DE2407168A1 - POWER SWITCHING DEVICE - Google Patents

Description

Applicant: Stuttgart, February 11, 1974-

üugiies Aircraft Company P 2827 S / nu

Gentinela Avenue and

Teale Street

Culver City, Calif., V. St. A.

PERFORMANCE EQUIPMENT

The invention relates to a power switching device for interrupting the one in a line HVDC system flowing current with a line switch arranged in this line between two connection points and a first arrangement which is connected in parallel to the line switch and is capable of the Direct current to lead and switch off that the

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Direct current takes over when the circuit breaker is opened, so that the circuit breaker deionize can, and which switches off the power after deionizing the line switch.

Circuit breakers of this type are known from US Pat. No. RE 27,557 and US Pat. No. 3,660,723. With these power switching devices the current to be interrupted is conducted in resistance branches that lead to the load of the HVDC system are connected in series.

In other known power switching devices, the current is conducted in resistors that are between the Transmission line and earth are arranged when the line leading to the load is interrupted. Examples US Pat. No. 3,390,305, 3,435,288, 3,476,978 and 3,489,951 describe such circuit breakers. Such a power switching device has a line switch and this line switch on both sides in each case a series combination of switch and resistor connected to earth. The disadvantage such a circuit breaker consists of that the voltage applied to the line switch is equal to the sum of the voltage drops across the two Grounded resistors is. This voltage can be avoided by turning the circuit breaker on the Load side is short-circuited to earth in order to avoid the voltage at the line switch on the load side, however, such a measure is not practically applicable in high performance systems.

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For a power switching device that can be used for many purposes, it is essential to master the components resulting voltages, both along the line and to earth, required. Furthermore should such a power switching device be able to open a circuit under load and to bring about an interruption in the event of an error.

The invention is based on the object of a power switching device to create that optimally meets these requirements.

This object is achieved according to the invention in that between the one connection point of the circuit breaker and another line of the HVDC system a second arrangement is connected, which turn on direct current, absorb energy when the current is flowing and can turn off the direct current again and serves to reduce the voltage between the one connection point and the to keep the other line below a first predetermined value, and that between the other connection point and the second arrangement switched to a third arrangement that absorb energy when the current flowing through them and can switch off this current and serves to lower the voltage between the two connection points to hold a second predetermined value.

The power switching device according to the invention thus combines the two so far in a certain way

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known types of Leiotungsschalteinrichtungen and can therefore be referred to as a hybrid power switching device will. In a preferred embodiment of such a hybrid power switching device is the Line switch a bypass switch connected in parallel, which enables the line switch to be closed open and deionize. On the line side of the line switch and earth is a series combination switched from a switch and a resistor. Between the load side of the line switch and the Connection point between the switch and the resistor of the series combination on the line side of the Switch is in turn a series combination of a switch and a resistor connected, so dali during voltages occurring during a shutdown process are limited and the current is printed to a lower value will.

The power switching device according to the invention is shown in able to switch off a normal load or interrupt it in the event of a fault. With all switching operations the voltage appearing on the components, including the line voltage to earth, is limited. It however, there is no short circuit to earth. The power switching device according to the invention is shown in FIG able to switch direct current of great strength at high voltages, so that the disconnection of a load and protection in the event of faults for HVDC systems with very high performance is possible.

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Further details and refinements of the invention emerge from the following description of the FIG Embodiments shown in the drawing. The features to be taken from the description and the drawing can be used individually in other embodiments of the invention can be used individually or in groups in any combination. Show it

Fig. 1 shows the schematic circuit diagram of an HVDC system with a power switching device according to the Invention,

Figs. 2 to 4 are diagrams of voltages at various Components of the circuit breaker according to Fig. 1,

FIGS. 5 to 7 are diagrams of the currents which the various components of the power switching device according to Fig. 1 flow through, and

8 shows the schematic circuit diagram of an HVDC transmission system with a further embodiment of a power switching device according to the invention.

