BOBAN - Building and Operating Broadband Access Network

Project P917-GI

BOBAN - Building and Operating Broadband AccessNetworkDeliverable 7

Medium voltage AC access network and customer equipment powering

Suggested readers:Managers, strategic planners, researchers and consultants involved in the field of broadbandaccess networks equipment and outside plant technologies

For full publication

May 2000

2000 EURESCOM Participants in Project P917-GI

EURESCOM PARTICIPANTS in Project P917-GI are:

• FINNET Group

• British Telecommunications plc

• Swisscom AG

• Cyprus Telecom Authority

• Deutsche Telekom AG

• France Télécom

• MATÁV Hungarian Telecommunications Company Ltd.

• TELECOM ITALIA S.p.A.

• Koninklijke KPN N.V.

• Telenor AS

• Hellenic Telecommunications Organisation S.A. (OTE)

• Portugal Telecom S.A.

• eircom plc

This document contains material which is the copyright of certain EURESCOMPARTICIPANTS, and may not be reproduced or copied without permission.

All PARTICIPANTS have agreed to full publication of this document.

The commercial use of any information contained in this document may require alicense from the proprietor of that information.

Neither the PARTICIPANTS nor EURESCOM warrant that the information containedin the report is capable of use, or that use of the information is free from risk, andaccept no liability for loss or damage suffered by any person using this information.

This document has been approved by EURESCOM Board of Governors fordistribution to all EURESCOM Shareholders.

Deliverable 7 Medium voltage AC access network equipment powering

2000 EURESCOM Participants in Project P917-GI page i (ix)

Preface

Broadband access network introduction has been discussed extensively during the lastten years within different research programmes in Europe. The search for a commonand ultimate strategy, guidelines and set of technologies somehow hampered real fielddeployment.

In any case the number of users who can really enjoy broadband services are not inproportion with the efforts put into standardisation over the years and V.34 modemsstill represent the gate to the info highway for most of us.

On the other hand, as a result of the extensive research efforts, a number oftechnologies are ready today or on the verge to be effectively exploited inimplementing the broadband access infrastructure. Unfortunately, and despite of thestandardisation efforts, the variety of technologies is made even more complex by thedifferences among vendor specific implementations.

After the successful experience of EURESCOM Project P614 “Implementationstrategies for advanced access networks”, that addressed introduction scenarios andtechnology appraisal, the BOBAN Project takes on board to investigate a wide rangeof issues insufficiently covered so far, such as testing, installation and operation ofbroadband access networks.

The quick evolution of the involved technologies and the major changes under way inthe telecommunication industry warrant a short study period to review the state of theart, after which the laboratory trials and demonstrator implementations can start.

It is also understood and incorporated into the BOBAN approach, that the accessnetworks will be based on a variety of technologies, and a major challenge will be toassure consistent operation across different systems.

BOBAN also aims to reflect the ideas raised and proposals discussed during theEURESCOM Senior Managers Conference (4th June 1998).

The main objectives of BOBAN are to:

• gain experience with the operation and management of some broadband accesssystems;

• develop methodology and procedures for access network monitoring andsupervision;

• demonstrate low-cost fibre based access systems;

• test and evaluate commercial and pre-commercial low cost DSL systems(particularly ADSL lite);

• understand the viability and the performances of power-line modems;

• provide a comprehensive and reliable assessment of equipment and systemsavailable or under development;

• understand the opportunities and the challenges of new powering solutions;

• develop requirements and demonstrate a prototype of broadband access cabinetincluding powering and mechanical parts;

• identify possible application scenarios and evaluate WDM systems for the accessnetwork;

Medium voltage AC access network equipment powering Deliverable 7

page ii (ix) 2000 EURESCOM Participants in Project P917-GI

• elaborate the specification for a common broadband access network planningtool;

• identify guidelines for optical access systems deployment

• define scenarios and guidelines for a cost effective migration of FTTH in theaccess network.

It is expected that the findings of the BOBAN Project will significantly contribute tothe Shareholders strategic decisions on how to upgrade their access networks toaccommodate broadband services.

This Deliverable is one out of a series of Deliverables BOBAN is producing tosummarise its findings in the different aspects it is studying. This Deliverable reportson the results of the investigations done regarding the powering solutions in the accessnetwork.

The results summarised in this Deliverable are particularly relevant for managers,strategic planners, researchers and consultants involved in work regarding thepowering issues of broadband access networks equipment.


2000 EURESCOM Participants in Project P917-GI page iii (ix)

Executive Summary

Why introduce remote powering?In a liberalised telecommunications market and with the upcoming unbundlingpolicies, where the customer can choose the service/access provider, the downtime ofnetworks (and the consequent loss of revenue) represents a key aspect of the quality ofservice for operators. In order to maintain networks with minimal downtime due topower outages, companies need cost effective and reliable powering of the outdoorplants.

Furthermore, the relative distribution of the power requirements in the central officecompared to those for the access network and customer equipment is shifting in anunprecedented way. Ten years ago, more than 90% of the power consumption tookplace in the central office and 10% in the access network and customer equipment.This situation is likely to be inverted in the next decade. Reasons are the increasedcomplexity of customer equipment, distributed intelligence and power hungrybroadband technology in the access network and at the customer premises. Varioussolutions have been proposed to power the access network equipment with DCpowering over the existing telecom cables and /or local AC powering with batterybackup. The drawback of these solutions is that they can either supply low power foran extended period of time (remote feeding through existing copper cables) or theycan deliver high power for a limited backup time period, but they cannot deliver both.

Why you should read this deliverable ?This Deliverable introduces a new technology for the reliable powering of the accessnetwork equipment. It should be of interest to anyone involved in the planning andengineering of powering aspects in outside plant technologies since it provides a goodintroduction and takes account of the technical and economic aspects of thesetechnologies. In addition, the results of the presented laboratory trials can serve aspractical guidelines for the planning personnel with regards to available hardwarecomponents and regulatory issues.

