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Project P917-GI
BOBAN - Building and Operating Broadband Access
Network
Deliverable 7
Medium voltage AC access network and customer equipment powering
Suggested readers:
Managers, strategic planners, researchers and consultants involved in the field of broadband
access networks equipment and outside plant technologies
For full publication
May 2000
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 EURESCOM
PARTICIPANTS, 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 a
license from the proprietor of that information.
Neither the PARTICIPANTS nor EURESCOM warrant that the information contained
in the report is capable of use, or that use of the information is free from risk, and
accept no liability for loss or damage suffered by any person using this information.
This document has been approved by EURESCOM Board of Governors for
distribution to all EURESCOM Shareholders.
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
Preface
Broadband access network introduction has been discussed extensively during the last
ten years within different research programmes in Europe. The search for a common
and ultimate strategy, guidelines and set of technologies somehow hampered real field
deployment.
In any case the number of users who can really enjoy broadband services are not in
proportion with the efforts put into standardisation over the years and V.34 modems
still 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 of
technologies are ready today or on the verge to be effectively exploited in
implementing the broadband access infrastructure. Unfortunately, and despite of the
standardisation efforts, the variety of technologies is made even more complex by the
differences among vendor specific implementations.
After the successful experience of EURESCOM Project P614 “Implementation
strategies for advanced access networks”, that addressed introduction scenarios and
technology appraisal, the BOBAN Project takes on board to investigate a wide range
of issues insufficiently covered so far, such as testing, installation and operation of
broadband access networks.
The quick evolution of the involved technologies and the major changes under way in
the telecommunication industry warrant a short study period to review the state of the
art, after which the laboratory trials and demonstrator implementations can start.
It is also understood and incorporated into the BOBAN approach, that the access
networks will be based on a variety of technologies, and a major challenge will be to
assure consistent operation across different systems.
BOBAN also aims to reflect the ideas raised and proposals discussed during the
EURESCOM Senior Managers Conference (4th June 1998).
The main objectives of BOBAN are to:

gain experience with the operation and management of some broadband access
systems;

develop methodology and procedures for access network monitoring and
supervision;

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 systems
available or under development;

understand the opportunities and the challenges of new powering solutions;

develop requirements and demonstrate a prototype of broadband access cabinet
including powering and mechanical parts;

identify possible application scenarios and evaluate WDM systems for the access
network;
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Medium voltage AC access network equipment powering
Deliverable 7

elaborate the specification for a common broadband access network planning
tool;

identify guidelines for optical access systems deployment

define scenarios and guidelines for a cost effective migration of FTTH in the
access network.
It is expected that the findings of the BOBAN Project will significantly contribute to
the Shareholders strategic decisions on how to upgrade their access networks to
accommodate broadband services.
This Deliverable is one out of a series of Deliverables BOBAN is producing to
summarise its findings in the different aspects it is studying. This Deliverable reports
on the results of the investigations done regarding the powering solutions in the access
network.
The results summarised in this Deliverable are particularly relevant for managers,
strategic planners, researchers and consultants involved in work regarding the
powering issues of broadband access networks equipment.
page ii (ix)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
Executive Summary
Why introduce remote powering?
In a liberalised telecommunications market and with the upcoming unbundling
policies, where the customer can choose the service/access provider, the downtime of
networks (and the consequent loss of revenue) represents a key aspect of the quality of
service for operators. In order to maintain networks with minimal downtime due to
power outages, companies need cost effective and reliable powering of the outdoor
plants.
Furthermore, the relative distribution of the power requirements in the central office
compared to those for the access network and customer equipment is shifting in an
unprecedented way. Ten years ago, more than 90% of the power consumption took
place 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 increased
complexity of customer equipment, distributed intelligence and power hungry
broadband technology in the access network and at the customer premises. Various
solutions have been proposed to power the access network equipment with DC
powering over the existing telecom cables and /or local AC powering with battery
backup. The drawback of these solutions is that they can either supply low power for
an extended period of time (remote feeding through existing copper cables) or they
can 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 access
network equipment. It should be of interest to anyone involved in the planning and
engineering of powering aspects in outside plant technologies since it provides a good
introduction and takes account of the technical and economic aspects of these
technologies. In addition, the results of the presented laboratory trials can serve as
practical guidelines for the planning personnel with regards to available hardware
components and regulatory issues.
The benefits for your company
The 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 in
the report indicate that remote 1000VAC powering is a technically feasible and
reliable solution especially for powering multiple cabinets when power cables can be
installed in existing infrastructure. The results of the laboratory trials performed
demonstrate and prove the simplicity and the robustness of the adopted topology.
 2000 EURESCOM Participants in Project P917-GI
page iii (ix)
Medium voltage AC access network equipment powering
Deliverable 7
D7 presents the results of the laboratory tests in detail. The following tests and their
results are covered in particular:

