JPS6239709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a half-wave extension method for extending an arc caused by a current from a low-voltage, large-current source in a synthetic test of an AC shield or breaker.

Verifying the capacity of a circuit breaker requires a large current and high voltage, but it is generally difficult to supply this directly from a single power source and perform a short circuit test with an actual load. For this reason, equivalent tests are performed to obtain similar results, and one known example is a synthetic test that is performed by combining two types of power sources: a low voltage, large current source and a high voltage, low current source.

An example of the circuit for the synthesis test is shown in FIG. 1, and its operating waveforms are shown in FIG. Figure 1 shows a synthetic test circuit called the parallel current superimposition method, where Gen is the generator, Lg is the reactor, Cg is the capacitor, S _H is the auxiliary disconnector, Sp is the sample or disconnector, Re is the resistor, Ce is a capacitor, Lv is a reactor, G is a gap, Cv is a capacitor, and Rec is a charging device. The test is conducted as follows. First, from the generator Gen to the large current Ig
is supplied to the test sample or disconnector S _H (Figure 2b) shows the generator voltage and Fig. 2c shows the waveform of the generator current), then at time To the test sample or disconnector S H The main contact of disconnector S _H opens. Let T ₁ be the time of the first zero point of current Ig, and T ₂ be the time of the second zero point.
Assume that the gap G is activated just before T ₂ to apply a small current Iv from the capacitor Cv charged to a high voltage (Fig. 2e), and the current is suddenly cut off at the zero point of this small current Iv. As shown in FIG. 2f, a re-electromotive voltage TRV is generated between the poles of the disconnector Sp.

In the above test, T ₂ −T ₀ is the arc time of the chopper or breaker, but in order to guarantee this arc time, the point of the first current zero point after the contact of the chopper or breaker is opened is
It is necessary to prevent the current Ig from being cut off at T ₁ , and the half-wave extension method is known as a method for forcibly continuing the arc in this part.

In the conventional half-wave extension method, as shown in FIG. 2d, a pulse current Ip having a polarity opposite to that of the current Ig is applied immediately before the zero point _T1 of the current Ig. That is, as shown in more detail in Figure 3,
At Tp of zero point T ₁ of current Ig, the current at that time
When pulsed currents with opposite polarity to Ig are applied, the resultant current becomes (Ig + Ip), and if the current slope at the current zero point of (Ig + Ip) is large to some extent, the breaker will not cut the current even when Ig + Ip = 0. Therefore, the arc continues for half a wavelength until the polarity of the current Ig reverses at zero point T ₁ and reaches the next current zero point T ₂ . A conventional half-wave extension circuit for obtaining such a pulse current is shown in FIG. In FIG. 4, the same reference numerals as in FIG. 1 represent the same elements.

To generate the above-mentioned pulse current, a discharge circuit is used consisting of capacitors C _p1 and C _p2 and resistors R _p and R _p2 . Capacitors C _p1 and C _p2 in advance
is charged, and a gap is established at T _p before the current zero point T ₁ .
By operating Gp, current Ip is superimposed on current Ig. The switch S is normally kept in a closed state, and when the arc continues at the current zero point _T1 , it is opened by the next current zero point _T2 .

As described above, the conventional half-wave extension circuit uses a discharge circuit composed of a resistor and a capacitor, but the problems are as follows. First, regarding the detection of the time Tp, the longer Tp is, the easier it is from the viewpoint of the detection method, that is, the operational accuracy of the gap Gp. However, when Tp is lengthened, it is necessary to increase the peak value of the superimposed pulse current Ip, and for this purpose, the resistors Rp and Rp ₂ must be made smaller, or the voltage charged to the capacitors C _p1 and C _p2 must be increased. There is a need. However, there is a limit to increasing the charging voltage of the capacitor because the withstand voltage of the reactor Lg and generator Gen is usually not very high. Also resistance
When Rp and Rp ₂ are made smaller, the time constant of the discharge circuit becomes smaller, so the discharge current Ip decreases by the time the current Ig reaches the zero point, and it virtually no longer serves as a current superimposition, failing to force the arc to continue. There are cases where Increase Tp, which represents the operating margin time,
Although it is possible to reduce the resistances Rp and Rp ₂ and still ensure arc continuation by increasing the capacitors Cp ₁ and Cp ₂ , this is not an economical method.

It is therefore an object of the present invention to provide a half-wave extension scheme which guarantees reliable arc continuity in an economical construction.

A feature of the present invention is that, just before the zero point _T1 of the current Ig described above, an oscillating current starting from the same polarity as the current Ig at that time is applied and superimposed. It has been found that half-wave extension can be achieved economically by making the current to be superimposed on the current Ig have the same polarity as the current Ig instead of having the opposite polarity as in the conventional method.