The benefits for your companyThe benefits can be summarised as follow:

• Installation and maintenance costs savings

• Improved reliability (of the power supply)

• Elimination of the battery at the remote location

• Considerable simplification of the power supply management

• Space saving inside the cabinet

• Independence from the power utility companies

• Shorter installation time

What are the main results ?The main message of D7 is, that the results of our investigations described in detail inthe report indicate that remote 1000VAC powering is a technically feasible andreliable solution especially for powering multiple cabinets when power cables can beinstalled in existing infrastructure. The results of the laboratory trials performeddemonstrate and prove the simplicity and the robustness of the adopted topology.


page iv (ix) 2000 EURESCOM Participants in Project P917-GI

D7 presents the results of the laboratory tests in detail. The following tests and theirresults are covered in particular:

• Efficiency and voltage drop measurements with different loads

• Inrush peak current at the turn on, minimised with the use of standardtransformers

• Effect of short dips and interruptions

• Short circuit rejection

• Surge and lightning protection

The laboratory tests produced very promising results, i.e.:

• Short dips and interruptions don’t produce over-currents or fuse blowing

• Short circuit rejection with oversized fuses results in a short small voltage drop

• Surge and lightning protection of the equipment is guaranteed

Besides the description of the laboratory tests D7 provides:

• Tested cables characteristics

• A detailed engineering guide

• Details and findings of the regulatory study that covered a number of Europeancountries

What next?EURESCOM Shareholders are in the process to upgrade their access network for thedelivery of broadband services. This Deliverable presented a new technology andstrategy for long term low power energy back-up. The proposed technology wassuccesfully tested and it is now time to reap the benefits of this work throughimplementing the technology in the access networks of the EURESCOMShareholders.


2000 EURESCOM Participants in Project P917-GI page v (ix)

List of Authors

Enrico Blondel, Swisscom Ltd.

Zoltán Janklovics, Matav, HT

Gábor Gerdai, Matav, HT

Fernando Morgado, Portugal Telecom, PT

Didier Marquet, CNET, FT


page vi (ix) 2000 EURESCOM Participants in Project P917-GI

Table of Contents

Preface .............................................................................................................................i

Executive Summary...................................................................................................... iii

List of Authors................................................................................................................v

Table of Contents ..........................................................................................................vi

Abbreviations ............................................................................................................. viii

Definitions .....................................................................................................................ix

1 Introduction.............................................................................................................11.1 Motivation ....................................................................................................21.2 Medium or “increased voltage”....................................................................3

2 Study on regulatory aspects ....................................................................................42.1 Overview of the national restrictions............................................................4

2.1.1 Introduction .....................................................................................42.1.2 Answers ...........................................................................................42.1.3 Analysis of results............................................................................5

2.2 Safety considerations....................................................................................52.2.1 Effect of Operating Procedures On Safety ......................................52.2.2 Avoiding Current Paths ...................................................................52.2.3 Maximising Contact Resistance ......................................................62.2.4 Precautions for service personnel ....................................................62.2.5 Other considerations ........................................................................6

3 Evaluation study and identification of an optimised solution for remotepowering .................................................................................................................7

4 Analysis of the RFI .................................................................................................84.1 Goal ..............................................................................................................84.2 Results ..........................................................................................................8

4.2.1 Single phase transformers................................................................84.2.2 AC-DC power supply systems.........................................................94.2.3 DC-AC inverters..............................................................................94.2.4 Cables ..............................................................................................9

5 Laboratory trial description and results ................................................................105.1 Laboratory set-up........................................................................................10

5.1.1 Scheme...........................................................................................105.1.2 Transformers..................................................................................105.1.3 Loads .............................................................................................105.1.4 Cables ............................................................................................11

5.2 Test description ..........................................................................................125.3 Results ........................................................................................................13

5.3.1 Efficiency and voltages measurements..........................................135.3.2 Inrush current measurements.........................................................145.3.3 Short dips and interruptions...........................................................145.3.4 Short circuit rejection ....................................................................155.3.5 Surge protection / filtering.............................................................165.3.6 Cables measurements.....................................................................20

6 Impact on network planning .................................................................................236.1 Planning considerations..............................................................................23


2000 EURESCOM Participants in Project P917-GI page vii (ix)

6.1.1 Investment costs ............................................................................ 236.1.2 Maintenance costs ......................................................................... 23

6.2 Scenario 1 – Centralised powering............................................................. 246.2.1 Features ......................................................................................... 246.2.2 Planning aspects ............................................................................ 25

6.3 Scenario 2 – Cluster powering ................................................................... 256.3.1 Features ......................................................................................... 266.3.2 Planning aspects ............................................................................ 26

6.4 Guideline to implement the cluster remote powering solution .................. 276.4.1 Dimensioning of transformers....................................................... 276.4.2 Calculation of the cable cross section ........................................... 276.4.3 Examples using the plots above .................................................... 30

6.5 Space saving considerations....................................................................... 31

References.................................................................................................................... 32


page viii (ix) 2000 EURESCOM Participants in Project P917-GI

Abbreviations

Uin Input voltage

Uout Output voltage

U500 Output voltage after 500VA transformer

U300 Output voltage after 300VA transformer

I300 Output current after 300VA transformer

I500 Output current after 500VA transformer

Iin Input current

CE Central Exchange

VE1, VE2, VEn Virtual Exchange 1, 2, n

LISN Line Impedance Simulation Network

C1, C2, Cn Cluster 1, 2, n

ONU Optical Network Unit

UPS Uninterruptible Power Supply

HV High Voltage

PF Power Factor

Pin Input power

Pout Output power

Pout500 Output power of the 500 VA transformer

Pout300 Output power of the 300VA transformer

η Efficiency

PFin Input power factor

PFout Output power factor

Uhvin Output voltage of the main transformer

Uhv500 Input voltage of the 500VA transformer

Uhv300 Input voltage of the 300VA transformer


2000 EURESCOM Participants in Project P917-GI page ix (ix)

Definitions

Remote powering is the ability to provide power to the equipment from a far placeduninterruptible source of energy.

Cluster in this case is the point of arrival of the medium or increased voltage line andthe place of the transformer. At this point only 230V is distributed.

Medium voltage is a voltage between 1kVrms and 16kVrms.

Increased voltage is defined over the normal mains voltage of 230/400Vrms but stillunder 1000Vrms and submitted to the low voltage regulation.


2000 EURESCOM Participants in Project P917-GI page 1 (32)

1 Introduction

The need for power in the Central Exchange (CE) will decrease in the coming yearsdue to the increasing amount of Virtual Exchanges (VE) moving the broadband accesspoint near to the customer. The number of VEs makes the maintenance of backuppower (batteries) in each VE difficult and expensive. The evolution of the accessnetwork will follow the way shown in the Figure 1 and Figure 2.