1 shows an HVDC transmission system 10 with an energy source 12 which is connected to a load 19 via an energy line 14 and an earth line 16. The hybrid power switching device 18 according to the invention is connected in the power line 14- and at the same time between the power line 14- and the earth line 16 in order to control the flow of energy to the load. One

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HVDC transmission of this type is more detailed in the US-PS 3 558 960 treated. This patent covers more in detail the energy source and the load. Furthermore, this patent shows that switching in of the transmission itunf5 as well as in one of the Main line branched line can be made. The power switching device 18 is both for switching operations suitable in the main line as well as in a branch line. She is also able to take the lead switch off under load and also interrupt if an error occurs.

The power switching device 18 comprises a line switch 20 which is in the power line 1A- between Connection points 1 and 2 is switched on. The line switch 20 can be a conventional mechanical switch be, which has a small impedance in the closed state and the peak voltages in the open state between the connection points 1 and 2 can withstand. With regard to the fact that the line switch an interrupter 22 with crossed fields is connected in parallel, which will be described in more detail later will be, and a certain voltage must be applied to such an interrupter so that it is conductive, is, it is desirable that the line switch 20 can generate some arc voltage so that the Conduction process in the interrupter 22 can be initiated. Presently is used to initiate the conductive State requires a voltage of around 1 kV. As a result, the line switch 20 should be able to

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be to create significant arc tension. Any common circuit breaker that has these properties such as an interrupter switch with magnetic quenching or with a large arc gap, is therefore suitable for this purpose. Another switch suitable for this purpose is in the U.S. Patent 3,750,061 (not prepublished).

A line 24 is from the one connection point 2 via a connection point 6 to a connection point 3 performed on the earth line 16. In the same way there is a line 26 between the other connection point 1 and a connection point 4 is connected on the ground line 16 via a further connection point 5. Between the lines 24 and 26, a capacitor 28 is connected ,. which controls the rate of voltage rise when the line switch 20 or the switching tube 22 is opened. As already mentioned, the interrupter 22 is with crossed fields between the lines 24 and 26 connected in parallel to the line switch 20. The interrupter 22 with crossed fields is a switching device that is able to transmit direct current and switch it off against a high voltage. Interrupter tubes with crossed fields of this type are described in US Patents RE 27,557, 3,638,061, 3,641,384, 3,604,977, 3,558,960, 3,714,510 and 3,678,289. These Documents make it clear that interrupters with crossed fields carry very strong direct currents and can switch off against high voltages.

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In a typical installation, the power source 12 may be capable of operating at normal line voltage; from 400 kV to deliver a current of 2000 A. These values are in the following as values per unit (per-unit) considered or briefly as 1 pu. For the purpose of explanation, the values are given with 1 pu voltage sources and Output currents normalized. The inductance of the plant is shown as a lumped element, and there will be no line or filter effects in the consideration introduced. The non-linear resistances are considered ideal. At an overvoltage value k = 1.5 are the non-linear resistances in the Voltage analysis considered as 1.5 pu DC voltage sources.

For the purpose of explanation, 1.5 pu is chosen as the maximum overvoltage. In modern energy transmission systems, an overload factor k = 1.7 is often encountered. For the purposes of explanation, however, a value k = 1.5 has been assumed. When the establishment is intended for a different overvoltage factor, this factor would of course have to be used in the design the circuit breaker for this system.

Modern non-linear resistors are components that do not obey Ohm's law, but whose resistance value depends on the strength of the current. In the present case, a large resistance is when the current is low and a small resistance is when the current is high

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he wishes. An ideal non-linear resistance would have an infinitely large resistance for the current O, However, breakdown and start conducting when its breakdown voltage has been reached. Modern non-linear resistors consist of silicon carbide and do not achieve the ideal behavior. The treatment However, the present power switching device, assuming ideal resistances, simplifies the Description. The voltage and current curves would be less ideal if the properties were more real non-linear resistances would be taken into account.

