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UDC 621.313.322
Khvalin D.I.
candidate of sciences (engineering), senior research worker Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine
DOI: 10.24412/2520-6990-2024-6199-19-23 WAYS FOR INCREASE OF POWERFUL TURBOGENERATORS RELIABILITY
Abstract.
A systematic analysis of turbogenerators reliability for different power is made and most often damaging main elements and component parts are determined. It is found that almost half of them are in the rotor and stator, one third of which are in the stator core and bars winding. Shown the influence of cooling type on the probability of turbogenerators unfailing operation for different power and the average specific ungenerate electricity due to stator defects for turbogenerators different types. It is concluded that a turbogenerator design complication and the use of new auxiliary systems for the cooling intensification with increasing power unit leads to the decrease of generator reliability. Therefore, three ways for compensate of turbogenerator reliability decrease are proposed: the system and methods control and diagnostics of generators main component parts, reserve, simplification of the main component parts design and non-use in number of auxiliary systems with help return to less efficient cooling.
Keywords: powerful turbogenerator, cooling system, damage, reliability indices, efficiency.
As a rule, the operation reliability of a high-use turbogenerators decreased when the use of new auxiliary systems with own specific defects causes generator failures as a whole, that is disconnections. A turbogenerator complication with the use degree rise occurs not only due to an increase in number of auxiliary systems, but also due to the design complication of a turbogenerator main component parts - stator, rotor, housing, etc., and is accompanied by the specific defects of these parts, typical for this system. These defects are as following [1-7]:
1) Only a turbogenerator without cooling systems.
- Defects in high-voltage stator insulation and aging insulation.
- Fastening slackening of the stator winding and
core.
- Pressing slackening and local heat of core.
- Presence of ferromagnetic objects into the stator.
- Coil and housing faults in the stator winding.
- Cracks of the rotor shaft, bandage rings and other rotor parts.
- Damage of rotor balancing.
- Damage of heat exchangers compactness (air-and gas-coolers, distillate coolers) and their binding elements .
2) A turbogenerator with hydrogen cooling system (indirect or direct).
- Damage of stator housing gas-compactness, rotor, and gas system elements.
- Damage of oil seals and shaft.
- Failures of gas-oil system elements.
- Presence of oil inside a generator.
3) A turbogenerator with water cooling of the stator winding.
- Damage of hydraulic tract joints compactness, including water-connecting pipes and insulation hoses.
- Cracks in the hollow copper conductors of the stator winding.
- Corrosion and obstruction of conductors.
- Damage of high-voltage insulation due to moisture.
- Failures of water cooling system elements for the stator.
4) A turbogenerator with water cooling of the rotor winding.
- Damage of hydraulic tract joints compactness, including water-distribution bushings and water-inlets.
- Cracks in the hollow copper conductors of the rotor coils.
- Corrosion and wear of copper conductors.
- Thermal imbalance.
The main reliability indices for turbogenerators are time between failures and readiness factor.
Average time between failures is defined as the ratio of the total operation time of an object with restoring efficiency to the mathematical expectation in number of failures during that operation. A statistical estimate of the average time between failures for an each turbogenerator can be obtained as the ratio of the total operating time for a given period to the number of failures during this period
ty
T =+, (1)
r
where r is the number of failures during the total operation time fe.
The readiness factor characterizes the ability of an object for required use at any time except for planned periods when its use is not provided. In the general case, it is defined as the ratio of operation time for a given period to the amount of operation and restoration time after failures during the same period
K =
, (2) ^Z + tRZ
where tRz is the time required for restoration after failures for a given period.
According to GOST 533-2000 reliability and durability indices for turbogenerators should not be lower shown in Table 1.
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Table 1
Turbogenerators reliability indices according to GOST 533-2000_
Index name Average value of index for a turbogenerator with power
to 350 MW over 350 MW
Readiness factor 0,996 (99,6 %) 0,995 (99,5 %)
Time between failures, hours 22000 18000
Resource between major repairs, years 8 5
Full period operation, years 40 40
to one and meet the limits of technological capabilities, that is at this stage it is impossible or entails great rise in price of Poi by improvement of the design and manufacture technology, then a turbogenerator complication due to the growth of power unit and the rise of use degree leads to the inevitable decrease of reliability operation and the rise of losses from unplanned repairs.