Efficiency and voltage drop measurements with different loads

Inrush peak current at the turn on, minimised with the use of standard
transformers

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 European
countries
What next?
EURESCOM Shareholders are in the process to upgrade their access network for the
delivery of broadband services. This Deliverable presented a new technology and
strategy for long term low power energy back-up. The proposed technology was
succesfully tested and it is now time to reap the benefits of this work through
implementing the technology in the access networks of the EURESCOM
Shareholders.
page iv (ix)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
List of Authors
Enrico Blondel, Swisscom Ltd.
Zoltán Janklovics, Matav, HT
Gábor Gerdai, Matav, HT
Fernando Morgado, Portugal Telecom, PT
Didier Marquet, CNET, FT
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Table of Contents
Preface ............................................................................................................................. i
Executive Summary ...................................................................................................... iii
List of Authors ............................................................................................................... v
Table of Contents .......................................................................................................... vi
Abbreviations .............................................................................................................. viii
Definitions ..................................................................................................................... ix
1
Introduction ............................................................................................................ 1
1.1 Motivation .................................................................................................... 2
1.2 Medium or “increased voltage” .................................................................... 3
2
Study on regulatory aspects .................................................................................... 4
2.1 Overview of the national restrictions ........................................................... 4
2.1.1 Introduction ..................................................................................... 4
2.1.2 Answers ........................................................................................... 4
2.1.3 Analysis of results ........................................................................... 5
2.2 Safety considerations.................................................................................... 5
2.2.1 Effect of Operating Procedures On Safety ...................................... 5
2.2.2 Avoiding Current Paths ................................................................... 5
2.2.3 Maximising Contact Resistance ...................................................... 6
2.2.4 Precautions for service personnel .................................................... 6
2.2.5 Other considerations ........................................................................ 6
3
Evaluation study and identification of an optimised solution for remote
powering ................................................................................................................. 7
4
Analysis of the RFI ................................................................................................. 8
4.1 Goal .............................................................................................................. 8
4.2 Results .......................................................................................................... 8
4.2.1 Single phase transformers ............................................................... 8
4.2.2 AC-DC power supply systems ........................................................ 9
4.2.3 DC-AC inverters.............................................................................. 9
4.2.4 Cables .............................................................................................. 9
5
Laboratory trial description and results ................................................................ 10
5.1 Laboratory set-up ....................................................................................... 10
5.1.1 Scheme .......................................................................................... 10
5.1.2 Transformers ................................................................................. 10
5.1.3 Loads ............................................................................................. 10
5.1.4 Cables ............................................................................................ 11
5.2 Test description .......................................................................................... 12
5.3 Results ........................................................................................................ 13
5.3.1 Efficiency and voltages measurements ......................................... 13
5.3.2 Inrush current measurements......................................................... 14
5.3.3 Short dips and interruptions .......................................................... 14
5.3.4 Short circuit rejection .................................................................... 15
5.3.5 Surge protection / filtering ............................................................ 16
5.3.6 Cables measurements .................................................................... 20
6
Impact on network planning ................................................................................. 23
6.1 Planning considerations.............................................................................. 23
page vi (ix)
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Deliverable 7
6.2
6.3
6.4
6.5
Medium voltage AC access network equipment powering
6.1.1 Investment costs ............................................................................ 23
6.1.2 Maintenance costs ......................................................................... 23
Scenario 1 – Centralised powering ............................................................ 24
6.2.1 Features ......................................................................................... 24
6.2.2 Planning aspects ............................................................................ 25
Scenario 2 – Cluster powering ................................................................... 25
6.3.1 Features ......................................................................................... 26
6.3.2 Planning aspects ............................................................................ 26
Guideline to implement the cluster remote powering solution .................. 27
6.4.1 Dimensioning of transformers ...................................................... 27
6.4.2 Calculation of the cable cross section ........................................... 27
6.4.3 Examples using the plots above .................................................... 30
Space saving considerations ...................................................................... 31
References.................................................................................................................... 32
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Medium voltage AC access network equipment powering
Deliverable 7
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