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, a square wave oscillating current is used as the oscillating current. In order to obtain this rectangular wave oscillating current, for example, as shown in FIG. 5a, a circuit is constructed in which a plurality of inductances L and capacitors c are connected in series in a π shape. In the circuit shown in Figure 5a, when the capacitor is charged to voltage E and the switch S is closed, the switch S has an amplitude E/Z (E is the capacitor charging voltage, Z) as shown in Figure 5b. =√
), period 4T (T=√×N; N is L, c
A rectangular wave oscillating current Ip of (the number of stages of the π-shaped circuit) flows.

According to the present invention, application of this rectangular wave oscillating current Ip is started immediately before the zero point _T1 of the current Ig from the low voltage large current source so that the polarity becomes the same as that of the current Ig at that time. However, in order to explain the advantages thereof, a case where the rectangular wave current Ip is applied with the opposite polarity to the current Ig and a case where the rectangular wave current Ip is applied with the same polarity will be explained below and the two will be compared.

Figure 6 shows the zero point T of the current Ig.The current is opposite to the _previous polarity.
FIG. 3 is a waveform diagram when Ip is applied. In FIG. 6, Tpm is the maximum value when detecting the current Ig before the zero point _T1 , and Δt indicates the variation range of the detection time (operation variation range of the gap Gp in FIG. 4). The combined current (Ig + Ip) is the current that flows through the test specimen and disconnector. In this case, in order to guarantee arc continuation, the amplitude E/Z of the rectangular wave current and the period 4T (in Fig. 6
2T is indicated by Ts) must be selected as follows.

Ts=Tpm+τ (1) It is necessary that τ>Tpm (here, T ₂
is the time from the zero point _T1 of current Ig until the polarity of current Ip is reversed). The reason for this is that when the polarity is reversed half a cycle Ts after the current Ip is applied,
This is because the polarity of the composite current (Ig+Ip) must not change. Therefore, the half period Ts of the square wave current Ip must be selected such that Ts>2Tpm (2).

Also, as the amplitude E/Z of the rectangular wave current Ip, the current Ip
It is necessary to make the value larger than the instantaneous value of the current Ig at the start of application of the current Ig. That is, E/Z>TpmdIg/dt (3) (here, dIg/dt indicates the slope of the current near the zero point of the current Ig).

FIG. 7 is a waveform diagram when application of the rectangular wave current Ip is started from the same polarity as the current Ig according to the present invention. In this case, the half period Ts of the rectangular wave current should just be Ts>Tpm (4). This shows that the period of the rectangular wave current can be selected to be about half as compared to Equation (2). Further, the amplitude E/Z of the current Ip may be as long as E/Z>{Ts-(Tpm-Δt)}dIg/dt(5). The reason for this is that before the zero point _T1 of the current Ig (Tpm−△
t), when the polarity of current Ip is reversed after half a cycle Ts, if the amplitude of current Ip is larger than the value of current Ig at that time, then the composite current (Ig
+Ip) can also be inverted (Figure 7b).

Comparing FIG. 6 and FIG. 7, it can be seen that in the method of FIG. 7, both the amplitude and period of the rectangular wave current Ip are greatly reduced. Being able to reduce the amplitude of the current Ip means that the charging voltage of the capacitor can be reduced in the circuit shown in Figure 5, and being able to shorten the period also reduces the overall √
This means that ×N can be made smaller, which leads to overall economy.

In the embodiment described above, the current from the low voltage high current source
Although the rectangular wave current has been selected as the arc half-wave extension current Ip superimposed on Ig, it is natural that other oscillating currents can be used as long as the conditions for arc continuation as a whole are satisfied.

In this way, unlike the conventional method, the present invention applies an oscillating current that starts from the same polarity as the current Ig before the zero point of the current Ig, thereby producing an economical and reliable half-wave. Extensions can be made.

[Brief explanation of the drawing]

Figure 1 is a composite test circuit diagram of an AC circuit breaker, Figure 2
The figure is an operating waveform diagram of the circuit in Figure 1, Figure 3 is a waveform diagram for explaining the conventional half-wave extension method, Figure 4 is a conventional half-wave extension circuit diagram, and Figure 5 is used in the present invention. An example diagram of the main part of a half-wave extension circuit, Figure 6 is a waveform diagram when applying a rectangular wave oscillating current with opposite polarity, and Figure 7 is a waveform diagram when applying a rectangular wave oscillating current with the same polarity according to the present invention. FIG. Sp: test sample or disconnector, Gen: generator, L: inductance, C: capacitor.

Claims (1)

[Claims] 1. In a half-wave extension method used in a composite test circuit for an alternating current shield or breaker equipped with a low-voltage, large-current source and a high-voltage, small-current source, the polarity of the low-voltage, large-current source is determined immediately before a predetermined current zero point of the low-voltage, large-current source. A half-wave extension method characterized by having an oscillating circuit that superimposes an oscillating current starting from the same polarity on a large current.