JP2006312882A

JP2006312882A - Steam turbine power generation plant and its operation method

Info

Publication number: JP2006312882A
Application number: JP2005134939A
Authority: JP
Inventors: Yuji Otsuka; 祐司大塚
Original assignee: Hitachi Engineering Co Ltd; Hitachi Ltd
Current assignee: Hitachi Engineering Co Ltd; Hitachi Ltd
Priority date: 2005-05-06
Filing date: 2005-05-06
Publication date: 2006-11-16

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine power generation plant capable of further reducing the minimum load and enlarging operation mode without making a large modification and review of the design. SOLUTION: A condenser vacuum adjustment device 22 for adjusting the vacuum of a condenser 10 is constructed to inject air into the condenser 10 during operation in a range between the preset maximum load and minimum load when reduction of the minimum load is commanded. By thus intentionally reducing the vacuum of the condenser 10, an amount of evaporation in a boiler 1 of the steam turbine power generation plant is increased and the minimum feedwater flow rate of the boiler is ensured so that the minimum load can be further reduced. COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は蒸気タービン発電プラント及びその運転方法に係り、特に、抽出空気配管を介して復水器内に空気を給排することで復水器内の真空度を制御して蒸気タービンのラビング振動を防止し、かつ発電プラントの最低運用負荷を引下げ得る蒸気タービン発電プラント及びその運転方法に関する。 The present invention relates to a steam turbine power plant and a method for operating the same, and more particularly, by controlling the degree of vacuum in the condenser by supplying and discharging air into the condenser via an extraction air pipe, and rubbing vibration of the steam turbine. The present invention relates to a steam turbine power plant that can prevent the occurrence of power failure and reduce the minimum operating load of the power plant, and an operation method thereof.

一般に、蒸気タービン発電プラントにおいて、部分負荷運用時や、冷却水が低下する冬季運転時には、復水器の真空度が定格真空度以上の高真空度に達してタービンケーシング等を負圧によって変形させることがある。そのため、タービンラビング振動が発生し、タービントリップに至ることがある。このような高真空度に復水器内が至らないように、例えば特許文献１に示すように、復水器の真空度を調整する真空度調整装置を設けている。 In general, in a steam turbine power plant, during partial load operation or during winter operation when cooling water decreases, the vacuum level of the condenser reaches a high vacuum level higher than the rated vacuum level, and the turbine casing and the like are deformed by negative pressure. Sometimes. As a result, turbine rubbing vibrations may occur, leading to a turbine trip. In order to prevent the inside of the condenser from reaching such a high degree of vacuum, for example, as shown in Patent Document 1, a vacuum degree adjusting device for adjusting the vacuum degree of the condenser is provided.

特開平５−１１３２９４号公報JP-A-5-113294

上記従来の技術は、復水器の高真空による蒸気タービンのラビング振動防止を主とするものであり、運転モードの拡大についての配慮がなされていなかった。即ち、近年、蒸気タービン発電プラントの運用負荷の増大を図るために、最高負荷と最低負荷を定めた通常モードの運転を行うように定められていても、最低負荷をさらに引下げる要求がある。そのために、蒸気タービン発電プラントの各部の大幅な改造や設計の見直しが必要になる問題がある。 The above-described conventional technique mainly prevents the rubbing vibration of the steam turbine due to the high vacuum of the condenser, and no consideration has been given to the expansion of the operation mode. That is, in recent years, in order to increase the operation load of the steam turbine power plant, there is a demand to further reduce the minimum load even if it is determined to perform the normal mode operation in which the maximum load and the minimum load are determined. Therefore, there is a problem that each part of the steam turbine power plant needs to be remodeled or the design must be reviewed.

本発明の目的は、大幅な改造や設計の見直しを行うことなく、最低負荷をさらに引下げて運転モードの拡大を行うことができる蒸気タービン発電プラントを提供することにある。 An object of the present invention is to provide a steam turbine power plant that can further reduce the minimum load and expand the operation mode without performing significant modifications or design revisions.

本発明は上記目的を達成するために、復水器の真空度を調整する復水器真空度調整装置を、予め設定された最高負荷と最低負荷の範囲で運転中に、最低負荷の引下げ指令があったとき、前記復水器内に空気を注入するように構成したのである。 In order to achieve the above object, the present invention is directed to a command for lowering the minimum load during operation of a condenser vacuum degree adjusting device for adjusting the vacuum degree of the condenser in a range of preset maximum load and minimum load. When there is, air is injected into the condenser.

