New designs of open extra-high-voltage switchgear for power plants

power plant power lines elp

Abstract

This article contains a description of open switchgear 330(345), 500 and 750(765) kV with 1-1/2 and 4/3 CB line diagrams, for thermal, hydro- and nuclear power plants, developed by the author.

All designs exclude wiring above CB installations. This creates favorable conditions for quick and safe replacement of their modules. New assemblies were designed with two-tier rigid tubular conductors, which make it possible to avoid construction of heavy and large material capacity bay portals.

The size of the switchgear can be significantly reduced by using such assemblies and in conjunction with new equipment arrangement.

The developed solutions reduce the costs of open switchgear construction, equipment repairs and maintenance. These designs can be also used for other configurations such as ring bus, transformer-busbars and others.

The Characteristics of Existing Switchgear

Switchgear with 1- 1/2 and 4/3 CB line diagrams are located in high-power electrical networks, where they simultaneously provide generation, transmission and distribution.

While developing switchgear designs, the following basic requirements should be met:

•          Ensuring favorable conditions for prompt crane circuit breaker repairs, including replacement of their modules,

•          Both transformer (generation) lines or transmission lines, which run in the same direction, should be connected to different busbar systems, because simultaneous loss of both lines is unacceptable.

•          Reduction of substation size and a decrease of switchgear material contents.

The following designs are usually used for 1- 1/2 CB diagram arrangements:

•          Designs with three-row CB installations and busbar systems located on external, opposite sides of switchgear. Post-type disconnect switches are used here,

•          Designs with the same layout, but with suspended types of disconnect switches and combined equipment,

•          Switchgear with single-row CB installations and slanting flexible wiring between CBs.

In such switchgear the wiring, not disconnected during CB repair, is located above the circuit breaker. Space for CB maintenance is limited by wiring height where modules are replaced. To provide comfortable and safe conditions for module replacement, switchgear bay portals should be elevated, heavy, with large material capacity. The most complicated bay portals are in switchgear with suspended disconnect switches, installed on portals, and with the combined equipment.

CB disconnect switches also limit CB repair zone, because they have moving pole with other voltage, located near the upper part of the circuit breaker (where breaker modules are replaced).

The reduction of switchgear space does not compensate for their materials.

Both switchgear have empty, unequipped bays for lines, connected to different busbar systems that run in the same direction. In these bays the portals with slanting wiring are constructed only. Thus the number of switchgear bays and substation space are increased.

Some characteristics of open switchgear with single-row CB installations are described below.

The unfavorable maintenance conditions are characteristic for the location of middle CBs, which are common for two lines and require frequently repair. Two flexible wiring bundles from adjacent CBs are suspended above them.

The switchgear are empty zones, primary located on the side of the transmission lines and partially on the side of the transformer (generator) lines (because the number of lines on both sides of the busbar systems is fewer then the number of CBs, installed in one row).

The required width, where transmission lines are connected to switchgear, is determined by line equipment set installation, including: a line disconnect switch, current and voltage transformers, capacitors, high- frequency carrier processing devices, line arrestors and insulation spaces between them. Each free zone between transmission lines is comparable to CB installation.

On the whole, free zones make up about 40 percent of total switchgear territory. These designs include more bay and busbar portals than switchgears with three-row CB installations.

Research has shown that when basic equipment with suspending wiring is concentrated into one location, the electromagnetic field exceeds safe strength value. This prevents operation and maintenance staff from occupying the area for extended time period.

Switchgear for a 4/3 CB line diagram are used where the number of transmission lines is more or less than the transformer (generation) lines.

The following designs were constructed:

•          Open switchgear with one transformer (generation) line and two transmission lines (with two-rows of CB installations),

•          Open switchgear with two transformer (generation) lines and one transmission line with shunt reactor (with single-row of CB installations).

The suspended disconnect switches, all structures and electrical assembles are similar to those of the open switchgear with 1-1/2 CB line diagrams. The wiring, not disconnected during circuit breaker repair, is also suspended above circuit breakers.

This article suggests more effective switchgear designs to achieve lower material capacity, favorable conditions for equipment repair and maintenance.

Distinctive Features of Open Switchgear

Designs №1-№3 are intended for 1- 1/2 CB line diagrams, designs №4-№6 are intended for 4/3 CB diagrams.

The switchgear drawings are given as fragments. Fragments of designs №1-№3 include two chains, in which lines, running in the same direction, are connected to different busbar systems. Fragments of designs №4-№6 include one chain. The total number of fragments make up the diagram of the open switchgear as a whole.

Busbar apparatus are omitted in these fragments for clarity. However, space for their installation and connection to busbar systems are provided. The rectangles denote high-frequency carrier processing equipment for transmission lines. The post-type disconnect switches are installed in all switchgear.

There is no wiring suspension above all CBs.

