10th STEAM TURBINE PROFESSIONAL MEET

HIGHER HPT FIRST STAGE PRESSURE & RECTIFICATION AT SITE

NTPC TANDA TPS

Presented by:

Brijesh Kumar (AGM/TMD)

Shahnawaz A Khan (Asst. Mgr/TMD)

Brief detail of U#1 HP Higher 1st Stage Pressure Problem

Tanda TPS: 4X110 MW Units TG : Skoda Power, Czech Make R&M of U#1 was carried out in Nov'2008 during

which following major jobs were carried out HPT: New HPT rotor placed. Refurbishent of HP nozzle segments done. Refurbishent of new HP diaphragms.

Brief detail of U#1 HP Higher 1st Stage Pressure Problem

Replacement of HP diaphragm#3. After R&M, higher 1st stage pressure of HPT was

observed in the range of 107 ksc.

Higher 1st stage pressure is leads to Lower turbine efficiency. Excessive force on turbine casing parting plane

fasteners causing life reduction. Higher drum pressure & MS piping pressure.

Brief detail of U#1 HP Higher 1st Stage Pressure Problem

Potential causes of high 1st stage pressure: Restricted nozzle. Deposition on the blades of HP rotor & diaphragms.

Checks during O/H of U#1

Following checks were carried out to find the cause of the problem:

Steam flowpath HP nozzle segment condition HP diaphragms for scaling/deposition HP rotor scaling/deposition

Findings

Flowpath readings & blade surfaces of rotor & diaphragms were found satisfactory.

No significant deposition was found on HP rotor blades as well as diaphragm blades.

After opening the HPT, condition of HP nozzles were found very healthy. So, it was further analysed & throat of the nozzles found to be very less that designed value.

Findings

Values found:

Average Value(mm)

HP Top Nozzle HP Bottom Nozzle

Before O/H Design Before O/H Design

Throat 14.7 16.10 14.56 16.10

Width 22.5 22.5 22.5 22.5

HP Nozzle

OUR APPROACH

In view of the above findings, the matter was discussed with Ex-BHEL expert & was decided to increase the throat of the nozzle segments while refurbishing it in-situ.

HP nozzle refurbishment job done by sandblasting, grinding, polishing & final finishing.

Readings after Nozzle repair at site:

Average Value(mm)HP Top Nozzle HP Bottom Nozzle

After O/H Design After O/H Design

Throat 16.04 16.00 16.00 16.00

Width 22.5 22.5 22.5 22.5

EEMG DATACHART DEPICTING 1st STAGE PR. WITH VARIOUS PARAMETERS

Readings after EEMG efficiency test.

U#1 Before O/H After O/H

Load (MW) 110.10 113.12

Main Steam Pressure before ESV (ksc)

133.05 131.10

Main Steam Temp before ESV (oC)

534.87 534.0

First Stage Pressure 107.5 103.6

HPT Efficiency 72.90 74.31

THANK YOU