このように、復水器の真空度を故意的に低下させることで、蒸気タービン発電プラントのボイラの蒸発量を増加させてボイラの最低給水流量を確保し、最低負荷をさらに引下げることを可能としたのである。 In this way, by deliberately reducing the vacuum level of the condenser, it is possible to increase the amount of evaporation of the boiler of the steam turbine power plant to ensure the minimum feed water flow rate of the boiler and further reduce the minimum load It was.

以上説明したように本発明によれば、大幅な改造や設計の見直しを行うことなく、最低負荷をさらに引下げて運転モードの拡大を行うことができる蒸気タービン発電プラントを得ることができる。 As described above, according to the present invention, it is possible to obtain a steam turbine power plant that can further reduce the minimum load and expand the operation mode without performing significant remodeling or design review.

以下本発明による蒸気タービン発電プラントの一実施の形態を図１及び図２に示す再生・再熱式蒸気タービン発電プラントに基づいて説明する。 Hereinafter, an embodiment of a steam turbine power plant according to the present invention will be described based on the regenerative / reheat steam turbine power plant shown in FIGS. 1 and 2.

本実施の形態による蒸気タービン発電プラントは、大きくは、ボイラ１と、高圧タービン２と、この高圧タービン２と同軸の中圧タービン３及び低圧タービン４Ａ，４Ｂと、前記高圧タービン２と同軸の発電機５とより構成されている。 The steam turbine power plant according to the present embodiment mainly includes a boiler 1, a high-pressure turbine 2, a medium-pressure turbine 3 and low-pressure turbines 4A and 4B that are coaxial with the high-pressure turbine 2, and power generation that is coaxial with the high-pressure turbine 2. And machine 5.

前記ボイラ１で発生した蒸気ａは、配管６によって前記高圧タービン２に導入され、仕事をした後、一部は低温再熱蒸気ｂとして配管７を介してボイラ再熱器８に導入される。低温再熱蒸気ｂはボイラ再熱器８によって昇温され、高温再熱蒸気ｃとなって配管９を介して中圧タービン３に導入される。中圧タービン３で仕事をし終えた蒸気ｄは低圧タービン４Ａ，４Ｂに導入されて仕事を行う。このように、蒸気を導入することで、高圧タービン２、中圧タービン３、低圧タービン４Ａ，４Ｂは回転し、それにより発電機５を駆動して発電が行われる。低圧タービン４Ａ，４Ｂで仕事をなし終えた蒸気の殆どは復水器１０内に導入される。 The steam a generated in the boiler 1 is introduced into the high-pressure turbine 2 through a pipe 6 and after working, a part thereof is introduced into the boiler reheater 8 through the pipe 7 as low-temperature reheated steam b. The low-temperature reheat steam b is heated by the boiler reheater 8, becomes high-temperature reheat steam c, and is introduced into the intermediate pressure turbine 3 through the pipe 9. The steam d that has finished working in the intermediate pressure turbine 3 is introduced into the low pressure turbines 4A and 4B to perform work. In this way, by introducing the steam, the high-pressure turbine 2, the intermediate-pressure turbine 3, and the low-pressure turbines 4 A and 4 B rotate, thereby driving the generator 5 to generate power. Most of the steam that has finished work in the low-pressure turbines 4 A and 4 B is introduced into the condenser 10.

復水器１０内に導入された蒸気は、冷却器１１によって冷却され、復水ｅとなる。復水器１０内の復水ｅは、復水ポンプ１２にて昇圧され、配管１３を経由し、低圧供給水加熱器１４にて昇温される。この低圧供給水加熱器１４は、低圧タービン４Ａからの抽気ｆを配管１５を介して導いて復水ｅを昇温させるものである。昇温された復水ｅは、中圧タービン３からの低温再熱蒸気ｇと共に脱気器１６で脱酸素後、ボイラ給水ポンプ１７で昇圧され、さらに、前記低温再熱蒸気ｂにより加熱される第２高圧給水加熱器１８及び高圧タービン２からの抽気ｈにより加熱される第１高圧給水加熱器１９で昇温された後、ボイラ１に給水される。 The steam introduced into the condenser 10 is cooled by the cooler 11 and becomes condensed water e. The condensate e in the condenser 10 is boosted by the condensate pump 12 and is heated by the low-pressure feed water heater 14 via the pipe 13. The low-pressure feed water heater 14 guides the bleed air f from the low-pressure turbine 4A through the pipe 15 to raise the temperature of the condensate e. The heated condensate e is deoxygenated by the deaerator 16 together with the low-temperature reheated steam g from the intermediate pressure turbine 3, then pressurized by the boiler feed pump 17, and further heated by the low-temperature reheated steam b. The temperature is raised by the first high-pressure feed water heater 19 heated by the second high-pressure feed water heater 18 and the extraction h from the high-pressure turbine 2, and then supplied to the boiler 1.

