Professional Circle "DELTA

Professional Circle
“DELTA”
Electrical Maintenance Department- KORBA

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Copyright © 2016 Your Company All Rights Reserved. 2
PC - DELTA
Date of formation Jan 2021
Team Members Executives of EMD
No. of Members 12
Frequency of meeting Every 2nd Thursday of month
or As required
Domain of Topics Technical , Material
Management & Safety
Achievement • Bagged First Prize at Station level
PC Convention in 2021
• Bagged Second Prize at RPCC in
Dec’2021

PC - DELTA
Sl no Name of Topic Lead Member Remark/Status
1 Unit #3 stator core issue Anand Pandey Closed
2 REF in Unit #2 Karan Tripathi Closed
3 Frequent tripping of Station Trf Ajit Chowdhary Closed
4 Frequent tripping of BPH OH lines Bipul Kumar Closed
5 SST voltage unbalance issue Anand Pandey Closed
6 Procurement through GEM Bipul Kumar Closed
7 U#7 Excitation System Problem Anand Pandey Closed
8 U#6 SOT Level low issue Anand Pandey Closed
9 SEF in U#1 Anand Pandey Closed
10 Generator Seal Failure at Balco , Korba Anand Pandey Closed
11 Generator Winding Failure at 135 MW
CPP @ Jharsuguda
Anand Pandey Closed

TOPIC
• Anand Pandey ( Sr Manager-EMD)
• Nitesh Khandelwal ( Sr Manager-MTP)
KORBA SUPER THERMAL POWER STATION
Techno- Commercial Assessment
for
Sustainable Operation
of
Old Turbo-Generator
Presented By:

Content
Commercial Impact on Failure of Capital Asset
3
1 Generator Condition Assessment
4 Real Time Case study : Korba U#3
Generator
5
6 Conclusion
2
Recent Major Avoidable Failures in Power
Plants
Learning from U#3 Stator Core Issue

Generator Condition Assessment
 Turbo-Generator is one of the costliest asset of Power Plant
 Its failure has huge commercial implication over utilities
 NTPC is running with large number of old fleet of generators
which have rendered service for more than 30 years
 Smart maintenance is necessary for Reliable and Sustainable
operation of units
 Correct Technical decisions play important role in profitability
 Conventional approach may be reviewed before taking a
technical decision having financial impact

Diagnostic Test for Generator condition Assessment
 Various Electrical & Mechanical Diagnostic Tests are done to
access the condition & Remaining Life of Generator
 Test for Core, Winding Integrity & Insulation and Rotor Health
are done during OH
Electrical Test
STATOR :
• ELCID
• Tan δ
• PD
• IR,PI,WDG-R
• PDCA
ROTOR :
• RSO
• Z, R, IR & PI
Mechanical Test
STATOR :
• Wedge Compression
• Baroscopic Inspection
• NFT
• UT, DP
ROTOR :
• Baroscopic Inspection
• Wedge Knock test

Recent Avoidable
Failures: CASE -01

Recent Avoidable Failures: CASE -01
A casual approach in MAINTENANCE or overlooking of
deviation in operating parameters may lead to catastrophic failure
300 MW CPP : Hydrogen leakage due to Seal System Failure

CASE-01
A LOSS IN SPRING TENSION OF SEAL RING
LEAD TO THIS AVOIDABLE FAILURE
Outage Duration : 35 days

Recent Avoidable
Failures: CASE -02

135 MW CPP : Winding Insulation Failure due to reduction in
Stator winding cooling water flow

Total Outage duration : 34 days
CASE -02
RCA revealed that the failure was
due to choking of cooling water tube
by some silicon sealant

135 MW CPP : Winding Insulation Failure due to reduction in
Stator winding cooling water flow
004374
LOAD 131.70 MW
TEMP 139.96

P/P pressure 0.3355
Flow 46.32 dL/sec
P/P pressure 0.4153
Flow 37.81
24% Increase in Pressure & 20% Reduction in Flow

Commercial
Impact of recent
Failure of Capital
Asset

Recent Failures:660 MW GENERATOR

• Fault Current Aprox 180 KA for 10ms
• 40KA > for 500 ms
180 KA for 10 ms
40 KA for 500 ms

• Pre-failure event were there
( aprox 20 days before)
• Abnormal Sound from Stator
• Increased Vibration
• Rise in Cold Gas Temperature
at TE side
• Core melt
• Bar broke from middle
• Hydrogen pressure reduced in secs
• Water inside stator casing
• Complete Stator & Rotor failed