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
page viii (ix)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
Definitions
Remote powering is the ability to provide power to the equipment from a far placed
uninterruptible source of energy.
Cluster in this case is the point of arrival of the medium or increased voltage line and
the 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 still
under 1000Vrms and submitted to the low voltage regulation.
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page ix (ix)
Deliverable 7
1
Medium voltage AC access network equipment powering
Introduction
The need for power in the Central Exchange (CE) will decrease in the coming years
due to the increasing amount of Virtual Exchanges (VE) moving the broadband access
point near to the customer. The number of VEs makes the maintenance of backup
service
area
power (batteries) in each VE Access
difficult
and
expensive. The evolution of the access
network will follow the way shown in the Figure 1 and Figure 2.
5.5 km
maximum
CE
Serving edge
Fig. 1 Today solution: each customer is directly connected to the CE
VE
Shortened
serving edge
VE
CE
5.5km
maximum
Current
exchange
serving
edge
2-3 km
maximum
VE
VE
Fig. 2 Future solution: a group of customers will be connected to a VE, each VE
connected to the CE
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Medium voltage AC access network equipment powering
Deliverable 7
The basic network topology shown in the figures above can be used to provide power
from the CE to the VE in the same way using the reliable power facilities still existing
in 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 to
perform 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 in
the access network. With the proposed solution it becomes possible to eliminate some
of 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 the
required manpower investment.
1.1
Motivation
Efficient usage of the space in the street cabinets has a great impact on the overall cost
of the access network. The place taken by metering, fuses and batteries in a standard
broadband cabinet can vary between 20% and 40% of the inside volume. With the
introduction of remote powering technology in a clustering manner offers the
advantages of increased reliability, simplification of the monitoring equipment and
reduced maintenance on serviceable parts beside the crucial space saving in the
cabinets by eliminating the batteries.
Another major motivation is the European Telecommunications Environmental
Charter. It is a common environmental policy of the signatories who commit
themselves to improve their environmental performance. To achieve this, an ETNO
working 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 environmental
benefits; and

a determination to manage our own operations in a way that minimises negative
environmental impacts.
The proposed solution of remote powering is fully in line with the objectives of the
ETNO Charter.
page 2 (32)
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Deliverable 7
1.2
Medium voltage AC access network equipment powering
Medium or “increased voltage”
The use of the term “Medium Voltage powering “ is due to the fact that the choice of
the powering voltage will not be considered as mandatory in this report. The goal is to
try to find a compromise between power level, voltage and distance that can satisfy
reliability and costs goals. The choice of a voltage as high as possible but as cheap as
possible imposes some restrictions on the choice of the voltage. One of the criteria is
the cost of medium voltage hardware which is very high compared to the low voltage
hardware. In such cases we can speak of increased voltage remote powering.
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page 3 (32)
Medium voltage AC access network equipment powering
2
Study on regulatory aspects
2.1
Overview of the national restrictions
2.1.1
Introduction
Deliverable 7
Before proceeding with the detailed study it is necessary to provide an overview of the
existing national standards, regulations and restrictions regarding remote powering to
estimate its feasibility.
An extended regulatory study covering the countries of the Project participants was
performed with the following questions:
2.1.2
1.
Is it allowed in general, to put together telecom (copper or fibre) and
energy/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 (AN
Cabinet or any other kinds of remote equipment) ?
5.
Are there any restrictions regarding the length or the voltage, if the voltage is
smaller than 1kV ?
6.
Are there any restrictions regarding the length or the voltage, if the voltage is
higher 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 regulatory
body ?
Answers
The Table 1 summarises the answers received in the extended regulatory study and
shows 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
--
--
--
--
--
--
--
page 4 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
Country
PT
Question
1.
2.
3.
4.
5.
6.
7.
8.
No
Yes
Law
Yes
No
No
Yes
No
70%
0%
10%
20%
50%
% of Yes 60 %
90%
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 own
outside plant equipment without important restrictions.
Q3: in each Country, the laws, security and safety considerations must be taken into
account and they could be very restrictive.
Q5 and 6: The voltage level and the distance are mostly not limited but some
economical considerations could have an important impact on the choice of the
voltage and the maximum distance.
Q7 and 8: It may be possible for electric utility companies to have a contract with the
municipality 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 foregoing
physiological responses occurring. The possibility of a response at a given voltage
level depends on the precautions taken in working with that voltage. These
precautions can range from minor measures (for sufficiently low voltages) to requiring
de-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 current
paths are unavoidable, maintaining the highest feasible contact resistance (total body
impedance).
2.2.2
Avoiding Current Paths
The use of insulation to preclude the formation of current paths through the body is
perhaps the most familiar of precautions. To this must be added such other forms of
protection as placement out of reach, or, for higher level voltages, providing baffles or
enclosures. Forms of insulation that rely in part on proper craft procedures are the use
of insulated tools and, for higher level voltages, insulated gloves. The intent of all
these is to prevent the establishment of a current path by preventing direct contact with
the energised conductors.
An effective precaution of minimising the creation of current paths involves
contacting only one conductor at a time. In essence, contact with an energised
conductor need not be avoided if, simultaneously, contact with earth grounded
conductors is avoided. Owing to the prevalence of grounded surfaces near
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Medium voltage AC access network equipment powering
Deliverable 7
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 arise
situations in which personnel will intentionally contact the energised conductor. The
current that results from this contact is limited by the combined skin impedance of the
contact points with the voltage and with the earth. This impedance will be largely
determined by the area of contact and wetness of the skin (voltage and frequency of
the source are also important, but these parameters are not under the control of the
individual contacting the source). Accordingly, personnel should make the minimum
area of contact possible, be mindful of large area contacts arising from leaning to or
lying on grounded surfaces, and attempt to maintain dry contacts.
The labelling of known appearances of high level voltages can serve to alert personnel
to appearances that require special precaution. Personnel encountering such a labelled
appearance should be instructed to follow recommended precautions to preclude
inadvertent 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 operations
being 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 exposed
circuits so that danger will be recognised and special work measure can be
applied,
d.) special safety precautions for the personnel during the work, such as switching
off, 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 may
occur, service personnel should not work alone.

