RU113884U1 - HYBRID CURRENT LIMITER - Google Patents

Abstract

1. Hybrid current limiter containing a superconductor with a series-connected high-speed switch and a parallel-connected shunt unit, resistance and EMF of the system, characterized in that it is equipped with an additional slow switch, a shunt switch, current sensors, a voltage sensor of the superconductor and a control and protection system, while the superconductor is located in a cryostat with liquid nitrogen, the slow-acting switch is connected in series with the shunt block and the shunt switch, and the inputs of the control and protection system are connected to the current sensors and the superconductor voltage sensor, and the outputs of the control and protection system are connected to the control circuits of the switches, while the outputs of the switches made with the possibility of their connection with substation switches. ! 2. Hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a reactor. ! 3. Hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a resistor. ! 4. Hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a transformer.

Description

The utility model relates to the field of electrical engineering, namely to hybrid current limiters (TRP).

A hybrid inductive type current limiter is known [1], in which a short circuit current (short circuit), initially flowing through a superconductor under the influence of its heating, is transferred to an inductive circuit, which shunts it. The disadvantage of [1] is that the entire set of power system modes is not considered and the goal is not to reduce the volume of the superconductor by eliminating the flow of currents through it during overload and switching.

A device [2] is known in which the primary winding of the transformer is included longitudinally in the load circuit, and superconductors with a resistive or inductive shunt are included in the secondary windings of the transformer. The disadvantage of [2] is that the presence of electromagnetic connections of the transformer makes it difficult to choose the design of a superconductor, and the device itself has a high cost due to complexity.

A device [3] is taken as a prototype, which contains: a superconductor of a joint venture, a resistive shunt, a high-speed switching device, a high-speed switch, resistance and EMF of the network, an inductance for displacing current from the joint venture to the shunt. The device operates as follows. Operating current flows through the switching device and switch. At the time of a short circuit (SC), after 100 μs, the device opens, and the current passes to the SP. After rapid heating of the joint venture and an increase in its resistance, the short-circuit current is displaced into the shunt.

The disadvantage of [3] is the complexity of the apparatus, which should have high speed, high throughput and high resource, as well as the lack of coordination of work in the event of short circuit, switching operations and overloads.

The technical task is to create a gas turbine with a limited amount of superconductor, allowing you to choose the current path depending on the mode of operation.

The technical result is to reduce the cost of a superconductor.

The technical result is achieved due to the fact that the hybrid current limiter containing a superconductor with a series-connected high-speed switch and a parallel connected shunt block, resistance and EMF of the system is equipped with an additional slow-acting switch, a shunt switch, current sensors, a voltage sensor of the superconductor and a control and protection system. The superconductor is placed in a cryostat with liquid nitrogen. The slow-acting circuit breaker is connected in series with the shunt block and the shunt switch. The inputs of the control and protection system are connected to current sensors and a voltage sensor of the superconductor. The outputs of the control and protection system are connected to the control circuits of the switches. The outputs of the switches are made with the possibility of their connection with the switches of the substation. The shunt block is made in three versions - in the form of a reactor, in the form of a resistor and in the form of a transformer.

The device is illustrated by drawings, where

figure 1 shows the device of the TRP with a shunt unit in the form of a reactor or resistor;

figure 2 shows the current shape of a three-phase short circuit in the absence of TRP;

figure 3 shows the shape of the short circuit current in the presence of TRP;

figure 4 shows the power of heat [J];

figure 5 shows the shape of the current TRP when you turn on the idle transformer with its residual magnetization

figure 6 shows the device of the gas turbine with a shunt block in the form of a transformer, in the secondary winding of which is included a superconductor.

The device contains (figure 1):

superconductor 1 (SP) in a liquid nitrogen cryostat, shunt SP block 2, main switch 3, additional switch 4, resistance 5 and EMF 6 of the system, control and protection system 7, current sensors in GTO circuits 8, 9, 10, shunt switch 11, voltage sensor 12 SP 1.

In the right part of figure 1, the modes are displayed from top to bottom:

I - close fault, II - remote fault, III - inclusion of an idle transformer, IV - inclusion of a braked engine. Solid lines correspond to power circuits, a rare dotted line corresponds to a measurement circuit, a frequent dotted line corresponds to a control circuit.

As the input signals of the control system 7 are used: the currents of the sensors 8, 9, 10, the voltage from the sensor 12, the heat generation energy of the joint venture and the form of current in it, the state of the switches 3, 4, 11 and switching devices adjacent to the TRP.

The shunt block 2 has several options:

Option 1 - the shunt block 2 is made in the form of a reactor or resistor;

Option 2 - the shunt block 2 is made in the form of a transformer.

