SE504399C2 - HV current rectifier installation - Google Patents

Abstract

Each gas-insulated thyristor group (e.g. VIa) has a number of phase connections (VAIA,VAIB,VAIC) for connecting to phases in a multi-phase a.c. voltage mains (AC). Each thyristor group has a d.c connection (LAIa) and a number of semiconductor thyristors (TYI1,TYI3,TYI5), each connected to the d.c connection and a phase connection. Each of the thyristor groups is arranged separately from other thyristor groups in a separate capsule (KAIa) which is common for the thyristors in the group. The current rectifier installation incorporates a three-phase six-pulse rectifier bridge (e.g. BI) with two three-pulse thyristor groups (VAIa,VAIb). A separate capsule (KAIa,KAb) is incorporate for each of the two current rectifier-bridge thyristor groups. The rectifier is for single or two-pole power transmission with h.v d.c. which for each pole has two series-coupled six-pulse current rectifier bridges (BI,BII).

Description

15 20 25 30 35 504 399 ten with publication numbers 0 172 554, testimonials 4 077 057 and 4 142 230, it is known that in the case of an HVDC converter each semiconductor valve can be arranged or by USA gas-insulated and encapsulated, which enables outdoor set-up. In this case, each valve (possibly half a valve or two half-valves connected in series) is arranged in a separate housing. An HVDC converter usually consists of two series-connected three-phase six-pulse bridges and thus has 12 semiconductor valves. Advantages of this design are that the enclosures with the valves mounted therein can be completed completely and the hob completely eliminated. rata enclosures at the factory and that the need for valve halls The large number of valves with their separators, however, makes a converter system complicated and has a relatively high price. Contributing to this is, among other things, the need to provide each enclosure with means for transmitting, between earth potential and the enclosure lying generally at high voltage potential, of gas for insulation and ventilation, of a coolant (gas or liquid) and of control and information signals to and from the valve. The completion of the valves in the factory has also involved relatively high transport weights in previous valve designs.

U.S. Pat. No. 3,445,747 discloses a fully encapsulated oil-insulated semiconductor converter, in which all the valves of the converter are arranged in a common space and together with the converter transformer form a single physical unit. At the high voltages and effects to which the invention relates, this would entail such large dimensions and transport weights that the described embodiment becomes completely unusable.

Through the article "Cabora Bassa HVDC Transmission: Oil Coled Thyristor Valves", F C Beriger, J Hengsberger, G W Juette, IEEE Transactions on Power Apparatus and Systems, vol. PAS-94, no.3, May / June 1975, pp. 1061-1071, is an outdoor HVDC system known, which has oil-insulated semiconductor valves with the valves mounted two and two in oil-filled tanks 10 15 20 25 30 35 S04 399 kar. Each tank then contains the two valves of a six-pulse bridge connected to one and the same AC outlet.

Since each tank contains two semiconductor valves with their current and voltage derivative limiting reactors, dimensions and transport weights become high. A further disadvantage is that many enclosures are needed (six enclosures at a 12-pulse converter) and that both DC connections of each enclosure must be insulated from the enclosure, which requires large insulation distances between the valves and the enclosure.

DISCLOSURE OF THE INVENTION The invention aims to provide a converter system of the type initially indicated, which offers a simpler and more economical construction than known systems of the type in question, in which the transport weights and transport dimensions can be significantly reduced, and which enables a better cooling. the reactors of the valves and a more efficient surge protection for the valves.

What characterizes a converter system according to the invention is stated in the appended claims.

By arranging a common enclosure for each valve group, a significant simplification of the construction and a reduction of weight and costs are obtained. According to a preferred embodiment of the invention, the enclosures of the valve groups are made divisible, and hereby a simplification of the assembly and a reduction of transport weights and dimensions is achieved.

According to a further preferred embodiment, the valves' current and voltage derivative limiting reactors are arranged outside the valve group enclosure, which has been found to provide a further significant reduction of the transport weights and further possibility for an improved surge protection for the semiconductor valves. DESCRIPTION OF THE FIGURES The invention will be described in more detail below in connection with the accompanying figures 1-5. Figure 1 schematically shows the invention applied to a 12-pulse HVDC converter. Figures 2a and 2b show an example of a pole of a converter system according to the invention. Figure 3 shows how the invention can be applied to a so-called back-to-back converter. Figures 4a, 4b and 4c show an example of a housing for a valve group. Figures 5a and 5b show another embodiment of an enclosure according to the invention with associated derivative limiting reactors.