Only personnel who have been instructed should be allowed to work on lines in
which voltages exceeding the safety limits.

When using insulating clothing (gloves, shoes), or insulated tools, or electrical
equipment 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 is
adequate and intact.

In order to avoid the use of special safety precautions, the work should be done at
times when the inducing line can be disconnected from its power supply.
page 6 (32)
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Deliverable 7
3
Medium voltage AC access network equipment powering
Evaluation study and identification of an optimised
solution for remote powering
This study will open the possibility to adopt the remote powering technology even at
medium to low power levels with extended backup time for the access network of the
future.
Further, eliminating batteries at the remote site will provide an environmentally
friendly solution.
After many trials to sketch a unique solution for all the possible topologies, the cluster
topology seems to be the best approach. It is flexible enough and can be adapted to
each case without modifying the concept.
This is the base idea used for all the investigations made on this Deliverable.
CE
C1
C2
Figure 3 Basic cluster powering topology
The cluster topology described in Figure 3 shows the selected solution for
measurements in the laboratory. In reality, the physical position of cluster C1 or C2
may be different and in some cases it could be combined in one of the cabinets or
placed anywhere (manhole, underground cabinet etc.).
The distance between CE and C2 should not exceed 5 to 6 km.
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Medium voltage AC access network equipment powering
4
Analysis of the RFI
4.1
Goal
Deliverable 7
The first goal of the RFI (Request For Information) was, to get an overview on the
existing and available hardware components on the European market to be used to
build a safe and simple remote powering distribution network.
The second goal was to provide information on the additional hardware to be included
in the CE.
The RFI was conducted in the form of a questionnaire which had the following
structure:

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 are
given 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 great
effort to obtain answers from the manufacturers. We could proceed with the analysis
only after receiving sufficient responses. Only 36% of the contacted manufacturers (13
out of the 36 contacted) gave satisfactory responses, even after repeated urging and
contacts.
4.2.1
Single phase transformers
Some important trends are emerging from the information received from the
manufacturers:

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 safety
specifications; they are also bulky and expensive.

The temperature range and IP (International Protection) degree must be specified
depending on the environmental conditions.
Following minimal specifications should be applied when the transformer is installed
in 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 temperature
range of +5 C to +40 C should be sufficient for the primary transformer.
page 8 (32)
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Deliverable 7
4.2.2
Medium voltage AC access network equipment powering
AC-DC power supply systems
There is a significant market of power systems in Europe. A number of manufacturers
are offering modular power supplies built of 100W and 300W modules designated for
local powering and having a dedicated controller and battery supervision with a range
of features. If remote powering is implemented, then there will be no need for such a
sophisticated 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 remote
powering. Now the need of a modular inverter can improve the reliability of the
topology. Some manufacturers are providing modular systems with different
approaches for the regulation and load sharing between modules. A bypass is also
offered to improve reliability in case of inverter failure. 1 kW and 3 kW single phase
modules are available on the market.
4.2.4
Cables
Cables for this purpose are available on the market. Experience shows, that for a
length 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 the
European market (only in the US). This is because in Europe the mains network is
three-phase and the cross section of the outer layer is always a third of the core cross
section.
 2000 EURESCOM Participants in Project P917-GI
page 9 (32)
Medium voltage AC access network equipment powering
5
Laboratory trial description and results
5.1
Laboratory set-up
Deliverable 7
The adopted solution reflects the cluster topology described above. The hardware used
is standard (low cost). The adopted voltage is 1000 V.
5.1.1
Scheme
230V Mains
1000V
Transformer
1.7 km LISN
2 Cabinet
simulation
300VA
1000V
Transformer
6.6kVA
UPS
Transformer
1.7 km LISN
4kVA
3 Cabinet
simulation
500VA
PE
Figure 4 Scheme of the laboratory setup
5.1.2
Transformers
The primary transformer used is a 4kVA / 50Hz / 230V primary and 500V/1000V
secondary voltage.
The secondary transformers are 300 VA and 500VA / 50Hz / 1000V/500V primary
and 230V secondary voltage. The secondary transformers are designed with the
following 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, the
primary transformer, which is located at the CE, can provide power for about 20
broadband 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
page 10 (32)
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Deliverable 7
Medium voltage AC access network equipment powering
Resistive loads are non-inductive ceramic resistors placed on a heat-sink and cooled
with a fan. They simulate a load of 120W per cabinet.
The choice for the resistive load is the following:
2 cabinets: 220 / 240W
3 cabinets: 147 360W
Each BB-Cabinet was simulated with a non-linear load according to EN50091-1 [1]
Rs
C
Rl
Uin
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 []; Rl=238 [] ;C= 628 [F]
300VA: Rs = 7.0 []; Rl = 397 [] ;C= 377 [F]
The practical values are:
500VA: Rs = 4.2 []; Rl=132 + 132//519 []; C= 470 + 220 [F]
300VA: Rs = 7.0 []; Rl = 270 + 132 []; C= 220 + 100 [F]
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 with
a Line Impedance Simulation Network (LISN), which is assembled with a
combination of resistors and capacitors to simulate long lines. The LISN is capable to
simulate 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)
 2000 EURESCOM Participants in Project P917-GI
page 11 (32)
Medium voltage AC access network equipment powering
Deliverable 7
Figure 6 Cables used for the trials: unscreened (left) and screened (right)
Power source
Load
Secondary
transformer
LISN
Primary transformer
Figure 7 Laboratory set-up with the power source in the background, the nonlinear 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 trials
was to get significant and relevant results to be considered by the engineering people
when 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
page 12 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7

