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SRF N-Series

Surge Reduction Filters – nVent ERICO Critec

Surge Reduction Filters are renowned for their application in critical sites, with common application to telecommunications sites, data centres, process control plants, defence installations, and airports.

The SRF (Surge Reduction Filters) product family combines high-energy surge diversion with surge filtering, making them ideal for primary service protection applications. Their efficient low pass filtering stage dramatically reduces the rate-of-voltage rise and the let-through voltage thereby substantially reducing the risk of physical equipment damage. They incorporate TD technology making them robust against AC power system temporary overvoltages, and their standards compliance to IEC 61643-11 Class I & Class II ensure maximum product performance with maximum product safety

Spark Gap Technology

The SRF N-Series has as its primary surge diversion stage a high-energy Spark Gap from each phase to neutral and from neutral to ground. These devices offer remarkable surge diversion capability (rated at 130 kA 8/20 μs, 50 kA 10/350 μs), that allows them to handle partial direct strike lightning currents. The range has been tested to the IEC standard Class I tests to ensure that the filter can be installed in a high lightning area and withstand those surge currents that can occur from a direct strike to the facility.
The design of the Spark Gaps used is such that they have fast operating characteristics while extinguishing after the surge has passed, drawing low levels of follow current even on high prospective short circuit current services

Single Phase

Single Phase

2 products
Three Phase

Three Phase

5 products

Filtering Technology

Surge protection devices may include a filtering stage to help condition the waveshape, thereby providing superior protection for sensitive electronics. This said, it is important to realize that a number of different topologies of filter circuit exist, each providing significantly different performance. At its simplest, a manufacturer may include a capacitor in parallel with the output. This may serve to reduce any fast ringing voltages and will also help absorb the energy in a small transient thereby providing a limited level of attenuation.

A far more effective approach is the series LC filter. This type of filter is connected between the surge limiting components and is in series with the supply powering the equipment. It consists of series inductors and parallel capacitors. Surge protection devices of this nature are often referred to as “two port” devices since they have a distinct input and output side.

The SRF N-Series use true series-connected LC filtering. Since the load current feeding the equipment to be protected has to go through the SRF, the inductors have to be rated to carry this load current. As a consequence, the range consists of a number of models to suit increasing load currents, with the larger current models being physically larger. In addition to the heavy-duty inductors, the capacitors used in this filter stage are of a special high-reliability type, having received safety approvals from a number of ratings agencies.

Benefits of SPDs with Filters

  • They reduce the transient voltage reaching the equipment.
  • They reduce the rate-of-rise of the leading edge of the impulse. The residual leading edge spike after a standard SPD, although it may only be 500 V to 900 V in amplitude, can cripple electronics due to its extremely high rate-of-voltage rise of 3,000-12,000 V/μs. Effective filtering reduces this rate-of-rise to less than 20 V/μs. This slower change in voltage is better withstood by electronic equipment using switched-mode power supplies. The filter also helps to attenuate small-signal RFI/EMI noise problems.
nVent Erico Critec SRF N-Series - Surge Reduction Filters
Surge Reduction Filters Brochure

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