The following kinds of two-tier rigid tubular conductors are provided: longitudinal/transverse, slanted, cross coupling and two-tier other assemblies.

The busbar systems are shown with flexible wiring on flat-top portals. However other solutions can be considered, such as using rigid busbar wiring. The busbar spans can be increased with implementation of T-shaped pylons with transition of the middle-phase wiring over the upper additional cross-arm.

In switchgear descriptions, the number of adjacent bays with a 1-1/2 CB diagram are shown in brackets.

DESIGN №1. DESCRIPTION

Dwg. 32-1a Design №1. One line diagram of 1-1/2 CB arrangement

Dwg. 32-1b Design №1. Physical layout (fragment)

1. CB installations

Both busbar systems are located in the switchgear center.

The first outer and the middle CBs are installed close to the external side of the one busbar system, in the half-bays 1(3) and 2(4) accordingly.

The second outer CB is located close to the external side of the other busbar system, in half-bay 3(5).

2. Transmission line connection unit

The line shunt reactor with its equipment set is installed near the transmission line going to the switchgear. The line assembly with a two-tier arrangement is provided with rigid tubular conductors on post insulators. Four (4) disconnect switches are connected to the assembly: the disconnect switches of the first outer and the middle CBs, the line and shunt reactor disconnect switches.

3. Transformer (generation)line connection unit

It includes a two-tier assembly, consisting of two sections:

•          Longitudinal section in bay 2(4) with the bridge in the upper tier, followed from the middle CB disconnect switch to the transformer line disconnect switch and output portal,

•          Transverse section in bay 3(5) with the rigid bridge in the lower tier, from the second outer CB disconnect switch. This bridge is connected with the upper bridge in bay 2 (4).

Apart from the output portals, the design does not have bay portals.

DESIGN №2. DESCRIPTION

Dwg. 32-2a Design №2. One line diagram of 1-1/2 CB arrangement

Dwg. 32-2b Design №2. Physical layout (fragment)

1. CB installations

The busbar systems are built one after another on the side of the transmission line going to the switchgear. Both outer CBs are located in the first row, behind the busbar systems, in bays 1(4) and 3(6). Line high-frequency carrier processing equipment is installed in bay 2(5), between the outer CBs. The middle CB and shunt reactor CB are located in the second row, in bays 2(5) and 3(6).

 2. Transmission line connection unit

Two-tier assembly is constructed in the central part of the switchgear, in bays 2(5) and 3(6). Four (4) disconnect switches are connected to it: the line disconnect switch, the second outer CB disconnect switch, the middle CB disconnect switch and the shunt reactor disconnect switch.

The shunt reactor, with its equipment set, is installed from the side of the transformer line going to the switchgear.

3. Transformer (generation) line connection unit

In bay 1(4) the connection between the outer and middle disconnect switches and the transformer lines is provided by flexible wiring, suspended on the intermediate bay portal and transformer line output portal, located between two busbar systems.

DESIGN №3.DESCRIPTION

Dwg. 32-3a Design №3. One line diagram of 1-1/2 CB arrangement

Dwg. 32-3b Design №3. Physical layout (fragment)

1. CB installations

Design №3 is created by using two switchgear bays.

The busbar systems are built one after another on the side of the transformer line going to the switchgear. The first outer CB is installed close to the busbars, in bay 2(4) in the first row. The middle CB -in bay 2(4) and the second outer CB-in bay 1(3) are located in the second row, behind the first outer CB.

 2. Transmission line connection unit

The unit is the same as the transmission line connection unit of design №1. In bay 1(3), lower level, the second outer CB is connected with two disconnect switches: with its busbar switch and with its CB maintenance disconnect switch.

3. Transformer (generation) line connection unit

In bay 2(4) the disconnect switches of the first outer and of the middle CBs are interconnected with a transformer line disconnect switch (with stepped phases).

The suspending wiring assembly has two sections:

•          Transverse wiring in bays 1(3) and 2(4), connected to a transformer line disconnect switch,

•          Longitudinal wiring in bay 1(3), between the intermediate portal and output transformer line portal, located between two busbar systems.

Both sections are interconnected in bay 1(3), in the upper tier.

DESIGN №4. DESCRIPTION

Dwg. 43-4a Design №4. One line diagram of 4/3 CB arrangement

Dwg. 43-4b Design №4. Physical layout (fragment)

The switchgear is based on the 4/3 CB diagram, with one transformer (generation ) line and two transmission lines without shunt reactors.

Each transmission line is connected between outer and middle CB, transformer (generation) line -between two middle circuit breakers.

1. CB installations

The busbar systems are located on external, opposite sides of the switchgear. The span of busbars includes three bays. Both outer CBs are installed in bays 2 and 3, close to their busbar systems. The middle CBs are placed in bays 1 and 2, in the same row where one of the outer CBs is located. The high-frequency carrier processing equipment for both lines is installed in line bays 1 and 3.

