IES65983B2 - Manufacture of switchgear - Google Patents

Abstract

An electrical switchboard is produced by assembling a frame using vertical and horizontal frame members 30, 31 connected to a base plate (32, Fig 3). Compartment side plates 34 and base plates 37 are mounted on the frame members to define compartments within which mounting plates of pre-assembled modules are mounted. Electrical components 43 on the modules are connected to main bus bars 20 by feeder bus bars 22 which extend through apertures 36 in the side plates 34. These apertures are covered by arc extinction barrier plates 45 of a plastics material which is highly insulative and has a high mechanical strength. The feeder bus bars 22 extend in a tight fit through apertures within the barrier plates. At intervals along the main bus bars, arc extinction barriers (51, Fig 7) are mounted each comprising two interconnecting halves (52) forming a tight fit around the bus bars 20. The barriers (51) are mounted on plates (57) connected to the frame members 30, 31. After mounting doors and enclosure panels around the main bus bars, the switchboard is tested at a voltage of 2 to 3 kV for more than 40 seconds.

Description

Manufacture of Switchgear The invention relates to manufacture of switchgear, and more particularly switchboards.

Switchboards are manufactured by mechanical and electrical mounting and connection of components so that they perform a specified electrical function. The electrical components used, such as fuses, circuit breakers, and switches are generally of a high quality and are unlikely to fail. It has, however, been found that the vast majority of faults are either caused by, or are not sufficiently contained by, incorrect mechanical design and production.

Heretofore, many improvements have been made, both to mechanical safety features and production methodology. Regarding the latter, PCT Patent Specification Nos.

WO 94/14307, WO 88/07810, and WO 88/05253 (Logstrup) describe improvements in modularity of construction. However, there is still a need for an improved construction method to provide good integrity of mechanical connections and also high efficiency.

Regarding safety features, the improvements which have been made relate to such things as door locks (DD 277,351, VEB), and arc-quenching metal grids (DE 3,436,108, ABB). However, it has been found that faults which arise can spread at an unacceptably high level through a switchboard, causing extensive damage and possibly danger to personnel. Such faults may arise due to foreign bodies entering the switchboard, rodent infestation, ingress of water etc.

There is therefore a need for a method of producing a 30 switchboard which provides improved integrity of mechanical interconnections and efficiency. There is also - 2 a need for a switchboard providing improved arc-quenching in the event of a fault.

According to the invention, there is provided a method of producing an electrical switchboard, comprising the steps of :assembling a frame comprising vertical and horizontal frame members and a rigid base plate; mounting output unit side and base plates on frame members to provide output unit compartments, a side plate for each compartment having an aperture; mounting vertical and horizontal main bus bars on the frame alongside rows and columns of compartments; constructing an output unit by :selecting a pre-assembled output module according to an electrical specification for the output unit, said module comprising electrical components mounted on a mounting plate; mounting the module in a compartment by connecting I the mounting plate in the compartment; and connecting components of the module with vertical bus bars by engaging feeder bus bars through an arc extinction barrier comprising a plate of material having a high mechanical strength and fire resistance, the barrier extending across the aperture in the compartment side wall; repeating said construction steps for each required output unit; mounting bus bar system arc extinction barriers at intervals along the main bus bars, said barriers each comprising an interleaving pair of barrier portions forming a tight fit around individual bus bars, each barrier half being of a material having a high mechanical strength and fire resistance; completing cabling and connection of auxiliary electrical components for the switchboard; completing mechanical fabrication of the substation, including mounting of doors and final enclosure panels around the main bus bars; and testing the switchboard, wherein testing includes a high voltage insulation impulse test at a voltage in the range 2kV to 3kV for a time duration in excess of 40 seconds.

In one embodiment, the arc extinction barriers are of a PVC plastics material.

Preferably, the arc extinction barriers are of a material having a volume resistivity of at least 10130hm.cm and a surface resistivity of at least 1014Ohm, and a dielectric strength characteristic of in excess of 30 kV/mm.

In another embodiment, the compartment side and base plates extend the full depth of the frame, and have support flanges at a pre-set unit depth for reception of mounting plates of output modules, whereby mounting of an output module forms an empty chamber behind an output unit in the switchboard.