Medium voltage AC access network equipment powering
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 1.7km
LISN using a precision power analyser.
The Table 2 shows the results for the two types of load including all information of the
setup 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;
Pout500 = 509.12 W;
Uout = 235V;
Iout = 2.12A;
PFout = 0.71
Uout = 231.42 V;
Iout = 2.20 A;
PFout = 1.0
Pout300 = 220W;
Pout300 = 304.08 W;
Uout = 234V;
Iout = 1.26A;
PFout = 0.74
Uout = 230.37 V;
Iout = 1.32 A;
PFout = 1.0
Line Simulation
7 x 110nF + 6 x 5
7 x 110nF + 6 x 5
Efficiency
 = 0.721
 = 0.796
 = (Pout500 + Pout300) / Pin
Table 2 Efficiency measurements
Voltage measurements at different points are shown in the Figure 8
Transformer
Transformer
3 Cabinet
simulation
LISN
500 VA
4 KVA
Transformer
2 Cabinet
simulation
LISN
300 VA
Loads
300VA + 500VA
500VA
300VA
Uin
229.32
229.40
229.43
Uhvin
1013.7
1014.8
1015.4
Uhv500
1004.1
1009.1
1011.8
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U500
234.79
235.77
242.35
Uhv300
1000.7
1008.6
1007.8
U300
234.03
242.70
235.58
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Medium voltage AC access network equipment powering
Deliverable 7
Loads
240W + 360W
360W
240W
Uin
229.19
229.33
229.44
Uhvin
1012.0
1013.8
1015.0
Uhv500
998.5
1004.7
1009.2
U500
231.42
232.78
242.25
Uhv300
993.5
1004.4
1004.1
U300
230.50
242.20
232.86
Loads
No load
Uin
229.60
Uhvin
1016.7
Uhv500
1015.6
U500
243.76
Uhv300
1015.2
U300
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 primary
transformer 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 is
to show the quality of the HV link when a load (equipment) is plugged in. The worst
case of inrush current is achieved with a non-linear load (charging of the input
capacitors with a high current peak).
inrush current measurement
40
Uin
Iin
30
Uin/10[V]; Iin[A]
20
10
0
-10
-20
-30
-40
-50
-60
0
0.05
0.1
0.15
0.2
Time [s]
Figure 9 Inrush current of the primary transformer
From our measurements some general conclusions can be drawn. The inrush current
capability of the source is a very important criterion for the engineering of the
transformers. The inrush current of the primary transformer should meet the limits of
ETS 300 132-1[3]. Due to this limitation, it is not recommended to use toroidal
transformers.
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
page 14 (32)
Test 2
Test 3
Test 4
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Medium voltage AC access network equipment powering
Voltage drop >95%
30%
40%
>95%
Duration
500 ms
200 ms
5000 ms
10 ms
Requirement
(see remark)
Result
Complies

