JPS62272721A - Semiconductor breaker - Google Patents

Abstract

PURPOSE:To reduce the number of arrestors connected in parallel by connecting an arrestor to each of parallel-connection GTO thyristors in parallel and damping resistors having a proper value in series with a free wheeling diode. CONSTITUTION:Let the gate turn-off time of the GTO thyristors 3, 4 be TG3, TG4 respectively and supposing of TG3<TG4, then a voltage across a snubber capacitor 3C exceeds a DC power voltage E when the GTO thyristors 3, 4 are turned off, thereby conducting the free wheeling diode 5, and a load current flows to the snubber capacitor 3C and the free wheeling diode 5. The overvoltage caused in the GTO thyristors due to the electromagnetic energy stored in a balance reactor inserted in series with the GTO thyristors is suppressed by the arrestor connected in parallel with each of the GTO thyristors connected in parallel.

Description

Detailed description of the invention 3. Detailed description of the invention [Technical field to which the invention pertains] The present invention connects a plurality of GTO thyristors in parallel, each having a snubber circuit connected in parallel, and connects these GTO thyristors to the same gate. Turn on at signal.

This relates to a semiconductor breaker that is turned off.

[Prior art and its problems]

When using multiple GTO thyristors connected in parallel, if there is a difference in the turn-off time when each GTO thyristor turns off, this difference in turn-off time will cause imbalance in the current shared by each GTO thyristor (
Turn-off time is defined as turn-off time - accumulation time + fall time). Generally, there are variations in the characteristics of semiconductor devices, and the above-mentioned turn-off times are not the same.

FIG. 4 is a main circuit connection diagram of a semiconductor breaker in which two GTO thyristors are connected in parallel. In this Figure 4, l
is the DC power supply, 2 is the power supply inductance, and 3.4 is the GTO
A thyristor 7 is a metal oxide nonlinear resistor (hereinafter referred to as an arrester), and 6 is a load including an inductance. For this load 6, a freewheeling diode 5 is connected in parallel.

Further, balance reactors 3L and 4L are connected in series to each of the GTO thyristors 3.4.

Furthermore, a snubber circuit 3S is connected to the GTO thyristor 3, and is configured by connecting a snubber capacitor 3C and a snubber resistor 3R in series, and connecting a snubber diode 3D in parallel to the snubber resistor 3R. Similarly, GTO thyristor 4 has a snubber capacitor 4C, a snubber resistor 4R, and a snubber diode 4D.
The snubber circuits 4S are connected in parallel.

The freewheeling diode 5 is connected to prevent the snubber capacitor from being overcharged by the energy stored in the inductance of the load 6 by shunting the load current to the 5 side when the load current is cut off.

FIG. 5 is an operational waveform diagram of each part of the DC cutoff device shown in FIG. 4, and the horizontal axis is the time axis. In Figure 5, (
A) is the turn-off signal, (B) is the current of GTO thyristor 3 ■1, and (C) is the voltage of GTO thyristor 3 ■
3. In (d), the currents t, c, (
E) is the current I4 of GTO thyristor 4, (E) is G
The voltage of TO thyristor 4 is 4, (G) is the current I4 of snubber capacitor 4C, and (H) is the current I of arrester 7.
1. (S) is the current I2 of the freewheeling diode 5, and (N) is the load current ■. It is shown.

Part 6 is a graph showing the fundamental characteristics of arrester current-voltage. Let the voltage of the arrester be v, and its current be i
When r, the vertical axis represents i, the horizontal axis represents ■, and Er represents the limiting voltage of the arrester. Figure 6 shows that when the arrester voltage vr exceeds the limit voltage E1, the current increases by 1r.
This shows that the voltage rises rapidly and exhibits constant voltage characteristics.

The operation of the semiconductor breaker will be described below with reference to FIGS. 4, 5, and 6.

The gate turn-off time of each GTO thyristor 3, 4 is TG3. TG4, and T due to element variations.
It is assumed that G3<TG4.