DESCRIPTION OF EMBODIMENTS Figure 1 shows a 12-pulse converter according to the invention for a pole in a single or two-pole HVDC transmission. It consists in a known manner of two DC-connected three-pulse three-phase bridges BI and BII. Each bridge has six thyristor valves, each consisting of a plurality of series-connected thyristors, for example the valves TYI1, TYI3 and TYI5, which together constitute the valve groups (three pulse groups) VIa and VIb in the upper figure of the bridge BI. Each bridge has two DC connections, LAIa, LAIb and LAIIa, LAIIb, respectively, as well as three phase connections, VAIA, VAIB, VAIC and VAIIA, VAIIB, VAIIC, respectively. The phase connections of the bridges are connected via transformers TI, TII to an alternating voltage network AC, whereby the transformers have different connection angles so that the desired twelve-pulse operation is obtained.

Each valve group in a bridge has a DC connection, which is the same as one of the bridge's DC connections, and three phase connections, which are the same as the bridge's phase connections. Each valve in a valve group (eg TYIl) is connected between the valve group (VIa) DC connection (LAIa) and one of the valve group's phase connections (VAIA).

According to the invention, each valve group is provided with a separate housing, KAIa, KAIb, KAIIa, KAIIb. These are shown in broken lines in the figure. The enclosures consist of metal housings, in which the valves are mounted. Each enclosure / housing is electrically connected to the DC socket of the valve group mounted in the housing. The housing will in this way be at a relatively fixed and well-defined DC voltage potential, which means that radio interference is kept to a minimum.

The housings with the valve groups are suitably mounted on insulating platforms and provided with connections for signals, ventilation and cooling in the manner described in the above-mentioned international patent application WO 93/17488.

Figure 2a shows in more detail an example of how the various units in a converter of the type shown in Figure 1 can be placed in relation to each other. The converter system is seen in the figure from above. The valves arranged in the enclosures are shown in broken lines. The figure shows the four enclosures KAIa - KAIIb, the valve groups of which are DC connected in series between the station's neutral rail N and pole P, which is later connected via a smoothing reactor GR either to a direct current line or - in the case of a back-to-back connection - directly with another converter in the same station. The two valve groups in the same six-pulse bridge have their phase connections connected to each other by means of rails SAI, SBI, SCI and SAII, SBII, SCII, respectively. The two transformers TI and TII are connected to these rails.

In the usual way, the valves are equipped with current and voltage derivative limiting reactors. Instead of arranging these reactors in the usual way in the valve itself, they are according to the invention arranged outside the enclosures of the valve groups. Each valve is connected in series with a reactor, and the reactors of the four valve groups form the reactor groups DRIa, DRIb, DRIIa, DRIIb shown in the figure. 10 2 20 20 30 30 50 50 399 Figure 2b shows in more detail one of the enclosures, namely the enclosure KAIIb with associated reactor group DRIIb. The enclosure has the bushings IBIIbA. IBIIbB, IBIIbC. The reactor group consists of the three reactors DRIIbA, DRIIbB, DRIIbC.

To reduce their emission of radio interference, the reactors are provided with electrically conductive enclosures, housings, screens or the like which completely or partially surround the reactors, and these enclosures or the like are electrically connected to each other and to the valve group enclosure KAIIb.

Valve diverters VAIIbA, VAIIbB, VAIIbC for protection of the valves against overvoltages are connected in parallel with each valve. They can either, as shown in Figure 2b, be arranged outside the valve group housing or, as will be described below, be arranged inside it.

Figure 3 shows an example of how the invention can be applied to a so-called back-to-back converter. Such a system consists of two converters arranged in the same station for controllable power transmission between two alternating voltage networks. The figure shows the two converters SR1 and SR2. Each converter is constructed in the manner shown in Figures 1 and 2, with one enclosure KA for each three-pulse group and with reactors DR, and is therefore only shown schematically. The inverters are connected on their alternating current sides to the two three-phase networks AC1 and AC2 and have their direct current sides connected by means of the rails BB1 and BB2. In the rail BB1, a smoothing reactor GR is connected.

Figure 4 shows an example of a housing according to the invention for a valve group. Figure 4a shows the enclosure seen from the side, figure 4b shows the DC voltage side of the enclosure and figure 4c shows the enclosure seen from above. The housing consists of a metal housing with three bushings IBA, IBB, IBC, which form the phase group of the valve group and are connected to the rails SA, SB, SC. The house is made in three parts, KAA, KAB, KAC.

