Situated in the highlands of Scotland, amongst beautiful scenery,
is one of the country’s most amazing technical achievements. This is the world’s
first high-level reversible pumped storage hydro electric scheme, built 1000m inside the
majestic Ben Cruachan. Commissioned in 1966, the 400MW power station was recently due for
refurbishment, and the World leaders in Hydro technology, VA Tech Hydro Gmbh of Austria,
were awarded the contract to carry out this difficult engineering task.
Cruachan
also doubles up as a tourist attraction, attracting many thousands of visitors. This was
to prove a major consideration when the removal of the generator stators had to be done.
The generator stators were built in situ, with only the outer casings being able to be
split. Normally this process would have been undertaken with the use of thermic lancing or
arc air gouging. However, since the stator laminations are coated with a type of
insulating varnish, these methods would have resulted in soot material being deposited
into the local atmosphere. As the power station doubles as visitor centre, these methods
were ruled out as unsatisfactory.
This left VA Tech Hydro with a problem, how do you cut metal without using a hot method
and whilst maintaining control.
Diamond Drilling and Cutting Services Ltd of Jarrow, Tyne & Wear were called to see if
they could find an alternative method of cutting the stators. The owners, Ken Ward and
estimator Dennis Brown, had heard that steel could be cut with diamond wire so the search
began to find a supplier to work with. They contacted many suppliers to find out what the
market had to offer, and after some further research they contacted UKdima Limited. UKdima
had not long since supplied wire to another company to cut solid steel, which had been a
resounding success. So when UKdima received the call they were confident they could help.
The initial problem was that UKdima were submitting proposed figures much lower than all
the other suppliers, i.e. the volume of wire to be used.
“When a supplier is quoting usage figures of less than one third of all the others,
this poses a real problem” said Dennis. “Are they right and the rest wrong? But
the main difference was that was that Millar Reid of UKdima continually asked questions
concerning the steel strength, how the machine was being set up and what kind of machine
was being used, etc” said Dennis of DD&C. The other problem was that DD&C
could not gain full technical information about the stators, because the original drawings
were missing. So when Dennis told Millar Reid this information, it was an opportunity for
Millar Reid to use his earlier engineering training, which was carried out with the
Electricity Board. “The steel strengths that we were being supplied just didn’t
make sense. I could not see why the manufacturer would use high quality steel in the
laminations of a stator” said Millar. For DD&C to quote using the information
available was going to prove difficult.
“The main information we used was based on the figures supplied by UKdima” said
Dennis, “i.e. the amount of wire that we would use, the time for each cut, etc. And
the other point we were informed of was that no one had ever carried out this type of
cutting operation anywhere in the world before, so we had to get it right!”
So, a week before Christmas the wire arrived, and all was set for a New Year start.
Unfortunately the overall project did not start on time, but this gave UKdima an
opportunity to do further ground work. UKdima visited the site and carried out a full
inspection of the job. This uncovered some other technical problems, including the fact
that there was machining to be done on the turbine and this could not be undertaken at the
same time as the cutting on the stators.
Meetings were organised with VA Tech Hydro and the various issues with the project were
highlighted. One other problem was the supply of cooling water for the wire and the
control of the water. The turbines are underneath the stator and the main contract had
programmed the machining to be done before the stator cutting, with the fitting of the new
turbine impeller. Also, the disposal of the cooling water would take place into the drains
from the power station, emptying straight into the loch, which just happens to have some
excellent fishing. It was unacceptable for us to contaminate the water supply with metal
filings, so an alternative solution had to be found. All this information was relayed back
to DD&C by UKdima.
When the eventual start date came, both Diamond Drilling and Cutting and UKdima were
onsite. “In the end the project was relatively easy” said Millar Reid, “but
what really helped was the attitude of the operatives of Diamond Drilling and Cutting.
Nothing was too much bother, they got their sleeves rolled up and got stuck in. They were
always looking to find faster ways of executing the job and this made a huge difference.
The first cut was completed in 11 hours and the wire was completely finished, compared to
the last cut of around 6 hours when upon completion the wire was almost like new.”
The water problem was solved using magnets to separate the steel particles from the
wastewater. This was because the operatives used their initiative and applied themselves
to the problems. They were a credit to Diamond Drilling & Cutting Services Ltd.
“The one thing that I will always remember about this project, was the gratitude
shown to both myself and the operators from the main contractor VA Tech Hydro. How often
does the main contractor shake your hand and say thank you!” commented Millar Reid.
