4 Switchgear
4.2 Standard Enclosure Configurations
As the name implies, this panel configuration serves two purposes:
As an incomer panel. This switches the incoming main supply onto the common horizontal busbar system of a metal-enclosed switchgear arrangement
As a feeder panel. This switches the main supply from the common horizontal busbar system of a metal-enclosed switchgear arrangement onto a specific feeder circuit.
The enclosure will always have a main circuit breaker (normally withdrawable), housed in its own compartment of the panel. An earth switch at the cable termination end of the circuit provides isolation during shutdown and maintenance. Interlocking ensures that the earth switch cannot be closed until the main circuit breaker is open and racked-out into the test position. Current transformers are fitted to interface with a protection relay for circuit breaker trip operation.
Depending on the required function, voltage transformers can be supplied. These can be 3-phase or single phase, either fixed or withdrawable style. A variety of low voltage equipment is used, which is mounted in its own segregated compartment, situated at the top-front of the enclosure assembly.
AuCom provides an Incomer Feeder Panel as part of its L-Series switchgear range. This is rated at 12 kV from 630 A to 2000 A. An IAC classification of 31.5 kA for 1 second is achieved by double skin compartments, special locking door designs and top-exit arc flaps for pressure release.
Incomer Feeder Panel (IFP)
Typical Incomer Feeder Panel
Front view Side view Rear view
1 Circuit breaker (withdrawable) 2 Current transformer set 3 Earth switch
4 Voltage transformer (fused and withdrawable)
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SWITCHGEAR
Direct Incomer Panel (DIP)
A direct incomer panel connects the incoming main supply onto the common horizontal busbar system of a metal enclosed switchgear arrangement, without any primary switching device.
An earth switch is typically provided at the cable termination end of the circuit for isolation during shutdown and maintenance. Access to earth switch operation must be interlocked with the supply end switchgear so that the earth switch cannot be closed onto a live circuit. Current and voltage transformers can be supplied as optional items, along with a variety of low voltage equipment, which is mounted in its own segregated compartment situated at the top-front of the enclosure assembly.
AuCom provides an Direct Incomer Panel as part of its L-Series switchgear range. This is rated at 12 kV from 630 A to 2000 A. An IAC classification of 31.5 kA for 1 second is achieved by double skin compartments, special locking door designs and top-exit arc flaps for pressure release.
Direct Incomer Panel (DIP)
Typical Direct Incomer Panel
Front view Side view Rear view
1 Current transformer set 2 Earth switch
3 Voltage transformer (fused and withdrawable)
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1
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Bus Coupler Panel (BCP)
A bus coupler panel connects two adjacent horizontal busbar systems together using a main circuit breaker (normally a withdrawable type), which is housed in its own compartment of the panel. The horizontal busbar system of metal-enclosed switchgear is usually situated towards the top of the panel enclosure. In order to physically connect two adjacent busbar systems together, a bus coupler panel must be used alongside a bus riser panel.
A main earth switch, current and voltage transformers and low voltage equipment can all be supplied as optional extras.
AuCom provides a Bus Coupler Panel as part of its L-Series switchgear range. This is rated at 12 kV from 630 A to 2000 A. An IAC classification of 31.5 kA for 1 second is achieved by double skin
compartments, special locking door designs and top-exit arc flaps for pressure release.
Bus Coupler Panel (BCP)
Typical Bus Coupler Panel
Front view Side view Rear view
1 Circuit breaker
2 Current transformer set 3 Earth switch
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2
3
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SWITCHGEAR
Bus Riser Panel (BRP)
A bus riser panel contains a vertical 3-phase bus which connects the output of a bus coupler panel at the bottom of the enclosure, to a horizontal busbar system at the top of the enclosure. In order to physically connect two adjacent horizontal busbar systems together, a bus riser panel must be used alongside a bus coupler panel.
Voltage transformers, along with low voltage equipment, can be supplied as optional extras.
AuCom provides a Bus Riser Panel as part of its L-Series switchgear range. This is rated at 12 kV from 630 A to 2000 A. An IAC classification of 31.5 kA for 1 second is achieved by double skin
compartments, special locking door designs and top-exit arc flaps for pressure release.
Bus Riser Panel (BRP)
Typical Bus Riser Panel
Front view Side view Rear view
1 Voltage transformer (fused and withdrawable)
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1
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Metering Panel (MTP)
A metering panel contains a primary horizontal busbar system with a bus tap-off that drops vertically to the bottom of the enclosure. The vertical bus is connected to voltage transformers, which can be of the fixed or withdrawable type. Sometimes a main earth switch is supplied. Metering equipment is often contained within the segregated low voltage compartment, located at the top-front of the enclosure.
AuCom provides a Metering Panel as part of its L-Series switchgear range. This is rated at 12 kV from 630 A to 2000 A. An IAC classification of 31.5 kA for 1 second is achieved by double skin
compartments, special locking door designs and top-exit arc flaps for pressure release.
Metering Panel (MTP)
Typical Metering Panel
Front view Side view Rear view
1 Earth switch
2 Voltage transformer (fused and withdrawable)
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2 1
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SWITCHGEAR
Busbar Systems
OverviewMedium voltage busbar systems consist of two general arrangements. The main switchgear distribution bus has three busbar sets (one set per phase) which run horizontally through all the panels in a line-up. These distribution busbars run through a dedicated chamber within each metal-enclosed panel. Segregation of busbar chambers, between adjacent panels, is provided by using insulated through-bushings. Inside the horizontal busbar chamber of each panel, a vertical feeder busbar system can be tapped off the main horizontal system, for incomer, feeder, bus-coupler, bus-riser, metering or motor starter circuit.