Serving edge

5.5 kmmaximum CE

Fig. 1 Today solution: each customer is directly connected to the CE

VE

VEVE

VE

5.5kmmaximum

Currentexchangeservingedge

Shortenedserving edge

2-3 kmmaximum

CE

Fig. 2 Future solution: a group of customers will be connected to a VE, each VEconnected to the CE


page 2 (32) 2000 EURESCOM Participants in Project P917-GI

The basic network topology shown in the figures above can be used to provide powerfrom the CE to the VE in the same way using the reliable power facilities still existingin the CE.

The CE power facilities work in well known conditions:

• environment

• climatic conditions

• operation conditions

• maintenance

• safety

• security

The VE, on the other hand, is exposed to harsher climatic conditions. It is difficult toperform maintenance at the VE and that leads to low safety and security levels,weakness of the VRLA batteries operating at higher temperature, etc.

This Deliverable proposes a solution for remote powering the active components inthe access network. With the proposed solution it becomes possible to eliminate someof the above problems.

Other advantages offered by this solution include the elimination of:

• power meters inside the cabinets and

• the need to make contracts with the local energy provider.

These result in substantial space savings in the cabinet and also large savings in therequired manpower investment.

1.1 Motivation

Efficient usage of the space in the street cabinets has a great impact on the overall costof the access network. The place taken by metering, fuses and batteries in a standardbroadband cabinet can vary between 20% and 40% of the inside volume. With theintroduction of remote powering technology in a clustering manner offers theadvantages of increased reliability, simplification of the monitoring equipment andreduced maintenance on serviceable parts beside the crucial space saving in thecabinets by eliminating the batteries.

Another major motivation is the European Telecommunications EnvironmentalCharter. It is a common environmental policy of the signatories who committhemselves to improve their environmental performance. To achieve this, an ETNOworking group on the Environment has been established.

This Charter describes the commitment to sustainable development through:

• the provision of products and services that provide significant environmentalbenefits; and

• a determination to manage our own operations in a way that minimises negativeenvironmental impacts.

The proposed solution of remote powering is fully in line with the objectives of theETNO Charter.



1.2 Medium or “increased voltage”

The use of the term “Medium Voltage powering “ is due to the fact that the choice ofthe powering voltage will not be considered as mandatory in this report. The goal is totry to find a compromise between power level, voltage and distance that can satisfyreliability and costs goals. The choice of a voltage as high as possible but as cheap aspossible imposes some restrictions on the choice of the voltage. One of the criteria isthe cost of medium voltage hardware which is very high compared to the low voltagehardware. In such cases we can speak of increased voltage remote powering.



2 Study on regulatory aspects

2.1 Overview of the national restrictions

2.1.1 Introduction

Before proceeding with the detailed study it is necessary to provide an overview of theexisting national standards, regulations and restrictions regarding remote powering toestimate its feasibility.

An extended regulatory study covering the countries of the Project participants wasperformed with the following questions:

1. Is it allowed in general, to put together telecom (copper or fibre) andenergy/power cables in the same duct or pipe ?

2. Can a telecom company do this ?

3. Trough which law is this area regulated ?

4. Even when the transported energy is for the telecom company’s own use (ANCabinet or any other kinds of remote equipment) ?

5. Are there any restrictions regarding the length or the voltage, if the voltage issmaller than 1kV ?

6. Are there any restrictions regarding the length or the voltage, if the voltage ishigher than 1kV?

7. Is there any problem to be expected with the electric utility companies ?

8. Is there any problem to be expected from the municipalities or any regulatorybody ?

2.1.2 Answers

The Table 1 summarises the answers received in the extended regulatory study andshows the feasibility of the proposed solution.

Country Question

1. 2. 3. 4. 5. 6. 7. 8.

CH Yes Yes Safety Yes No No No Yes

CY No Yes Security -- No No No Yes

DT Yes only DC Yes -- ? ? ? No No

FT Yes Yes Security Yes No -- No Yes

HT Yes Yes Security Yes No No No Yes

IT Yes Yes Law Yes No Yes Yes Yes

NL No Yes Law Yes -- -- -- --

NT Yes Yes Safety Yes No No -- No

OG No -- -- -- -- -- -- --



Country Question

1. 2. 3. 4. 5. 6. 7. 8.

PT No Yes Law Yes No No Yes No

% of Yes 60 % 90% 70% 0% 10% 20% 50%

Table 1 Summary of the answers

2.1.3 Analysis of results

Q1, 2 and 4: in general it is allowed to provide remote power for the one’s ownoutside plant equipment without important restrictions.

Q3: in each Country, the laws, security and safety considerations must be taken intoaccount and they could be very restrictive.

Q5 and 6: The voltage level and the distance are mostly not limited but someeconomical considerations could have an important impact on the choice of thevoltage and the maximum distance.

Q7 and 8: It may be possible for electric utility companies to have a contract with themunicipality and this restricts the distribution and transportation of electrical energy.

2.2 Safety considerations

These safety considerations are based on the ITU directives.

2.2.1 Effect of Operating Procedures On Safety

Work operations on energised conductors entail some possibility of the foregoingphysiological responses occurring. The possibility of a response at a given voltagelevel depends on the precautions taken in working with that voltage. Theseprecautions can range from minor measures (for sufficiently low voltages) to requiringde-energisation before contact (for high level voltages).

Safety precautions can generally be viewed as contributing to two goals; first,avoiding the creation of current paths through the body; and second, when currentpaths are unavoidable, maintaining the highest feasible contact resistance (total bodyimpedance).

2.2.2 Avoiding Current Paths

The use of insulation to preclude the formation of current paths through the body isperhaps the most familiar of precautions. To this must be added such other forms ofprotection as placement out of reach, or, for higher level voltages, providing baffles orenclosures. Forms of insulation that rely in part on proper craft procedures are the useof insulated tools and, for higher level voltages, insulated gloves. The intent of allthese is to prevent the establishment of a current path by preventing direct contact withthe energised conductors.

An effective precaution of minimising the creation of current paths involvescontacting only one conductor at a time. In essence, contact with an energisedconductor need not be avoided if, simultaneously, contact with earth groundedconductors is avoided. Owing to the prevalence of grounded surfaces near



telecommunication workspaces (equipment chassis, support strand, cable screen, etc.),avoiding contact with earth, even when atop a pole may be difficult.