As can be seen from FIG. 5(a), turn-off signals are simultaneously applied to the gates of both GTO thyristors 3.4 at time TO. At this point, both GTO thyristors 3.4 are in a conductive state, and the current flowing through each is equal. Ii =
Assume that 14 = To /2.

When the turn-off time TG3 passes from time To to time T1, the GTO thyristor 3 is turned off, so the current that had been flowing through the GTO thyristor 3 until then flows into the snubber capacitor 3C. As a result, the current 3 of the GTO thyristor 3 decreases as shown in Fig. 5 (b).

(See (d)). However, L and L are the inductances of the balance reactors 3L and 4L, respectively, and C is the capacitance of the snubber capacitor 3C.

On the other hand, the current flowing through the GTO thyristor 4 increases as follows from time Tl.

After the turn-off time TG4 has elapsed from time To, time T2
When this occurs, the GTO thyristor 4 is turned off. Here, if ΔTG=TG4-TG3, the cutoff current ITJ of the GTO thyristor 4 is expressed by , and the current increase ΔI is expressed by .

When the GTO thyristor 4 is turned off, the current flowing through the GTO thyristor 4 flows into the snubber capacitor 4C (see (e) and ()) in FIG. 5).

After this, take snubber capacitors 3C and 4C and axle 3L.
, 4L constitute an LC resonance circuit, and the oscillating current is superimposed.

At time T3, when the voltage of the snubber capacitor 3C exceeds the limit voltage Er of the arrester 7, current begins to flow through the arrester (see FIGS. 5(c) and 5(h)). However, Er≦
V is the allowable repetitive peak voltage of the GTO thyristor.

At time T4, the current flowing through the arrester 7 reaches the load current I0. At the same time, the current flowing through snubber capacitor C4 decays to zero. At this time, the voltage of the GTO thyristor 4 becomes maximum. This maximum voltage value V4F is the snubber capacitor 4C
The current of the capacitor 4C when the voltage reaches the arrester limit voltage Er can be expressed as.

With this, the turn-off operation of the GTO thyristor is completed.

Equation (4) is the balance reactor L3. It is shown that as L4 is increased, the current increase amount Δ■ becomes smaller.

Furthermore, equation (5) indicates that the maximum voltage value of the GTO thyristor 4 increases as the balance reactor L4 becomes thicker. Maximum voltage value V4p of GTO thyristor 4
is its allowable repetitive peak voltage V.

If it exceeds this value, the GTO thyristor 4 will be destroyed.

Therefore, in order to suppress the current increase amount ΔI, balance reactor L3. When L4 is increased, the maximum voltage value of GTO thyristor 4 ■4. The capacitance C of the snubber capacitor 4 must be increased in order to suppress the permissible repetitive peak voltage (1) to less than 8, which has disadvantages such as an increase in the size of the device. Furthermore, since the load current after being cut off is only attenuated by the loss of the on-voltage of the freewheeling diode, there is a drawback that the load current cut-off time is longer.

[Purpose of the invention]

An object of the present invention is to store energy in a balance reactor when a balance reactor is connected in series to each GTO thyristor in order to suppress current imbalance caused by variations in turn-off time when GTO thyristors are connected in parallel. prevents overvoltage of the GTO thyristor caused by electromagnetic energy,
Furthermore, the load current cut-off time (the time from when the GTO thyristor turns off until the fault current decays to zero) is set to a practical time, reducing the energy consumption of the arrester and reducing the number of parallel arrester elements. It's about doing.

[Key points of the invention]

The present invention focuses on the limiting voltage characteristics of the arrester, and suppresses the overvoltage of the GTO thyristor generated by the electromagnetic energy stored in the current balance reactor by connecting the arrester in parallel to each of the GTO thyristors connected in parallel. This is what I am trying to do. At the same time, we focused on the fact that by connecting a damping resistor of an appropriate value in series with the freewheeling diode, the electromagnetic energy of the load inductance can be shared between the arrester and the damping resistor while maintaining a practical cutoff time. This makes it possible to reduce the number of parallel arrester elements.