The dividing lines between the three parts are shown by the dashed lines Q-Q and R-R in the figures. Each housing part is arranged for mounting one of the three valves that make up the valve group. For example, a valve is mounted in the enclosure part KAC, which consists of the six thyristor modules MCl - MC6. These are placed in three levels above each other, two modules on each level, and electrically connected in series. In the same way, the valve arranged in the housing part KAA consists of the six modules MA1 - MA6 and the valve arranged in the housing part KAB consists of the six modules MB1 - MB6. Each module consists in a manner known per se of a plurality, for example six, series-connected thyristors with associated means for voltage sharing, protection, control, cooling, etc. The anodes of the three valves are electrically connected to each other, to the metal housing KAA / KAB / KAC and to the DC connection LA.

The three housing parts are manufactured separately, after which the thyristor modules are mounted in each part. This can be done very easily because each part is open from at least one side and the accessibility is therefore good. The parts are then assembled and the required test is performed. After testing, the housing is disassembled into its three parts. These are provided (with remaining thyristor modules) with temporary side walls for protection during transport and are transported separately to the installation site, where they are finally assembled and put into operation.

Figure 5 shows another preferred embodiment of a valve group with enclosure. Figure Sa shows the valve group with associated reactor group seen from the side, and figure Sb shows the same units seen from above. In the same way as described in connection with Figure 4, the valve group's enclosure consists of three parts, KAA, KAB, KAC, each with one of the valve group's three valves and with associated bushings IBA, IBB, IBC. In the example shown, each valve consists of six thyristor modules, of which, for example, the modules MCl - MC6 are shown in Figure 5a. The modules are arranged in two levels above each other. Because each valve is connected to the housing at its left end in the figure, and because the modules are connected to each other in the manner shown in the figure, the voltage between the valve and the housing is zero at the DC connection LA and grows successively towards the implementation IBA / IBB / IBC. The housing is therefore suitably constructed in the manner shown in the figure with the lowest height at the direct current connection and with successively increasing height in the direction of the bushings. In this way, with a minimum of housing dimensions, sufficient insulation distance is obtained between each module and the wall of the housing. In this embodiment, the valve diverters are located inside the valve group housing, and this can, as shown in Figure 5a, be designed in such a way that a sufficient height is obtained for mounting the valve diverters. The enclosure, which is generally located at a high DC potential in relation to ground, is arranged on insulators, of which the insulators IS1 and IS2 are shown in the figure, which in turn are supported by a foundation F1.

The three reactors DRA, DRB, DRC belonging to the valve group are, as shown in the figure, mounted on insulators (eg ISC) which are supported by suitable foundations (F2).

The above-described embodiments of the invention are examples only, and a large number of other embodiments are conceivable within the scope of the invention.

The invention has thus been described above for the in practice completely dominant case where the converters in the plant are connected to three-phase AC mains. However, fasts other than 3 are conceivable. Furthermore, only 12-pulse converters composed of two series-connected six-pulse bridges have been described above. Other forms of converters can also be used in a system according to the invention, for example six-pulse or 24-pulse converters.

Above, only the case has been described, where each valve group is three-pulse and its housing is divisible into three parts, one for each valve in the group. Alternatively, other forms of divisible enclosures may be used within the scope of the invention. Likewise, if desired, a valve group can be made with a non-divisible enclosure. This can be particularly suitable at lower operating voltages, since the dimensions and weight of the enclosures will then be lower and a division may be unnecessary from a transport point of view. Particularly in the case of back-to-back inverters, non-divided valve group enclosures may be suitable, since such inverters generally operate at lower voltages.

In the converters described above, each valve consists of six thyristor modules, but depending on the voltage resistance of the thyristors and the operating voltage of the system, the number of modules can be larger or smaller.

In the examples described above, the valves' current and voltage derivative limiting reactors are arranged outside the enclosures of the valve groups. Alternatively, they can instead be arranged inside the valve group enclosures, for example included in the thyristor modules.

The invention has been described above applied to thyristor converters. However, the invention can be applied to converters with other types of semiconductor valves, for example diode rectifiers.

As appears from the above description, a converter system according to the invention offers significant advantages compared with previously known systems of the same type. By arranging a common enclosure for the valves in one and the same valve group, a significantly simpler and economically more advantageous construction is obtained than if each valve or half-valve is provided with its own separate enclosure in a known manner.

