CN1529394A - A Short Circuit Fault Current Limiter Utilizing Solid State Switches - Google Patents

Abstract

A short-circuit fault current limiter using a solid-state switch, which is characterized in that it includes: a transformer, the primary side of the transformer is connected in series to the grid bus; a parallel resonant circuit includes a capacitor C, an inductor L, and a thyristor K, wherein the inductor L and the thyristor K is connected in parallel with capacitor C after being connected in series, and both ends of capacitor C are connected in parallel at the secondary side of the transformer; voltage detection and trigger circuit. The current limiter of this structure cuts off the peak of the short-circuit current of the power grid system, and has a very good restraint effect on the entire short-circuit current, avoiding the impact of large currents on electrical equipment, and the use of fault current limiters can also Correspondingly, the interrupting capacity of the circuit breaker is reduced, which brings economic benefits. At the same time, the invention has a simple structure, the thyristor K only needs to be closed and does not need to be turned off, and the closing time is less than 200ms, thereby effectively improving the service life and reliability of the thyristor.

Description

A Short Circuit Fault Current Limiter Utilizing Solid State Switches

technical field

The invention relates to the field of power system automation and belongs to flexible AC power transmission technology, in particular to a short-circuit fault current limiter which uses a solid-state switch to control the short-circuit fault current and its rising rate of the power system.

Background technique

The development of power electronics technology has made flexible power transmission technology (FACTS) widely valued in the automatic control of power systems. In the past, system parameters (such as voltage, phase, impedance, etc.) control. In quite a lot of FACTS control devices, the core component is the adjustable reactor working under high voltage and high current conditions. For example, the power system fault current limiter is one of the FACTS control devices. To sum up, the fault current limiters currently being researched and tested can be divided into the following two categories:

1. A fault current limiter consisting of a fast-acting turn-off transistor (GTO) switch in parallel with an impedance. During normal operation, the GTO is fully turned on. When the fault current reaches the set value, the GTO is turned off, and the impedance is connected in series to the grid bus to limit the current. The disadvantage of this current limiter is that GTO operates under high voltage and high current conditions for a long time, with poor reliability, large device loss, difficult to solve heat dissipation problems, complex control system and high price. References for this type of technology include: T Ueda, Solid-state current limiter for power distribution system, IEEE Transaction on Power delivery.Vol.4, pp.1796, Oct.1993.

2. Superconducting current limiter. Domestic and foreign experts on superconducting current limiters have done a lot of research work, and the representative articles published by domestic and foreign experts include: "Research Progress in Electric Power Application of Superconducting Fault Current Limiters", Ye Lin, Power System Automation, Vol.23 , NO.7, 1999.4. Due to the complex technology of the superconducting system, the rectifier element works under high voltage and high current conditions for a long time, so the reliability is poor, the additional loss of the device is also large, and the price is expensive.

Contents of the invention

The object of the present invention is to provide a short-circuit fault current limiter using a solid-state switch with fast response, reliable operation, simple structure, low loss, easy fabrication and low cost in view of the problems and deficiencies in the prior art.

Technical scheme of the present invention is realized like this:

A short circuit fault current limiter utilizing a solid state switch, characterized by including:

A transformer with a suitable transformation ratio whose magnetic circuit is linear and whose iron core is in an unsaturated state during the normal operation of the grid system and during the short-circuit fault time, and the primary side of the transformer is connected in series with the grid busbar;

A parallel resonant circuit, including a capacitor C with a suitable capacity, an inductor L with a suitable inductance, and a thyristor K, where the inductor L and the thyristor K are connected in parallel with the capacitor C, and the two ends of the capacitor C are connected in parallel to the two sides of the transformer Secondary side;

A voltage detection circuit for detecting the secondary side voltage of the transformer and controlling and driving the trigger circuit according to the voltage, and a trigger circuit for generating a pulse voltage to trigger whether the thyristor K is turned on or not according to the control driving signal of the voltage detection circuit.

Wherein the voltage detection circuit comprises a voltage transformer and a voltage comparator connected in parallel at both ends of the capacitor C, wherein the output terminal of the voltage transformer is connected to one input terminal of the voltage comparator, and the other input terminal of the voltage comparator is connected to a reference voltage, Its output end contacts the trigger circuit input end.

