Evolution of the S1 range of insulation testers

Stephen Drennan, Managing Director,
Dover manufacturing site

Back in the Pleistocene era of electrical equipment development – in 1889, to be precise – the first in the genus ‘insulation tester’ was developed by Sidney Evershed, who subsequently trademarked the Megger brand in London in 1903. Different test environments led, of course, to the evolution of different insulation testers. These ranged from the Wee Megger, which thrived in the nooks and crannies of LV equipment servicing, to the Series 1 tester at the top of the food chain, which was destined to have a long symbiotic relationship with utility engineers working in challenging high voltage environments.

Right from those early days, the Series 1 established itself as the long-term partner of the utility engineer due to its reliability and unrivalled measuring range. For the HV equipment in the electricity network, the higher voltages and the higher MΩ ranges provide by the Series 1 were crucial benefits. As this was an analogue technology, the high measuring range was referred to as ‘high sensitivity’, which might confuse today’s engineers who would perhaps associate this phrase with a delicate disposition! In reality the Series 1, in its top-quality wooden case, was known for its durability and long service life.

In fact, in 1996 a Megger product manager visited a Bonneville Power Administration (BPA) site in Portland, Oregon to discuss BPA’s testing and measuring requirements. He discovered that one of the Megger testers they were using on the site was an unfamiliar model. In answer to his question, “When did you buy this?” BPA’s purchasing manager consulted an asset book and answered “In 1951!” The Series 1 tester was actually older than the Megger product manager and it was still fully functional.
As well as extended measuring range, another key aspect of  the Series 1 products was its heavy-duty design with the capability to supply the current and power necessary for testing longer utility cables. The Series 1 had a beefy generator and this could be driven by either by a hand-crank or, for those who didn’t fancy employing someone to turn the handle continuously for 10 minutes to perform a polarisation index test, by a motor.

During the 1990s, the analogue tester retreated into a few niche habitats, such as mines and military applications, because digital instruments gave users extra functions and higher performance at lower cost. The days of using an analogue tester that struggled to measure up to 1 TΩ were past; digital testers delivered 5 TΩ and above.

The Series 1 utility tester, however, evolved to match the engineer’s changing requirements. The analogue Series 1 instruments were superseded by the new digital S1 series. These still provided the higher ‘heavy duty’ current needed to deal with utilities’ capacitive cables, along with the high measuring range, although the latter was now much less of a stand-out feature.
The utility environment was also changing. With higher transmission voltages and more compact substation design, the common-or-garden insulation tester was increasingly suffering from the effects of electrical noise in the test environment. So the S1 series evolved an unparalleled ability to deal with high electrical noise environments.

At much the same time, the move away from in-house technical departments in many utilities around the world gave rise to an increasing role for service companies contracted to maintain networks for the owner of the ‘wires’. This led to further demands on the S1 testers.

A utility company usually knows exactly where its assets are going to be next year – the same place as this year!  In service companies, however, ‘have tester, will travel’ became an increasing part of the business model as contracts were sought far and wide. This led to an increase in demand for instruments that work reliably in all environments. Deserts and mountains, monsoon rains and snow – the service companies said, “We need the product to work where we work!”  So the S1 range evolved again.
With an increased altitude specification, high-IP weatherproof ratings, a fully specified guard terminal, robust construction and impeccable performance, today’s S1 series instruments continue to hold their key position in the HV ecosystem.