ZA200801702B - Isolating and bypass apparatus for medium voltage switching equipment - Google Patents

Description

~2008701 702

BACKGROUND TO THE INVENTION

THIS invention relates to a bypass apparatus for medium voltage switching equipment.

In medium voltage three-phase power distribution systems there is a requirement for apparatus capable of isolating and bypassing certain items of operational equipment, for example voltage regulators and circuit : breakers, so that the item can be taken off-line, i.e. bypassed, for replacement, maintenance or other purposes without interrupting the continuity of electrical supply to consumers.

In the past the components of the isolating and bypass apparatus have been mounted, along with the item of operational equipment, on an existing support structure, typically a pole, where the main MV (medium voltage) line is terminated by strain insulators and bypassed by appropriate bypass switches and a jumper connection arrangement. The apparatus allows the item of equipment to be bypassed and isolated so that it can be removed or worked on in situ.

In practice, the various components of the apparatus are supplied separately to the site where they are to be installed. On site, the individual components are installed on the supporting structure and are connected to one another by suitable electrical cables. The installation procedure is accordingly labour intensive and time consuming and requires high level supervision.

An additional problem is that the number of components involved, as well as the need to maintain proper MV electrical clearances between the three phases, requires that the installation take place on a number of different horizontal cross-arms mounted to the support structure. Because the available space is limited, it is most common for the bypass switches to be mounted on top of the supporting structure, on a cross-arm situated above the main MV conductors.

This means that the bypass switches are difficult’ to access if any maintenance needs to be carried out, for example on their main contacts. If such maintenance is required, it is essential that the power supply be switched off, i.e. there is an interruption of the power supply to consumers.

Also, the difficulty in accessing the bypass switches requires that the switches be connected, typically by a series of metal rods supported by guides on the main support structure, to a lever-type actuator at the bottom of the support structure. For security of normal power supply, this actuator must normally be locked and for safety reasons it must be appropriately earthed. Earthing is traditionally achieved by means of interconnected rods driven into the ground.

Conventionally the disconnecting isolating links are mounted on a separate horizontal cross-arm and are arranged to be operated from ground level by means of a portable fibre-glass rod. These links are pivotal in nature. oo

SUMMARY OF THE INVENTION

According to the invention there is provided an isolating and bypass apparatus for three phase medium voltage switching equipment, the apparatus comprising a unitary assembly mountable on a support structure carrying a first cross-arm supporting strain insulators to which MV conductors are connected, the unitary assembly including:

- a second cross-arm, - mounting means for mounting the second cross-arm to the support structure, - a three phase, pivotal, ganged bypass switch assembly supported by the second cross-arm; - an operating lever for the bypass switch blade assembly, the operating lever being operable in use from ground level by a portable operating rod, : - sets of single phase isolating switches for the three phases supported by the second cross-arm, the sets of isolating switches being openable and closeable from ground level by means of the portable operating rod, the isolating switches when open serving to isolate an item of MV electrical equipment normally connected to the MV conductors.

The support structure is typically in the form of a pole with the mounting means comprising a bracket which can be mounted on the pole and to which the second cross-arm is connected.

In the preferred embodiment, the operating lever for the bypass switch assembly is of a pivoted, pull-to-open, pull-to-close type, and switch blades of the bypass switch assembly are commonly mounted on a shaft and the operating lever is connected to the shaft with respective ends thereof on opposite sides of the shaft, such that the respective ends can selectively be pulled downwardly, by means of the operating rod, in order to pivot the shaft, and hence the switch blades of the bypass switch assembly, between respective open and closed positions.

The preferred apparatus also includes jumpers which are connected to the switch blades and which carry live line clamps at their ends connectable in use in live line mode to the MV conductors.

The respective ends of the operating lever may carry hooks which are selectively engagable by the operating rod in order to pivot the operating lever in opposite directions.

The preferred isolating switches include pivoted isolating links having : attachment points thereon which are engagable by means of a hook on the operating rod, whereafter the operating rod may be pulled downwardly to cause the isolating links to pivot to open positions.

In the preferred arrangement, the isolating links make contact, when in closed positions, with terminals and the apparatus includes conductors which are connected to the terminals and which are connectable to terminals of the item of MV electrical equipment. In one example, where the item of MV equipment is an automatic reclosing circuit breaker (ARC), the conductors of the apparatus are connectable to bushing insulators of the

ARC. :

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 shows a side view of an isolating and bypass apparatus, according to the invention, for three phase medium voltage switching equipment;

Figure 2 shows a front view of the apparatus; and

Figure 3 shows a plan view of the apparatus.

