Earlier
days up to 250 MW most of the foundation was rigid and casted along with the
main column foundation. But now a days all the TG deck foundation are casted
having Spring /viscous dampers in between. This type of foundation has some
added advantage on turbine erection and size of turbine column. All the
foundation above 500MW and above is having such type of foundation. In BHEL we
use GERB spring as our standard spring supplier wherever I worked.
The spring
element in 500MW machines and further higher rating machines are used with
visco dampers. The springs units are not supplied to site with required
pre-tension values through these are supplied with some amount of pre-tension.
The required pre-tension of the spring units are done at site before its installation
in position. A special device for pre-compression of these springs units is
also supplied by spring supplier.
The
shuttering of RCC slab of TG deck is furnished before installation of these
spring units. The top surface of individual column where these spring units are
mounted should be within accuracy of +00 mm to -3.00 mm. If necessary these may
be corrected by chipping before installations of the spring units. The level
deviation among various columns is permitted +00 mm to -5.00 mm in total including
individual column variation of +00 mm to -3.00 mm.
The
bottom shuttering of pedestal must be cut over the column head for lowering the
spring units. After lowering the spring unit the cover steel plates are placed in position with shuttering supports.
An air gap of about 5.00 mm to 10.00 mm is left between cover plate and spring units for
settlement of deck during casting. The visco dampers are also filled up at site only with visco liquids
supplied by spring supplier. Each spring units are placed over the resistance pad to avoid movement
of the spring units during operation of the machine. Similarly the resistance pad is given on top of the steel shim to avoid the shifting of the shim during operation of the machine. Each spring unit is provided with 10.00 mm of steel shim for future adjustment.
The
TG deck springs are released after installation of all Turbine Generator
components including piping and the condenser has to be filled up to operating
level including CW pump in operation for full load condition. The shims
provided for additional compression of the spring units are also adjusted
during this stage, the final alignment of various rotors and turbine casing are
done after release of the spring unit. The Generator hydrogen cooler & LP heater
if any inside the condenser are to be filled up in cooling water space for
their operating condition before release of TG desk spring. The insulation of
various casing / pipe lines including cladding if any are also to be installed
otherwise the equivalent weight is to be incorporated before release of desk
spring. All the pipe lines connected with the Turbine and Generator should be
made available on permanent hangers and supports to avoid any additional load
on the TG deck afterwards. The TG deck should also be made free all- around to
avoid any obstruction in its movement.
During
release of TG deck springs and final alignment of rotors the condenser spring
is also to be kept in floating condition considering that condenser neck
welding is already done. Similarly the condenser spring measurement should be
with in + 1.00 mm otherwise the shims may be adjusted in condenser springs. No
adjustment of TG deck springs or condenser springs are permitted after final
alignment of the rotors. During any subsequent adjustment of TG deck spring the
final alignment of all rotors are to be checked.
There
are finer points of spring installation and releasing but we need not to
discuss now. Basics of installation and releasing are given above. There are
few important activity needs to be
performed which will be indicated very briefly.
-
Condenser neck welding having spring loaded foundation.
-
Assembly of breach nut.
-Turbine
Insulation
-
Turbine Integral piping and other piping. It is better to identify the scope of
piping between IBR/Non IBR. This demarcation should be available with
construction man. Any deviation from IBR norms will attract problems from
statutory authority. Therefore system wise identification is needed. In general
oil lines ,water lines ,air lines and Gas lines are not under IBR but some of
the steam lines are under the scope of IBR. Interpretation of IBR authority
varies from state to state therefore one should take state IBR authority in
confidence.
For
above works it is advised to follow the OEM’s practice in vogue. All the OEM (
original Equipment Manufacturer)
detailed it in there erection manual.
One
should follow the approved FQP ( field Quality Plan) for measurement and records of various
reading in the log sheets of FQP . This will help in analysing any future
problem.
PS:-
I have a eight page technical document given by M/s GERB with supplied spring.
Interested person to receive the document as reference may send request to my
mail
dguha1952@gmail.com
Civil protocol for placement of VIS. Please note the number of reading.
