BEST OPERATING & MAINTENANCE PRACTICES RELATED
TO
21 MW & 16 MW STEAM TURBO-GENERATORS
Dr T. G. Sundara Raman
Seshasayee Paper & Boards Limited
IPPTA Zonal Seminar
Best Maintenance Practices in Pulp & Paper Mill to
Improve Profitability
18th
Pune
July 2014
1
Steam turbo-generators
Generator Winding Section
• Power generation enhancement is directly related to increase in
current produced [I**2]
• In turn , it heats up the core winding [stator and rotor].
• It results in winding temperature increase.
• Heat is dissipated to air in closed circulation on the exterior
enclosed air duct.
• Hot air in turn is cooled by cooling water flowing inside the finned
tubes of the heat exchanger.
• The cycle continues with windings being kept below a set
temperature with alarm set at 85 deg C and trip at 95 deg c.
Steam turbo-generators
in SPB –Erode Unit
• CPP- 21 MW Double Extraction
Condensing Steam Turbo-generator of
BHEL
• Chemical Recovery Complex- 16 MW
Extraction Back Pressure Steam TurboGenerator of BHEL
Power input rating of the Generators
Rated
Power
21 MW
16 MW
Power
Factor
0.80
0.80
Power input
[MVA]
26.25
20.0
CASE -1
21 MW STEAM TURBO-GENERATOR
21 MW STG Air Water Circuit -Existing
.
21 MW Steam Turbo-GENERATOR
Temperature record of Generator Winding and other related temperatures
PF : High [0.97-0.98 ]
Before Cleaning
of HX
After Cleaning of
HX
05/06/14: 14 h
19/06/14 : 20 h
0.97
0.98
MW
15.3
15.3
#1
C
85.3
77.2
8
#2
C
-
-
-
#3
C
88.1
80.1
8
#4
C
76.1
73.6
3
#5
C
72.9
65.2
8
#6
C
86.7
78.3
8
#7
C
87.5
79.4
8
#8
C
89.6
81.2
8
Cold air temperature
C
54/56
49
6
Hot air temperature
C
65/66
58/59
7
CW in temperature
C
37
35
2
CW out temperature
C
42
39
3
Date/Time
P.F.
Power Generation
Temperature
reduction ,°C
Winding Temperature
100
21 MW ST GeneratorTem perature Schedule
[Before & After Cleaning of Air & Water Sides]
Temperature Deg C
90
80
70
60
50
40
30
20
W1 W2 W3 W4 W5 W6 W7 W8
Bef Clean
After Clean
Cold Air
Hot Air
CW in
CW out
CASE -2
• 16 MW STEAM TURBO-GENERATOR
16 MW STG Air Water Circuit -Existing
Power input rating of the Generators
21 MW
16 MW
Rated Power
Power Factor
0.80
0.98
0.80
0.98
Power input
[MVA]
26.25
20.6
20
16.3
16 MW Steam Turbo-GENERATOR
Temperature record of Generator Winding and other related temperatures
IMPACT OF HIGH & LOW PF ON WINDING & AIR TEMPERATURES
Temperature
increase ,°C
0.98
0.81
13/06/14
11/06/14
After
After
MW
11.13
10.7
#1
C
72.2
81.8
10
#2
C
74.0
82.7
9
#3
C
73.0
83.5
10.5
#4
C
75.0
83.7
9
#5
C
71.7
82.5
9
#6
C
73.6
83.5
10
Cold air temperature
C
42/41
44.6/44.4
3
Hot air temperature
C
59.6/55.6
62.2/58.8
3
CW in temperature
C
27
28
CW out temperature
C
34
35
Power Factor
Date/Time
Cleaning of HX
Power Generation
Winding Temperature
ΔT : 7°C
16 MW ST GeneratorTem perature Schedule
Temperature Deg C
90 [Impact of High & Low P.F.on Winding Temperatures]
80
70
60
50
40
30
20
W1 W2 W3 W4 W5 W6 W7 W8
PF :0.98
PF:0.81
Cold Air
Hot Air
CW in
CW out
21 MW Generator
Issue : High Winding Temperature
•
High Cooling water inlet temperature of ~ 36 37°C due to poor cooling tower performance.
• Cooling water chemical treatment need to be
improved & should be commensurate with the
operating COC.
• All the 8 coolers are on line.
16 MW Generator
Issue : High Winding Temperature
• CW temperature differential across generator
had gone up from 4°C to 7°C.
• More than heat dissipation, probably cooling
water flow through generator cooler would have
dropped. CW flow restriction needs to be looked
into & cleared.
Winding temperature increase Due to
• Stator & Rotor Core heat losses directly
proportional to square of increasing current
• Copper & Iron Core heat loss with increase in
Winding temperature associated with the above
• Frictional Heat & Field Losses
• Reduced Power factor results in Reactive
Power loss
• Harmonic current heat losses
Heat loss reduction achieved
through
• Increase in Power Factor
• Reduced Generation load
• Harmonic loss reduction
Winding temperature reduction
Achieved through • Lowered hot air temperature
• Lowered cold air temperature
• Lowered inlet cooling water temperature
• High cleanliness of air ducts & HX exterior
• Minimal dirt/deposits over the winding coils
• Ensuring Quality cooling water devoid of
suspended impurities & foulant ( scales).
MEASURES ADVOCATED
• Quality cooling water to be ensured
• Periodic cleaning of heat exchanger tubes ( waterside)
• Occasional cleaning of air side/duct off dust/dirt
• Occasional cleaning of winding coil exterior ( during
annual shut of the STG), if there is approach.
• Cooling tower & chemical conditioning of CW to be
in order.
CONCLUSIONS &
RECOMMENDATIONS
• Quality cooling water to be ensured
• Periodic cleaning of heat exchanger tubes
( water-side)
• Occasional cleaning of air side/duct off
dust/dirt
• Occasional cleaning of winding coil exterior
( during annual shut of the STG), if there is
approach.
CONCLUSIONS & RECOMMENDATIONS
• Ensure desired rate of cooling water flow ( say to maintain 2.5
to 3.5 Deg C temperature differential)
• Cooling tower & chemical conditioning of CW to be in order.
• High Power factor leads to lowered heat losses from the
Generator resulting in reduction in Winding temperatures.
• All of the above if practiced on a sustained basis would ensure
longevity of the Generator unit , thereby resulting in 100%
availability of the same.
GALVANIC CORROSION OF HX
&
MITIGATIONAL MEASURES
Cathodic Protection
• Tube sheet and finned tubes are of different
materials.
• Hence there will be Galvanic Corrosion due to
high Electrochemical Potential difference
between the materials resulting in corrosion of
tube sheet.
• Hence Zinc anode ( sacrificial anode) pieces
are installed over the tube sheet cover to
ensure longevity life of tube sheet/tubes.
WAY FORWARD
• For ensuring Winding temperatures to be well within the
recommended limits , be it at full load or low power
factor operation of the Generator, both water and air
sides are to be cleaned off deposit/silt/foulant on
sustained basis.
• As for cooling water, the quality should be good devoid
of foulant; the cooling water temperature should be
preferably <34°C & the flow should be maintained to
have low temperature difference (say 3 to 4 °C).
• Zinc bars attached to the tube sheet should be checked
at any available opportunity to be healthy
• The successful operating concept shall be extended to
all Generator Air water Heat exchangers for increased
Productivity
.
Good Maintenance
.
Practice
Ensures Productivity
27