Ideally, each output unit arc extinction barrier is produced by punching apertures corresponding to the crosssection of the feeder bus bars, and force-fitting the feeder bus bars through said apertures.

In a further embodiment, the method comprises the further sub-step for constructing an output module of mounting a shroud of insulating material around the feeder bus bars within the compartment.

According to another aspect, the invention provides an electrical switchboard comprising :a frame comprising vertical and horizontal frame members mounted on a rigid base plate; a plurality of output units mounted in at least one series alongside which main bus bars are mounted, each output unit comprising a compartment formed by a pair of side plates and a base plate between which a mounting plate is connected and which supports electrical components of the output unit, said components being connected to main bus bars by feeder bus bars which extend through an aperture in the side plate, said aperture being covered by an arc extinction barrier of a plastics material having high mechanical and high insulative characteristics, the feeder bus bars passing through apertures within the barrier in a force fit; and a plurality of arc extinction barriers mounted at intervals along the main bus bars, each of said barriers comprising a pair of interleaving halves, each comprising a plate of plastics material having highly insulative and mechanical strength properties and comprising interleaving separators to surround all of the main bus bars in a tight fit, said barriers being mounted on plates connected to the vertical and horizontal frame members externally of the output unit compartments .

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which :Fig. 1 is a flow chart illustrating a production method of the invention in overview; Fig. 2 is a schematic representation of a switchboard; Fig. 3 is a perspective view of a frame of a switchboard at an early stage of production; Fig. 4 is a set of perspective views of various components of an output unit of the switchboard; Figs. 5, 6(a) and 6(b) are perspective side and plan views of an output unit of the switchboard; and Fig. 7 shows an arc extinction barrier for main bus bars and the manner in which it is connected.

Referring to the drawings, there is shown in Fig. 1 a method 1 for the production of an electrical switchboard. A produced switchboard is shown in diagrammatic form in Fig. 2 and is indicated by the numeral 15. The method steps are indicated by the numerals 2 to 12. Before describing the method in detail, the switchboard 15 is now briefly described. The switchboard 15 comprises a frame 16 which supports a number of output units 17. The output units 17 include switching and routing components for output electrical devices such as exhaust fans, cold water boosters, sets of power sockets, cooking equipment etc.. Power is provided to the switchboard 15 by a primary connector 18 incorporating an isolator. This is connected to a main bus bar system 19. comprising vertical bus bars 20 and horizontal bus bars 21. The vertical bus bars 20 are connected by feeder bus bars 22 to the various output units 17.

Referring now to Fig. 1 and to Figs. 3 to 7, the manner in which the switchboard 15 is produced, and its construction in more detail are now described. In step 2 of the method, an initial frame is produced. Such a frame is illustrated in Fig. 3 and indicated by the numeral 29. The frame 29 comprises a number of vertical frame members 30 inter-connected by horizontal frame members 31. These are mounted on a base comprising a rigid steel base plate 32 having a base frame of angle-section members. In the end product, the base provides for stability of the switchboard and a large degree of protection from such things as foreign body entry or water contact with the output units and conductors generally. The vertical and horizontal frame members 30 and 31 have pre-prepared threaded holes at regular intervals throughout for ease of assembly by bolting in a modular manner.

Side plates 34 and base plates 37 are mounted on the frame members 30 and 31 to form compartments for the output units 17 in step 3. The side plates 34 have flanges 35 at a pre-set distance from the front of the frame 29 and the side walls 34 have elongate vertically-extending apertures 36 adjacent the front end. This construction provides a set of universal compartments which may be used in a versatile manner as described below. As is also clear from Fig. 3, there is a good deal of space between the compartments and the frame members at the extremities, both underneath the compartments and alongside them. These spaces are for enclosing the bus bar system 19 and other conductors such as cables.

In step 4 the vertical and horizontal main bus bars 20 and 21 are mounted in the spaces around the compartments. In this case, the bus bars are 200 mm2 or possibly larger in cross-section and are of hard-drawn copper material.

The vertical and horizontal bus bars are interconnected at junctions using copper T-joint connectors.