2.2.3 Maximising Contact Resistance

For all this efforts to avoid to enable a current path through the body, there will arisesituations in which personnel will intentionally contact the energised conductor. Thecurrent that results from this contact is limited by the combined skin impedance of thecontact points with the voltage and with the earth. This impedance will be largelydetermined by the area of contact and wetness of the skin (voltage and frequency ofthe source are also important, but these parameters are not under the control of theindividual contacting the source). Accordingly, personnel should make the minimumarea of contact possible, be mindful of large area contacts arising from leaning to orlying on grounded surfaces, and attempt to maintain dry contacts.

The labelling of known appearances of high level voltages can serve to alert personnelto appearances that require special precaution. Personnel encountering such a labelledappearance should be instructed to follow recommended precautions to precludeinadvertent contact and to establish cautious contacts when intended.

2.2.4 Precautions for service personnel

The following precautions may be applied as appropriate to the working operationsbeing performed and the type of line involved:

a.) marking of all line maps with warnings,

b.) marking of all accessible parts of the installations and equipment with warnings,

c.) the issue of special instructions to the personnel likely to have access to exposedcircuits so that danger will be recognised and special work measure can beapplied,

d.) special safety precautions for the personnel during the work, such as switchingoff, use of insulated tools, use of insulating clothing (like gloves, shoes, etc.),insulating the work place, etc.

2.2.5 Other considerations

• If work has to be done on lines in which voltages exceeding the safety limits mayoccur, service personnel should not work alone.

• Only personnel who have been instructed should be allowed to work on lines inwhich voltages exceeding the safety limits.

• When using insulating clothing (gloves, shoes), or insulated tools, or electricalequipment which is isulated from earth, such as soldering irons, portable lamps,linemen’s telephone sets, etc., care should be taken to ensure that the insulation isadequate and intact.

• In order to avoid the use of special safety precautions, the work should be done attimes when the inducing line can be disconnected from its power supply.



3 Evaluation study and identification of an optimisedsolution for remote powering

This study will open the possibility to adopt the remote powering technology even atmedium to low power levels with extended backup time for the access network of thefuture.

Further, eliminating batteries at the remote site will provide an environmentallyfriendly solution.

After many trials to sketch a unique solution for all the possible topologies, the clustertopology seems to be the best approach. It is flexible enough and can be adapted toeach case without modifying the concept.

This is the base idea used for all the investigations made on this Deliverable.

C2C1

CE

Figure 3 Basic cluster powering topology

The cluster topology described in Figure 3 shows the selected solution formeasurements in the laboratory. In reality, the physical position of cluster C1 or C2may be different and in some cases it could be combined in one of the cabinets orplaced anywhere (manhole, underground cabinet etc.).

The distance between CE and C2 should not exceed 5 to 6 km.



4 Analysis of the RFI

4.1 Goal

The first goal of the RFI (Request For Information) was, to get an overview on theexisting and available hardware components on the European market to be used tobuild a safe and simple remote powering distribution network.

The second goal was to provide information on the additional hardware to be includedin the CE.

The RFI was conducted in the form of a questionnaire which had the followingstructure:

• Single phase transformers

• AC-DC power supply systems

• DC-AC inverters

• Cables

Only components available from local manufacturers were considered in the RFI.Components such as fuses and connectors were not considered.

The list of manufacturers and their respective selected products and components aregiven in the Annex to this Deliverable.

4.2 Results

The RFI process consisted a substantial part of our work. It took a lot of time and greateffort to obtain answers from the manufacturers. We could proceed with the analysisonly after receiving sufficient responses. Only 36% of the contacted manufacturers (13out of the 36 contacted) gave satisfactory responses, even after repeated urging andcontacts.

4.2.1 Single phase transformers

Some important trends are emerging from the information received from themanufacturers:

• Standard transformers are available at low cost.

• Due to the high inrush current the use of toroidal transformers should be avoided.

• High voltage transformers (over 1000Vac) must comply with stronger safetyspecifications; they are also bulky and expensive.

• The temperature range and IP (International Protection) degree must be specifieddepending on the environmental conditions.

Following minimal specifications should be applied when the transformer is installedin the outdoor cabinet: IP23 and an operating temperature range of +5 °C to +60 °C.

In the CE, the temperature stress is not so high, so IP20 and an operating temperaturerange of +5 °C to +40 °C should be sufficient for the primary transformer.



4.2.2 AC-DC power supply systems

There is a significant market of power systems in Europe. A number of manufacturersare offering modular power supplies built of 100W and 300W modules designated forlocal powering and having a dedicated controller and battery supervision with a rangeof features. If remote powering is implemented, then there will be no need for such asophisticated controller and thus investment costs can be reduced.

4.2.3 DC-AC inverters

The use of the reserve 48V-DC power in the CE is one way to provide remotepowering. Now the need of a modular inverter can improve the reliability of thetopology. Some manufacturers are providing modular systems with differentapproaches for the regulation and load sharing between modules. A bypass is alsooffered to improve reliability in case of inverter failure. 1 kW and 3 kW single phasemodules are available on the market.

4.2.4 Cables

Cables for this purpose are available on the market. Experience shows, that for alength over 1 km, stock cable and dedicated purpose made cable have the same price.A cable made on order offers the advantage that the special requirements,performance, special marking, etc. are guaranteed to be met. Concentric full neutral(ceander) cables with the same core and outer copper section are not available on theEuropean market (only in the US). This is because in Europe the mains network isthree-phase and the cross section of the outer layer is always a third of the core crosssection.



5 Laboratory trial description and results

5.1 Laboratory set-up

The adopted solution reflects the cluster topology described above. The hardware usedis standard (low cost). The adopted voltage is 1000 V.

5.1.1 Scheme

6.6kVAUPS

Transformer

1.7 km LISN3 Cabinetsimulation

PE

230V Mains

1.7 km LISN

Transformer2 Cabinetsimulation

300VA

500VA4kVA

1000V

1000V Transformer

Figure 4 Scheme of the laboratory setup

5.1.2 Transformers

The primary transformer used is a 4kVA / 50Hz / 230V primary and 500V/1000Vsecondary voltage.

