Technical Development of UHV AC Transmission and Transformation Equipment

UHV series compensation device

For large-scale construction of ultra-high voltage projects, core equipment is the key.

In order to promote the further development of UHV AC transmission technology, the latest technical development of key equipment

such as UHV AC transformer, gas insulated metal enclosed switchgear (GIS), series compensation device and lightning arrester is

summarized and prospected.

The results show that:

The allowable value of electric field strength when the partial discharge probability of UHV transformer is 1 ‰ shall be selected as the

allowable field strength;

Magnetic leakage control measures such as magnetic shielding at the end of the body, electrical shielding of the oil tank,magnetic shielding

of the oil tank, and non magnetic conducting steel plate can effectively reduce the magnetic leakage and temperature rise of 1500 MVA

large capacity UHV transformer;

The breaking capacity of the UHV circuit breaker can reach 63kA. The synthetic test circuit based on the “three circuit method” can break

through the limit of the test equipment and complete the breaking test of the 1100kV circuit breaker;

It is clear that the amplitude and frequency of VFTO are limited by installing damping resistors on the static contact side of “vertical”

disconnectors;

From the point of view of continuous operation voltage, it is safe to reduce the rated voltage of UHV arrester to 780kV.

The future UHV AC power transmission and transformation equipment should be deeply studied in terms of high reliability,large capacity,

new working principle and performance parameter optimization.

UHV AC transformer, switchgear, series compensation device and lightning arrester are the main core equipment of UHV AC transmission

project. This time, we will focus on sorting out and summarizing the latest technological development of these four types of equipment.

Development of UHV series compensation device

The UHV series compensation device mainly solves the following problems: the influence of the application of series compensation on

the system characteristics, the optimization of the key technical parameters of the series compensation,the strong anti electromagnetic

interference capability of the control, protection and measurement system, the design and protection of the super capacitor bank, the

flow capacity and operation reliability of the series compensation spark gap,the pressure release capacity and current sharing performance

of the voltage limiter, the quick opening and closing capacity of the bypass switch, the damping device, the fiber column The structure

design of current transformer and other key technical issues. Under the conditions of ultra-high voltage, ultra-high current and ultra-high

capacity, the problem that a number of key technical indicators of the series compensation main equipment reach the performance limit

has been overcome,and the ultra-high voltage series compensation primary equipment has been developed, and all of them have achieved

localization.

Capacitor bank

Capacitor bank for series compensation is the basic physical component to realize the series compensation function, and is one of the key

equipment of the series compensation device. The number of UHV series compensation capacitors in a single set is up to 2500, 3-4 times

that of 500kV series compensation. It is faced with a large number of series parallel connection problems of capacitor units under large

compensation capacity. A double H-bridge protection scheme is proposed in China. Combined with fancy wiring technology, it solves

the coordination problem between the sensitivity of unbalanced current detection of capacitors and the control of injected energy, and also

solves the technical problem of possible burst of series capacitor banks. The entity diagram and wiring schematic diagram of series capacitor

banks are shown in Figures 12 and 13.

                                                 Figures 12  Capacitor bank

                                             Figures 13 Wiring mode

Pressure limiter

In view of the extremely demanding reliability requirements of UHV series compensation, the method of resistor chip matching is specially

optimized, and the shunt coefficient between columns is reduced from 1.10 to 1.03 after nearly 100 resistor chip columns of each phase

voltage limiter are connected in parallel (each resistor chip column is connected in series by 30 resistors). The specially designed pressure

release structure is adopted, and the pressure release capacity reaches 63kA/0.2s under the condition that the porcelain jacket pressure

limiter unit is 2.2m high and there is no arc separator inside.

Spark gap

The rated voltage of the spark gap for UHV series compensation reaches 120kV, which is much higher than 80kV of the spark gap for UHV

series compensation; The current carrying capacity reaches 63kA/0.5s (peak value 170kA), 2.5 times that of the ultra-high voltage gap. The

developed spark gap has such performances as accurate, controllable and stable trigger discharge voltage, sufficient fault current carrying

capacity (63kA, 0.5s), hundreds of microseconds trigger discharge delay, fast recovery capability of main insulation (after passing 50kA/60ms

current, the recovery voltage per unit value reaches 2.17 at an interval of 650ms), strong electromagnetic interference resistance, etc.

Series compensation platform

A compact, heavy load, high seismic grade UHV series compensation platform has been designed, forming the unique international UHV

series compensation true type test and research capability; The three-dimensional mechanical and field strength analysis model of complex

multi equipment is established, and the compact layout and support scheme of three section bus type platform equipment with integrated

and large enclosure structure is proposed, which solves the problems of anti-seismic, insulation coordination and electromagnetic environment

control of overweight platform (200t); The UHV series compensation true type test platform has been built, which has formed the large-scale

external insulation coordination, corona and space field strength, electromagnetic compatibility of weak current equipment on the platform

and other test capabilities of the series compensation platform, filling the blank of UHV series compensation test research.

Bypass switch and bypass disconnector

A large capacity arc extinguishing chamber and a high-speed operating mechanism were developed, which solved the problems of guidance

and mechanical strength of 10m ultra long insulated pull rod under high-speed action. The first SF6 porcelain column type bypass switch

with T-shaped structure was developed, with a rated current of 6300A, a closing time of ≤ 30ms, and a mechanical life of 10000 times;

The method of adding auxiliary vacuum circuit breaker to the main contact and switching current by the main pole is proposed. The first

open type bypass disconnector is developed, and the switching current switching capacity is greatly improved to 7kV/6300A.

Electromagnetic compatibility of weak current equipment on the platform

The technical problems such as transient overvoltage control on UHV series compensation platform and electromagnetic compatibility of

weak current equipment under high potential and strong interference have been overcome, and the series compensation platform

measurement system and spark gap trigger control box with extremely strong anti electromagnetic interference capability have been

developed. Figure 14 is the field diagram of UHV series compensation device.

The international first set of UHV fixed series compensation device independently developed by China Electric Power Research Institute

has been successfully put into operation in the expansion project of UHV AC test demonstration project. The rated current of the device

reaches 5080A, and the rated capacity reaches 1500MVA (reactive power). The main technical indicators rank first in the world. The

transmission capacity of the UHV test demonstration project has been increased by 1 million kW. The goal of stable transmission of 5

million kW by single circuit UHV lines has been achieved. So far, safe, stable and reliable operation has been maintained.

Figure 14  1000KV UHV Series Compensation Device