During a shutdown process, the current is transferred from the line switch 20 to the interrupter 22, by opening the line switch 20 after the switching tube 22 is put into line readiness has been. After the line switch 20 is opened and deionized, the interrupter 22 is switched off. If too much energy is stored in the system to allow easy shutdown, this can happen the interrupter 22 be a circuit arrangement connected in parallel, which consists of a series combination of a further interrupter with crossed fields and an energy absorbing resistor, preferably with non-linear characteristic. Such an arrangement is shown in FIG. In this case, when the interrupter 22 with crossed fields is opened, the energy is reduced by the current is passed through the energy absorbing resistor. Such additional energy absorbing branches

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are dealt with in U.S. Patents RE 27,557 and 3,660,723.

In series in the line 24 between the connection points 2 and 3 are a switching tube 30 with crossed fields, a resistor 32, which is shown as a non-linear resistor, and a switch 3 ^ switched. In in the same way, a switching tube 36 is in the line 26 between the connection points 1 and 4 in series crossed fields, a resistor 38 », which is shown as a non-linear resistor, and a switch 40 switched. The interrupters 30 and 36 are capacitors 4-2 and 44 connected in parallel, showing the change in voltage over time on the switching tubes with crossed Control fields. A resistor 46, again shown as a non-linear resistor, connects lines 24 and 26 between connection points 5 and

The switching tubes 30 and 36 are identical to the switching tube 22, while the switches 34 and 40 with the line switch 20 can be identical. However, the requirements for switches 34 and 40 differ somewhat the requirements of the line switch 20, so that they can have a different structure. Interrupters with Crossed fields, such as the interrupters 30 and 36, can not according to the current state of the art reliably switch on in the correct working state when a voltage is first applied to them. if for example, the switch 3 ^ in the power switching device would be missing according to Fig. 1, the interrupter 30 could not be directly between the energy

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Line 14 and the ground line 16 are switched. Consequently the entire 1 pu would be on the interrupter. If an attempt were made, the interrupter Turning on 30 under these circumstances could be an arc discharge rather than a glow discharge arise so that the tube could no longer be switched off. For this reason, stick with the present one State of the development of these switching tubes, the switches 34 and 40, the voltage source η of the tubes 30 and remote until their management is desired.

Fig. 2 illustrates the voltage between terminals 1 and 2 during the time of shutdown. FIG. 3 illustrates the time profile of the voltage between connection points 2 and 3. FIG. 4 illustrates the time course of the voltage between points 1 and 4. Referring to FIG. 4, consider this pointed out that the connection point 3 has the same potential as the connection point 4, which is why in Fig. 4 the The voltage shown there is designated as the voltage between the connection points 1 and 3. Because the sum of the voltages along the loop between the connection points 1, 2, 3, 4 and 1 result in the amount 0 must, the voltage between points 1 and 3 (Fig. 4) is equal to the difference between those shown in Figs. 3 and 2 shown voltages.

In order to illustrate the operation of the circuit breaker, it is assumed that the circuit breaker 20 is closed and from a normal

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Current of strength 1 pu flows through it, while the voltage 1 pu drops across the load. So it is about the normal state, and a disconnection of the load in this state is now illustrated, in contrast to shutdown under an error condition. During normal power transmission there is a voltage drop at the line switch 20 between the connection points 1 and 2, as shown in FIG. 2, equal to 0, while between the connection points 2 and 3 and also 1 and a voltage 1 pu prevails. It can be seen that the voltage of FIG. 3 minus the voltage of FIG. 2 is equal to the voltage of FIG. At the time t, the beginning of the load disconnection, the switches 3 ^ and 40 open, and there is no voltage on the interrupters 22 and 36. The interrupters are however brought into such a state that they begin to conduct as soon as a sufficiently high voltage is applied will. At time t, the line switch 20 is opened and the line current is transmitted to the switching tube 22. The voltage drop on currently known interrupters with crossed fields is about 500 V. This value is not visible in the idealized curves in FIGS. In the time from t to t, - becomes the line switch 20 is opened and deionized so that it can withstand the nominal voltage of 1.5 pu.

