5-7High-Voltage Power Electronic Substations

After the 2003 blackout in the United States and parts of Canada and (shortly after) a number of black-outs in Europe, new HVDC and FACTS projects are gradually coming up to enhance the system security and to “squeeze” more power out of the grids [4,6,9,32,54,55]. One example is the Neptune HVDC project in the United States. The task given by Neptune Regional Transmission System LLC (RTS) in Fairfield, Connecticut, was to construct an HVDC transmission link between Sayreville, New Jersey, and Duffy Avenue, Long Island/New York. As new overhead lines could not be built in this densely populated area, power had to be brought directly to Long Island by an HVDC cable transmission, bypassing the AC sub-transmission network. For various reasons, environmental protection in particular, it was decided not to build a new power plant on Long Island near the city in order to cover the power demand of Long Island with its districts Queens and Brooklyn, which is particularly high in summer. The Neptune HVDC inter-connection is an environmentally compatible, cost-effective solution that helps meet these needs.

“Snapshots” from the inauguration on 10-11-2007

FIGURE 5.6 Neptune HVDC—a view of Station Duffy Avenue inside: the cable, indoor smoothing reactor, and thyristor converter.

HVDC converter station B2B Ridgefield

New Jersey

New York

49th street Manhattan

345 kV high voltage cable (AC)

Hudson transmission project Ridgefield (New Jersey), USA

Power exchange Increase in stability Sharing of Reserve Capacity No increase in short-circuit power Customer:

Hudson transmission Partners LLC System data:

Rating 660 MW Voltage 170 kV DC

Thyristor 8 kV LTT 2013

FIGURE 5.7 Hudson Transmission Project—second HVDC (B2B) to strengthen the power supply system of New York.

The low-loss power transmission provides access to various energy resources, including renewable ones.

The interconnection is carried out via a combination of submarine and subterranean cable directly to the network of Nassau County, which borders on the city area of New York. Figure 5.5 shows in the upper part a photo of the Sayreville station, which is connected via world’s first 500 kV DC MI cable (mass impreg-nated, lower part of the figure) to the station Duffy Avenue, Long Island. A view of the station Duffy Avenue inside the valve hall with the thyristor converters suspended from the ceiling, the indoor DC smoothing reactor (indoor for reasons of noise reduction) and the monopolar cable is given in Figure 5.6.

During trial operation, 2 weeks ahead of schedule, Neptune HVDC proved its security functions for system support and blackout prevention in megacities in a very impressive way. On June 27, 2007, a black-out occurred in New York City. Over 380,000 people were withblack-out electricity in Manhattan and Bronx for up to 1 h, subway came to a standstill and traffic lights were out of operation. In this situation, Neptune HVDC successfully supported the power supply of Long Island and thus of 700,000 households.

In Figure 5.7, a second DC project in the area of New York, in this case with B2B and a short AC cable through the Hudson River, is shown. The benefits of this additional DC “energy bridge” in the Megacity New York are depicted in the figure.

The grid developments in Europe progress in a similar way. A number of new DC projects are already in operation and more are coming up, for the same reasons as in the United states, refer to Figure 5.8.

The DCs provide power trading opportunities by means of excellent controllability of HVDC, they build power highways across the ocean (Figure 5.8, lower part) and connect Northern and Southern parts of Europe, and they enable interconnection between the different asynchronous parts of ENTSO-E (e.g., in Denmark, Figure 5.8, upper part).

China is presently the country with the largest number of HVDC links in the world. Due to rapidly growing industries in this emerging country, the demand on power generation as well as on power mission is continuously increasing. Nowadays, a large number of bulk power UHV AC and DC trans-mission schemes over distances of more than 2000 km are under planning for connection of various large hydro power stations. Some of the DC projects are shown in Figure 5.9, right part. In the left part of the figure, an example of the 3000 MW HVDC project Gui-Guang I in Southern China is depicted.

Odense

FIGURE 5.8 Europe—the HVDC portfolio is growing too.

5-9High-Voltage Power Electronic Substations

FIGURE 5.9 HDVC Projects in China enable low-loss West-to-East transmission of hydro-power-based electrical energy produced in the country’s interior to coastal load centers (right side). Sending station of long-distance overhead line transmission Guizhou-Guangdong I (left side).

The next generation HVDC is the Yunnan–Guangdong ±800 kV UHV DC Project, world’s first HVDC project in the UHV range and one of the most important power links in Southern China. It connects Chuxiong in the Yunnan province to Suidong in the Guangdong province over a distance of 1418 km.

This project and its new technology present a major step forward in the HVDC technology and provide a new level of efficiency in power transmission [85]. Figure 5.10 shows a view of the UHV DC sending station Chuxiong with valve halls and the relatively small DC yard on the right side and the huge AC yard equipment on the left and middle part of the picture. This gigantic project was, in fact, the kickoff for the DC Super Grid development, worldwide. The utility China Southern Power Grid and Siemens succeeded to put pole 1 of this first UHV DC into operation in December 2009 and pole 2 in June 2010.

A simplified single line diagram for the basic configuration is shown in Figure 5.11. It can be seen that the solution for the Yunnan–Guangdong project consists of a series connection of two 12-pulse bridges with 400 kV rated voltage each. In order to enable uninterruptible power transfer during connection and disconnection of individual groups, DC bypass switches, DC bypass disconnect switches, and group dis-connect switches are included in the arrangement. It should be noted that even though the transportation limitation is the most important reason for selecting such an arrangement with smaller transformer units, also system security aspects are a crucial issue: increased power availability is possible compared to single 12-pulse bridge designs since any outage of a single group does only affect 25% of the installed power capability. Especially for a link with such large power rating of 5000 MW or more, this is an important aspect for the system redundancy. This high redundancy will be even more important when the next generation of a UHV DC voltage level of 1100 kV with an increased power output of 10 GW comes into application.

A view of the 400 and 800 kV converter buildings is depicted in Figure 5.12 and the 800 kV converter hall inside is shown in Figure 5.13—the left side shows the large transformer bushings entering the valve hall, where they are connected to the converter on the right side. The 800 kV DC wall bushing (right side

World’s first 800 kV UHV DC–5000 MW

2009/2010

Example of HVDC “Bulk”

FIGURE 5.10 UHV DC Yunnan–Guangdong: from “3D” to reality—view of the sending station Chuxiong.

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