LVDC-Redefining Electricity
First International Conference on Low Voltage Direct Current
International
Electrotechnical
Commission
Bureau of
Indian Standards
New Delhi, India,
26 & 27 October 2015
Session B1
Public Electrical Systems-Last Mile
Summary
Tero Kaipia
Session Chairman
Finland
Session speakers:
Dr. Abdullah Emhemed (UK), Mr. Jintae Cho (KR), Mr. Pasi Nuutinen (FI),
Dr. Worajit Setthapun (TH), Dr. Mario Tokoro (JP)
Overview of Use-Cases and Applications
presented
Last-mile LVDC networks on urban areas and LVDC networks
on organised rural or sparsely populated areas
Life cycle economics and material efficiency are the drivers
Applicable both for renovation of existing grids and for grid expansion or
creating local microgrid islands
In renovation of the existing local AC networks by replacing it partly or entirely with
LVDC networks
Benefits are based on increase of transmission capacity, controllability and
safety
long transmission distances (possibly over 10 km), less customers (“range
extender”)
short transmission distance (from hundreds of meters to few kilometers), more
customers (“capacity extender”)
Using earlier installed LVAC cables in LVDC systems and replacing parts of MVAC
network
Converters as parts of protection – new methods for fault identification and
separating
Overview of Use-Cases and Applications
presented
Residential and small-business area microgrids / DC
communities that are a part of the local utility
distribution
Operating both independently from in interaction with the rest of the
utility network (medium voltage, MV)
Superior platform for local energy exchange (markets) and renewables
based living
The same functionalities can be build on top of the last mile LVDC
infrastructure
Benefits are mainly based on improved controllability and respective
flexibility
Motivation for public LVDC distribution
Potential benefits for DSOs
Improved technical performance and
economics
Releases additional
11kV/0.4kV
generation and
demand headroom
Defers
reinforcement
Reduced losses
Better control of peak demands
75% of EU houses are
energy inefficient
Existing MV network
Reduced energy waste and losses
Unipolar
or bipolar
cable
connections
Reduced fault level
Load
Enhanced voltage profile
Load
variable
speed ac
source
More efficient for renewables
Easier to connect multiple
sources, and no phase balance
and synchronisation issues
Powerful ICT platform for
integrating various smart grid
functionalities
1% in EU energy savings
cuts gas import by 2.6%
Better utilisation
of existing assets
Offers more flexible market
mechanism with better
stimulation of customers
More suitable for devices
generate and consume DC
(80% of todays load are DC)
Power converter interfaces are
becoming more mature and their
associated costs are declining
Better control of energy leads to
better market services and consumers
cost savings
Potential benefits for end-users
and society
Introduced use cases
Range extender
UK
MV Supply
Utility DC grid
Capacity extender
Korea
11/0.4kV
NOP
750 VDC underground cable
Local communications network
ADSL/3G internet connection
Finland
CEI 3
DC
AC
Rectifying substation
with directly connected
converterless BESS
Community DC µGrid
19 houses connected
Thailand
DC
AC
AC
DC
Japan
CEI 2
CEI 1
house 1
house 2
house 19
...
switch
switch
switch
350VDC
Power Line
switch
Communication Line
switch
switch
switch
switch
switch
DC
AC
Stakeholders driving Innovation
Visionary research institutes
Push towards sustainable energy systems having innovation
opportunities
Distribution network companies (DNOs, DSOs)
Pressures to improve/renew the networks
(Eco) Communities
Clean and affordable energy and sustainable living
Power electronics manufacturers
In collaboration with above, new business cases
DC entrepreneurs
A new breed looking for innovations to grow business
Governmental bodies (in some countries)
Guidance through regulations and other incentives
Electricity suppliers and other service providers
Infrastructure enabling growing services business
Markets and Market Evolution
Expected breakthrough within the next 5-10 years,
pioneering utilities are already in move:
ScottishPower, Elenia, KEPCO, etc.
Utilities expect proof of feasibility and standardized
solutions
Case studies have shown that remarkable savings can be
achieved
Korea and Finland: ±750 V LVDC can bring 5-10 % total savings for the
DSO with 20-40 % LVDC coverage (case-specific savings can be ~30 %)
Life-cycle management and reliability of equipment = ?
Chicken or the egg problem with standardization!
Large overall markets for the right solution
over 2 trillion €/year global markets in distribution network
refurbishment, what is the share of LVDC?
DC Voltage Level Selection – Transmission
capacity and economics
Considered distribution
(mains) voltages:
323 V
350 V
>1000 V
±750 V
Capacity extender
Finland
390
Unipolar, FIN
Bipolar, FIN
380
370
360
350
600
700
800
900
1000
1100
Pole voltage [VDC]
1200
1300
Range extender
Finland
550
Total costs [kEUR]
Total costs [kEUR]
400
1400
540
Bipolar, FIN
530
520
510
600
1500
Unipolar, FIN
700
800
Karppanen, J., et al. (2015). “Effect of Voltage Level Selection on Earthing and Protection of LVDC Distribution Systems”. In Proc. of ACDC2015.
Korea
Bipolar, KOR
250
200
1000
1100
Pole voltage [VDC]
Korea
225
Unipolar, KOR
costs [kEUR]
l costs [kEUR]
300
900
Unipolar, KOR
Bipolar, KOR
220
1200
1300
1400
1500
Voltage levels and network architecture
350V DC Line
PV: 3-5kWp
Batt.: 5kWh
house 1
PV: 100kWp
Batt.: 500kWh
house 2
house 19
...