The secondary transformers are 300 VA and 500VA / 50Hz / 1000V/500V primaryand 230V secondary voltage. The secondary transformers are designed with thefollowing criteria:

2 x 120W / PF 0.75 = about 300VA

3 x 120W / PF 0.75 = about 500VA.

The chosen topology can deliver power for 5 broadband cabinets. However, theprimary transformer, which is located at the CE, can provide power for about 20broadband cabinets. This must be taken into account in the economic study.

5.1.3 Loads

The following loads were used for the laboratory trials:

• Resistive load for the maximum power rating

• Non-linear load according to EN50091-1 [1] to simulate the real situation



Resistive loads are non-inductive ceramic resistors placed on a heat-sink and cooledwith a fan. They simulate a load of 120W per cabinet.

The choice for the resistive load is the following:

2 cabinets: 220Ω / 240W

3 cabinets: 147Ω / 360W

Each BB-Cabinet was simulated with a non-linear load according to EN50091-1 [1]

Uin

Rs

RlC

Figure 5 Scheme of the non-linear load

The power dissipation per cabinet is 120W (160VA)

A non-linear load is assumed in order to have a cheap power supply inside the cabinet(no PF correction)

The calculations according to EN50091-1 [1] give the following results:

500VA: Rs = 4.2 [Ω]; Rl=238 [Ω] ;C= 628 [µF]

300VA: Rs = 7.0 [Ω]; Rl = 397 [Ω] ;C= 377 [µF]

The practical values are:

500VA: Rs = 4.2 [Ω]; Rl=132 + 132//519 [Ω]; C= 470 + 220 [µF]

300VA: Rs = 7.0 [Ω]; Rl = 270 + 132 [Ω]; C= 220 + 100 [µF]

Note: 300VA and 500VA are the nominal powers of each secondary transformer

5.1.4 Cables

In the first phase of the trials the cables were not available. They were simulated witha Line Impedance Simulation Network (LISN), which is assembled with acombination of resistors and capacitors to simulate long lines. The LISN is capable tosimulate about 3.4 km of cable.

In the second phase, two types of cables were tested:

• 3 x 4mm2 LNPE PURWIL non flammable 1 kV cable unscreened (1km)

• 2 x 4mm2 LN Betaflam FE5 1kV screened with 2 copper bands (1km)



Figure 6 Cables used for the trials: unscreened (left) and screened (right)

LISN

Load

Power source

Primary transformer

Secondarytransformer

Figure 7 Laboratory set-up with the power source in the background, the non-linear load at the right and the LISN in the middle

5.2 Test description

The following trials were performed in the Swisscom laboratory. The goal of the trialswas to get significant and relevant results to be considered by the engineering peoplewhen building a remote power feeding network using this topology.

• Efficiency and voltage measurements

• Inrush current measurements

• Short dips and interruptions

• Short circuit rejection

• Surge protection / filtering



• Cable characteristics

5.3 Results

5.3.1 Efficiency and voltages measurements

Efficiency measurements were made with the two types of load and the 2 x 1.7kmLISN using a precision power analyser.

The Table 2 shows the results for the two types of load including all information of thesetup and the effect of the load type reflected to the input (voltage and current).

Load Non-linear Linear (resistive)

Input Pin = 799W;Uin = 229.53V;Iin = 4.608A;PFin = 0.755

Pin = 1021 W;Uin = 229.2 V;Iin = 4.85 A;PFin = 0.918 ind.

Output Pout500 = 356W;

Uout = 235V;Iout = 2.12A;PFout = 0.71

Pout300 = 220W;

Uout = 234V;Iout = 1.26A;PFout = 0.74

Pout500 = 509.12 W;

Uout = 231.42 V;Iout = 2.20 A;PFout = 1.0

Pout300 = 304.08 W;

Uout = 230.37 V;Iout = 1.32 A;PFout = 1.0

Line Simulation 7 x 110nF + 6 x 5Ω 7 x 110nF + 6 x 5Ω

Efficiency

η = (Pout500 + Pout300) / Pin

η = 0.721 η = 0.796

Table 2 Efficiency measurements

Voltage measurements at different points are shown in the Figure 8

Transformer

300 VA

Transformer

500 VA

3 Cabinetsimulation

2 Cabinetsimulation

Transformer

4 KVA

LISN

LISN

Loads Uin Uhvin Uhv500 U500 Uhv300 U300300VA + 500VA 229.32 1013.7 1004.1 234.79 1000.7 234.03

500VA 229.40 1014.8 1009.1 235.77 1008.6 242.70300VA 229.43 1015.4 1011.8 242.35 1007.8 235.58



Loads Uin Uhvin Uhv500 U500 Uhv300 U300240W + 360W 229.19 1012.0 998.5 231.42 993.5 230.50

360W 229.33 1013.8 1004.7 232.78 1004.4 242.20240W 229.44 1015.0 1009.2 242.25 1004.1 232.86

Loads Uin Uhvin Uhv500 U500 Uhv300 U300No load 229.60 1016.7 1015.6 243.76 1015.2 244.77

Figure 8 Voltage measurements with differents load

5.3.2 Inrush current measurements

The main goal of the inrush current measurement is to show that the primarytransformer can be connected to a weak mains source such as an UPS or inverter.These sources provide only a limited inrush current capability. The secondary goal isto show the quality of the HV link when a load (equipment) is plugged in. The worstcase of inrush current is achieved with a non-linear load (charging of the inputcapacitors with a high current peak).

-60

-50

-40

-30

-20

-10

0

10

20

30

40

0 0.05 0.1 0.15 0.2

Uin

/10[

V];

Iin[

A]

Time [s]

inrush current measurement

UinIin

Figure 9 Inrush current of the primary transformer

From our measurements some general conclusions can be drawn. The inrush currentcapability of the source is a very important criterion for the engineering of thetransformers. The inrush current of the primary transformer should meet the limits ofETS 300 132-1[3]. Due to this limitation, it is not recommended to use toroidaltransformers.

5.3.3 Short dips and interruptions

Load: non-linear and resistive

Tests according EN 300-386-2 V1.1.3 (1997-12) Chapter 5.2.4 [2]

Test 1 Test 2 Test 3 Test 4



Voltage drop >95% 30% 40% >95%

Duration 10 ms 500 ms 200 ms 5000 ms

Requirement(see remark)

• No over voltages

• No over currents

• No oscillations

• No fuse blowing

Result Complies Complies Complies Complies

Table 3 Test results of voltage drops ans short interruptions

Note: This system is not a power supply but the relevant tests are described in thementioned standard. The performance criteria described in EN 300-386-2 [2] are notapplicable.

