MAREX 2016 - Organic Power

HVDC TRANSMISSION OVERVIEW
WHY HVDC?
The resource that this initiative wishes to
harness and condition, via wind energy
convertors and energy storage, is geographically
removed from the identified
markets for electricity (the greater Dublin
area and the UK). Woodland is the ideal
location for a connection to both markets.
The problem is how to get the power there.
Overhead power lines are the object of
much public opposition as they are percieved
by many to be visually obtrusive
and some people have concerns regarding
potential risks from electromagnetic
radiation (whether real or imagined).
To allay these concerns, the use of DC
gives 2 distinct advantages, firstly, due
to a much reduced heat loss in DC cables,
they can be buried undersea and
underground without cooling systems
at high voltages, and secondly, electromagnetic
radiation is also much reduced.
Bipolar 700MW Cable used for Norned
THE CABLE
At this preliminary stage, it is very difficult
to describe with any certainty, the actual
specifications of the cable that will be used.
However, given the distances involved
and the obvious benefits of redundancy in
the system, 2 bipolar cables with a high
power rating would appear to be a promising
option. 800MW rated bipolar cables
are commercially available and may be
suitable for the MAREX proposal operated
using Voltage source Commutation Power
control. This would allow each cable to be
operated at 500MW initially with the potential
for increasing the power carried later.
EIRGRID may operate a 600MW connection
cap to the national grid, and
this may constrain the potential power
to be carried by the cable proposed to
connect to the EIRGRID AC system
at Woodland. The rated capacity of
the existing HVDC interconnector to
the UK is 500MW and this limits the
power that can be connected to that.
The advantages of the VSC bipolar
HVDC configuration are:
• Undersea cables, where
high capacitance causes
additional AC losses.
• Endpoint-to-endpoint longhaul
bulk power transmission
without intermediate ‘taps’,
for example, in remote areas.
• Increasing the capacity of an
existing power grid in situations
where additional wires are
difficult or expensive to install
• Power transmission and stabilization
between unsynchronised
AC distribution systems
• Connecting a remote generating
plant to the distribution grid,
• Stabilizing a predominantly AC
power-grid, without increasing
prospective short circuit current
• Reducing line cost. HVDC
needs fewer thinner conductors
as there is no need
to support multiple phases.
• Synchronize AC produced by
renewable energy sources
• VSC technology provides a
straight forward AC side connection.
The modular multilevel
converter principle renders AC
harmonic filters superfluous.
• A standard transformer design
can be used without special requirements
to withstand DC
voltage or harmonic currents.
• Converters do not produce
any significant high frequency
noise, so outdoor installation of
AC- and DC reactors (if necessary)
and switchgear is feasible.
CABLE INSERTION
At an initial level of examination it is
expected that the cable route from
Glinsk to Woodland will have the following
insertion methods:
• 2 no. 500MW Outdoor convertor
at Glinsk
• 500m Cross shore horizontal directional
drilling section in tunnelled
cable duct.
• 65km approx. smartjet subsea
insertion 2m below sandy substrate.
• 5km approx sand plough insertion
1.2m deep across intertidal
shore Sligo Bay to pier head.
• 1.5km approx. Under road
trench to rail head.
• Verge trench 1.2m deep alongside
permanent way 190km
• Surface trough insertion accross
bridges and through stations.
• Horizontal directional drillingwhere
exceptionally required
in narrow sections of available
wayleave along permanent
way.
• Under Road trench 1.2m deep
from permanent way to Woodland
substation.
• 2 no. 500MW convertors at
Woodland
CABLE COSTS
At this preliminary stage costs are
hard to estimate, however, ballpark
indication from extrapolation,
allows an estimate in the region
of €300,000,000 to be suggested.
This would be paid for in principle
by connection charges, and use
of system charges would cover
running cost. A combined capacity
connection for MAREX would
comprise around 2810MW, indicating
a connection charge of approx.
€100,000-120,000/MW.
Organic Power Ltd