Remote Site Unit & Central Processing Module : the winning combination

Remote Power Feeding

The Remote Power Feeding concept uses the copper twisted pair to transmit the 48VDC SELV power from the Central Office or from the Lex to a Remote Platform (ONU) located in an outdoor street cabinet or an underground enclosure.

The distance can go up to 10 Km (6 miles). Practically, to limit losses, distances are kept under 6Km (4miles).

The concept is based on the RFT-C as defined in the standard EN60950-21. The RPF has been designed according to the most severe safety standard : IEC 479-1 Tab DC2.

It guarantees comfort and enhanced safety conditions for technicians and operators who may have to be in contact with the energized leads.

Advantages

• Very compact solution. Up to 360W plus redundancy can be supplied within a volume as small as 5 dm 3. It leaves so a maximum of space for telecom equipments in the street cabinet and it is probably the only practical solution for UGS.
• It avoids batteries on site, which have severe drawbacks.
• It uses the energy that is available in the LEX where investments have been optimised to achieve the most cost effective solution for back-up.
• Maintenance is limited to electronic devices with high MTBF
• Very high availability. The availability of the service is much higher than 99,99% while redundancy is implemented. Availability of DC source can be considered as infinite.
• Uses twisted pairs, which are made available thanks to the market changes.

BPS exclusive functionalities

• BPS design offers a level of efficiency which is one of the best proposed on the market and keeps it almost constant even when the systems does not operate at full load.
• Extreme compactness.
• Modular architecture that allows “hot swap” and “hot extension” functions.
• Easy installation and deployment thanks self testing and automatic identification of twisted pairs.
• Enhanced monitoring WEB compatible for remote supervision and easy diagnostic.

Typical application

• End-to-end solution with control of the deployment and the supply chain.
• Cost effective power solution for incumbent telecom operators going for the “DSL over existing copper” business model.
• Especially convenient for underground enclosures.

Note : for total transparency the maintenance cost of twisted pairs has been taken into consideration to calculate the remote power feeding OPEX. However, the actual trend into the market is a moving toward wireless communication. This leaves some pairs idle. They have to be maintained anyway. If the remote power feeding does not share these expenses the cost of services that keeps using the copper haul shall be revised.

Product structure

Energize twisted pairs with voltages higher than 48Vdc is hazardous and generate quite justified fears.

A first attempt to make safe such a system has been achieved with RFT-C (or RFT-V) as defined in the standard EN60950-21. It describes maximum voltages and current that can be carried on the twisted pairs.

Another standard, the IEC 479-1, results from medical experiments. It describes and classifies the effects of electrical shocks in several levels according to the voltage and the current that may flow through a human body for a given period of time:

Level 1 (Tab DC1) --> No effect

Level 2 (Tab DC2) --> Safe

Level 3 (Tab DC3) --> Likely Safe

This DC-3 zone has the following physiological effects:

“Usually no organic damage to be expected. Increasing current magnitude and time, reversible disturbances of formation and conduction of impulses in the heart may occur”.

The standard also quantify the probability to get hurt by the electrical shock: 0,14%. Highest risk occurs for people with heart disease.

In most countries level 3 is forbidden and level 2 only is permitted. The DC-2 level (with a current under 25 mA) is to be applied in order to avoid all major problems to human operators in all conditions.

The RFT-C corresponds to level 3 only. The BPS level of hand-to-hand current meets the DC-2 level of IEC 60479-1 and is typically less than 20 mA.

This feature has been checked with a body resistance from 300 to 12.000 Ohms (320V@25mA). Such high impedances should be chosen to fully represent the field reality under dry conditions and because contact surfaces between fingertips and conductors are small when twisted pairs are involved.

The RLP from BPS has been designed according to the most severe safety standard: IEC 479-1 Tab DC2

Safety issue

The Central Power Module is located in the Central Office (CO) or the Local Exchange (LEX). It performs the power conversion and ensures management of the whole structure. Furthermore it offers enhanced monitoring features.

The power is transmitted through copper twisted pairs by groups of 4.

On the remote platform the Remote Power Unit collects the power from twisted pairs and converts it to deliver a 48Vdc voltage to the active equipment.

The Central Power Module (CPM) located at the UP side in the Central Office or LEX takes power from the 48V DC telecom system.

CPM performs the 48V to +/-160VDC (adjustable value) conversion, sends the power over each twisted pair, controls, limits the current in each pair and assures the overall system monitoring