2. Transmission lines connection units

The line assemblies between the outer and middle CBs are built by using longitudinal/transverse rigid wiring. In bay1 the longitudinal bridge in the upper tier, between the outer and middle CB disconnect switches, is connected to the transverse lower tier bridge from the outer CB disconnect switch in bay 2. Similarly, in bay 3 the longitudinal bridge in the upper tier, between the line and outer CB disconnect switches, is connected with the transverse lower tier bridge from the middle CB disconnect switch in bay 2. The disconnect switch connections to the transverse bridges in bay 2 have slanting phase rigid wiring.

3. Transformer (generation) line connection unit

The assembly connects the middle CB disconnect switches and the transformer line disconnect switch.

The assembly arrangement includes the following sections:

•          Two transverse sections (paralleled with busbars), with two insulators in each section. Insulators are installed along the axes of the middle CB disconnect switch outer phases and along the axis of the closed outer posts of busbar portals. These sections are located in the upper tier.

•          Cross coupling two-tier sections on the border of bays 1 and 2: in the upper tier- from one middle CB disconnect switch in bay 1 to the closer insulator in bay 2; in the lower tier- from the other CB disconnect switch in bay 2 to the closed insulator in bay1.

•          Rigid wiring below busbar system.

 Conductors from the middle phases of the CB disconnect switches, which run under transverse wiring sections in the low tier, are interconnected and joined with the middle phase of the transformer line disconnect switch. Conductors from outer insulators are connected to the outer phases of the transformer line disconnect  switch.

Notes:

1. The tubular vertical supports of the upper tier are installed on insulator and disconnect switch flanges.

2. The tubular wiring of the lower tier is installed on insulator and disconnect switch flanges directly.

Apart from the output portals, the design does not have bay portals.

It is also possible to connect the shunt reactor set to one of two transmission lines (the shunt reactor set location should be from transmission line side).

DESIGN №5. DESCRIPTION

Dwg. 43-5a Design №5. One line diagram of 4/3 CB arrangement

Dwg. 43-5b Design №5. Physical layout (fragment)

The switchgear was developed for the 4/3 CB diagram, with two transformer (generation) lines and one transmission line with shunt reactor. Each transformer line is connected between the outer and middle CBs. The transmission line with shunt reactor is connected between the middle CBs.

1. CB installations

The busbar systems are built on the opposite sides of the switchgear. The outer CBs are connected to busbar systems in bay 1 and 3 accordingly. The middle CBs are installed in bays 1 and 2. The shunt reactor with equipment set is located on the side of the transformer line going to the switchgear.

2. Transmission line connection unit

The line assembly, made below one busbar system, connects the folowing disconnect switches: two disconnect switches of the middle CBs, line and shunt reactor disconnect switches. Two cross coupling sections are located on the internal and external sides of the busbar system. These sections were described in design №4.

3. Transformer (generation) line connections units

The transformer line connections to the switchgear are similar to the connections of transmission lines in design №4 (i.e., by using longitudinal/traverse and two-tier phase slanting arrangements). Short bridges join line disconnect switches with proper output line portals.

Apart from transmission and transformer line output portals, the design does not have bay portals.

DESIGN №6. DESCRIPTION

Dwg. 43-6a Design №6. One line diagram of 4/3 CB arrangement

Dwg. 43-6b Design №6. Physical layout (fragment)

The switchgear is recommended for 4/3 CB diagram with two transmission lines with shunt reactors and one transformer (generation) line. Each transmission line is connected between the outer and middle CBs, while the transformer line is connected between two middle CBs.

1. CB installations

Both busbar systems are built on the side of the transformer line going to the switchgear. The single-row CB installation is provided in switchgear (apart from shunt reactor sets, located with reactors on the side of the transmission lines going to switchgear).

2. Transmission line connection units

The switchgear has two identical assemblies with two-tier rigid tubular wiring, installed on post insulators. Four disconnect switches are connected to each assembly: the outer and middle CBs, the transmission line and shunt reactor disconnect switch.

3. Transformer (generation) line connection unit

Two middle CB disconnect switches and the transformer line disconnect switch are connected using a cross coupling section which is specified in the switchgear design №4 description.

Apart from transmission and transformer line output portals, there are no bay portals in the switchgear.

Reference Literature:

1. L.I. Dvoskin. "Diagrams and switchgear designs". i.Moscow, Energoatomizdat, 1985

2. V.A. Evtushenko, A.A. Chunikhin. "Suspended disconnect switches" i. Moscow, Energoatomizdat, 1988

3. A.P. Dolin, G.F. Shangin. "Open switchgear with rigid wiring." i. Moscow, Energoatomizdat, 1988

4. M.A. Safyan. Author’s certificate №1391430 "Extra-high- voltage switchgear," 87.

5. L.D. Gustov. "Open switchgear 500 kV with suspended disconnect

 switches," Power generation stations, №5, 1977 

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