64
Standardization for MVDC grids
7.
.
It possible that the definition MVDC voltages
might need vary depending the application
and/or the safety requirements particular
application. Except for the IEC reference [73], the
voltages defined Table 7-3 are system voltages
between the positive (+) and negative (–) the DC
link.
All equipment must rated this value
accordingly. For example, in
defining rated current for MVDC converters, the
rated short circuit current MVDC converter
can have significantly different maximum peak
and duration depending the converter topology. But there are systems where the full system
voltage occurs between one polarity and ground,
while other (symmetrical) systems have ground
potential halfway between the line voltages. Currently
there commonly agreed set voltage
range definitions.3 Voltage definitions
Amidst the need update existing standards
and the creation new standards the initial
conundrum defining operating voltages in
MVDC power systems and technology. Given the
volume the new standards required for the
unique aspects MVDC technology and device
operations, and the important differences with
AC grid operation, several focus areas can be
suggested for immediate and near-term attention. shown Table 7-3, voltage
definitions vary across different organizations and
industries.
These are outlined below the rest this section.
§ MVDC circuit breaker operation and
maintenance procedures
7.
This obliges switchgear associated with MVDC
converters cope with significant range of
short circuit current duration and maximum peak.1. that, for example, MVDC marine
applications might different voltage range
from MVDC electricity grid applications.2.1. This
could lead situation where some equipment
might only rated for the line-to-ground voltage
and not for the full system voltage.7 Cables
§ MVDC cable design and testing
§ MVDC cable operation and maintenance
procedures
As can seen, broad range standards and
guidelines are likely required fully support
the widespread rollout MVDC grids.6 Switchgear
§ Specifications for MVDC switchgear and
controllers
§ MVDC surge arrester design and testing
7.5 Circuit breakers
§ MVDC circuit breaker design and testing
§ Circuit breaker ratings including short circuit
breaking current, making current, dissipated
energy during breaking, etc.2.
Complicating the definition MVDC voltages
is the issue symmetry grounding design of
the system. This results rated voltage
for the system kV, while some equipment
in each leg would only need rated for
5 kV.3 kV.1. Two examples
can illustrate this issue:
§ railway system with system voltage
of kV, and where one pole connected to
the tracks, has the rated voltage 3.
7.4 Device ratings
Due substantial differences from their AC
counterparts, care will needed define the
ratings devices MVDC grids. This situation comparable today’s
HVDC systems, where some converter station
equipment has lower rating than the whole
system.
§ MVDC grid distribution system with kV
system voltage designed symmetrically with
two legs.
7.2