: For clarity of illustration, certain components have been omitted from

Figures 2 and 3.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT ST

In the Figures, the numeral 10 indicates a support structure in the form of a conventional, vertical pole, typically of timber. The pole 10 carries a first cross-arm assembly 12 supporting strain insulators 14 to which respective ends of MV (medium voltage) overhead conductors 15 are connected at points 16.

The numeral 18 indicates a conventional ARC (automatic reclosing circult breaker) which is mounted on the pole 10, some distance below the cross- arm 12, by means of a mounting bracket 20. The conventional bushing insulators, three sets of two, of the ARC are indicated by the numeral 19.

An isolating and bypass apparatus according to the invention is indicated generally by the numeral 22. The apparatus includes a mounting bracket 24 to which a second cross-arm 26 is connected. The mounting bracket 24 is formed with mounting holes 28 by means of which it can be mounted securely to the pole 10, at a position between the first-cross-arm 12 and the

ARC 18, by means of bolts 30 seen in Figure 1.

The cross-arm 26 carries a three phase, pivotal, ganged bypass isolator switch assembly 32 which is typically similar to the known TRILINK™ configuration manufactured and sold by the present applicant. The assembly has three switch blades 34, which are mounted pivotally on a : shaft 36. The lower ends of the blades 34 are connected by, actuating linkages including insulating links 40, to a lower shaft 42 supported rotatably by the cross-arm 26. Connected fast to the shaft 42 is an operating lever 44 with hooks 46 at its ends. The arrangement is such that rotation of the shaft 42 is transmitted, via the actuating linkages, to the blades 34 with the result that the blades are pivoted between open and closed positions indicated in Figure 1 by full and broken lines respectively.

In their closed positions, the upper ends of the blades make electrical contact with terminals 48 carried by post insulators 50 supported by the cross-arm 26.

The apparatus 22 also includes three sets or pairs of isolating links 51, two for each phase. Conductors 52 extend from the bushing insulators 19 of the

ARC 18 to terminals 54, situated below the terminals 48 and carried by post insulators 55 supported by the cross-arm 26. Lower ends of the isolating links 51 are connected pivotally relative to the terminals 54. The links have hook attachment points in the form of eyes 56 towards their upper ends.

When closed, the upper ends of the isolating links 51 make electrical contact with the terminals 48. When open, the isolating links 51 hang downwardly. The closed and open positions of the isolating links are shown in Figure 1 in full and broken lines respectively.

Jumpers 58 are connected to the lower ends of the switch blades 34 through the terminals 48 and carry live line clamps 60 at their free ends.

The assembly 22 described above is assembled under factory conditions and is supplied to site as a unit for use with the ARC already on the pole.

Without interrupting the existing current supply, the assembly is raised to the relevant elevation on the pole and is fixed in position by the bolts 30.

The ARC conductors 52 are connected as necessary and the line clamps are connected to the overhead MV conductors 15 using the known technique of “live line working”. : In normal operation, the bypass switch blades 34 are in the open position illustrated in full lines in Figure 1 and the isolating links 51 are in the closed position illustrated in full lines. In each phase, current flows from the overhead MV cable through the associated jumper 58, through the associated isolating link 51, through the associated terminal 54, through the

ARC conductor 52, through the ARC and back to the overhead MV conductor 15 on the other side of the pole 10 along a corresponding path.

If the ARC is to be taken off line for any reason, eg for maintenance or replacement, the bypass switches are closed. This is achieved by means of an elongate operating rod, typically of an insulating material such as fibre glass and typically of telescopic construction, manipulated from ground level. The rod or “hook-stick” has a hook at its upper end which is engaged with the hook 46 seen in Figure 1 at the left hand (as illustrated) end of the lever 44. Pulling the operating rod down pivots the lever in the direction indicated by the arrow 70. The consequential rotation of the shaft 42 is transmitted via the insulating links 40 of the actuating linkages to cause pivotal movement of the switch blades 34, about the axis of the shaft 36, in the direction of the arrow 72. The switch blades are accordingly pivoted from their full line, open positions to their broken line, closed positions as seen in Figure 1. For each phase this establishes a bypass current path from the MV conductor 15 on one side of the pole, through the associated jumper 58 and through the associated switch blade 34 to the corresponding components serving the MV conductor 1 5 on the other side of the pole.

