TEXT 19.High Voltage Power Electronics Substations

The dramatic development of power electronics in the past decades has led to significant progress in electric power transmission technology, resulting in special types of transmission systems, which require special kinds of substations. The most important high-voltage power electronic substations are converter stations, above all for high-voltage direct current (HVDC) transmission systems, and controllers for flexible ac transmission systems (FACTS).

High-voltage power electronic substations consist essentially of the main power electronic equipment, i.e., converter valves and FACTS controllers with their dedicated cooling systems. Furthermore, in addi­tion to the familiar components of conventional substations, there are also converter transformers and reactive power compensation equipment, including harmonic filters, buildings, and auxiliaries.

Most high-voltage power electronic substations are air insulated, although some use combinations of air and gas insulation.

Basic community considerations, grounding, lightning protection, seismic protection, and general fire protection requirements apply as with other substations. In addition, high-voltage power electronic substations may emit electric and acoustic noise and therefore require special shielding. Extra fire protection is applied as a special precaution because of the high power density in the electronic circuits.

Frequency converters transmit power between systems with different constant or variable frequencies. Some examples are converters between variable speed machines and power grids, energy storage converters, converters for railroad systems, and, most importantly, HVDC (High Voltage Direct Current transmission).

HVDC converters convert AC power to DC power and vice versa. They terminate DC transmission lines and cables or form back-to-back asynchronousAC system couplings. When connected to DC transmission lines, the converter voltages can be on the order of a million volts (±500 kV) and power ratings can reach thousands of megawatts. With back-to-back converters, where DC line economies are not a consideration, the DC voltage and current are chosen so as to minimize converter cost. This choice results in DC voltages up to and exceeding 100 kV at power ratings up to several hundred megawatts.

The AC system or systems to which a converter station is connected significantly impact the station’s design in many ways. This is true for harmonic filters, reactive compensation devices, fault duties, and insulation coordination. Weak AC systems (i.e., low short-circuit ratios) represent special challenges for the design of HVDC converters.

Typical ratings of FACTS controllers range from about thirty to several hundred MVA. Normally, FACTS controllers are an integral part of AC substations. Like HVDC, they require controls, cooling systems, harmonic filters, fixed capacitors, transformers, and building facilities. Static VAr Compensators (SVC) have been used successfully for many years, either for load (flicker) compensation of large industrial loads, or for transmission compensation in utility systems. Harmonic filter and capacitor banks, as well as(normally air core) reactors, step down transformers, a building, breakers and disconnect switches on the high voltage side, and heavy duty busbars on the medium voltage side characterize most SVC stations. The power electronic (thyristor) controllers can have air or liquid cooling. A new type of controlled shunt compensator, called STATCOM, uses voltage source inverters. STATCOM requires fewer harmonic filters and capacitors than an SVC, and no reactors at all. This fact makes the footprint of a STATCOM station significantly more compact than that of a conventional SVC.

The ease with which FACTS stations can be reconfigured or even relocated, may be important and can influence the substation design. Changes in generation and load patterns may make such flexibility desirable.

HVDC and FACTS controllers allow steady-state, quasi-steady-state, dynamic, and transient control actions and they provide important equipment and system protection functions. Fault monitoring and sequence of event recording equipment are used in most power electronics stations. Typically, these stations are remotely controlled and offer full local controllability. Man-machine interfaces are often highly computerized, with extensive supervision and control being exercised via monitor and keyboard.

1. Read and translate the text.

2. Answer the questions to the text.

1) Why did special kinds of substations become necessary?

2) What is special with high-voltage power electronic substations?

3) Why is special shielding required for high-voltage power electronic substations?

4) What does the station’s design depend on?

5) What is the maximum load of HVDC and FACTS?

6) What type of cooling does the thyristor have?

7) Where are the SVC used in? What are they used for?

8) What are the advantages of STATCOM?

3. Find information about modern compensators (FCSC and TCSC) and discuss them with your partner.

4.  Put the following words in the correct order to form a sentence.

1) gas, insulation, HVP Electronic Substation, air, some,  combinations, of, and, use.

2) Be, remotely, they, controlled, can, easily.

3) Emit,substations, noise,in addition, electric, may, high-voltage power, and, acoustic, electronic.

4) Many, have, for, successfully, been, SVC, years, used.

5) substation, what, influence, the, can, design?

5. Match the words from the text with their corresponding definitions.