Reduced turbogenerators reliability with transition to a more complex design solutions related to cooling intensification is illustrated in Tables 2-4 shows the probabilities of unfailing operation Poi for the main generator component parts obtained by processing the damage operational data of many machines for a series of years [2, 8]. It can be seen that the transition from air to indirect hydrogen cooling for a power 25-30 MW leads to a decrease in the probability of a generator unfailing operation Pot from 0,92 to 0,78-0,82. The transition from indirect hydrogen cooling to direct hydrogen cooling of the rotor for a power 50-100 MW leads to a decrease in Pot from 0,74-0,87 to 0,62-0,66.
Table 2
Cooling type influence on the probability of turbogenerators unfailing operation with a power 25 -30 MW
Turbogenerator component parts Cooling type and generator type
Air T2-25-2 Hydrogen TGV-25 Indirect TV2-30-2
Stator 0,97 1,0 0,98
Rotor 0,97 0,98 0,99
Brush-contact apparatus 0,99 0,99 0,97
Exciter and excitation system 0,99 0,99 0,98
Gas-compactness (generator housing, pipelines, fittings, etc.) - 0,95 0,96
Shaft oil seals and oil supply system - 0,9 0,89
Turbogenerator as a whole 0,92 0,82 0,78
Table 3
Cooling type influence on the probability of turbogenerators unfailing operation with a power 50-100 MW_
Turbogenerator component parts Cooling type and generator type
Indirect hydrogen Direct hydrogen
TV-50-2 TV-60-2 TV2-100-2 TVF-60-2 TVF-100-2
Stator 0,99 0,98 0,98 0,95 0,96
Rotor 0,98 0,98 0,97 0,99 0,97
Brush-contact apparatus 0,98 0,96 0,97 0,95 0,94
Exciter and excitation system 0,99 0,96 0,93 0,95 0,91
Gas-compactness (generator housing, pipelines, fittings, etc.) 0,97 0,97 0,91 0,9 0,9
Shaft oil seals and oil supply system 0,96 0,86 0,95 0,79 0,86
Turbogenerator as a whole 0,87 0,74 0,74 0,66 0,62
as a whole without exciter and excitation system 0,88 0,77 0,80 0,7 0,68
as a whole without seals and gas system 0,94 0,88 0,86 0,85 0,8
It is also used for analyze the forced downtime factor
q = 1-K. (3)
These indices fully determines the probability of unfailing operation during a given period operation t
P0 = K exp (-t/T). (4)
Because the probability of a turbogenerator unfailing operation Pot is defined as the product of the probability of unfailing operation Poi for its component parts and auxiliary systems
n
Pot =np. , (5)
i=1
it is clear that the use of each new system will be accompanied by a decrease in the probability of a turbogenerator unfailing operation as a whole, unless simultaneously the probability of unfailing operation for all or a certain number of component parts and auxiliary systems is increased accordingly. But if the Poi are close
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Table 4
Cooling type influence on the probability of turbogenerators unfailing operation with a power 150-300 MW
Turbogenerator component parts Cooling type and generator type
Direct hydrogen Direct hydrogen plus water cooling of the stator winding
TGV-200 TGV-300 TVV-165-2 TVV-200-2
Stator 0,96 0,97 0,87 0,78
Rotor 0,92 1,0 0,99 1,0
Brush-contact apparatus 0,9 0,54 0,86 0,93
Exciter and excitation system 0,79 0,8 0,86 0,95
Gas-compactness (generator housing, pipelines, fittings, etc.) 0,75 0,68 0,74 0,93
Shaft oil seals and oil supply system 0,8 0,84 0,75 0,86
Turbogenerator as a whole 0,38 0,24 0,34 0,55
Stator and rotor 0,88 0,97 0,86 0,78
The transition influence to stator water cooling with direct hydrogen cooling of the rotor for turbogenerators with a power 150-300 MW can only be estimated by eliminating the influence of the sharp difference Poi for excitation systems, brush-contact apparatus and other component parts for turbogenerators of different types. For that end in view can compare Po for the «rotor-stator» complex this value is 0,88-0,97 without water cooling of the stator winding (for TGV-200, TGV-300) and decreases to 0,78-0,86 with water cooling of the stator winding (TVV-165-2, TVV-200-2).