No over voltages

No over currents

No oscillations

No fuse blowing
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 the
mentioned standard. The performance criteria described in EN 300-386-2 [2] are not
applicable.
5.3.4
Short circuit rejection
This trial demonstrates the excellent behaviour of the system regarding short-circuit
rejection in a fault situation.
Uout
Uin,Iin
Transformer
Transformer
4 KVA
500 VA
LISN 1.7 km
Transformer
3 Cabinet
simulation
2.5A T or F
2 Cabinet
simulation
300 VA
Iout, short circuit point
Figure 10 Short circuit rejection test set-up scheme
The fault was produced on the secondary side of the 300VA transformer with a
switch. The fuse was intentionally chosen to be twice the rating of the transformer to
simulate a worst case situation.
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
Deliverable 7
short-circuit with a fuse of 2.5A fast blow
40
Uin
Iin
Uout
Iout
Uin/10[V]; Iin[A]; Uout/10[V]; Iout[A]
30
20
10
0
-10
-20
-30
-40
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Time [s]
Figure 11 Short circuit rejection with a 2.5 A fuse fast blow
short-circuit with a fuse of 2.5A slow blow
50
Uin
Iin
Uout
Iout
Uin/10[V]; Iin[A]; Uout/10[V]; Iout[A]
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
Time [s]
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 60ms
blowing time can be expected without significant voltage drop at the far end of the
system.
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 the
surge pulse, according to EN61000-4-5 [4], is applied at the input of the primary
transformer .
page 16 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
2.
Medium voltage AC access network equipment powering
to get out figures from lightning applied direct on the duct or pipe choosing the
worst case of metal pipes.
For the first test, the set-up is the same as the one shown in Figure 10 and the voltage
observed is always the one at the secondary side of the 500VA and at the secondary
side 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 behind
the 300VA transformer (#12 C)
The coupling voltage is 2 kV L-PE. Behind the 500VA transformer a surge of about
120V 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 the
decoupling network and the non-linear load.
The set-up for the second trial was realised with the aid of a big overvoltage generator
of 100kA surge capability as shown in Figure 15.
 2000 EURESCOM Participants in Project P917-GI
page 17 (32)
Medium voltage AC access network equipment powering
Uin
Transformer
Deliverable 7
960 m cable
Ch. A
4 KVA
Overvoltage
generator
4 m pipe
shunt
40 m cable
Transformer
Uout
Ch. B
3 Cabinet
simulation
500 VA
LISN 1.7 km
Transformer
2 Cabinet
simulation
300 VA
Figure 15 Lightning protection test set-up scheme
Figure 16 Generator with the metal pipe in the foreground and a snapshot of the
current waveform during the test (ev. #90)
The tests were carried out at two selected cables. The peak current was increased from
about 10kA to 40kA in 10kA steps, which represents a realistic lightning impact on
the cable. The transients on the input and output voltage were recorded.
page 18 (32)
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Medium voltage AC access network equipment powering
Table 4 shows the measurement results for the stock cable. The ground wire was
connected to the ground at both ends.
Peak shunt
voltage
[Vpk]
Peak shunt
current
[kApk]
Transient voltage at
the input
[Vpp]
Transient voltage at
the 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 peak
current with the unscreened cable
Table 5 shows the measurement results for the order made screened cable. The screen
was connected to the ground at both ends.
Peak shunt
voltage
[Vpk]
Peak shunt
current
[kApk]
Transient voltage
at the input (Uin)
[Vpp]
Transient voltage at
the 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
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Medium voltage AC access network equipment powering
Deliverable 7
Figure 18 Input (#90A) and output (#90B) voltage waveforms at -38kA peak
current 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 15
kV. The attenuation of the injected signal is very important, and the experiment
shows, that after 40m, the signal is smaller than 100V and practically disappears.
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 the
attenuation of the cables.
Unscreened 3x4 mm2
100
90
80
Transmission
Reflection
70
Impedance [ohms]
5.3.6
60
50
40
30
20
10
0
0.0
5.0E+06
10E+06
15E+06
20E+06
25E+06
30E+06
Frequency [Hz]
Figure 19 Impedance measurements up to 30 MHz on the unscreened cable
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Medium voltage AC access network equipment powering
Unscreened 3x4 mm2
90
Transmission
80
Reflection
70
Attenuation [dB/km]
60
50
40
30
20
10
0
0
5000000
10000000
15000000
20000000
25000000
30000000
Frequency [Hz]
Figure 20 Attenuation measurement up to 30MHz on the unscreened cable
Screened 2x4mm2
100
Transmission
90
Reflection
80
Impedance [ohms]
70
60
50
40
30
20
10
0
0
5000000
10000000
15000000
20000000
25000000
30000000
Frequency [Hz]
Figure 21 Impedance measurement up to 30MHz on the screened cable
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Screened 2x4mm2
60
Transmission
Reflection
50
Attenuation [dB/km]
40
30
20
10
0
0
5000000
10000000
15000000
20000000
25000000
30000000
Frequency [Hz]
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 great
advantage of the screened cable is in its mechanical strength and the ease of ist
installation 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 copper
cables in the same duct or pipes.
page 22 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
6
Medium voltage AC access network equipment powering
Impact on network planning
Several solutions exist for medium voltage AC access network powering. For the
proper 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 the
site of the installation), etc.
The network structure should be chosen first. Two scenarios are possible:
6.1