When executing the shunt block 2 according to option 1:

The operation of the device (figure 1) is as follows. In operating mode, at rated current I _nom and lower values, switches 3 and 4 are closed. Current flows through superconductor 1 and switch 4, because the resistance of the SP at a value of I _nom below the critical current SP - I _cr close to zero. When a short circuit occurs (modes I, II), the resistance of the joint venture increases sharply, the current passes to the shunt unit 2, and the switch 4, upon a signal from the current sensor 8, when the setpoint of the control system 7 is increased (approximately 2-3I _nom ) is turned off when the current switch through zero. The short-circuit current in the SP circuit is switched off by the high-speed circuit breaker 3 approximately 0.01 s after the occurrence of the short-circuit, and the circuit of the shunt block 2 is turned off after 0.1 s by the slow-circuit breaker 4.

In the control and protection system 7, by the signals from the current sensor 8 and voltage 12, the heat dissipation power of the joint venture and its temperature T are calculated, so that when T exceeds the value T _{pr of the} superconductor, the control system gives a signal to turn on the switch 11, however, in modes I, II, the switch 11 is blocked by a signal from the control and protection system 7.

During switching operations (modes III and IV - respectively, switching on an idle transformer and a braked motor) the level of inrush currents of the magnetization of steel of a transformer or motor depends on their power and is usually 3-4 times lower than short-circuit currents, but their duration can reach 100 network periods. In these modes, it is unacceptable to turn off the switch 3, i.e. control and protection system 7 blocks the shutdown of the switch 3 and unlocks the inclusion of the bypass switch 11.

The control and protection system 7, based on the switching signals of the devices at the substation, as well as by the magnitude of the current in the joint venture (sensor 8) or the heat dissipation capacity of the joint venture (sensors 8 and 12), includes a switch 11 that shunts the joint venture. Preliminarily, the current, due to heating of the superconductor 1, passes to the shunt unit 2. After turning on the switch 11, the current passes to the circuit of switches 11 and 3. After a time of 1-2 s (determined by the reclosure cycle time and the cooling time constant of the joint venture), the switch 11 is turned off. Typically, the current setting and the response delay to turn on the switch 11 is 1.5I _nom and 1-2 ms.

In the event of a current overload due to a decrease in consumer load, when the current in the joint venture circuit exceeds I _cr , the superconductor resistance exceeds the resistance of the shunt unit 2 and the current from the joint venture goes to the shunt unit 2 by switching off the switch 3. By the signal of the current sensor 8, the shunt unit 2 is usually 1,3I _nom and with a time delay of less than the thermal constant of isolation time of the reactor 2 (usually 1-3 min), the control and protection system 7 includes a switch 11 for a time determined by the duration of the overload; switch 3 remains closed.

Thanks to the proposed device of FIG. 1, the volume of the superconductor and the heat generation energy in it are reduced by about 4 times, because power is proportional to the square of the amplitude of the current and the duration of its flow. The amplitude of the current is reduced due to the presence of the shunt unit 2, and the duration is the presence of switches 3, 4 and 11.

The operation of the proposed device is illustrated in figure 2-4, in relation to a 10 kV power system with a capacity of 300 MVA, the system resistance is inductive 0.4 Ohm, quality factor 50. The nature of the transient processes in resistive current limiters THAT is very specific. Due to the fact that the resistance of the joint venture at the beginning of the process is small (for I <I _cr ), the initial part of the process up to a quarter of the network period is determined by the EMF and the network resistance (as well as the load resistance). After reaching the site I> I _{cr the} resistance of the joint venture due to heating increases sharply and the "tail" of the current is determined by the resistance of the joint venture and the shunt block 2 (figure 1). The influence of the operating current is very large and the worst case is the maximum operating current.

Figure 2 shows the current shape of a three-phase short circuit (mode I) in the absence of TRP. The amplitudes of the short-circuit shock current and the steady state are 44 and 22 kA, respectively (the process decays in a time of 0.6-0.8 s). Figures 3 and 4 show the forms of short-circuit current and heat dissipation power in the TRP according to the scheme of figure 1, with the upper curve of figure 3 corresponding to the absence of bypass SC (no shunt block), the lower curves, respectively, for inductive and resistive shunt of the joint venture (various options shunt block 2). It can be seen that the effect of shunting the joint venture with the help of a shunt block allows reducing the current load of the joint venture from 2350A to 1745 (1727) A and reducing the volume of the superconductor, as well as the heat generation capacity in the cryostat from 22.2 to 14 (13) MW.

Figure 5 shows the shape of the current TRP (in switches 3 and 11) when you turn on the idle transformer (mode III) voltage of 10 kV with a capacity of 10 MVA with its residual magnetization. This case corresponds to the closure of the contacts of switches 3 and 11, and 11 is closed by the response signal of the switching device of III substation or from sensors 8, 10, which reveal a sharply asymmetric current shape in the TRP circuit, with an increase in the setpoint current of ~ 2I _nom . In this case, there is no current in the circuit of the joint venture and the reactor. Similarly to the specified mode, when an overload occurs, the current in the TRP flows through switches 3 and 11.