Very volumetric data in 1993-2005 and 20062010 years (after operating time) for large group of a turbogenerators with a power 165, 200, 300 MW are given in [8]. According to these data the average specific ungenerate electricity due to stator defects is calculated (Table 5). For a turbogenerators with hydrogen cooling of the stator winding the specific ungenerate in 2006-2010 years was 2 kW-h/gen.yr, and for a turbogenerators with water cooling of the stator winding -4,7 kW-h/gen.yr, that is more than twice. The average values for the whole period from 1993 to 2010 years were 5,6 and 6,9 kW-h/gen.yr respectively, that is 23 % higher with direct water cooling against gas.
Table 5
The average specific ungenerate electricity due to stator defects for turbogenerators different types
Generator type and stator winding cooling 1993-2005 years 2006-2010 years Total
Ungener- ate, kW-h/yr Number of turbogenerators Ungener- ate, kW-h/yr Number of turbogenerators Ungenerate
kW-h/yr 19932005 per 1 generator 20062010
Direct hydrogen
TGV-200 293,7 74 104,9 84
TGV-300 691,5 66 203,9 69
As a result 985,2 140 308,8 153 7,04 2,02
Average magnitude 5,6
Direct water
TGV-200M 344 15 38,2 26
TVV-165-2 261,1 64 418,5 68
TVV-200-2 445 13 119,2 13
TVV-200-2A 35,3 15 51,2 23
TVV-320-2 230,5 62 322,3 69
As a result 1315,9 169 949,4 199 7,78 4,77
Average magnitude 6,9
It is stated in [8] that for turbogenerators with a power 200-1000 MW the lowest forced downtime factor q = 0,2-0,3 % has generators 200-300 MW with hydrogen cooling, q increases to 0,5 % and more for power 200-500 MW and higher with stator hydrogen-
water cooling and rotor hydrogen cooling, q increases significantly above 0,5 % (normal) and reaches 1-2 % and more for turbogenerators with rotor water cooling. Foreign statistics gives quantitatively similar results (Fig. 1).
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Fig. 1 The relative duration of turbogenerators forced downtime
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Thus, a turbogenerator design complication and the use of new auxiliary systems for the cooling intensification with increasing power unit leads to the decrease of generator reliability [9-11].
Therefore, the system and methods control and diagnostics of generators main component parts (SCDG) for compensate this decrease in the reliability of a turbogenerators were developed. The purpose of SCDG is early detection of progressive errors in the operation of generators component parts and auxiliary systems that can causes forced disconnections and large losses, as well as timely elimination of these errors, for example during planned-preventive repairs. The effective functioning of SCDG increases the operation reliability (Poi) of generators component parts and auxiliary systems and therefore economically advisable, despite the need of the cost for creation and maintenance of SCDG on conditions that SCDG have the high reliability and the low probability of false diagnoses.
Another way for ensure reliability with complication of a turbogenerator and auxiliary systems is reserve. Thus, it is necessary to reserve unreliable excitation systems due to the low quality of component parts and the large quantity of systems elements.
Finally, the third way for ensure reliability is simplification of the main component parts design and non-use in number of auxiliary systems with help return to less efficient cooling on conditions that it ensures given power unit with a modern technical solutions [12-15]. In this case, the inevitable reconsideration of the approaches and criterions previously adopted from the standpoint of economic efficiency (for example, specific losses reduction per 1 kW of installed power) towards the increase in reliability and the reduction in price of maintenance, even if are material use deterioration and efficiency reduction.
Conclus ions
A turbogenerator design complication and the use of new auxiliary systems for the cooling intensification with increasing power unit leads to the decrease of generator reliability. Therefore, the system and methods control and diagnostics of generators main component parts for compensate this decrease in the reliability of a turbogenerators were developed. Another way for ensure reliability with complication of a turbogenerator and auxiliary systems is reserve. Finally, the third way for ensure reliability is simplification of the main component parts design and non-use in number of auxiliary systems with help return to less efficient cooling on conditions that it ensures given power unit with a modern technical solutions.
Literature
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