At the time t ^ the switches 3 ^ and are closed at the same time and the switching tube 22 with crossed fields is switched off. The interrupters 30 and 36 can also be _{in line readiness during the time from t Q} to t ^

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so that they become conductive when switches 34- and 4-0 are closed. The opannun ·; at the power switching device increases in the time from ty to tp, as FIG. 2 shows, at a speed which is determined by the capacitor 28 which limits the speed of the voltage increase. Assuming that ideal non-linear resistances do not conduct until the voltage has reached the Vert 1.5 pu, the voltage increase between times t 1 and tp is from 0 to 1.0 pu according to FIG. 2 by the speed of the Voltage rise determined on the capacitors provided for limiting the voltage rise, as described above. The capacitors must absorb the current that flowed through the interrupters until the resistors begin to conduct. The line current remains constant during this short period of time, which is less than 1 ms.

When the voltage between connection points 2 and 3 reaches the value 1.5 pu at time tp, as shown in FIG. 3 shows the voltage between these points is clamped at 1.5 pu to reduce the voltage between the Bnergieleline 14 and the earth line 16 to a maximum voltage to limit. As a result, the insulation between the lines is not overloaded. If the Voltage between the connection points 2 and 1 increases, this voltage is taken up by the resistor 4-6, which at time t, begins to conduct to the tension between to clamp points 2 and 1 to the value 1.5 pu, as shown in FIG. As a result of the tension

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subtraction reduces the voltage at the stand 38 between connection points 1 and 3 on O, so daii resistance 38 never begins to conduct. The desk 40 could therefore also have been left open. When switching off the load as described so far, it would be the branch between connection points 4 and 5 is not required. However, this branch is required when the power switching device works in the opposite direction, i.e. when the energy source and load are interchanged are and it is necessary to use the energies stored in the reactances of both the energy conduction and to disconnect the load from the energy source. In this case the voltage between the connection points is 1 and 2 and separately between the connection points 1 and 4 are limited to a value of 1.5 pu, around that when switching off to limit occurring maximum voltage.

At these voltages, the strength of the current is reduced from the initial value 1 pu, as shown in FIGS. 5, 6 and 7. The current flowing in the loop from the energy source 12 via the energy line 14, the connection points 2, 6 and 3 and then back to the energy source is _{denoted by I x} and is shown in FIG. 5. The current flowing in the loop comprising load 19 and connection points 4, 3, 6, 5 and 1 is illustrated as current Ip in FIG. For the purposes of the analysis, both the energy source 12 and the load 19 are considered as a voltage source with the nominal voltage 1.0 pu. As stated above, the inductances of the system are considered to be lumped elements

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and no line or filter effects are taken into account. The non-linear resistances are considered ideal and treated as sources of a DC voltage of 1.5 pu. If the left loop in FIG. 1 is viewed, it can be seen that there is a Voltage 0.5 pu. is applied, 30 dan the otrom with a speed of 0.5 pu per unit time, as shown in FIG. 5, in which the time interval between t * and t ^ form the unit of time. When going through the in Fig. 1 right loop for the current I ~ can be seen that the voltage of the load 19 is algebraic to the equivalent voltages of the non-linear resistances 32 and 46 are added, a voltage of 1 pu is applied to inductance 48 and the drop in current is 1.0 pu per unit of time. Consequently the current falls in this loop up to time t ^ the value O.

The current flowing through resistor 32 is the same the difference between the currents I ^ and Ip. As Fig. 7 shows, the current increases from the value 0 at time t ^ to the value 0.5 pu at time t ^. Then he falls during the next time unit, which ends at time tj- the value 0. 6 and 7 show that the absorbed by the resistors 32 and 46 in this example Energies are the same.