In step 5, a number of pre-assembled output modules are chosen to complete the output units which are required by the electrical specification. An output module 40 is illustrated in Fig. 4 and this comprises a mounting plate 41 having rearwardly-extending flanges 42. Various electrical components 43 indicated diagrammatically in Fig. 4 are mounted on the mounting plate 41 whereby their connectors are at a pre-set distance from the side edge of the mounting plate 41. It has been found that preassembly of the electrical components in this manner provides for very simple output unit construction. Further, quality of the electrical interconnections is improved because they are made separately from the mechanical fabrication operations and because they are pre-tested for mechanical integrity. Use of such modules also reduces production lead time.

For each of the output modules 40, a set of feeder bus bars 22 of hard drawn copper is produced. The feeder bus bars 22 are produced by use of a CNC bending machine which carries out programmable and repeatable bending. Two bus bars 22 are shown in Fig. 4. ' For an output unit rating of less than 100A, the crosssectional area is 80 ram2, and 120 mm2 when the rating is greater than 100A.

The edges of the bus bars 22 are squared to ensure good electrical contact with conductors to which they are connected.

An important part used in production of the output units is a feeder bus bar arc extinction barrier 45. This comprises a plate 46 of a FVC-based plastics composition marketed under the Trade Name MAKROLON™. This material has a Class A fire-resistance rating and provides both very highly insulative properties and also very high mechanical strength. Indeed, regarding mechanical strength, the material has a no failure characteristic for Charpy Impact Strength and a Notched Impact Strength of 10 kJ/m2. The material has a tensile strength at 23°C of 60 MPa and an elongation at break characteristic of greater than 80%. Regarding electrical properties, the plate 46 has a volume resistivity of greater than 1015 Ohm/cm and a surface resistivity of greater than 1014 Ohm.

It has a dielectric strength of 35 kV/mm. It will therefore be appreciated that the barrier 45 is virtually shatter-proof with effectively unlimited mechanical strength and is also very highly insulative. The plate 46 also has a set of punched apertures 47 located for reception of the feeder bus bars 22 in a very tight fit h whereby no gap is present around the bus bars 22. The barrier 45 also has bolt holes 48 for connection to a * compartment side plate 34.

Another compartment for output units is a protective shroud 50, also of Makrolon™ material. This is formed in a C shape with an extension piece on one side by bending on a former which is line-heated locally at the apex line which forms the shroud corners.

The various parts of the output units shown in Fig. 4 are assembled together in step 6 as shown in Figs. 5, 6(a) and 6(b) to provide an output unit. The flanges 35 in the compartments provide a pre-set position for the mounting plate 41 of the output modules 40. Thus, all output modules are at the same distance back from the front of the frame 29 and are very easily mounted. Where an output module 40 is not to be used, for example, where a large component which requires the full depth of the frame is to be inserted, the side walls 34 define the necessary enclosure along their full depth.

As shown in Figs. 5(a), 6(a), and 6(b), the barrier 45 is mounted by bolting flush on the side wall 34 in step 7 to cover the aperture 36 and to allow passage of the feeder bus bars 22 into the output unit for connection with the components 43. The barrier 45 therefore provides a very effective arc quenching barrier to both prevent main bus bar system faults entering the output unit, and also to contain faults within the output unit between the sidewalls 34. It will also be appreciated that this arrangement may be very easily assembled by relatively low-skilled personnel.

In step 8, the protective shroud 50 is clipped in place around the feeder bus bars 22 which extend into the output unit as shown by interrupted lines on the output module 40 in Fig. 4. For clarity, the shroud 50 is not shown in Figs. 5, 6(a) and 6(b).

A similar arrangement to that shown in Figs. 5, 6(a) and 6(b) applies to each output unit along the height of the vertical bus bars 20.

