INTRODUCTION

The new HUKLINK range of in-line disconnectors is a complete review of existing problems introducing new materials by a team with extensive and worldwide experience in medium-voltage switchgear design. The design concentrates 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.

This unique design represents the ultimate in low cost concepts for the isolation of spur-line connections, particularly those which are lightly loaded. These circuits may not justify the cost of traditional isolating devices and associated supports, yet when solidly connected to the system  they may be of considerable nuisance value in lightning conditions. The HUKLINK combines the function of the spur-line strain insulator with a disconnector operated by a portable insulated operating rod, and as such, replaces the usual strain insulator and the low-level cross-arm which would be required for other forms of disconnector. Furthermore, the jumper connections and fittings are simplified with the HUKLINK. The strain insulator is mounted horizontally with fittings for a clevis thimble at one end, the other secured with a bracket to the pole. This also secures the pilot insulator, mounted at right angles to the line. 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.

INSULATION

The HUKLINK incorporates Cycloaliphatic Epoxy insulators which have extended inserts (S.A. Pat. 87/448) to give improved voltage stress control over the end fittings, resulting in extraordinary low RF noise and improved impulse level. Silicone composite insulators are also available.

SAFETY ASPECTS

The arrangement has maintained the concept of normal two insulator devices, wherein the support point is earthy in respect to the line conductors. Any possible surface leakage currents, which may occur due to atmospheric contaminants, will be conducted to earth. This will add to the safe operation of the system over and above the normal safety precautions taken when engineers are working on the line. Stainless steel fasteners are available on request.

RATINGS

The standard off-load unit for rural lines is 200Amps with a short time current rating of 4kA for 3 seconds, equivalent to 6,9kA for 1 second. The contact arrangement comprises the moving blade which is made of copper, and the fixed spring contact which is made from laminations of phosphor bronze. Both contact surfaces are electro-plated with 25 microns of hard silver. An alternative contact arrangement rated at 400Amps is available for higher load / short circuit current ratings. Voltage ratings are based on 24kV highest system voltage, with a BIL of 150kV, and 173kV across the isolating distances. A 36kV design is also available.

OFF LOAD/LOAD BREAK

The HUKLINK in its most simple form (Type 2) is an OFF-LOAD disconnector, but it can also incorporate the stainless steel spring wire arcing contacts which have been so successfully used on the TRILINK. This is the HUKLINK type 2LB, suitable for loads up to 250/350kVA. For higher load break capacities a HUKSWITCH can be employed.

OPERATION

An innovative feature of the HUKLINK, which is designed for operation by a linesman's portable operating rod (hook-stick), is that it is a PULL-TO-CLOSE link, as well as PULL-TO-OPEN. This avoids the use of the hook-stick in the compressive mode, where it might bend, a feature that makes it extremely user friendly and popular with operating engineers.

AUTO-RECLOSER BYPASS

A separate application drawing No. LG0320, shows how the HUKLINK can be used with advantage in recloser / sectionaliser installations, incorporating all the isolators and by-pass unit in a pole top installation.