FIELD OF INVENTION
The present invention relates to a device for continuously circulating cooling water
through equipment mounted on 400 kV and above insulated platforms from
circulating equipment located at ground level. More particularly the invention
relates to a device for circulating cooling water between the ground equipment
and the equipment mounted on the high voltage platform installed as part of
Flexible AC transmission system device.
BACKGROUND OF THE INVENTION
Various power electronic devices are presently used to improve the capacity and
performance of transmission lines. Most of these devices belong to the Flexible AC
Transmission System (FACTS) family. Some of these devices like Fixed Series
Capacitors (FSC) and Thyristor Controlled Series Capacitor (TCSC) are connected
in series with the high voltage transmission lines. In such cases, some components
of the device are mounted on raised platforms insulated from the ground. The
height of the platform depends on the insulation level, which in turn, depends on
the transmission line voltage (generally 400kV and above).

The components that are generally mounted on the platform are Capacitor banks,
spark-gap, Metal Oxide Varistors, air-core reactors, Current Transformers, Potential
Transformers and Power Electronics devices like Thyristor Valve.
Generally, these platform-mounted power electronics equipment (e.g. Thyristor
Valve) require water cooling. De-ionised water with very low conductivity is
popularly used as coolant so as to keep the unavoidable leakage current through
the water to a minimum level. Closed loop De-ionised water circuit is used for
cooling which comprises of the Water Circulation Unit (WCU) and a set of Heat
Exchangers (HE), all located at ground level. Refer Figure-1 for the general
arrangement of components. During operation, the WCU circulates de-ionised
water continuously through the equipment mounted on the platform and the heat
exchanger in a closed loop. Sometimes an Expansion Tank (ET) is provided at a
height.
The flow of water between the equipment mounted on high voltage platform and
the WCU at ground level poses some problems due to the huge difference in
electrical potentials between the two locations. The same problems also apply to
the fibre-optic cables that are required to be connected between the Thyristor
Valve on high voltage platform and the Control Panel (CP) at ground level.

In prior art (Figure-2), a single hollow porcelain insulator (5) of suitable height and
large diameter is used for accommodating the inlet and outlet water pipes (4) and
a bunch of fibre-optic cables (6) for a particular platform (2). The de-ionised water
for cooling is transported through two polymer pipes as inlet and outlet with
suitable end connections at platform level and ground level. The inlet and outlet
pipes at the platform level are generally connected to the platform mounted
equipment (1) using stainless steel tubes. In cases, where, the column is placed
directly below the equipment, the same polymer pipes extend up to the
equipment. Polymers such as Polypropylene (PP), Ultra High Density Polyethylene
(UHDP), Polyvinylidene Flouride (PVDF) etc have been used to manufacture the
pipes. Suitable corona rings (3) are used as required.
The hollow porcelain insulators are installed vertically, adjacent to the platform or
below the platform reaching up to the platform level. The height of the hollow
insulator depends on the voltage level of the platform. As shown in fig.2, metallic
housings (7,8) are provided at the top and bottom of the hollow insulators at both
ends.
After installation of the pipes and laying of the fibre-optic cables in the hollow
insulator, the bottom end is suitably sealed. Insulating oil is then filled in the
insulator under vacuum and properly sealed to prevent entry of dust and moisture.

This method involves major field activities like elaborate and time-consuming
installation work, filling oil under vacuum, sealing against moisture ingress,
periodic checking of oil properties during maintenance and arresting oil leakages, if
any.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a device for circulating
cooling water through equipment mounted on a 400 kV and above insulated
platform which avoids the use of insulating oil and eliminates the hazardous
process of checking, filling and sealing of oil.
Another object of the invention is to propose a device for circulating cooling water
through equipment mounted on a 400 kV and above insulated platform which
makes the system maintenance free.
A still another object of the invention is to propose a device for circulating cooling
water through equipment mounted on a 400 kV and above insulated platform
which is simple, reliable and faster to install.

A further object of the invention is to propose a device for circulating cooling water
through equipment mounted on a 400 kV and above insulated platform which
reduces the cost.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows the general arrangement of components in a TCSC system
Fig.2 - shows arrangement used in prior art
Fig.3 - shows arrangement used in the present invention
Fig.4a - shows the construction of the insulated water column
Fig.4b - shows a test set up of the insulated water column
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
With the advent and ready availability of dry type Composite Optical Signal
Columns, there is no need for installing fibre-optic cables inside oil-filled hollow
insulators. These Optical signal columns are basically composite insulators with
fibre-optic cables embedded in them and are meant for such high voltage
applications. The optical signal columns are hung from the platform and anchored
to the ground at the bottom end.