Centralised powering, and

Cluster powering
Planning considerations
General aspects should be taken into consideration in case of planning of the new
systems:

Choice of the right solution according to the input conditions (power
consumption, distances, using the existing possibilities, applicable devices, other
considerations).

Checking of the operating conditions of the elements of the chosen solution (for
example, the equipment installed in the street cabinets should tolerate more
extreme 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. Both
investment and maintenance costs should be taken into account.
6.1.1
Investment costs
The investment costs of the power system consist of three parts:
6.1.2

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)
Maintenance costs
The main aspects are the following:

energy costs

costs of the monitoring, repairing of the broken equipment, changing of the
damaged equipment and batteries
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
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The energy costs consist of three parts:
6.2

monthly price of the reserved energy

used (measured) energy consumption

penalties (for the wrong power factor, energy overstepping)
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 and
remote feeding. Each VE is powered by the CE with remote feeding. Each VE has a
pair of transformers. All the low voltage/medium voltage transformers are installed in
the CE and the medium/low voltage transformers are installed in the VEs.
CE
VE1
Tr
m/l
Tr
l/m
AC
UPS
Telecom lines
Tr
l/m
Tr
m/l
Medium voltage power lines
VEn
Tr m/l: 1000V/230V transformer
Tr l/m: 230V/1000V transformer
Medium voltage power lines
Telecomunication 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 for
increasing the availability, but it is not necessary).
The power consumption of the powered VEs is limited (by the transformers and
cables).
page 24 (32)
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Deliverable 7
6.2.2
Medium voltage AC access network equipment powering
Planning aspects
The starting points are the following:

The number and energy demand of the powered VEs, as well as the distances
between 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 for
dimensining the AC UPS installed in the CE. Another criterion is the availability of
the primary AC power source. The necessary back-up time of the batteries depends on
this parameter. (Note: Generator sets are installed in the larger CEs. This fact should
be considered in the calculation of the resulting availability. Further information can
be found about these questions in earlier EURESCOM documents, (e.g.: in the P614
Deliverable 12 [5]).
Batteries can be dimensioned according to the power consumption and the back-up
time. The energy demand of the AC UPS consists of
6.3

the total summed serviceable energy demand,

the charging energy (for batteries)

the losses of UPS (on account of efficiency)
Scenario 2 – Cluster powering
In case of cluster powering, a chosen VE (street cabinet, etc.) feeds the other VEs (and
the customer premises) (see Figure 24). The feeding VE has a connection to the public
mains and its equipment is locally powered by its local power supply with back-up
batteries. The other VEs are powered by medium voltage AC powering. Each VE has
a pair of transformers. All the low voltage/medium voltage transformers are installed
at the feeding VE via an AC distributor unit. The feeding VE doesn’t contain AC
UPS, because usually it has not got enough space for this equipment. Therefore the
powered VEs should contain local power supply with back-up batteries.
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
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Public mains
VEfeeding
AC
distribution
VE1
Local
power
supply
Tr
m/l
Tr
l/m
To the CE
Local
power
supply
Telecom lines
Tr
l/m
Tr
m/l
Medium voltage power lines
Local
power
supply
VEn
Tr m/l: 1000V/230V transformer
Tr l/m: 230V/1000V transformer
Medium voltage power lines
Telecomunication line
Figure 24 Cluster powering (medium voltage AC powering)
6.3.1
6.3.2
Features

This system doesn’t contain AC UPS and, therefore, back-up batteries should be
installed on each site (together with the local power supplies).

The power consumption of the powered VEs consists of the power demand of the
telecommunication and auxiliary equipment and the charging power of the backup batteries.
Planning aspects
The criteria are the following:

The number and energy demand of the locally powered VE and all the remote
powered VEs, and the distances between the locally powered VE and each
additional 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 installed
in these cabinets.

the charging energy consumption of the local batteries (the necessary back-up
time depends on the availability of the public mains at the remote feeding VE!).