Commercial Impact on Failure of Capital Asset
 Loss incur on failure of any capital asset:
 Loss due to material
 Loss due to services
 Loss as Recovery of Fixed cost
 Loss as variable cost
 Loss due to incentive
 Loss due to startup cost
 Loss involve other hidden cost

Commercial Impact of Failure of Capital Asset
Case study : 660 MW Generator Failure
Sr. No PO No. Service PO description Amount
( In Lakh)
1 4000268046 Dismantling of NTPC Barh U3 Generator Stator 139.0
2 4000268215 Dismantling of HT, LT, control cables and cable trays and restoration work after stator
movement at NTPC Barh.
24.1
3 4000268190 Dismantling and restoration of 11KV SPBD HT bus duct sections for Generator Stator
shifting at NTPC BARH
3.6
4 4000269163 TRANSPORTATION OF 660 MW GENERATOR STATOR WITH ACCESSORIES
(ODC CONSIGNMENT) FROM NTPC BARH TO NTPC SIPAT.
1663.5
5 4000269558 Dismantling and Erection of NTPC Sipat U-1 Generator Stator 110.1
6 4000271958 Supervision Services by OEM for dismantling, erection and commissioning of 660 MW
Electrosila Generator
405.0
7 4000272532 TRANSPORTATION OF 660 MW GENERATOR STATOR (ODC CONSIGNMENT)
FROM UNIT 1 TG BAY TO UNIT 2/3 TG BAY AT NTPC SIPAT
25.0
8 4000280379 Supply and apply of putty over Generator End leads of Unit1 of NTPC Sipat. 25.8
9 4000282937 Supervision and inspection of cargo at Fathuwa, Haldia and Mumbai for Generator
Stator loading and unloading
9.9
10 4000282938 Supervision and Inspection of cargo at Tuticorin port for generator stator unloading
and loading
2.3
Total Service Cost 24.08 Cr.

Case study : NTPC Sipat 660 MW Unit#1 Generator failure
Sr. No PO No. Material PO description Amount
( In Lakh)
1 4000271962 Procurement of complete set of new wound stator for 660MW Electrosila make
Generators(Pool spares).
5425.0
2 4000272317 Procurement of Materials for repair of Electrosila make 660MW generator stator of
Unit1 NTPC Sipat
391.7
3 -- Electrosila make 660MW generator Rotor cost 2000.0
Total Material Cost 78.17 Cr.
 Unit was under shutdown from
28.10.2021 to 16.07.2022,
Total 260 days generation loss
was 4251 MU.
 Loss due to Annual fixed cost
recovery is approx. 130 Cr
 Loss due to startup 7.65 Cr.
Total commercial Loss
including Material +
Services + Startup cost
+ Fixed cost recovery is
aprox. 304 Cr.

200 MW U#3 KORBA : STATOR CORE ISSUE
 Unit#3 First Synchronization on 17th
March’1984.
 During Capital OH, Electrical Test revealed
shorting of core laminations
 8 no. core packets at different locations
were affected.
 Even after chemical cleaning/ Mechanical
repair of core, condition did not improve.
 New Stator was available at SSTPS only
 Sustainable operation with reliability was
questionable.
 Commercial Impact was substantial for
replacement with new Stator.

Anticipated loss for NTPC KORBA 200 MW Unit#3 Generator
stator problem :
 For replacement of Generator Stator, Unit shutdown might be
for approx. 60 days, and total Generation loss could be 288
MU.
 Loss due to Transportation cost from Singrauli to Korba,
other services and material cost: Approx 29 Cr.
 Loss due to Annual fixed cost recovery Zero.
( Annual DC for Korba FY 2020 -21 was 96.63%)
 Loss due to Startup 0.75 Cr.
 Incentive Loss :13.10 Cr.
 Profit Loss due to Marginal
Contribution : 0.47 Cr.
Total commercial
Loss could be approx.
43.32 Cr

Real Time Case study : Korba U#3
Generator
Identification of Inter Core lamination
Shorting during ELCID Test
#KORBA UNIT -03

Generator
 The stator core is constructed from stacks of steel
laminations.
 Laminations are insulated to limit the induced eddy
currents
 Large TG may weigh over 200T and contain some 200000
such laminations.
 If laminations get electrically shorted , they can allow
significant eddy fault currents leading to HOTSPOTS
 Local ‘Hotspots’ which, even if modest, can affect the
integrity and life expectancy of nearby conductor
insulation.

