INSULATION

The TRISWITCH incorporates Cycloaliphatic Epoxy insulators, which have extended inserts (S.A. Pat. 87/4484) to give improved voltage stress control over the end fittings, resulting in extraordinary low RF noise. The low mass of the operator insulator is a key factor in the minimal operating energy required and results in the high closing speed, which is attainable when using a spring actuator as described later. The vandal resistance of this class of insulator is now well known.

RATINGS

The standard off-load unit for rural lines is 200Amps with a tested short time current rating of 4kA for 3 seconds, equal to 6kA for 1 second. Alternative ratings of 10 and 16kA are also available for higher fault ratings, also including up to 630Amps. Voltage ratings are based on 24kV highest system voltage, with a BIL of 150 kV.

LOW LEVEL MECHANISM

When a padlocking facility is an essential requirement, a low level operating mechanism can be provided as an optional extra. This mechanism incorporates a special feature, which enables it to be used with the TRILINK spring-close mechanism. Refer to drawing no. LG0529.

LOAD BREAKING CAPABILITY

The TRISWITCH obtains its load-breaking capacity by the addition of a well-proven Arc Control Device as used in the U.S.A. for many years.

This moulded arc control device, known as the ARCTRAP is manufactured from specially stabilised material, which encloses the moving arc contact. As the contact withdraws from the device after the main contacts have separated, the resulting snap-action provides de-ionisation of the arc within the enclosure. The final contact movement provides a safe isolating distance in air, with no leakage path between the contacts giving the conventional safety distance for maintenance without the need for an extra isolator.

The various stages of the contact movement are shown, where in the closed position the current flows through the main contacts, bypassing the arcing circuit. As the device starts to open, the arc circuit makes contact to bypass the main contacts, which then open in an off-load mode.

LOAD BREAKING CAPABILITY (cont)

Continued movement of the contact systems reaches a point where the current is finally broken on the arcing contacts. This takes place when the spring action of the `C' shaped lever withdraws at high speed from the ARCTRAP, which cools and extinguishes the arc.

This new combination transforms what was previously classified as a switching isolator into a fully rated switch, suitable for main-line switching and for application at key points such as branch points beyond the recloser/sectionaliser, where local switching is essential for economical network operation - but where tank-type devices cannot be afforded.

The load-breaking capacity of the ARCTRAP is 630Amps on 11kV circuits and 200Amps on 24kV circuits. The spring operated closing mechanism is strongly recommended for the TRISWITCH because it achieves a high closing speed completely independent of the effort of the operator. In this form it can be used for closing-in on loaded circuits with an absolute minimum of contact burning.

The TRISWITCH can now be fitted with a 24Vdc motorised actuator, current transformers and auto-sectionaliser logic/fault indicator and is fully compatible with SCADA control systems. See also TRISEC.

The TRISWITCH can also be fitted with fault-make contacts for 7.5kAp when used with the spring close mechanism. Tungsten-tipped contacts are available for higher making capacities.

The load-breaking capacity of the ARCTRAP is 630Amps on 11kV circuits and 200Amps on 24kV circuits. The spring operated closing mechanism is strongly recommended for the TRISWITCH because it achieves a high closing speed completely independent of the effort of the operator. In this form it can be used for closing-in on loaded circuits with an absolute minimum of contact burning.

The TRISWITCH can now be fitted with a 24Vdc motorised actuator, current transformers and auto-sectionaliser logic/fault indicator and is fully compatible with SCADA control systems. See also TRISEC.

The TRISWITCH can also be fitted with fault-make contacts for 7.5kAp when used with the spring close mechanism. Tungsten-tipped contacts are available for higher making capacities.

INTRODUCTION

The TRISWITCH is a gang-operated load-break switch and represents a complete review of existing problems and the availability of new materials by a design team with extensive worldwide experience in medium voltage switchgear design. The design has concentrated on the cost effectiveness of devices for rural electrification, especially for those in the Third World environment. High standards of performance and operator safety have been combined with low installed cost and vandal resistance.

The triangular formation of the insulators and the contact blade results in a very strong arrangement with all the operating forces and reactions being contained within the assembly on its own steel cross-arm. As a result the interconnecting phase linkage is in no way dependent upon the pole structure for its continued freedom of movement. The assembly merely requires two bolts to attach it for single pole mounting. Other arrangements are available for 'H' pole structures. The standard arrangement is designed for operating by a linesman's portable insulated operating rod, (link-stick) with a downward movement for both opening and closing. This PULL-TO-OPEN, PULL-TO-CLOSE action eliminates all problems associated with ground level actuators and the attendant costs and risks of earth mats and their connections. A portable locking device with insulated insert can be applied to the operating lever to lock in either position. See drawing no. LG0945.