Additional considerations that have to be made in order to convert the above analysis of the ideal circuit arrangement into a real circuit arrangement in

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To put relationship, have to take into account that one Silicon carbide resistor is not an ideal nonlinear resistor. The deviations from the ideal require the use of capacitors to absorb overcurrents. A suitable place for one Capacitor is between lines 24 and 26 where capacitor 28 is located. Hence the capacitor should 28 be calculated so that it has capacity to absorb overcurrents. Furthermore, in a real circuit arrangement in which the energy source 12 is a rectifier and the load 19 is an inverter is, the control panel will affect the actual voltages. For example, the inverter control would reduce the inverter voltage over time so that the current Ip flows for a longer period of time would.

The switch-off process is finally ended by the switching tubes 30 and 36 with crossed fields being switched off will. Simultaneously or a short time before, the switches 34 and A-O are opened, so that through switching off the corresponding interrupters, the arcs in switches 34 and 40 are extinguished. The switches 34 and 40 can be triggered Vacuum sections instead of mechanical switches.

The power switchgear is responsible for rectifying a fault not as difficult as turning off the load because of the voltage between the lines 14 and 16 has a reduced value. Instead of this

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muli a current whose strength is greater than 1 pu is interrupted and reduced to 0 without the voltage 1.5 pu at any point in the power switching device is exceeded. In the event of a fault to the right of the circuit breaker and one Voltage between connection points 2 and 5 close to zero the start of a disconnection process by the power switching device leads to a voltage increase Episode. When the voltage reaches 1.5 pu, it is clamped in the manner described above. In the same In this way, the line and load reactances cause a voltage rise in the right-hand side of the power switchgear, when the current is reduced. Again, there is tension between points 1 and 2 limited to 1.5 pu so that no overvoltages can occur.

Fig. 8 illustrates a power switching device 50 between an energy source 52 and a load 5 ^ is switched. The connection is made by means of a power line 56 and a ground line 58. It can be seen that the power switching device 50, apart from a few details, with the power switching 18 of FIG. 1 is identical. So instead of the switches 34- and 40 in the power switching device 50 spark gaps 60 and 62 are used. These are precision spark gaps that break through and conduct when a precisely predetermined voltage is reached. A suitable spark gap is in one Essay by Joseph C. Osterhout: "Separation of Gap

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Functions - A New Concept in Station Glass Lighting Arrestor Design "in IEEE Transactions on Power Apparatus and Systems, Volume PA3-91, No. 5, 1972, pages 2104 bis 2112. This paper deals with pressurized, pre-ionized radio operator lines that are reproducible breakdown at a precisely determined voltage. The spark gap holds in the power switching device 50 60 stood at a voltage and prevented a current conduction through this branch until the voltage was sufficient has risen above 1 pu, for example to 1.5 pu, whereupon the spark gap breaks down and directs. After the onset of the power line, the voltage drop on this branch will be due to the non-linear Resistance determined, which is connected in series to the conductive spark gap. The power line stops until the interrupter 76 arranged in this branch with crossed fields is switched off. Thereupon the spark gap 60 can regain its dielectric strength.

Another difference in the structure of the power switching device according to FIG. 8 to the power switching device according to Fig. 1 is in the additional impedance branches, which serve to absorb energy before the line current is passed through resistor 64, which corresponds to resistor 46 of FIG. There are in 8 shows two additional branches, each with a switching tube 66 or 70 with crossed fields and one for each in Series connected resistor 68 and 72, respectively, are shown. The branches with the interrupter 66 or 70 and the in

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Series connected resistors 68 and 72 are respectively the resistor 64- connected in parallel. The impedance levels formed by these branches become one after the other switched off in order to gradually increase the impedance and pass the conduction current through resistor 64-. In most cases, only one such intermediate stage is likely to be required. Still are in the power switching device according to FIG. 8, two such stages are shown as an example.