When executing the shunt block 2 according to option 2:

Figure 6 shows an example of the implementation of the TRP, in which the shunt block 2 is made in the form of a transformer, in the secondary winding of which the superconductor 1 is connected in series with the switch 4, and the primary winding of the shunt block 2 is shunted by the switch 11. The designations of the elements correspond to figure 1. The switch 4 provides a reduction in the duration of the short-circuit current in a superconductor; switch 3 disconnects the short-circuit current in the load circuit and is consistent with the relay protection settings; the switch 11 shunts the shunt block 2 and SP 1 in the modes of switching operations and overload. The control and protection system 7 similarly to figure 1 distinguishes emergency, switching and overload modes, choosing the current path in the TRP.

The device in the circuit of Fig.6 works as follows. In operating mode, switches 3, 4 are closed, switch 11 is open. The load current flows through the primary winding of the shunt unit 2 and the switch 3. The direct bias current from the auxiliary source flows through the SP (element 1) and the secondary winding of the shunt unit 2 (this circuit corresponds to [3] and is not shown).

At the moment of short circuit occurrence (modes I, II), according to the signal from the current sensor 8, the control and protection system 7 gives a signal to turn off the high-speed circuit breaker 4. The bias current breaks and the shunt block 2 leaves the saturated state with a sharp increase in the resistance of the shunt block 2, which limits short circuit current.

The slow-acting switch 3 disconnects the limited short-circuit current after 0.1 s upon a signal from the control and protection system 7. After the short-circuit is eliminated, switches 3 and 4 return to their initial closed state, switch 11 is locked.

In modes III, IV, according to signals from sensors 8, 9, 10, as well as signals from the circuit of the block contacts of the substation circuit breakers, the control and protection system 7 when the current setting is ~ 2I _nom and the sharply non-sinusoidal current form in the primary winding of the shunt unit 2 (from sensor 9) gives a signal to turn on a high-speed bypass switch 11. A similar procedure is performed when a signal is received about the overheating of the joint venture (from sensors 8 and 12).

In continuous load modes, when the current in the primary winding of the shunt unit 2 (from sensor 9) is sinusoidal and the current in amplitude and duration exceeds the preset settings, the control and protection system 7, similar to the previous modes III, IV, gives a signal to close circuit breaker 11, open circuit breaker 4, and switch 3 remains on. Upon receipt of a signal from the sensor 10 about a decrease in the current in the load circuit (from the sensor 10) to the rated value I _{nom, the} switch 11 opens and 3 closes.

The use of the device of FIG. 6 is advisable at high voltages (110 kV and higher), however, it is more expensive than in FIG. 1, because the cost of the specific installed power of the shunt block 2 in the embodiment in the form of a transformer is approximately three times higher than the cost of the shunt block 2 in the embodiment in the form of a reactor or resistor.

The GTO circuit in Fig. 1 is preferable for low voltages of 1-10 kV and can be implemented on the basis of already installed dry and concrete reactors and slow-acting switches 3, with the addition of a superconductor in the cryostat 1, switching devices (high-speed) 4 and 11, a control system and protection 7 and current sensors 8, 9, 10 and voltage 12.

The TRP circuit of FIG. 6 can be implemented for any voltage class (110 kV and higher), however, it is more expensive than FIG. 1, because development of a special toroidal transformer with combined insulation and a superconductor in liquid nitrogen is required [3].

Sources of information taken into account when preparing the application:

1. US patent No. 3703664, class H02H 9/02, published 11/21/1972

2. E. Oyarbide Usabiaga, F. Gil Garcia, L. Garcha-Tabarus, JL Peral, R. Jturbe, JM Rodrhguez, E. Urretavizcaya, P. Martiner Cid, X. Granados. Superconducting Hybrid Fault Current Limiter ^∧ Manufacturing, Modeling and Simulations, IEE Trans of Applied Superconductivity, 9 (2), 1999

3. M. Steurer, H. Brechna, K. Frohlich. A Nitrogen Gas Cooled, Hybrid, High Temperature Superconducting Fault Current Limiter, Swiss Federal Institute of Technology ETH, CH-8092 Zurich, Switzerland (prototype)

Claims (4)

1. A hybrid current limiter comprising a superconductor with a series-connected high-speed switch and a parallel connected shunt block, resistance and EMF of the system, characterized in that it is equipped with an additional slow-acting switch, a shunt switch, current sensors, a voltage sensor of the superconductor and a control and protection system, while the superconductor is placed in a cryostat with liquid nitrogen, a slow-acting circuit breaker is connected in series with the shunt block and the shunt yuschim switch, and inputs control and protection system are connected to the current sensors and superconductor sensor voltage and outputs for control and protection system are connected to the switch control circuit, wherein the outputs of switches configured to be connected to the substation breakers. 2. The hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a reactor. 3. The hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a resistor. 4. The hybrid current limiter according to claim 1, characterized in that the shunt block is made in the form of a transformer.