Digital microhmmeter used for automated resistance testing

Overhead Line Fittings (UK) works with the National Grid, power distribution network operators and their contractors to provide bespoke insulators, fittings and conductor accessories used in the installation and maintenance of overhead power cables. As part of the services provided to customers, the company operates an in-house test facility at its headquarters in Atherstone, Warwickshire.

Within this facility the company has recently been testing bimetallic joints to assess how an oxide-inhibiting compound can reduce the rate of corrosion between electrical connections. This is a major problem that costs utilities companies millions of pounds a year in maintenance and repair costs, and it can also cause delays to essential services such as railways when power distribution lines fail.

OLF's testing involved a heat cycle process and a Cropico D05000 digital microhmmeter was used to measure resistance. A current of 700A was passed through a bimetallic joint in a cycle of one hour energised and 40 minutes de-energised. Humidity levels averaged 60 per cent during the testing, which was conducted on both compound-treated and non-treated joints continuously for 96 hours.

Automated testing

Resistance readings were taken automatically at the rate of two per second; these showed that resistance rose as the galvanic corrosion started to attack the joint. Moreover, the testing confirmed that an oxide-inhibiting compound can have a positive impact on the electrical performance of the type of bimetallic joints used on transmission and distribution power lines.

Carl Ford, general manager at OLF, said the high-performance capabilities of the D05000 had led to the decision to order another unit for the company's operation in China for a similar test and measurement programme. He comments: "The DO5000 is a very good instrument, offering superb performance, reliability and accuracy. It has fulfilled all expectations and has impressed within the demands of the testing environment."

The Cropico DO5000 microhmmeter enables highly accurate low-resistance measurements to be undertaken to ensure that products meet relevant technical performance standards and specifications. Programmable current levels and the selection of different test speed settings give the DO5000 tester the flexibility to measure accurately the resistance values of different cable products. These include single-end and plain soft wires through to bunched, stranded and large-diameter rope-type conductors. Accurate and reliable in-line cable resistance measurements taken in this way enable cable manufacturers to maintain optimum operating efficiencies in terms of copper raw material use.

Cropico's DO5000 forms part of a comprehensive range of precision measurement instruments available from the company, which is part of the Seaward Group. Follow the link for more information about the Cropico DO5000 digital microhmmeter.