the energy losses (transformers, power lines).
page 26 (32)
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Medium voltage AC access network equipment powering
The summed energy demand at the connection point of the public mains (at the remote
powering VE) can be calculated from the summed serviceable remote feeding energy
demand and the local energy demand (including the energy demand of the local
battery).
Comparing Scenario 1 and 2 it is apparent, that the availability of the public mains has
a 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 to
dimension critical components.
6.4.1
Dimensioning of transformers
Transformers can be easily dimensioned due to the fact that the inductivity and
capacity of the cables can be neglected if the distance doesn’t exceed 10 km and the
voltage is below 2 kV. The first step is to know the maximum power drawn per
cabinet. A physical limit is about 120W of heat dissipation inside the cabinet and can
be assumed as maximum. The power factor at the input of the transformer in the VE
can be assumed to be 0.9 and the efficiency to be 90%. This gives a result of 150VA at
the input of the cabinet. It is recommended to dimension the transformers in the VEs
with a slightly high output voltage at no-load, e.g. 245V. This approach will prevent
any problem in case of short circuits.
The primary transformer must be calculated to deliver the amount of power in VA
necessary for the total number of VEs plus the power losses in the cable. The output
voltage 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 single
phase system with the following formula:
U 
P. l.100. Rw.cos  Xl.sin  
U 2 .cos
where:
P: transmitted power [kW]
l: distance [m]
Rw: specific cable resistance [/km]
Xl: specific cable inductance [/km]
U: nominal voltage [V]
U: Voltage drop [%]
: phase angle of the load
The plots below (Figure 25 to Figure 28) are calculated for a single copper wire at a
temperature 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 =0.9 and the frequency is 50 Hz.
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
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Since we are working with low voltage and not high voltage, the choice of the voltage
level should not exceed 1000V in any case for economical reasons.
Taking care of transformer tolerance and a low security margin, a nominal voltage of
900V 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 pair
but be careful with crosstalk effects depending on the cable type.
A power ratio of min. 1:4 between the main transformer and the biggest cluster
transformer 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 any
SPICE based simulation program can be used. However, the ring topology has some
problems with the dimensioning of the fuses.
Cable cross section in function of P.l; U=1000[V]
0.01
0.5%
1%
2%
3%
5%
7%
10%
15%
A [mm2]
0.1
1
10
10000
100000
1e+006
1e+007
P.l [W.m]
Figure 25 Dimensioning plot for 1000V
page 28 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
Cable cross section in function of P.l; U=900[V]
0.01
0.5%
1%
2%
3%
5%
7%
10%
15%
A [mm2]
0.1
1
10
10000
100000
1e+006
1e+007
P.l [W.m]
Figure 26 Dimensioning plot for 900V
Cable cross section in function of P.l; U=400[V]
0.01
0.5%
1%
2%
3%
5%
7%
10%
15%
A [mm2]
0.1
1
10
10000
100000
1e+006
1e+007
P.l [W.m]
Figure 27 Dimensioning plot for 400V
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
Deliverable 7
Cable cross section in function of P.l; U=230[V]
0.01
0.5%
1%
2%
3%
5%
7%
10%
15%
A [mm2]
0.1
1
10
10000
100000
1e+006
1e+007
P.l [W.m]
Figure 28 Dimensioning plot for 230V
6.4.3
Examples using the plots above
Example 1:
Voltage: 900V
P1 = 600W; l1 = 1300m
P2 = 300W; l2 = 1500m
Drop 5%
load cos  = 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 reverse
calculation give approx. 3% of voltage drop.
Example 2:
Voltage: 400V
P1 = 120W; l1 = 600m
Drop: 10%
load cos  = 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]).
page 30 (32)
 2000 EURESCOM Participants in Project P917-GI
Deliverable 7
Medium voltage AC access network equipment powering
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  = 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 of
remote 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 powering
depends also on the local regulation of the energy supplier. Figure 29 shows an
extreme case, where a very large power meter is used, but the space saving can easily
reach 30% of the inner space of the cabinet.
 2000 EURESCOM Participants in Project P917-GI
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Medium voltage AC access network equipment powering
Deliverable 7
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 – “Electromagnetic
compatibility and Radio spectrum Matters (ERM); Telecommunication network
equipment; Electromagnetic Compatibility (EMC) requirements; Part 2: Product
family standard”; 1997
[3] European Standard (Telecommunication series) ETS 300 132-1 – “Equipment
Engineering (EE); Power supply interface at the input to telecommunications
equipment; Part 1: Operated by alternating current (ac) derived from direct current
(dc) sources”; 1996
[4] European Standard EN 61000-4-5 – “Electromagnetic Compatibility (EMC); Part
4: Testing and measurement techniques; Section 5: Surge immunity Test”; 1995
[5] EURESCOM Project P614 Deliverable 12 – “Definition of the suitable powering
issue”; 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: Ericsson
Components AB, J. Akerlund: Telia AB, INTELEC 1998
page 32 (32)
 2000 EURESCOM Participants in Project P917-GI