As a further alternative, instead of the one shown in FIG illustrated spark gaps 60 and 62 triggered vacuum gaps can be used. A triggered vacuum path did not need to break through at exactly a given voltage; it would instead the conductive state in the vacuum path is triggered by suitable voltage sensors. It would then be the Start conducting the vacuum path when the circuit breaker is in a suitable state. A suitable one Vacuum path is dealt with in US Pat. No. 3,290,54-2.

As a further alternative, instead of a series connection, a device for switching on, such as the switch 34- or the spark gap 60, a resistor such as the non-linear resistor 32 or 74-, and a disconnection device, such as an interrupter 30 or 76 with crossed fields, a single unit which performs these functions. For example, a lightning protection device for

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designed for such a purpose. Currently known Lightning protection devices are not able to absorb sufficient energy for the present purpose. Furthermore, they do not provide reliable insulation when the power is switched off. Therefore, the previously known lightning protection devices for the use of such power switching devices not yet fully suitable. However, it is conceivable that a further development towards lightning protection devices leads to an accurate switch-on, adequate energy absorption, as well as insulation at suitable voltage and suitable recovery the dielectric strength after switching off the current.

The present invention has been described on the basis of preferred embodiments. It goes without saying that it is not restricted to these embodiments, but rather numerous modifications are possible without departing from the scope of the invention set by the following claims.

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Claims (8)

- ΖΛ - Claims {1.lLeistungsschalteinrichtung for interrupting the pjjnp.r in \ ~, S line of a HVDC transmission system flowing stream with an in this conduit between two Anschluiipunkten arranged line switch and a parallel-connected to the line switch first arrangement which is able to perform the direct current and switch off, which takes over the direct current when the line switch is opened so that the line switch can deionize, and which switches off the current after deionizing the line switch, characterized in that between the one connection point (2) of the line switch (20) and one Another line (16) of the HVDC system is connected to a second arrangement (30, 32, 3 ^) that can switch on direct current, absorb energy when the current is flowing and switch off the direct current again and serve to control the voltage between one connection point ( 2) and the other line (16) below a first predetermined value, and that between the other The connection point (1) and the second arrangement (30, 32, 3 * 0) are connected to a third arrangement (36, 46) which can absorb energy when the current is flowing through it and which can switch off this current and which serves to control the voltage between the two To keep connection points (1 and 2) below a second predetermined value. 409841/0653 - 2Z- 2. Power switching device according to claim 1, characterized in that the first arrangement has an between the two connection points (1 and 2) switched interrupter (22) with crossed fields. 3. Power switching device according to claim 1 or 2, characterized in that the second arrangement (30, 32, 34) from the series connection of one Interrupter (30) with crossed fields for switching off direct current and an arrangement (32, 34-) for switching on direct current and absorbing of energy when the current is flowing. 4. Power switching device according to claim 3, characterized characterized in that the third arrangement (36, 46) at the connection point (6) between the interrupter (30) and the arrangement (32, 34) for switching on Connected to direct current and absorbing energy, 5 · Power switching device according to one of the preceding Claims, characterized in that the third arrangement (36, 46) from the series circuit comprising a switching tube (36) with crossed fields and a resistor (46). 6. Power switching device according to one of the preceding Claims, characterized in that a further arrangement (38, 40) for switching on Direct current and absorbing energy between the 409841/0653 third arrangement (36, 46) and the other line (16) is connected. 7. Power switching device according to claim 3 and / or 6, characterized in that the arrangement (32, 34 · 38, 40) for switching on direct current and Absorbing energy comprises a switch-on element (30; 40) and a special resistor (32; 3β). 8. Leiütun ^ sschalteinrichtung according to one of the preceding Claims, characterized in that the one connection point (2) with the energy source (12) and the other connection point (1) is connected to the load (19) of the HVDC system and the energy source (12) and the load (19) are also connected to the other line (16) of the HVDC system. 4.0 98 A-1/065 3 Blank page