In step 9, barriers 51 are mounted at intervals along the main bus bar system 19 to provide additional protection. Each barrier 51, as shown in Fig. 7, comprises a pair of halves 52 which are plates of Makrolon™ material having interleaving separators 53, each terminating in a step configuration 54 for comprehensive interconnection. Each of the halves 52 has a set of two bolt holes 56 for connection to a plate 57 which is mounted through the vertical and horizontal frame members on both sides of the compartments. Separators 53 are machined to a very fine tolerance to provide a tight fit around the bus bars such as the horizontal bus bars 21 shown in Fig. 7. It has been found that for 10 or 12 mm main bus bars, the separators 53 should have a separation of 30 mm between phases. This provides for very comprehensive arcquenching within the main bus bar system 19. Again, it will be appreciated that connection of the barriers 51 is very simple, while at the same time, they provide for very comprehensive safety in operation of the switchboard.

In step 10, the various cables and auxiliary electrical components are connected both inside and outside the compartments to complete the electrical requirements and in step 11 the mechanical fabrication is completed. The latter involves enclosing the main bus bar system 19, and mounting doors and various switch handles.

Finally, in step 12 the switchboard is tested. A very important aspect of the testing is that there is a high voltage insulation impulse test whereby a voltage in the range of 2 to 3 kV is applied for in excess of 40 seconds. In one embodiment, the applied voltage is 2.5 kV and the duration is 60 seconds. These voltages are applied between phases and neutral and between the phases and earth. There is also a mains test at 380 and 220 Volts, a functional test using control sequences and various tests to check the voltage levels of components. In addition, there are mechanical operational tests of circuit breakers, switchfuses, isolators, MCB's, contactors, overloads, fuses and various other components such as ammeters, volt meters, ELCB's. It has been found that the electrical tests and in particular the impulse tests very comprehensively detect any faults within the system.

The invention is not limited to the embodiments hereinbefore described but may be varied in construction and detail.

Claims (7)

1. A method of producing an electrical switchboard, comprising the steps of :assembling a frame comprising vertical and horizontal frame members and a rigid base plate; mounting output unit side and base plates on frame members to provide output unit compartments, a side plate for each compartment having an aperture; mounting vertical and horizontal main bus bars on the frame alongside rows and columns of compartments; constructing an output unit by :selecting a pre-assembled output module according to an electrical specification for the output unit, said module comprising electrical components mounted on a mounting plate; mounting the module in a compartment by connecting the mounting plate in the compartment; and connecting components of the module with vertical bus bars by engaging feeder bus bars through an arc extinction barrier comprising a plate of material having a high mechanical strength and fire resistance, the barrier extending across the aperture in the compartment side wall; repeating said construction steps for each required output unit; mounting bus bar system arc extinction barriers at intervals along the main bus bars, said barriers each comprising an interleaving pair of barrier portions forming a tight fit around individual bus bars, each barrier half being of a material having a high mechanical strength and fire resistance; completing cabling and connection of auxiliary electrical components for the switchboard; completing mechanical fabrication of the substation, including mounting of doors and final enclosure panels around the main bus bars; and testing the switchboard, wherein testing includes a high voltage insulation impulse test at a voltage in the range 2kV to 3kV for a time duration in excess of 40 seconds.

2. A method as claimed in claim 1, wherein the arc extinction barriers are of a PVC plastics material.

3. An electrical switchboard comprising :a frame comprising vertical and horizontal frame members mounted on a rigid base plate; I a plurality of output units mounted in at least one series alongside which main bus bars are mounted, each output unit comprising a compartment formed by a pair of side plates and a base plate between which a mounting plate is connected and which supports electrical components of the output unit, said components being connected to main bus bars by feeder bus bars which extend through an aperture in the side plate, said aperture being covered by an arc extinction barrier of a plastics material having high mechanical and high insulative characteristics, the feeder bus bars passing through apertures within the barrier in a force fit; and

4. 5 a plurality of arc extinction barriers mounted at intervals along the main bus bars, each of said barriers comprising a pair of interleaving halves, each comprising a plate of plastics material having highly Insulative and mechanical strength properties and

5. 10 comprising interleaving separators to surround all of the main bus bars in a tight fit, said barriers being mounted on plates connected to the vertical and horizontal frame members externally of the output unit compartments.

6. 15 4. A method substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings. 5. An electrical switchboard substantially as hereinbefore described with reference to, and as illustrated in the

7. 20 accompanying drawings.