it is configured to be non-conductive, tap switching can be performed even with a minute current load.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a tap switching device on load according to an embodiment tζ of the present invention, Fig. 2 is a voltage-current characteristic diagram of a non-linear resistance, Fig. 8 is an operational diagram of tap switching, and Fig. 4 is FIG. 5, which is a block diagram of a conventional on-load tap switching device, is a diagram showing the phase relationship between the outputs of a conventional voltage sensor and a current sensor. In the figure, (la,) to (1d) are thyristor elements,
(2a) - (2C) are tap selectors, (aa) -
(8C) is a tap, (4) is a transformer winding, (6) is a current detector, (6) is a voltage sensor, (8) is a gate logic circuit, (9) is an ignition circuit, and un is a tap switch. Rise detection contact,
(6) is a tap switching falling detection contact, (2) is a nonlinear resistor, □□□ is a current sensor output detection circuit, CL4 is a switch, (to) is a current-carrying contact, σQ is a drive mechanism, and aη is a minute current load. . Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In a transformer that switches the taps by connecting a thyristor switch in which thyristors are connected in antiparallel to multiple taps of a transformer each having a different voltage, when the current in the load circuit is below the sensitivity level of the current detector, An on-load tap switching device characterized in that the tap is switched by making the thyristor switch non-conductive and allowing the current of the load circuit to flow through a nonlinear resistor connected in parallel with the thyristor switch. (2) A thyristor switch in which thyristors are connected in antiparallel is connected to the first terminal and the third terminal of a tap selector having a first terminal, a second terminal, and a third terminal, respectively, and In a device that switches the tap of a transformer by connecting a conductor to the terminal No. 2, when switching the tap, the first terminal and the third terminal are connected to the tap, and when the tap is used, only the second terminal is connected. is connected to the tap, and in the transition process of the tap selector, one tap and either the first terminal and the second terminal or the second terminal and the third terminal come into contact at the same time. An on-load tap switching device characterized by: