HVDC converter station

A converter station, the system is at a high voltage direct current transmission (HVDC), in which the conversion of three-phase current to direct current ( and vice versa) takes place. Thus it can be made ​​from direct current three-phase depending on need and of three-phase DC. A converter station includes addition to the converter always also

• A three-phase switchgear,
• Converter transformers,
• Harmonic filters and
• A DC switchgear.

• 3.1 Space Requirements
• 3.2 Location factors
• 3.3 converter stations in Germany
• 3.4 Former converter stations in Austria

Components

Converter Hall

The converter hall, also valve hall (English valve hall) called, is the building in which the power converter, typically thyristors, formerly mercury arc rectifiers are housed. Mercury arc rectifiers were installed in the converter hall on insulators, while thyristors are either erected on isolators or suspended from the ceiling. Although the latter requires a more stable floor construction, but the construction can possibly survive earthquakes better than a static structure. Often this multiple valve functions in one element unites ( Thyristorturm ). In addition to the converter hall there is often an additional building where the control electronics, equipment for cooling and monitoring equipment for the power supply of the auxiliary facilities and social rooms are housed.

Since the inverter cause high electrical voltage to earth during operation, the inverter hall must not be entered during the operation of the plant. As a rule, therefore, is to take a look at the system, can a window provided in the annex building, from which the control is based. As many high-voltage DC transmission systems are remote-controlled, remote control devices are frequently installed.

In some high-voltage direct current transmission systems ( HVDC Cahora Bassa like ) were used converters, which are installed in oil-filled containers outdoors. In such systems, which are the exception, there is no converter hall.

DC switchgear

The DC switchgear almost always has a smoothing choke for smoothing the direct current. Its inductance is from 0.1 H to 1 H. The smoothing inductor can be designed as an air coil or a coil with an iron core. In the latter case, it looks similar to a high-voltage transformer, and is as such usually oil-cooled. As air coils running smoothing reactors similar in design usually carrier frequency trap coils in high voltage lines, but have much larger dimensions. They are like this usually mounted on insulators. For DC switchgear are also always DC current and DC voltage instrument transformers. Air chokes have the advantage of producing less noise than iron chokes. For this purpose are the DC output in series, and lying parallel to these transducers are used.

Occasionally also special DC filters are used to eliminate high frequency noise. Such filters are particularly needed when a message delivery by the carrier frequency method is to take place in the range between 30 kHz and 500 kHz on the DC line or when the DC cord is designed as a transmission line, which passes in close proximity to residences. These can passive nature, consisting of LC elements, or active in nature, consisting of a transformer and protection via capacitors coupled amplifier may be giving a spurious signal to the 180 degrees phase shifted signal on the line and thus the wegregelt disorder. Such a system is used in the Baltic HVDC cable.

Converter

The converter is designed for all since the mid-1970s using thyristor, whereby to reduce the effort for the harmonic filter, almost always used 12-pulse three phase rectifier. On older systems are still occasionally mercury -arc rectifier in use. While these each rectifier is installed individually, in 4 thyristor power converter valves to a module, summarized the Thyristorturm. For the realization of a complete converter 3 Thyristortürme are therefore necessary.

In systems that are not operated with current link but with voltage intermediate circuit, instead of thyristors are usually IGBTs used. In these systems, the structure of the converter differs fundamentally from those with thyristors.

Converter transformers

The converter transformers are not only used to adjust the voltage of the three-phase network to which the HVDC, but also by the particular circuit ( star-star - delta starting) for the elimination of many harmonics, if the converter is running in 12-pulse circuit and is operated only in this circuit. Since the windings of the converter transformers cause a DC potential to ground, the insulation of the windings of these transformers should be particularly sized. Converter transformers can be implemented for power ratings up to 300 MVA as a complete unit. For higher power multiple units are possible for reasons of transport. This can be either two three-phase units ( with 2 coils ) or three single-phase units ( with 3 windings ) are used. The latter option has the advantage that only one type of transformer is required, which makes economical to provide the replacement transformer.

Since the converter transformers are traversed by a strong harmonic- containing stream, they generate more noise than comparable transformers in substations normal, what to consider in establishing them. An in-use converter transformer produces a much " kernigeres " noise than a normal three-phase transformer. Converter transformers are situated in the immediate vicinity of the converter. In some modern plants these are housed in buildings of the converter hall, which also gives a better noise protection.

Harmonic Filters

In systems with sechspulsigem operating arise odd harmonics from the 5th order. To eliminate the harmonic filters are used. For pure reactive power generation can be connected in parallel to the harmonic filter capacitor banks or reactors.

Other filters

For 12- pulse converter systems often satisfy one or two tuned to the 12th and 24th harmonic bandpass filter as only harmonics of order 12 × n 1 and n × 12 - apply 1 (n = integer ). In addition, also tuned series resonant circuits may be used.

In addition to the harmonic filters frequently even filters for eliminating interference signals in the frequency range of the PLC equipment ( 30 kHz to 500 kHz ) are present. These filters are usually located in the immediate vicinity of the three-phase output of the converter transformer. They consist of a coil through which the load current, at which a capacitor is placed in parallel. In addition, synchronous phase shifters are used.

Three-phase switchgear

The actual three-phase switching converter station will not differ in principle from that of a normal substation. You can have transformer boxes for other voltage levels.

Converter stations for HVDC Kurzkupplungen

Converter stations for HVDC Kurzkupplungen not differ in principle from those for long-distance transmissions. However, in such systems involves the converter hall usually both converters. Because the length of the direct-current line is very short, no complicated analog filter is necessary.

Others

Space requirements

The area required for a converter station with 600 MW transmission power and a transmission voltage of 400 kV is about 300 × 300 meters.

Location factors

Because of converter stations noise and high frequency noise can give rise to such a system should not be necessarily in the vicinity of residential areas. You may be too surrounded by a noise barrier. As with normal substations is to ensure that in the event of an accident, no oil from transformers or other components may enter groundwater.

Converter stations in Germany

• GKK Etzenricht ( HVDC short coupling, 160 kV, 600 MW, started operation in 1993, since 1995, decommissioned)
• Converter station Lübeck- Herrenwyk the HVDC Baltic Cable (450 kV, 600 MW, operating recording 1994)
• Converter station Bentwisch the HVDC Kontek (400 kV, 600 MW, operating recording 1996)
• Offshore HVDC systems are systems for high-voltage direct -current transmission from offshore wind power on land. They are insufficiently used in Germany, as offshore wind farms, in contrast to the UK and Denmark built farther away from the coast (already HVDC BorWin1 is in operation after hallway, more are under construction ).

Former converter stations in Austria

• GK Duernrohr ( HVDC short coupling, 145 kV, 550 MW, started operation in 1983, since 1996, decommissioned)
• GK Vienna-Southeast ( HVDC short coupling, 160 kV, 600 MW, started operation in 1993, since 1996, decommissioned)