Its basic working principle and process are: when the power system is working normally, the voltage on the primary side of the transformer connected in series in the grid bus is less than a small voltage, such as 50V (for 10KV lines), and the secondary side of the transformer is correspondingly The voltage on the side is also relatively low. If it is lower than 500V, that is, the voltage detected by the voltage transformer is low and lower than the reference voltage of the voltage comparator, the system is considered to be in a normal state. When a short circuit occurs in the system, the voltage on the secondary side of the transformer can easily reach dozens of times the voltage during normal operation. If the reference voltage is selected as 5 to 10 times the normal voltage, after a short circuit occurs, the voltage on the secondary side rises to the reference voltage For a short time, the thyristor is closed at this time, so that the line presents a large impedance, thereby suppressing the fault current.

When the system is running normally, the voltage comparator outputs a low level to the trigger circuit. The trigger circuit is not excited, and it does not generate a trigger pulse to the thyristor K, so that the thyristor K is in a disconnected state, so that the impedance of the primary side of the transformer is very small , has almost no impact on the grid operation. When a short-circuit fault occurs in the power system, the voltage on the grid bus is almost all added to the primary side of the transformer, and the voltage on the secondary side also rises rapidly at this time, and the voltage transformer detects a higher voltage, such as greater than 2500V , 5 to 10 times higher than the normal working voltage, higher than the reference voltage of the voltage comparator, at this time the voltage comparator outputs a high level to the trigger circuit, which stimulates the trigger circuit to work, so that the trigger circuit sends a trigger pulse to the thyristor K, The thyristor K is turned on instantaneously, so that the inductance L and the capacitor C generate parallel resonance, so that the transformer immediately presents a large impedance, which effectively limits the short-circuit current in the grid bus. When the thyristor K is closed for a period of time, such as 100-200ms, the circuit break The switch acts to disconnect the faulty line, and there is no current flowing through the primary side of the transformer, so that the thyristor K (solid-state switch) is naturally turned off, waiting for the next short circuit of the power grid system to work again, which makes the peak of the short circuit current of the power grid system cut off , and has a good inhibitory effect on the entire short-circuit current, avoiding the impact of large currents on electrical equipment, and the use of fault current limiters can also reduce the breaking capacity of the circuit breaker accordingly, bringing economic benefits. The current limiter of this structure has a simple structure, and the thyristor K only needs to be closed without being turned off, and the closing time is less than 200ms, so that the service life and reliability of the thyristor can be effectively improved, and the object of the present invention is achieved.

Below in conjunction with accompanying drawing, describe basic structure of the present invention and working process and principle in detail:

Description of drawings

Figure 1 is a schematic diagram of the structure of the device of the present invention in a power system; where R _s and L _s are equivalent resistance and inductance on the power supply side of the power system, R _L and L _L are equivalent line resistance and inductance in the power system, and u _s is the system equivalent power supply.

Figure 2 is a transformer circuit diagram during normal operation of the power system;

Fig. 3 is a transformer circuit diagram when the power system is short-circuited;

Fig. 4 is the equivalent circuit diagram of series transformer;

Figure 5 is a T-type equivalent circuit diagram of a series transformer in normal operation of the power system;

Figure 6 is a T-type equivalent circuit diagram of a series transformer when the power system is short-circuited.

