When it comes to medium voltage switchgear, installing equipment that will stand the test of time, as well as delivering safety and availability of power supply is crucial.

Comparatively speaking NHP delivers a medium voltage switchgear range that guarantees the highest projected life span to market, through specific designs and rigorous testing.

Aging factors affecting durability

Service life span of medium voltage switchgear is largely limited by aging factors which inevitably decrease the initial specified life span.

1. Loss of tightness of the vessel containing the insulating and arc quenching gas (where used), mainly influenced by ambient temperature, insulating gas temperature and consequent pressure. Gas leakage leads to the following failure modes:

a. Failure to break load current by gas-filled load break switches

b. Insulation failure in gas insulated switchgear due to leakage from the gas-filled tank containing busbars and all switching
devices (RMU)

2. Degradation of the insulating parts under the influence of moisture, heat and dielectric stress, leading to eventual insulation failure.

3. Corrosion of metal parts under the influence of humidity and heat. The most critical failure mode is corrosion of driving mechanisms leading to increased friction and eventual failure to operate switching devices.

NHP’s DF2 is an air-insulated switchgear with SF6-filled load break switch, therefore only factors 1a, 2 and 3 apply from the list above.

Design and testing to determine endurance

NHP’s European switchgear supplier SGC has designed and tested a DF2 series switchgear for a service life span of 50 years, by using a special product design, materials and technologies to mitigate each of the above mentioned aging factors.

A 50-year life span has been confirmed by applying far more stringent test regimes than required by IEC 62271.200 and applied to a typical switchgear rated for 30 years’ service life.

The DF2 has passed three non-mandatory environmental type tests to a highest criteria set in the relevant IEC standard as summarised in Figure 1, and thus has proved its excellent longevity while subjected to extreme levels of major aging factors.

This has allowed NHP to claim 50 years life span under normal service conditions.

DF2 modular switchgear design allows for creating rational, economical and custom-made combinations of medium voltage cubicles at 17.5kV. A truly versatile solution, it is used in primary distribution substations, secondary distribution ring networks, motor control, wind generation and more.

Robust driving mechanisms and interlocks, combined with clear synoptics ensure safety of manual operation. A patented internal arc quenching system ‘The Arc Killer’ enhances personnel safety and protects switchgear from internal arc faults.

NHP service and support

Not only does NHP offer medium voltage switchgear that is robust with the highest level of safety, but it ensures significantly reduced downtime, reduced maintenance costs and low installation costs.

As well as equipment that is purposely built to last, NHP promises ongoing service and support throughout the entire project lifecycle from tendering through to switchgear commissioning and required life span services.

This partner content is brought to you by NHP Electrical Engineering Products. For more information, visit

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