Ratings
The nominal current rating (Ir) of an incomer busbar system usually matches the rating of the main busbar system it is feeding. Likewise, bus-coupler and bus-riser systems have the same current rating as the main busbar system they are connecting. A feeder circuit busbar system has a nominal current rating to match the expected load.
The nominal current rating is determined by the cross sectional area, shape and configuration of the individual phase bars.
The short-time withstand current rating (Ik) of the busbar system must be greater than the highest expected symmetrical fault current at the point of installation. This rating is for a short-time withstand period of 1 or 3 seconds (tk). All busbar systems installed in the same switchgear line-up usually have the same short-time withstand current/time rating.
The nominal voltage rating (Ur) of a busbar system must be greater than the installation's operating voltage. This voltage rating determines the minimum phase-to-phase and phase-to-earth busbar clearances.
The nominal frequency rating (fr) of a busbar system must match the installation's operating frequency.
NOTE
The nominal current must be derated for high ambient temperatures (usually above 40 °C).
The nominal voltage and insulation ratings of a busbar system must be adjusted for altitudes over 1000 metres.
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Design
Busbar system design must consider:
adequate minimum required clearance between phases and phase to earth
selection of adequate busbar insulator standoffs
bolting arrangements for continuous busbar connections
thermal effects on busbar and insulator standoffs under normal and fault conditions
electrodynamic forces applied to busbars and insulator standoffs under fault conditions
avoidance of mechanical resonance under normal operating and fault conditions Voltage ratings and clearance
IEC 62271-1 gives typical voltage ratings for busbar systems and insulator standoffs.
Typical voltage ratings and minimum clearances for busbar systems and insulator standoffs Rated voltage Power frequency withstand
voltage Lightning impulse withstand
voltage Clearance –
Source: derived from IEC 62271-1 Current ratings and dimensions
The nominal current rating of a busbar is determined by the type of material, shape and cross sectional area of the bar and the maximum permissible temperature rise of the material. If the busbar is carrying AC current, the operating frequency has a slight effect on the busbar rating due to magnetic skin effect.
A busbar system has a short-time withstand current rating. The temperature rise in the event of a short circuit condition must not exceed the thermal limits of busbar standoffs.
Typical current ratings and nominal dimensions for medium voltage busbar systems NOTE
Dimensions should be used as a guideline only and may vary.
The dimensions stated in this table are based on bare copper at ambient temperature of 40 °C, maximum permissible temperature rise of 50 °C, operating at 50 Hz.
1600 100 x 10 12.5/16/20/25/31.5/40/50 0.5/1/2/3
2000 100 x 6 (2 bars)
2500 100 x 10 (2 bars)
3150 100 x 3 (3 bars)
Source: current rating information is derived from IEC 62271-1
1 Most medium voltage switchgear including busbar systems have short-time withstand ratings of 16 kA, 20 kA, 25 kA or 31.5 kA for 3 seconds.
SWITCHGEAR Temperature rise
During short circuit conditions the busbar will rise in temperature, depending on the level of short circuit current and time duration. This temperature rise must not exceed the thermal limits of any equipment in contact with the busbar.
Maximum permissible temperature rise for bolt-connected devices, including busbars Material and dielectric medium Maximum permissible
temperature (°C)
Temperature rise above 40 °C ambient
(°C) Bolted connection (or equivalent)
Bare copper, bare copper alloy or bare aluminium alloy
In air 90 50
In sulphur hexafluoride (SF6) 115 75
In oil 100 60
Silver or nickel coated
In air 115 75
Source: derived from IEC 62271-1 NOTE
When engaging parts with different coatings, or where one part is of bare material, the permissible temperature and temperature rise shall be those of the surface material having the lowest permitted value.
Electrodynamic withstand
During short circuit conditions, the peak current associated with the first loop of the fault current produces electrodynamic forces which stress the busbar and insulator standoff supports. Stress on the busbars must not exceed the limits of the material used. Bending forces must not exceed the mechanical limits of the insulator standoffs.
Electrodynamic forces
Busbars (parallel) Support
d
Resonant frequency
The busbar system must be checked for potential resonance under normal operating conditions and fault conditions.
This is done by calculating the natural resonant frequency of the system, which must meet the following criteria:
50 Hz supply: not within the ranges 48 Hz to 52 Hz and 96 Hz to 104 Hz
60 Hz supply: not within the ranges 58 Hz to 62 Hz and 116 Hz to 124 Hz Calculation requirements
Busbar systems are subjected to thermal and electrodynamic stresses under normal operating conditions, but more so under short circuit fault conditions. It is important to ensure the busbar system will function safely under all known conditions. When checking the design, the most important considerations are the nominal operating current, expected fault current at the point of installation, average ambient temperature and the altitude of the installation.
To check the safety of a busbar system:
Check that the current rating of the busbar system (Ir) exceeds the expected nominal current. Main factors affecting the busbar rating are busbar material and configuration, ambient temperature and maximum permissible temperature rise.
Check the maximum expected temperature rise of the busbar during a short circuit fault. In the event of short circuit current flow (Ith), the surface temperature of a busbar must not exceed the thermal limits of any material coming in contact with it (ie insulator standoffs).
Check the maximum expected electrodynamic forces imparted on the busbars and insulator standoffs, due to the peak short circuit fault current (Idyn). Do not exceed the mechanical limitations of the material.
Check that the busbar system will not resonate under normal operating and fault conditions.
Refer to Busbar Calculations on page 149for calculation details and examples.
Busbar bolting arrangements
Typical busbar bolting details for single overlap copper bar Bar width
Source: Copper for Busbarshttp://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/homepage.shtml
1 Number of bolts based on using high-tensile steel or bronze (CW307G, formerly C104)