Detailed ways

As shown in Figures 1 to 6, the present invention includes: a transformer with a suitable transformation ratio whose magnetic circuit is linear and whose iron core is in an unsaturated state during the normal operation of the power grid system and during the short-circuit fault time, and the primary side string of the transformer Into the grid bus; a parallel resonant circuit, including a capacitor C with a suitable capacity, an inductor L with a suitable inductance, and a thyristor K, wherein the inductor L and the thyristor K are connected in parallel with the capacitor C after being connected in series, and the two ends of the capacitor C Parallel connection on the secondary side of the transformer; when designing the series transformer, capacitor and inductance of this embodiment, the transformer should first meet the following conditions: the transformer core is in an unsaturated state during the normal operation of the system and when a short-circuit fault occurs; The road is linear. For this reason, it is better to use good magnetic materials when designing transformers, so that r _m can be ignored, and the excitation reactance is x _m . Therefore, in the above two cases, it is ensured that the excitation impedance Z _m and the transformer leakage impedance are constant, and that they have nothing to do with the magnitude of the injection current at the secondary side of the transformer. As shown in Figure 1 and Figure 4, when the primary side winding AX of the transformer is connected in series in the line, the transformation ratio $\tilde{k}=W_2/W_1,$ $k={\left(\tilde{k}\right)}^{-1},$ (k<1). From the transformer structure: ${\stackrel{\&CenterDot;}{u}}_1={\stackrel{\&CenterDot;}{I}}_1{\stackrel{\&CenterDot;}{Z}}_1-\stackrel{\&Center\; Dot;}{\mathrm{E.}}={\stackrel{\&Center\; Dot;}{I}}_1{\stackrel{\&Center\; Dot;}{Z}}_1+{\stackrel{\&Center\; Dot;}{I}}_m{\stackrel{\&Center\; Dot;}{Z}}_m={\stackrel{\&Center\; Dot;}{I}}_1{\stackrel{\&CenterDot;}{Z}}_1+({\stackrel{\&CenterDot;}{I}}_1+{{\stackrel{\&CenterDot;}{I}}_2}^{\&prime;}),$ Among them, Z ₁ =r ₁ +jx _1σ , Z _m =X _m are the primary side leakage impedance and excitation impedance of the transformer respectively; ${\stackrel{\&CenterDot;}{I}}_m={\stackrel{\&Center\; Dot;}{I}}_1+{{\stackrel{\&Center\; Dot;}{I}}_2}^{\&prime;};$ ${{\stackrel{\&CenterDot;}{I}}_2}^{\&prime;}=I_2/k$ is the transformer secondary side current the converted value of . Therefore, when the power grid is operating normally, the solid-state switch K is not conducting. At this time, the series transformer circuit and its T-shaped equivalent circuit are shown in Figure 2 and Figure 5: Design the capacitor C so that x _c ′ and x _2σ ′ Equivalent, that is, the capacitor C and the secondary side leakage reactance L _2σ of the transformer are required to be close to the series resonance state. Secondary side equivalent impedance Z _eq ′=r ₂ ′+j(x _2σ ′-x _c ′), |Z _eq ′|<<|X _m |, so the equivalent impedance of the whole transformer at this time ZZ ₁ +Z _ea ′, because |Z| is very small, it has almost no impact on the grid operation. When a short-circuit fault occurs in the system, a trigger pulse is sent to the solid-state switch K. If the inductance L is designed so that the inductance L resonates with r and C in parallel (that is, satisfies ω ₀ ² L ² C+R ² C=L), then the transformer at this time The impedance of the secondary circuit is equivalent to that of the excitation circuit. At this time, the equivalent circuit diagram of the series transformer and its T-shaped equivalent circuit diagram are shown in Figure 3 and Figure 6. The equivalent impedance of the entire transformer is Z=Z ₁ +Z _eq ′∥ Z _m , because |Z _eq ′| is of the same order of magnitude as |Z _m |, the transformer presents a large impedance, which greatly reduces the short-circuit current.

In this design, a detection circuit for detecting the secondary side voltage of the transformer is included, and the trigger circuit is driven by the voltage control to control the conduction of the thyristor. Since the solid-state switch only needs to be turned on and does not need to be powered off, it is sufficient to use a thyristor as a switching device, which controls the cost of the current limiter. Here, the voltage detection circuit and the trigger circuit have mature circuits, and ordinary technicians can obtain a variety of structural components without creative work. This article will not describe their structural components in detail. In this embodiment, the voltage detection circuit includes a voltage transformer and a voltage comparator connected in parallel at both ends of the capacitor C, wherein the output terminal of the voltage transformer is connected to one input terminal of the voltage comparator, and the other input terminal of the voltage comparator The reference voltage is connected, and its output terminal is connected to the input terminal of the trigger circuit, and the trigger circuit is triggered by an optocoupler.

Claims (2)

1. A short-circuit fault current limiter utilizing a solid-state switch, characterized in that it comprises: A transformer with a suitable transformation ratio whose magnetic circuit is linear and whose iron core is in an unsaturated state during the normal operation of the grid system and during the short-circuit fault time, and the primary side of the transformer is connected in series with the grid busbar; A parallel resonant circuit, including a capacitor C with a suitable capacity, an inductor L with a suitable inductance, and a thyristor K, where the inductor L and the thyristor K are connected in parallel with the capacitor C, and the two ends of the capacitor C are connected in parallel to the two sides of the transformer Secondary side; A voltage detection circuit for detecting the secondary side voltage of the transformer and controlling and driving the trigger circuit according to the voltage, and a trigger circuit for generating a pulse voltage to trigger whether the thyristor K is turned on or not according to the control driving signal of the voltage detection circuit. 2. The short-circuit fault current limiter utilizing a solid-state switch according to claim 1, wherein said voltage detection circuit includes a voltage transformer and a voltage comparator connected in parallel at both ends of the capacitor C, wherein the output terminal of the voltage transformer One of the input terminals of the voltage comparator is connected, the other input terminal of the voltage comparator is connected to the reference voltage, and its output terminal is connected to the input terminal of the trigger circuit.

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