Generator
• During ELCID test of U#3 Stator Core High Fault current recorded
• This indicated Shorting of inter Core Lamination
• Shorting of Inter Core Laminations is a serious issue
• Assessment for sustainable operation has to be done technically by
ascertaining this impact on actual temperature rise of machine
Slot No. Fault Current (mA)
3 112
4 144
12 588
13 131
39 208
40 152
41 417
49 357
ELCID FAULT CURRENT DATA

Generator
SLOT NO – 12 & 13
Fault Current : 588 mA
Fault Current : 131 mA
ELCID Graph

Generator

Generator
Core Ring Loop Flux test at 80% Flux density was performed to
identify real time impact of shorting on temperature rise
Acceptance Criterion
 The temperature
difference between a hot
spot and an equivalent
normal one should not
exceed 10 Deg. Celsius
after one hour
 Test was terminated with
in 10 mins
Temp during Core Flux test as
recorded by Thermo-vision Camera
Slot
No.
16:31:00 16:35:00 16:43:00
3 31 52 52
4 31 53 53
12 31 57 72
13 31 56 72
39 31 52 75
40 31 52 53
41 31 55 70
49 31 57 83

Generator
Slot 49 Slot 12
 Present day practice is not to allow the temperature of any part of
the stator core (including hotspots) to exceed 100 °C during
magnetic heating
 A core with damaged interlaminar resistance quickly reach 100
°C.

Generator
 Physical/Hand feel of temperature at HOTSPOT points was
normal
 It was decided to repeat the test with Non-Magnetic RTDs at
the faulty core packets
 RTD data was provided in UCB through DAS for real time
monitoring, trending & recording for future reference
 During Repeat test once again IR scanning data was same as
previous
 However, RTD data was well with in limit and under acceptance
norm
 Based on the data captured during ring flux test M/C was
cleared for Operation

DYNAMIC TREND OF TEMPERATURE RISE
VALUES

LEARNING
 Not different things but different approach was adopted to
ascertain the norms for acceptance
 IR scanning works on principle of emissivity of Infra Red
Light hence may mislead if surface is shinny
 Data from IR scanning shall be cross verified before taking
any major decision
 A technically correct decision helped to bring back
Machine in time thereby avoiding any commercial loss

Knowledge Sharing
Technical Paper for Korba U#3 case sent for acceptance at
“17th IndiaDoble Power Forum”

Conclusion
 Properly maintained equipment reduces downtime by minimizing
catastrophic failures
 Optimal Performance of Aux. System like Excitation System, Seal Oil System,
Cooling Water System & Hydrogen Gas system is must for Sustainable
operation of Generator
 Trend analysis of operating parameters provides the actionable points for
OH
 Daily monitoring of critical parameters should be done
 Any deviation must be investigated thoroughly
 Slippage in above approach may lead to failure of machine
 Physical Inspection by Generator Expert with sufficient experience during
OH is always beneficial
DAILY GEN
CHECKLIST

THANK-YOU
ANY QUERRIES??

Daily monitoring Checklist
BACK

DYNAMIC TREND OF TEMPERATURE RISE
BACK

Commercial data (KORBA)
Total Outage in days of Unit#3 60 days
Total MU Loss 288 MU
Fixed cost recovery NIL
Oil cons 150 KL
Oil Cost 50000 Rs / KL
Total Startup cost 75 Lakh
SG for FY 2020-21 % ST-1 & 2 92.13 %
SG for FY 2020-22 MU ST-1 & 2 15756.52 MU
Normative ST-1 & 2 17100.92 MU
MU loss due to U#3 outage after APC 262.08 MU
Incentive Loss( 50 Paisa/Kwh) 1310.4 Lakh
Profit Loss due to MC (1.81 Paisa/Kwh) 47.40 Lakh
Marginal Contribution FY 2020-21 for ST-1&2 3581.8 Lakh
SG for FY 2020-21 for ST-1 &2 19805.46 MU
Marginal Contribution FY 2020-21 for ST-1&2 1.81 Paisa/Kwh

200 MW stator replacement cost
Transportation cost from Singrauli to Korba 2 Cr
Dismantling and Erection Generator Stator 0.75 Cr.
Supervision Services by OEM for
dismantling, erection and commissioning
1 Cr.
New Stator procurment 25 Cr.
Other Misleneous charges 0.25 Cr.
Total Material and Services 29 Cr.

KORBA STAGE-1 & 2 AND STAGE-3 CAPACITY CHARGES
FY 2019-20 2020-21 2021-22 2022-23 2023-24
ST-1 & 2
Total Fixed
Cost (in Lakh)
103745 106177 109004 111223 113849
Capacity Chage
( in Paisa/kwh)
71.18 73.05 74.99 76.52 78.11
ST-3
Total Fixed
Cost (in Lakh)
49024 48638 48412 48112 40601
Capacity Chage
( in Paisa/kwh)
140.07 139.35 138.71 137.84 116.01

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