The number of enclosures is significantly lower - typically only a third as large - and thereby significantly reduces the cost of the enclosures themselves, and the supply of the valves with cooling, ventilation, control and information signals, etc. is significantly simplified. By making the valve group enclosures divisible, and preferably so that each part contains a single valve, according to a preferred embodiment of the invention it is achieved that transport weights and dimensions can be kept low even if all assembly work ( except for the final assembly of the enclosure parts) is carried out in the factory before transport to the installation site. This advantage is especially important in systems for high operating voltages and thus with large dimensions of the valve group enclosures. Furthermore, by making the enclosures divided, their interiors are easily accessible from the side, thereby simplifying the assembly of the thyristor modules.

In the preferred embodiments described above, the current and voltage limiting reactors of the valves are arranged outside the valve group enclosures. This achieves several benefits. Since the weight of the reactors constitutes a significant part of the total weight of a valve - in a typical case about one third - a corresponding sharp reduction in the transport weight of the valve group housing or its parts is phased. The cooling of the reactor is furthermore significantly better at the described location outdoors than when located inside the valve group housing with its higher temperature. Finally, the described location of the reactors enables the valve diverters for protection of the valves against overvoltages in the manner described above to be placed directly over the valves' series-connected semiconductor elements instead of over the combination of the valve's semiconductor elements and reactors. It has been found that this location according to the invention provides lower overvoltages and a more effective protection of the valves.

According to a further development of the latter embodiment, the valve diverter is located inside the valve group housing.

This enables a simpler and more economical design of the diverter, which is further protected against precipitation, pollution and other environmental impacts.

Claims (10)

1. 0 15 20 25 30 35 11 504 399 In the valve groups described above, the thyristor modules are arranged in two or three levels one above the other. This arrangement of the modules on several levels provides a compact structure. Particularly advantageous is the embodiment shown in Figure 5, where the method shown for connecting the modules in series ensures that the voltage between adjacent modules does not become higher than a "module voltage". PATENT REQUIREMENTS 1. High-voltage and high-power inverter system , in encapsulated design for outdoor placement, and comprising a plurality of gas-insulated valve groups (eg VIa), each of which has a plurality of phase connections (VAIA, VAIB, VAIC) connected to the phases of a multiphase AC network ( AC), - a direct current connection (LAIa) Qch - a plurality of semiconductor valves (TYI1, TYI3, TYI5), each connected between the direct current connection and a phase connection, characterized in that each of the valve groups (eg VIa ) is arranged separately from the other valve groups in a separate housing (KAIa) which is common to the valves in the valve group. Converter system according to claim 1, comprising a three-phase six-pulse converter bridge (eg BI) with (VAIa, VAIb), can be drawn (KAIa, two three-pulse valve groups a / that the device comprises a separate housing KAIb) per. for each of the converter bridge's both valve groups Converter system according to claim 2 for a single or two-pole power transmission with high-voltage direct current, which for each pole comprises two series-connected six-pulse current (BI, BII), converter bridges characterized by the device 10 15 20 25 30 35 12 504 399 for each pole comprises four separate enclosures (KAIa, KAIb, KAIIa, KAIIb), one for each valve group. Converter system according to one of the preceding claims, characterized in that the housing for a valve group can be divided into several parts for transport (KAA, KAB, KAC). Converter system according to Claim 4, characterized in that the housing is divisible into a number of parts equal to the number of valves in the valve group. Converter system according to Claim 5, characterized in that each canister part (eg KAC) is arranged to accommodate a semiconductor valve (MCl - MC6). 7. A converter system according to any one of the preceding claims, characterized in that the housing is electrically connected to the direct current connection (LA). A converter system according to any one of the preceding claims, characterized in that it comprises one (DRA, DRB, for each valve in a valve group, which reactors are current and voltage derivative limiting reactor DRC) arranged outside the valve group enclosure and connected to each of the valve group terminals. Converter system according to claim 8, known as - (RSA, RSB, RSC) which are electrically connected to the valve group housing. t e c k n a d a v that the reactors have screens Converter system according to Claim 8, characterized in that an overvoltage protection (VAC) is provided for a valve in the form of a valve diverter connected between the DC group of the valve group (LA) and its phase connection. 10 13 504 399 ll Converter system according to claim 10 core1ec: kr1ad. awr that the valve diverter is arranged inside the valve group housing (KA). Converter system according to any one of the preceding claims, wherein each valve consists of a plurality of electrically connected modules (eg MCl - MC6), each comprising a plurality of series-connected semiconductor components, characterized in that the modules belonging to one and the same valve are arranged in a plurality of levels one above the other.