As shown in fig.3, in the new device of the present invention for circulating cooling
water to the platform mounted equipment (1), two vertical hollow insulator
columns (9) are installed adjacent to each other beside the platform (2). The
hollow insulator columns (9) are made up of a number of vertically assembled
individual porcelain hollow insulators (6) mounted on a metal frame (5). The inner
diameter of the insulators is chosen to be the same as the pipe diameter used for
circulating the cooling water (depends on flow rate). The hollow columns can be
built up of required number of standard hollow insulators by stacking one above
the other, with suitable gaskets in between two hollow insulators and between
hollow insulators (6) and stainless steel pipes (4), to get the required overall
height. The overall height is dictated by the air and creepage distance required for
that particular voltage level. The choice of height of individual insulator is based on
the standard height available with the manufacturer.
Suitable polymer or stainless steel pipes (4) can be fitted at either end to make up
the connections between the platform mounted equipment (1) and the ground
level equipment. Suitable corona (3) rings can be mounted at the top to avoid
corona discharge.
The field installation work is much faster, easier and cheaper in this method.
Absence of oil and associated work related to checking, filling and sealing of oil
makes the system maintenance-free. Use of smaller individual insulators makes

transport and field handling easier. In case of any damage/crack in a portion of
the insulator column, the full column need not be replaced.
If the net height of the water column and the inner diameter of the insulator are
maintained same as that in prior art, the resistance of the water column in the
new design remain same.
Even though two separate insulated water columns are used for inlet and outlet in
the new art as compared to the single insulated water column in the prior art,
there is no increase in the Basic price of the columns due to the following reasons:
- Smaller and standard hollow insulators are much cheaper compared to a
single non-standard insulator of large height and diameter because
standard hollow insulators are manufactured in bulk for general purpose
use.
- Use of oil, top and bottom housing and elaborate sealing arrangement for
oil are avoided, thus reducing cost.
There is no increase in the overall cost also. The additional cost incurred for the
Optical signal column is offset by the reduction in cost incurred at field for
installing and commissioning of the oil filled columns and savings due to reduction
in maintenance cost.

Two insulated Water Columns suitable for 420kV were designed and built, based
on the method described above, using standard hollow insulators. A test setup was
made (Figure 4a & 4b) using the two columns and a water circulation unit
circulating de-ionised water through the water columns and the following tests
were conducted on it.
1. Power Frequency Voltage Withstand Test (Dry)- 630kV for 1 minute.
2. Lightning Impulse Voltage Withstand Test (Dry)- 1425kV, Both polarities.
3. Switching Impulse Voltage Withstand Test (Wet)- 1050, 15 shots, Both
polarities.
4. Radio Interference Voltage Test (Dry)- 305kV rms.
After successfully carrying out the tests, three pairs (one pair for each phase
platform) of Insulated Water Columns were successfully erected and
commissioned at a TCSC installation in India.
The invention as described is only illustrative of the possible arrangements.
Changes and modifications in accordance with these principles may readily occur
to those skilled in the art without departing from the scope and spirit of the
invention.

WE CLAIM
1) A device for circulating cooling water through equipment mounted on a
400kV and above insulated platform comprising:
a plurality of vertical hollow insulator columns (9) being mounted on at least
one metal frame (5);
at least one platform (2) having platform mounted equipment (1) mounted
on it;
a plurality of polymer or stainless steel pipes (4) for connecting the platform
mounted equipment (1) with ground level equipment;
a plurality of corona rings (3) being mounted at the top for avoiding corona
discharge;
characterised in that the vertical hollow insulator (9) consists of individual
hollow insulators (6) stacked one above the other and mounted on a metal
frame.
2) A device for circulating cooling water through equipment mounted on a
400kV and above insulated platform as claimed in claim 1, wherein two
vertical hollow insulator columns (9) are installed adjacent to each other
beside the platform (2).

3) A device for circulating cooling water through equipment mounted on a
400kV and above insulated platform as claimed in claim 1, wherein
insulators are made of porcelain.
4) A device for circulating cooling water through equipment mounted on a
400kV and above insulated platform as claimed in claim 1, wherein inner
diameter of the insulators (6) is same as pipe diameter (4).
5) A device for circulating cooling water through equipment mounted on a
400kV and above insulated platform as claimed in claim 1, wherein a
suitable gasket is placed between two hollow insulators (6) and between
hollow insulators (6) and stainless steel pipes (4).

A device for circulating cooling water through equipment mounted on a 400kV and
above insulated platform consists of two vertical hollow insulator columns (9)
which are installed adjacent to each other beside a platform (2) having platform
mounted equipment (1) mounted on it. The vertical hollow insulators made of
porcelain consist of individual hollow insulators (6) stacked one above the other
and mounted on a metal frame (5). A plurality of polymer or stainless steel pipes
(4) connect the platform mounted equipment (1) with ground level equipment. A
plurality of corona rings (3) are mounted at the top to avoid corona discharge
inner diameter of the insulators (6) are provided same as pipe diameter (4).
Suitable gaskets are placed between two hollow insulators (6) and between hollow
insulators (6) and stainless steel pipes (4).