— M.S. Rao, Senior Vice President & Head - Mumbai Transmission,
Reliance Infrastructure Ltd
In a pioneering effort, Reliance Infrastructure Ltd has acquired the
capability for design, development and construction of extra high
voltage (EHV) substations that occupy 90 per cent less space than
conventional substations. This innovation is most suited for
applications in cities where substations have to be located in
congested load centres and where procuring additional land is a
perennial constraint. RInfra has almost completed the construction
of three such substations and work on a few more is underway.
M.S. Rao in an exclusive exchange tells us more on this path
breaking innovation. An interview by
Venugopal Pillai.
To start with, please describe from a technical standpoint, the
composition and design of the compact EHV substation
designed by Reliance Infrastructure.
Historically, EHV stations, which are generally air insulated
substations (AIS), are kept outside the cities and subtransmission
levels feed the load centers. With the increase in
concentrated loads (because of changing lifestyles and
vertically expanding buildings) and the geographic spread of
the cities, it has become imperative that EHV network be
located near load centers-right in the midst of the cities.
These substations should also have additional special
requirements like:
- Minimal exposure of live elements
- As minimum space as possible with least footprint
- Specific mitigation plan for fire and safety aspects
- Fulfilling of all essential technical requirement like earthing,
etc within the limited space
Considering all the above requirements, the compact 220kV
EHV substation of Reliance Infrastructure was built in a space
of approx 3,500 sqm (square metres) with a vertical
configuration. The station comprises 4 layered building
structure (excluding the underground cable cellar) housing all
major electrical equipments such as 220kV and 33kV GIS bays,
control panels, capacitor banks, etc. The 220/33kV
transformers along with the accessories are installed adjacent
to the building.
Tell us more on the space saving achieved by these compact
EHV substations as opposed to conventional AIS substations.
Conventionally an AIS EHV substation requires about 30,000
sqm to 40,000 sqm of space. The new-design compact
substation could be accommodated by us in about 3,500 sqm
saving about 90 per cent of the area requirement! This could be
achieved not only by simply converting AIS into GIS, but also a
lot of thinking and discussion which has gone into redesigning
of the transformer radiators, sump-pits and meticulous revisit
of entire layout of the equipments, etc. for space saving.
What were the key challenges faced in the development,
construction and design of the EHV stations?
Yes, we did face challenges in the development and
construction of these compact EHV substations. Some of them
were:
- Being a unique tailor-made project and the first of its kind,
the availability of turnkey contractors (EPC) with knowledge
of intercity requirements and other technicalities, municipal
regulations, etc were not available.
- Space constraint in urban cities, to get the entire chunk of
land in one parcel
- Dependency on overseas manufacturers for 220kV GIS and
EHV cables due to which logistics, commissioning time line,
technical requirement were not authentically known
beforehand
- Non-availability of suitable skilled manpower
- No special set of regulations for this kind of infrastructure
project from city authorities concerned
- Limited working hours in view of Municipality regulation and
public convenience
- Traffic restrictions in shifting the bulk equipments like GIS,
transformers etc, causing difficulty in maneuvering the
trailers in the limited plot size
The unique design challenges that we took care of included
the earthing mat design in view of the compact plot size. There
was special earthing requirement for each floor of the building. Also SDH communication with latest relays was used for this
purpose, as there was non availability of conventional PLCC
system due to the usage of EHV cables.
We perceive that with growing urbanization, metropolitan
cities would definitely need space-saving measures such as
compact EHV substations. What is your view, and do you see
this RInfra technology being adopted even by non-RInfra
circles?
Certainly! We can definitely see that in the coming years these
types of compact stations would be a necessity in other cities
also. Because of the load growth, these compact stations will
become a technical compulsion. All transmission utilities would
need to adopt the technology for the cities over a period of time.
Now, with the proven and established solution of the
compact substations, it would be a good idea to revisit the
transmission planning for all mega cities.
Please discuss the concerted effort put in by RInfra and the
equipment suppliers (transformers, capacitors, etc) in
devising this compact EHV substation.
When we started with the idea of this design, we attempted to
contact different contractors and manufacturers for making this
concept a reality. In this process, we faced challenges such as:
- EHV GIS and cables alongwith the terminations etc were
required to be imported and not many indigenous vendors
had all the technical and dimensional details
- Most of the consultants were having the expertise in AIS
stations only and could not relate to our specific requirement
of multi-layered EHV stations
- While attempting to get civil contractors, available vendors
in cities were not very familiar with industrial building and
that too one that would withstand the forces exerted by GIS
bays during operations, etc.
With this background, we initiated an internal study to design
the stations. We did multiple revisions for optimization,
matching the statutory requirements and suitably
accommodating the station requirements in the available
space. The same got validated by the equipment vendors
concerned, individual consultants, etc. before finally initiating
the construction.
We have also worked with a few transformer manufacturers
in further optimizing the space by changing the winding
configuration from standard YD11 with NGT to YZ11 with NGR
too mounted on the transformer tank. Similarly, the radiators
were mounted on the tank to reduce the footprint area.
We were required to interconnect the overhead line to the
EHV cable in a minimal space. Against the conventional space
requirement of 18m x 18m, we managed to interconnect the
overhead line with the EHV cable in a minimal space of 8m x 8m.
This could be achieved by constructing an ultra narrow base
tower on which pre-completed termination was lifted to the top
of the tower at 45m with a special arrangement. In this, we got
good support from one Indian supplier who supplied the cable
and carried out the erection.
With the substation being installed and physically available
for visualization, we believe many vendors and contractors can
be developed for similar stations in future.
Working in conjunction with EHV compact substations, is
RInfra planning to employ other space-saving measures like
high-voltage conductors in urban centres?
In conjunction with these EHV compact substations, RInfra has
also undertaken the challenging task of laying EHV cables. In
absence of sufficient right of way (ROW) available for the
overhead lines, EHV cables are the only solution for providing
the much needed connectivity.
RInfra is also looking at further space optimizing solutions
such as higher ampacity conductors, GIL (Gas Insulated Lines)
for bringing more power through lesser availability of ROW on
a case to case basis.
Also, in association with the STU (state transmission utility)
that is the statutory agency for planning of the network, we are
working for the various requirements of FACTS, HVDC-IGBT
technology etc for the city requirement. This technology will
substantially improve the quality of the power (by mitigation
flicker, harmonics etc) and bring bulk power to the city through
underground cables.
In these new generation substations, we are using latest
protection systems (including the differential protection for
lines), SCADA, monitoring through cameras etc.