[Embodiments of the invention]

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention.

In FIG. 1, 1 is a DC power supply, 2 is a power supply inductance, 3 and 4 are GTO thyristors, and 6 is a load including an inductance. 5 is a freewheeling diode,
10 is a damping resistance.

Each GTO thyristor 3.4 has a snubber circuit 3.
3.43 are connected in parallel, and current balance reactors 3L and 4L are connected in series, respectively.

The snubber circuit 3S includes a snubber capacitor 3C and a snubber resistor 3R connected in series, and a snubber diode 3D connected in parallel to the snubber resistor 3R. Snubber circuit 4
S also includes a snubber capacitor 4C, a snubber resistor 4R, and a snubber diode 4D, which are connected in the same way. Further, arresters 8.9 are connected in parallel to each of the GTO thyristors 3 and 4.

FIG. 2 is an operational waveform diagram of each part of the main circuit of the embodiment according to the present invention shown in FIG. 1, and the horizontal axis is the time axis. This second
In the diagram, (a) shows the turn-off signal, (b) shows the current of GTO thyristor 3, (c) shows the voltage of GTO thyristor 3, V8, and (d) shows the current I3 of snubber capacitor 3C.
(E) Current I8 of arrester 8, (F) Current I4 of GTO thyristor 4, (G) Voltage ■4 of GTO thyristor 4, (H) Current ■4 of snubber capacitor 4C (
In January, the current of arrester 9 is ■1, and the load current is on (nu). ,
The current I of the freewheeling diode 5 is shown in (h).

The operation of each part of the breaker will be explained below with reference to FIGS. 1 and 2.

The gate turn-off time of GTO thyristors 3 and 4 is set to TG3. TG4, and assume that T(,3<TG4) due to variations in the turn-off time of the elements.

At time TO, a turn-off signal is applied to the gates of both GTO thyristors 3.4 at the same time (see FIG. 2(a)). At this point, both GTO thyristors 3.4 are conducting and the current flowing through each is equal, 13 = Ia = T
. /2. ■. represents the current of the load 6.

When the turn-off time TG3 passes from time To and reaches time T1, the GTO thyristor 3 turns off, so the current that had been flowing through the GTO thyristor 3 flows into the snubber capacitor 3C, and the inductance L3 of the current balance reactors 3L and 4L. ．． The resonant current waveform is attenuated by L4 and the capacitance C of the snubber capacitor 3C. The current flowing through the GTO thyristor 4 increases by that amount, but is suppressed by the current balance reactors 3L and 4L (see FIGS. 2(b), (d), and (f)).

When the turn-off time TG4 elapses from time To and reaches time T2, the GTO thyristor 4 turns off.

When the GTO thyristor 4 is turned off, the current flowing through the GTO thyristor 4 flows into the snubber capacitor 4C (see Fig. 2).

(See (h)).

At time T3, the voltage of the snubber capacitor 3C exceeds the DC power supply voltage E, which causes the freewheeling diode 5 to conduct, and the load current begins to flow in a shunt manner between the snubber capacitor 3C and the freewheeling diode 5.

At time T4, the voltage of the GTO thyristor 3 exceeds the limit voltage Er of the arrester 8. As a result, the current flowing through the snubber capacitor 3C is diverted to the arrester 8, and the G
The maximum voltage of TO thyristor 3 is the arrester limit voltage E,
(See Figure 2 (c), (d), and (e)).

Therefore, the load current is divided between the arrester 8 and the freewheeling diode 5.

At time T5, the voltage of the GTO thyristor 4 also exceeds the limit voltage E of the arrester 9. As a result, the current flowing through the snubber capacitor 4C is commutated to the arrester 9, so that its maximum voltage is suppressed to the limit voltage Er by the arrester (see FIGS. 2(a)), (h), and (s)).

With this, the turn-off operation of the GTO thyristor is completed.

