Remote Radio Unit (RRU) DC feed protection

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Remote Radio Unit (RRU) DC feed protection

RRU DC feed protection has been under discussion in the ITU-T since the 2011 Raycap paper "Lightning current through MOV based SPDs in RRH applications" by Mr Politis Zafiris, which detailed some waveform measurements made on a 24 m tower. The 2012 Protection Engineers group presentation "Towering Powering protection problem on Remote Radio Head (RRH) cellular systems" gave details the unexpected DC feed protection surge waveshape and the reasons for it. The ITU-T Recommendation K.97 (02/2014): "Lightning protection of distributed base stations" gives a more comprehensive explanation of the DC feed surge protection.

During the SPDC Fall 2014 meeting, the protection of the DC feed was the subject of an afternoon discussion. Coincidentally, there was a WG 3.6.3 contribution in preparation on this topic. The contribution is an analysis to determine the factors affecting the MOV requirements. Recommendations are not made because there are many variables such as the lightning flash to be comprehended, tower structure and tower height.That contribution has now been posted at

http://pes-spdc.org/system/files/filedepot/382/remote_radio_unit_rru_dc_...

The analysis reveals two things

  • Beyond certain decay time to peak current ratios, the current decay in the MOV-based SPD is a linear ramp rather than being an amplitude truncated waveshape of the original lightning stroke.
  • The MOV stress can be expressed as an energy requirement.

The energy rating of MOVs were often decried as marketing ploys. Now the energy ratings are becoming more widely accepted as evidenced by their use to describe HV arrester parameters.

Edited by: admin on 2 Nov 2014 - 11:24