350VDC
Power Line
switch
switch
switch
switch
switch
switch
switch
switch
switch
Communication Line
Adapted from presentation
by Dr. Mario Tokoro
Step-up/down
Voltages, Safety and Other Issues
Main criteria in voltage selection:
life-cycle economics
need to increase transmission capacity
availability of equipment and appliances
compliance with some existing national standards or
regulations
Favours higher
voltages
Favours lower
voltages
High voltage system is not automatically unsafe, but
safety, voltage and earthing are strongly interconnected
Voltage selection is a trade-off between technology and
economics
Different applications and use cases need different voltages
Operational environment dictates the architecture and voltage
Voltage affects directly on economics through component
costs and indirectly via application potential
Voltages, Safety and Other Issues
Band II (LVDC)
1500V
200V
400V
Dangerous and could kill
in case of direct contact
TN: single line contact
(line-to-earth)
IT: line-to-line contact
Band I (ELVDC)
Comparable safety margin
can be provided only with
3-wire system with
grounded middle point
120V
60V
Comparable safety
margin as for AC for
direct contact
(IEC60479) can be
provided in 2-wire &
3-wire systems
30V
0V
For <30V and in
normal dry
conditions for <60V,
basic protection is
not required for SELV
and PELV systems
Protection for safety : RCDs are not widely and commercially available for DC
TN-S safe
solution for
below 400 V
systems in
buildings and
homes
Protection for equipment: detecting, locating, and interrupting DC faults are challenging
Over 120 V DC can
electrocute
*The IEC 23E/WG2 workshop, “DC distribution system and consequences for RCDs”
IT safer on
higher voltages
needed in utility
grids
Earth potential rise in case of earth fault in
earthed system with different voltage levels and
earthing resistances. Red layer illustrates the limit
of earth potential rise of 120 VDC.
Earth potential rise in case of fault between pole
and earth in earth isolated system with different
voltage andisolation levels. The used earth
resistance value was 5 Ω.
Karppanen, J., et al. (2015). “Effect of Voltage Level Selection on Earthing and Protection of LVDC Distribution Systems”. In Proc. of ACDC2015.
Voltages, Safety and Other Issues
High speed protection required
Feeding short-circuit current with converter is not reasonable 
oversizing, poor efficiency and reliability, high costs…
Conventional mechanic protection devices and fault detection
methods are not an ideal solution  adaptation of
unconventional methods
Communications assisted and power electronics based protection
techniques with fault identification based on high resolution
measurements of current and voltage behaviour
The developed fast acting DC protection has demonstrated more
resilient performance for future LVDC networks by offering:
Fast detecting and
locating DC faults
Good level of
selectivity
Fast interrupting DC
faults at low level
Fast reclosing
function
Present Standards
Some applied and mentioned standards
IEC 61660-1 dynamic mathematical model of DC system short circuit behavior (+
respective ANSI/IEEE guidelines)
(IEC) EN 61439-1 ja -5 (pre 2015: 60439-5) Low-voltage switchgear and controlgear
assemblies, general rules and rules for assemblies used in public networks
IEC 60947-2 Low-voltage switchgear and controlgear
(IEC 61000-6-3, -3-2, -3-3, -3-12, IEC 61204-3) EN61800-3:2004 General EMC
requirements for converters (adjustable speed drives)
EN 50162 Protection against corrosion by stray current from direct current systems
IEC 60364 –series, Low-voltage electrical installations, partly applicable also for utility
LVDC
CENELEC HD 603 Low voltage power cables (IEC 60502-1 needs amending to match with
the European regulations)
National standards (amendments to IEC) and guidelines
Only few standards are complete from DC perspective,
review required
New national activities have been started in many countries
(India, Japan, US, UK, NL, etc.)
Standardization development needs
Voltages and EMC (compatibility in public DC networks, voltage and
current quality requirements for different architectures)
Cables and line structures, related installation components
EMC requirements for converters used in LVDC networks
Definitions for conformity testing
Non conventional power electronics based protection methods for
overcurrent and short circuit protection
Arc detection and suppression
Earth leakage identification
Solutions have been and are
constantly developed
Electrical working safety is also part of system perspective, is it
covered by SEG 4 and should it be?
So far the gaps in standardization have been filled with custom
solutions in introduced installations  experiences for developing
the standards
Also many unwritten practices exist among industry…
Key outcomes of the Session
Both top-down and bottom-up approaches indicate beneficially of utility
level LVDC distribution
Both approaches seem to converge towards similar basic architectures
although technical properties may differ regionally
Pivotal characteristics are economic feasibility and transmission capacity
Imminent standardisation gaps are related to overall EMC requirements,
utility grid embedded converters, novel protection methods and
respective testing requirements
In case of LVDC distribution, converters are crucial parts of the distribution
system and belong to the equipment
Requirements for converter design from system perspective need to be
emphasized
Standardisation of the exact distribution voltage level used in public
network is not crucial as long as there are clear definitions for the rated
voltages of the equipment and allowed voltage variation
E.g. equipment rated for 1500 V, 1200 V, 900 V, 600 V, 400 V
Guidelines for the system designer, how to select components for a particular
system
Summary
Rapidly changing energy ecosystem has created
demand for public LVDC systems
On utility level LVDC distribution becomes asset for the
whole energy system and community
Bind together lower level applications and installations to
become a part of local LVDC power system
Offers easy to manage platform for implementing local
energy exchange (markets)
Large markets for the right solutions, but ‘chicken or the
egg’ situation with standardization is holding back
implementation – SEG4 work crucial for resolving the
situation.
Thank You!