5.3.4 Short circuit rejection

This trial demonstrates the excellent behaviour of the system regarding short-circuitrejection in a fault situation.

Transformer Transformer

Transformer 2.5A T or F

300 VA

500 VA

Iout, short circuit point

UoutUin,Iin 3 Cabinet

simulation

2 Cabinetsimulation

4 KVA

LISN 1.7 km

Figure 10 Short circuit rejection test set-up scheme

The fault was produced on the secondary side of the 300VA transformer with aswitch. The fuse was intentionally chosen to be twice the rating of the transformer tosimulate a worst case situation.



-40

-30

-20

-10

0

10

20

30

40

0.02 0.04 0.06 0.08 0.1 0.12 0.14

Uin

/10[

V];

Iin

[A];

Uo

ut/

10[V

]; Io

ut[

A]

Time [s]

short-circuit with a fuse of 2.5A fast blow

UinIinUoutIout

Figure 11 Short circuit rejection with a 2.5 A fuse fast blow

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Uin

/10[

V];

Iin

[A];

Uo

ut/

10[V

]; Io

ut[

A]

Time [s]

short-circuit with a fuse of 2.5A slow blow

UinIin

UoutIout

Figure 12 short circuit rejection with a 2.5 A fuse slow blow

In conclusion, one can see from Figure 11 and Figure 12 that a maximum of 60msblowing time can be expected without significant voltage drop at the far end of thesystem.

5.3.5 Surge protection / filtering

Two trials were performed on the system with the following goals:

1. to observe and measure the filtering performances of the whole system, when thesurge pulse, according to EN61000-4-5 [4], is applied at the input of the primarytransformer .



2. to get out figures from lightning applied direct on the duct or pipe choosing theworst case of metal pipes.

For the first test, the set-up is the same as the one shown in Figure 10 and the voltageobserved is always the one at the secondary side of the 500VA and at the secondaryside of the 300VA transformer.

Figure 13 Voltage waveform at the input of the main transformer

Figure 14 Voltage waveforms behind the 500VA transformer (#12 B) and behindthe 300VA transformer (#12 C)

The coupling voltage is 2 kV L-PE. Behind the 500VA transformer a surge of about120V occurs, while behind the 300VA transformer, the surge is reduced to about 20V.

For the tests between L-L (1kV) the surges disappear after the first transformer.

Remark: the distortion of the measured voltage is due to the high impedance of thedecoupling network and the non-linear load.

The set-up for the second trial was realised with the aid of a big overvoltage generatorof 100kA surge capability as shown in Figure 15.



Transformer

Transformer

Transformer

300 VA

500 VA

Uout

Ch. B

Uin

Ch. A

3 Cabinetsimulation

2 Cabinetsimulation

4 KVA

LISN 1.7 km

40 m cable

960 m cable

4 m pipe

shunt

Overvoltagegenerator

Figure 15 Lightning protection test set-up scheme

Figure 16 Generator with the metal pipe in the foreground and a snapshot of thecurrent waveform during the test (ev. #90)

The tests were carried out at two selected cables. The peak current was increased fromabout 10kA to 40kA in 10kA steps, which represents a realistic lightning impact onthe cable. The transients on the input and output voltage were recorded.



Table 4 shows the measurement results for the stock cable. The ground wire wasconnected to the ground at both ends.

Peak shuntvoltage[Vpk]

Peak shuntcurrent[kApk]

Transient voltage atthe input

[Vpp]

Transient voltage atthe 500VA

transformer output[Vpp]

3.17 19.02 -- --

4.58 27.48 -- 53

6.30 37.80 61 32

Table 4 Measurement results with the unscreened cable

Figure 17 Input (#77a) and output (#77b) voltage waveforms at -38kA peakcurrent with the unscreened cable

Table 5 shows the measurement results for the order made screened cable. The screenwas connected to the ground at both ends.

Peak shuntvoltage[Vpk]

Peak shuntcurrent[kApk]

Transient voltageat the input (Uin)

[Vpp]

Transient voltage atthe 500VA

transformer output(Uout) [Vpp]

3.20 19.20 -- --

4.62 27.72 50 84

6.28 37.68 25 50

Table 5 Measurement results with the screened cable



Figure 18 Input (#90A) and output (#90B) voltage waveforms at -38kA peakcurrent with the screened cable

The surge protection measurements shows the filtering behaviour of the transformers.In the second test, the injected voltage along the pipe reaches peak values of up to 15kV. The attenuation of the injected signal is very important, and the experimentshows, that after 40m, the signal is smaller than 100V and practically disappears.

5.3.6 Cables measurements

The following parameters were measured on both 1 km long cables:

• Impedance

• Attenuation

• Resistance

• Capacitance

The following plots (Figure 19 to Figure 22)shows the impedance Zc and theattenuation of the cables.

Unscreened 3x4 mm2

0

10

20

30

40

50

60

70

80

90

100

0.0 5.0E+06 10E+06 15E+06 20E+06 25E+06 30E+06

Frequency [Hz]

Imp

edan

ce [

oh

ms]

Transmission

Reflection

Figure 19 Impedance measurements up to 30 MHz on the unscreened cable



Unscreened 3x4 mm2

0

10

20

30

40

50

60

70

80

90

0 5000000 10000000 15000000 20000000 25000000 30000000

Frequency [Hz]

Att

enu

atio

n [

dB

/km

]Transmission

Reflection

Figure 20 Attenuation measurement up to 30MHz on the unscreened cable

Screened 2x4mm2

0

10

20

30

40

50

60

70

80

90

100

0 5000000 10000000 15000000 20000000 25000000 30000000

Frequency [Hz]

Imp

edan

ce [

oh

ms]

Transmission

Reflection

Figure 21 Impedance measurement up to 30MHz on the screened cable



Screened 2x4mm2

0

10

20

30

40

50

60

0 5000000 10000000 15000000 20000000 25000000 30000000

Frequency [Hz]

Att

enu

atio

n [

dB

/km

]

Transmission

Reflection

Figure 22 Attenuation measurement up to 30 MHz on the screened cable

Screened 2x4 mm2 Unscreened 3x4 mm2

Resistance [Ohm/km] 4.50 4.65

Capacitance [nF/km] 98.24 108.0

Zc [Ohm] see Figure 21 see Figure 19

Attenuation [dB/km] see Figure 22 see Figure 20

Table 6 Measurements results of the cables

In conclusion, one can say, that the two cables are electrically similar, but the greatadvantage of the screened cable is in its mechanical strength and the ease of istinstallation in ducts or pipes. In addition, the choice of using a screened cable,crosstalk problems can be avoided when the cables run together with telecom coppercables in the same duct or pipes.



