RXD

Switchgear design

The cabinet of the switchgear is made of folded steel sheets joined with rivets. The walls and partitions create a self- supporting structure. Hot galvanized steel sheeting is used in the construction of the cabinets.
Solid round-head steel rivets are used to attach the structural elements. The outside walls of the extreme opposite bays are additionally equipped with two-part lateral shields, made of steel sheeting. On the top of the cubicle an auxiliary circuitry cabinet is mounted. Primary busbars run between bays aided by gland plates made of non-magnetic material with isolator bushings, which support the primary busbars. Outgoing busbars are lead out of primary busbars.
The primary busbar compartment can be isolated during service operation by inserting the isolating plate into the guiderails through a slot located above the door. The interlock control mode allows the cubicle door to be opened. A primary switch can be installed permanently or as a withdrawable module. The withdrawable module in the operating and test/open position is located in the cubicle behind closed doors. After opening the door it is possible to rack it out into the isolation position. Mechanical indicators of the circuit breaker and arming of the operating mechanism position are visible through the inspection window.
In accordance with LSC (Loss of Service Continuity) classification, the RXD switchgear cubicle meets the criteria of the LSC2A category. Non-compartment double module switchgear cubicles meet this requirement when the withdrawable module is set in the open position. When undergoing service, the high-voltage power supply cables of the bay must be de-energised and grounded, and the circuit should be disconnected and isolated (physically and electrically) from the primary busbars. The primary busbars may be energized. The terminals for the connecting cables or busbars are located on the lower part of the cubicle. Also installed in this location: current transformers, a grounding switch and, depending on operation needs, optional: voltage transformers, Ferranti current transformers and surge arresters. The grounding switch is equipped with a manual operating mechanism. Its position is signaled by a position indicator. The bottom of the cubicle is closed with a split floor cover which is also a gland plate. Plate openings are covered by rubber glands. Cable clamp supports and assembly supports for installation of Ferranti current transformers are mounted on the bottom of the cubicle.

The cubicle doors are made from steel sheeting. The door is equipped with hinges and locks, which withstand stress comparable to an explosion. Hinges enable the door to be opened widely, at an angle of about 135O. The door is reinforced with suitably shaped and welded reinforcing profiles. The cubicle door is equipped with an inspection window which enables the visual assessment of the withdrawable module's position and switching operations. The construction of the door enables the circuit breaker (when in the operating position) to be mechanically switched off while the door is closed.

Explosion relief panels
The openings located at the top of the cubicle are covered with explosion relief panels. Their function is to depressurize the compartment in case of arc fault. A rapid pressure increase inside the switchgear’s cubicle results in plastic bolts breaking and the explosion relief panels opening. These work together with limit switches installed at the top of the switchgear. The limit switches, which are activated by the opened explosion relief panels, send an impulse that triggers the power switch. It reduces the effects of the arc fault which occurred inside the cubicle.

The withdrawable module is a system composed of a racking system and, depending on the bay function: a circuit breaker, contactor, a set of voltage transformers with fuses, or short-circuiting block. The racking system mechanically attaches the withdrawable module to the switchgear bay. Its frame is coupled with the bay by double-sided locking in cutouts in the guide rail.
The withdrawable module’s racking system unit is moved between the operating and test/open positions by means of hand- or electric-driven crank mechanism, when the door is closed. The operating and test/open positions are indicated using position indicators when the mechanism is in the exact position.

The auxiliary circuitry compartment (low voltage compartment) is constructed as a control cabinet and is utterly isolated from the high voltage zone of the switchgear. The cabinet has a separate steel housing and can be prefabricated independent of the switchgear’s high current part. The cabinet is designed for installation of: protection device assemblies, metering apparatus and control gear, and automation systems. The cabinet is mounted on the roof of the switchgear cubicle. There are openings for cable trays, cable glands and low voltage leads in the bottom, side, and back walls of the cabinet. These openings are covered with plates, which can be drilled according to design. A perforated assembly plate fixed to the back wall of the cabinet was designed for apparatus installation. The apparatus can also be fixed to the side-walls of the cubicle.
It is possible to modify the cabinet’s design to the customer’s needs after consultation with the manufacturer.

Busbars
Primary busbars
A single, three-phase busbar system is used as a primary busbar in the switchgear and is located in the top, back part of the cubicle (see Figure 1a, b, c. Bay equipment).
There are also selected copper flat bars with rounded edges, that have cross sections corresponding to the switchgear’s rated voltage.
The primary busbars are supported on distribution busbars and isolator bushings located in the lateral partitions.

Distribution busbars
Distribution busbars are made from flat bars with rounded edges, which have cross sections corresponding to the switchgear’s rated voltage.

Insulating components
Epoxy resin bushings are used in the switchgear. These are support bushings, which support the primary busbars and isolator bushings, allowing busbars to run through switchgear bays, each mounted in gland plates in the bay side-walls.

Protective grounding
Each cubicle has a grounding cable in the form of a copper busbar with a cross-section of 40x5 mm located at the bottom, back of the cubicle. To form the grounding system, these busbars are connected by bridges between separate cubicles. The grounding system ends with terminals on the left and right sides of the switchgear cubicle. They are used as a connection to the site grounding system.

Cable connections
Connection compartments are constructed to connect single or multiple core cables in synthetic insulation.

Protection and interlock system

After prior consultation with the manufacturer, the switchgear cubicle can be equipped with mechanical and electric interlocks required by standards and to improve operator safety, such as:

Mechanical interlocks:

1. prevent the withdrawable module from sliding in or out of the in/out operating position when the circuit breaker is closed (standard requirement),
2. allow closing and opening of the circuit breaker only in its test/open operating position (standard requirement),
3. allow closing the grounding switch only in the test/open or withdrawable module isolation positions,
4. prevent switching the position of the withdrawable module from the test/open to operating position if the grounding switch is closed,
5. prevent opening the switching compartment door if the withdrawable module is in the operating or intermediate positions,
6. prevent opening the cable compartment door if the grounding switch is open (does not apply to RXD36),
7. prevent changing the breaker’s withdrawable module from the test/open position to the isolation position until the control cable power unit of the breaker is in the open position,
8. a service racking system designed to transport withdrawable modules can be equipped with a coupling mechanism, which prevents changing the position of the racking system even when its wheels are unlocked (optional),
9. a service racking system, which transports the withdrawable modules, can be constructed to allow changing the position of the withdrawable module from the racking system to the bay only after their mechanical coupling (optional),
10. a service racking system, which transports the withdrawable modules, can be constructed to make the expansion of the bay possible only after locking the withdrawable module in the bay or by the racking system (optional),
11. allow halting the operating mechanism of moving partitions which cover the fixed contacts in the switching compartment,

After consultation with the manufacturer it is possible to use additional key interlocks.
Electrical interlocks:

1. prevent closing the circuit breaker if its auxiliary circuits are not powered; only mechanical opening of the circuit breaker is possible (standard requirement),
2. prevent switching the withdrawable module to the operating position without the power supply to the control circuits,
3. prevent access to the grounding switch operating mechanism when closing of the grounding switch is additionally affected by, for example, the primary busbar grounding switch can be closed only when the withdrawable modules in that particular section are in the test/isolation position,
4. prevent access to the operating mechanism of the withdrawable module when changing its position is additionally affected
5. prevent opening of the door when the grounding switch is in the open position.

Interlocks, except those required by applicable standards, are designed to fit to a particular project. After consultation with the switchgear’s manufacturer, it is possible to install additional interlocks, which operate based on miniature connectors and electromagnetic locks.
The door design allows unlocking them in case of emergency and access to the compartment when it is needed.