Current flow through the MV conductors 15 is accordingly uninterrupted.

Thereafter the isolating links 51 are opened in order to isolate the ARC.

This is once again achieved by means of the same or a different glass-fibre operating rod or “hook-stick”, typically of telescopic construction, which is manipulated from ground level. A hook at the upper end of the rod is engaged with the eye 56 of each link and the rod is pulled down to swing the isolating link from its closed to its open position. The ARC is accordingly safely isolated while current flow is maintained in the overhead conductors 15.

After maintenance or replacement of the ARC, the procedure described above is carried out in reverse in order to place the ARC back on line. It will be understood that in the reverse procedure the hook 46 at the right hand (as illustrated) end of the operating lever 44 is pulled down to return the operating lever to the position seen in Figure 1, and that the operating lever is accordingly of a pull-to-open, pull-to-close type.

Specific mention has been made of isolating and bypassing of an ARC. It will however be understood that the principles of the invention are equally applicable to other items of MV equipment which may need to be taken off line periodically for maintenance or replacement.

An important advantage of the invention as exemplified above is the fact that the isolating and bypass apparatus is supplied as a unitary item of equipment which can be installed rapidly and with little difficulty or supervision on a pole or other supporting structure without interrupting current supply.

As a result of the compact configuration of the isolating and bypass components, the apparatus requires only a single cross-arm, in the above example the cross-arm 26, which can conveniently be located beneath the first or main cross-arm, in the above example the cross-arm 12, of the supporting structure.

Claims (10)

1. ) | lll CLAIMS oh i An isolating and bypass apparatus for three phase medium voltage switching equipment, the apparatus comprising a unitary assembly mountable on a support structure carrying a first cross-arm supporting strain insulators to which MV conductors are connected, the unitary assembly including: - a second cross-arm, ‘ : - mounting means for mounting the second cross-arm to the support structure, - a three phase, pivotal, ganged bypass switch assembly supported by the second cross-arm; - an operating lever for the bypass switch blade assembly, the operating lever being operable in use from ground level by a portable operating rod, - sets of single phase isolating switches for the three phases supported by the second cross-arm, the sets of isolating switches being openable and closeable from ground level by means of the portable operating rod, the isolating switches when open serving to isolate an item of MV electrical equipment normally connected to the MV conductors.
2. 2. An isolating and bypass apparatus according to claim 1 wherein the support structure is in the form of a pole and the mounting means Co comprises a bracket which can be mounted on the pole and to which the second cross-arm is connected.
3. 3. : An isolating and bypass apparatus according to either one of the preceding claims wherein the operating lever for the bypass switch assembly is of a pivoted, pull-to-open, pull-to-close type.
4. 4. An isolating and bypass apparatus according to claim 3 wherein switch blades of the bypass switch assembly are commonly mounted on a shaft and the operating lever is connected to the shaft with respective ends co thereof on opposite sides of the shaft, such that the respective ends can selectively be pulled downwardly, by means of the operating rod, in order to pivot the shaft, and hence the switch blades of the bypass switch assembly, between respective open and closed positions.
5. 5. An isolating and bypass apparatus according to claim 4 and comprising jumpers which are connected to the switch blades and which carry live line clamps at their ends connectable in use in live line mode to the MV conductors.
6. 6. An isolating and bypass apparatus according to claim 4 or claim 5 wherein the respective ends of the operating lever carry hooks which are selectively engagable by the operating rod in order to pivot the operating lever in opposite directions.
7. An isolating and bypass apparatus according to any one of the preceding claims wherein the isolating switches include pivoted isolating links having attachment points thereon which are engagable by means of a hook on the operating rod, whereafter the operating rod may be pulled downwardly to cause the isolating links to pivot to open positions.
8. 8. An isolating and bypass apparatus according to claim 7 wherein the isolating links make contact, when in closed positions, with terminals and the apparatus includes conductors which are connected to the terminals and which are connectable to terminals of the item of MV electrical equipment.
9. 9. An isolating and bypass apparatus according to claim 8 wherein the conductors of the apparatus are connectable to bushing insulators of an item of MV electrical equipment in the form of an ARC.
10. 10. : An isolating and bypass apparatus substantially as herein described with reference to the accompanying drawings. DATED THIS 21ST OF FEBRUARY 2008 : SPOOR a APPLICANTS PATENT ATTORNEYS