The overvoltage generated in the GTO thyristor due to the electromagnetic energy stored in the balance reactor inserted in series with the GTO thyristor to suppress current imbalance caused by variations in the turn-off time of individual GTO thyristors is It can be suppressed by an arrester connected in parallel to each of the thyristors.

After this, the electromagnetic energy of the load is consumed by the arresters 8 and 9 and the current limiting resistor lO, the load current is attenuated to zero, and the shutoff is completed.

FIG. 3 is a graph showing the relationship between the energy consumption of the arrester, the cut-off time, and the damping resistor 10. Let the resistance value of the damping resistor 10 be R, the energy consumption of the arrester be Q, and the cut-off time be T. Q is on the vertical axis.

T is plotted, and R is plotted on the horizontal axis. This graph shows that when the damping resistance R is made smaller, the energy consumption of the arrester becomes smaller, but the cut-off time T becomes longer.

Q, , , T, , o represent the energy consumption and cut-off time of the arrester in the absence of a freewheeling diode, respectively. For example, the cutoff time is T=T, >
If T is selected, the damping resistance becomes R=R, and
The energy consumed by the arrester is Q=Q, <Q~. Therefore, by appropriately selecting an appropriate cutoff time T, the energy consumption of the arrester can be reduced.

〔Effect of the invention〕

When a plurality of GT○ thyristors are connected in parallel and used, variations in the turn-off times of individual GTO thyristors cause an imbalance in the current shared by each GTO thyristor. In order to suppress this, a current balance reactor is connected to each GTO thyristor. However, if the inductance of the balance reactor is increased in order to suppress current imbalance, there is a problem in that the electromagnetic energy stored in the reactor generates an overvoltage in the GTO thyristor when it is cut off, leading to destruction of the GTO thyristor.

According to the present invention, overvoltage of the GTO thyristors can be suppressed by connecting an arrester in parallel to each of the G'TO thyristors connected in parallel, so there is no need to use a snubber capacitor with a large capacitance as in the past. Therefore, it is possible to avoid increasing the size and cost of the device.

Furthermore, by connecting a damping resistor in series with the freewheeling diode, the load current can be attenuated quickly.At the same time, by selecting an appropriate value of the damping resistor, the electromagnetic energy of the load inductance can be absorbed into the arrester while maintaining a practical cut-off time. Since the energy consumption of the arrester can be reduced by sharing the energy with the current limiting resistor, the number of parallel arrester elements can be reduced, making it possible to further downsize the device and reduce costs.

[Brief explanation of drawings]

Fig. 1 is a main circuit connection diagram of an embodiment of the present invention, and Fig. 2 is a main circuit connection diagram of an embodiment of the present invention.
The operating waveform diagram of the embodiment of the semiconductor breaker according to the present invention shown in the figure, Figure 3 is a graph showing the relationship between the energy consumption of the arrester, the cut-off time, and the current limiting resistance, and Figure 4 is the main circuit of the conventional semiconductor breaker. 5 is an operating waveform diagram of the conventional semiconductor breaker shown in FIG. 4, and FIG. 6 is a graph of the voltage-current characteristics of the arrester. 1 is DC power supply, 2 is power inductance, 3゜4 is GT
O thyristor, 3L, 4L are balance reactors, 3S
, 4S is a snubber circuit, 5 is a freewheeling diode, 6 is a load, 8.9 is an arrester (metal oxide nonlinear resistor), 1o is an attenuation (a); M concave

Claims (1)

[Claims] 1) In a semiconductor breaker, a plurality of gate turn-off thyristors (hereinafter referred to as GTO thyristors) each having a snubber circuit connected in parallel are connected in parallel, and these GTO thyristors are turned on and off by a common gate signal. A balance reactor is connected in series to each GTO thyristor in order to suppress the current imbalance caused by variations in the turn-off time of the GTO thyristors. A metal oxide nonlinear resistor is connected in parallel with each GTO thyristor, and a series connection circuit of a diode and a resistor is connected between the load side terminals of the circuit breaker, and the load current is returned to this series connection circuit when the current is cut off. A semiconductor breaker characterized in that the load current is rapidly attenuated by