6 Impact on network planning

Several solutions exist for medium voltage AC access network powering. For theproper planning, the following starting conditions should be known:

• The structure of the telecommunications network (star, ring, etc.),

• The power consumption of the powered equipment,

• The distances between the powered and the powering points,

• Other points of view, for example the necessary back-up time (depending on thesite of the installation), etc.

The network structure should be chosen first. Two scenarios are possible:

• Centralised powering, and

• Cluster powering

6.1 Planning considerations

General aspects should be taken into consideration in case of planning of the newsystems:

• Choice of the right solution according to the input conditions (powerconsumption, distances, using the existing possibilities, applicable devices, otherconsiderations).

• Checking of the operating conditions of the elements of the chosen solution (forexample, the equipment installed in the street cabinets should tolerate moreextreme climatic conditions; remote monitoring should be possible, etc.).

• Calculating of the costs (investment costs, maintenance costs).

One of the most important steps of the planning is the cost calculation. Bothinvestment and maintenance costs should be taken into account.

6.1.1 Investment costs

The investment costs of the power system consist of three parts:

• Equipment costs (rectifiers, transformers, AC UPSs, cables, batteries, connectors,fittings, fuses, other devices)

• Civil work costs (laying of the cables, assembling of the devices)

• Energy costs (changing - extending according to the increased energy demands -of the contracts (entry costs) with the energy supplier)

6.1.2 Maintenance costs

The main aspects are the following:

• energy costs

• costs of the monitoring, repairing of the broken equipment, changing of thedamaged equipment and batteries



The energy costs consist of three parts:

• monthly price of the reserved energy

• used (measured) energy consumption

• penalties (for the wrong power factor, energy overstepping)

6.2 Scenario 1 – Centralised powering

In this scenario all the VEs are powered by the CE (see Figure 23). There is a UPS(with large back-up batteries and generator engine) installed at the CE for local andremote feeding. Each VE is powered by the CE with remote feeding. Each VE has apair of transformers. All the low voltage/medium voltage transformers are installed inthe CE and the medium/low voltage transformers are installed in the VEs.

ACUPS

Trl/m

Trl/m

Telecom lines

Medium voltage po-wer lines

Trm/l

Trm/l

VE1

VEn

CE

Tr m/l: 1000V/230V transformerTr l/m: 230V/1000V transformer

Medium voltage power linesTelecomunication line

Figure 23 Centralised medium voltage AC access network powering

6.2.1 Features

The feeding of the VEs is uninterruptible by the UPS installed in the CE. Therefore,back-up batteries do not need to be installed in the VEs (it is possible to use them forincreasing the availability, but it is not necessary).

The power consumption of the powered VEs is limited (by the transformers andcables).



6.2.2 Planning aspects

The starting points are the following:

• The number and energy demand of the powered VEs, as well as the distancesbetween CE and each VE shall be known.

• The availability of the primary AC power source at the CE

The remote power demand of the VEs consists of

• The summed energy demands of VEs,

• the summed energy losses (transformers, power lines, etc.)

• the possible extension demand in the future.

The result is the summed serviceable energy demand. This is one of the criteria fordimensining the AC UPS installed in the CE. Another criterion is the availability ofthe primary AC power source. The necessary back-up time of the batteries depends onthis parameter. (Note: Generator sets are installed in the larger CEs. This fact shouldbe considered in the calculation of the resulting availability. Further information canbe found about these questions in earlier EURESCOM documents, (e.g.: in the P614Deliverable 12 [5]).

Batteries can be dimensioned according to the power consumption and the back-uptime. The energy demand of the AC UPS consists of

• the total summed serviceable energy demand,

• the charging energy (for batteries)

• the losses of UPS (on account of efficiency)

6.3 Scenario 2 – Cluster powering

In case of cluster powering, a chosen VE (street cabinet, etc.) feeds the other VEs (andthe customer premises) (see Figure 24). The feeding VE has a connection to the publicmains and its equipment is locally powered by its local power supply with back-upbatteries. The other VEs are powered by medium voltage AC powering. Each VE hasa pair of transformers. All the low voltage/medium voltage transformers are installedat the feeding VE via an AC distributor unit. The feeding VE doesn’t contain ACUPS, because usually it has not got enough space for this equipment. Therefore thepowered VEs should contain local power supply with back-up batteries.



Localpowersupply

Trl/m

Trl/m

Telecom lines

Medium voltage po-wer lines

Trm/l

Trm/l

VE1

VEn

VEfeeding

Tr m/l: 1000V/230V transformerTr l/m: 230V/1000V transformer

Medium voltage power linesTelecomunication line

Localpowersupply

Localpowersupply

Public mains

To the CE

ACdistribution

Figure 24 Cluster powering (medium voltage AC powering)

6.3.1 Features

• This system doesn’t contain AC UPS and, therefore, back-up batteries should beinstalled on each site (together with the local power supplies).

• The power consumption of the powered VEs consists of the power demand of thetelecommunication and auxiliary equipment and the charging power of the back-up batteries.

6.3.2 Planning aspects

The criteria are the following:

• The number and energy demand of the locally powered VE and all the remotepowered VEs, and the distances between the locally powered VE and eachadditional VE should be known.

• The availability of the public mains at the locally powered VE.

The energy consumption of remote powered VEs can be calculated from:

• the energy consumption of the telecommunications and other equipment installedin these cabinets.

• the charging energy consumption of the local batteries (the necessary back-uptime depends on the availability of the public mains at the remote feeding VE!).

• the energy losses (transformers, power lines).



The summed energy demand at the connection point of the public mains (at the remotepowering VE) can be calculated from the summed serviceable remote feeding energydemand and the local energy demand (including the energy demand of the localbattery).

Comparing Scenario 1 and 2 it is apparent, that the availability of the public mains hasa great importance and impact in case of Scenario 2.

6.4 Guideline to implement the cluster remote powering solution

We are not attempting to provide a step by step engineering guide but rather an aid todimension critical components.

6.4.1 Dimensioning of transformers

Transformers can be easily dimensioned due to the fact that the inductivity andcapacity of the cables can be neglected if the distance doesn’t exceed 10 km and thevoltage is below 2 kV. The first step is to know the maximum power drawn percabinet. A physical limit is about 120W of heat dissipation inside the cabinet and canbe assumed as maximum. The power factor at the input of the transformer in the VEcan be assumed to be 0.9 and the efficiency to be 90%. This gives a result of 150VA atthe input of the cabinet. It is recommended to dimension the transformers in the VEswith a slightly high output voltage at no-load, e.g. 245V. This approach will preventany problem in case of short circuits.

The primary transformer must be calculated to deliver the amount of power in VAnecessary for the total number of VEs plus the power losses in the cable. The outputvoltage at no-load should be equal to the nominal input voltage at the VE.

6.4.2 Calculation of the cable cross section

The required cable cross section of a given topology can be calculated for a singlephase system with the following formula:

( )∆U

P l Rw Xl

U=

+. . . .cos .sin

.cos

1002

ϕ ϕϕ

where:

P: transmitted power [kW]

l: distance [m]

Rw: specific cable resistance [Ω/km]

Xl: specific cable inductance [Ω/km]

U: nominal voltage [V]

∆U: Voltage drop [%]

ϕ: phase angle of the load

The plots below (Figure 25 to Figure 28) are calculated for a single copper wire at atemperature of 20°C. This means that the length should be multiplied by a factor of 2.

The load is assumed to be linear at cos ϕ=0.9 and the frequency is 50 Hz.



Since we are working with low voltage and not high voltage, the choice of the voltagelevel should not exceed 1000V in any case for economical reasons.

Taking care of transformer tolerance and a low security margin, a nominal voltage of900V is a suitable choice.

As a first approach in our calculations let’s to start calculations assuming a ∆U of 3%.

The 230V plot of Figure 28 is useful for low distance distribution in cluster topology.

The 400V plot of Figure 27 can be used for remote powering on existing copper pairbut be careful with crosstalk effects depending on the cable type.

A power ratio of min. 1:4 between the main transformer and the biggest clustertransformer should be observed. This will guarantee a good rejection of short-circuits.

The given formula is not suitable to calculate a ring topology. For this purpose anySPICE based simulation program can be used. However, the ring topology has someproblems with the dimensioning of the fuses.

0.01

0.1

1

1010000 100000 1e+006 1e+007

A [m

m2]

P.l [W.m]

Cable cross section in function of P.l; U=1000[V]

0.5%1%2%3%5%7%

10%15%

Figure 25 Dimensioning plot for 1000V



0.01

0.1

1

1010000 100000 1e+006 1e+007

A [m

m2]

P.l [W.m]


0.5%1%2%3%5%7%

10%15%


0.01

0.1

1

1010000 100000 1e+006 1e+007

A [m

m2]

P.l [W.m]


0.5%1%2%3%5%7%

10%15%




0.01

0.1

1

1010000 100000 1e+006 1e+007

A [m

m2]

P.l [W.m]


0.5%1%2%3%5%7%

10%15%


6.4.3 Examples using the plots above

Example 1:

Voltage: 900V

P1 = 600W; l1 = 1300m

P2 = 300W; l2 = 1500m

Drop 5%

load cos ϕ = 0.9

P.l = 600 x 1300 x 2 + 300 x (1300 + 1500) x 2 = 3.24e6 [Wm]

in the 900V plot (Figure 26) for 5% drop is a cross section of 1.7 [mm2] given

The practical choice of 2.5 [mm2] (next cross section) can be made and a reversecalculation give approx. 3% of voltage drop.

Example 2:

Voltage: 400V

P1 = 120W; l1 = 600m

Drop: 10%

load cos ϕ = 0.9

P.l = 120 x 600 x 2 = 144e3 [Wm]

in the 400V plot (Figure 27) for 10% drop is a cross section of 0.2 [mm2] given

The transport can be realised with existing copper pairs (e. g. d = 0.6 or 0.28 [mm2]).



Here, the restriction of 60 mA given in EN 60950 per copper pair must be applied.Now, we can calculate the current and the number of pairs.

I = P / U x cos ϕ = 120 / 400 x 0.9 = 333 [mA]

n = I / 60mA = 333mA / 60mA = 5.55 pairs

This means that min. 6 parallel copper pairs should be used.

The back calculation for 400 [V], 1.68 [mm2] and 144e3 [Wm] give a voltage drop of< 3 [%].

6.5 Space saving considerations

Figure 29 illustrates the space saving that can be achieved through the introduction ofremote AC powering in case of an existing broadband cabinet (ONU).

Figure 29 The framed area shows the possible space saving in an actual ONU

The space saving comparison between local powering and remote AC poweringdepends also on the local regulation of the energy supplier. Figure 29 shows anextreme case, where a very large power meter is used, but the space saving can easilyreach 30% of the inner space of the cabinet.



References

[1] European Standard EN50091-1 - “Uninterruptible power systems (UPS) Part 1:General and safety requirements”; 1993

[2] European Standard (Telecommunication series) EN 300 386-2 – “Electromagneticcompatibility and Radio spectrum Matters (ERM); Telecommunication networkequipment; Electromagnetic Compatibility (EMC) requirements; Part 2: Productfamily standard”; 1997

[3] European Standard (Telecommunication series) ETS 300 132-1 – “EquipmentEngineering (EE); Power supply interface at the input to telecommunicationsequipment; Part 1: Operated by alternating current (ac) derived from direct current(dc) sources”; 1996

[4] European Standard EN 61000-4-5 – “Electromagnetic Compatibility (EMC); Part4: Testing and measurement techniques; Section 5: Surge immunity Test”; 1995

[5] EURESCOM Project P614 Deliverable 12 – “Definition of the suitable poweringissue”; August 1998

[6] EURESCOM Project P518, "Telecommunications and the Environment",Deliverable 3.4, 1997

[7] „Remote power feeding – Report from a field trial“, S.E. Söderberg: EricssonComponents AB, J. Akerlund: Telia AB, INTELEC 1998

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BOBAN - Building and Operating Broadband Access Network