一方、前記復水器１０は、抽出空気配管２０を介して連結された空気抽出器２１により、抽気することで所定の真空度を維持するようにしている。さらに、前記空気抽出器２１の上流側の抽出空気配管２０には、復水器真空度調整装置２２が設けられており、部分負荷運用時や冷却水が低下する冬季運転時における復水器１０の真空度の変化を調整している。 On the other hand, the condenser 10 maintains a predetermined degree of vacuum by extracting air with an air extractor 21 connected via an extraction air pipe 20. Further, the extraction air pipe 20 upstream of the air extractor 21 is provided with a condenser vacuum degree adjusting device 22, and the condenser 10 at the time of partial load operation or winter operation when cooling water is lowered. The change in the degree of vacuum is adjusted.

前記復水器真空度調整装置２２は、空気吸込み口２３を先端に備えた空気吸込み管２４を前記抽出空気配管２０の前記空気抽出器２１よりも上流側に連結しており、この空気吸込み管２４には復水器真空調整弁２５と復水器真空調整止弁２６とが空気流入方向の順に設けられている。前記復水器真空調整弁２５は、圧力調整器２７と圧力発信器２８とによって開度を調整され、前記復水器真空調整止弁２６は前記復水器真空調整弁２５と電気的又は機械的に連動して開閉すると共に、緊急時には圧力スイッチ２９の作動に伴って全閉するようにしている。前記圧力発信器２８と圧力スイッチ２９とは、配管３０を介して復水器１０内の圧力によって作動するように構成されている。 The condenser vacuum degree adjusting device 22 connects an air suction pipe 24 having an air suction port 23 at the tip thereof to an upstream side of the air extractor 21 of the extraction air pipe 20, and this air suction pipe 24 is provided with a condenser vacuum adjustment valve 25 and a condenser vacuum adjustment stop valve 26 in the order of the air inflow direction. The condenser vacuum adjustment valve 25 is adjusted in opening degree by a pressure regulator 27 and a pressure transmitter 28, and the condenser vacuum adjustment stop valve 26 is electrically or mechanically connected to the condenser vacuum adjustment valve 25. In conjunction with the operation, the pressure switch 29 is fully closed in an emergency. The pressure transmitter 28 and the pressure switch 29 are configured to be operated by the pressure in the condenser 10 through the pipe 30.

上記構成の復水器真空度調整装置２２の運転は、図２及び図３に示すように、蒸気タービン発電プラントの通常運転時には、復水器１０の真空度を維持するために、復水器１０の胴体から抽出空気配管２０を経由して空気抽出装置２１によって復水器１０内部の非凝縮ガスや微少な空気漏れを外部に放出している。一方、復水器１０内の真空度が定格真空度以上の第１高真空度（例えば７３５ｍｍＨｇ）に達したことを圧力発信器２８が検出すると、圧力発信器２８は圧力調整器２７を介して復水器真空調整弁２５に開指令を与えて開かせ、さらに第１高真空度を超えて第２高真空度（例えば７４０ｍｍＨｇ）になった場合には、復水器真空調整弁２５を全開するように弁開度を制御するように構成されている。このような復水器真空調整弁２５に連動して復水器真空調整止弁２６の開度も制御される。他方、復水器１０内の真空度制御が不調となって真空度が低下した場合には、真空極低トリップを回避するために、圧力スイッチ２９によって、復水器真空調整弁２５との連動よりも優先させて復水器真空調整止弁２６を強制的に閉じさせる（保護インターロック）。 As shown in FIGS. 2 and 3, the condenser vacuum degree adjusting device 22 having the above-described configuration is operated in order to maintain the degree of vacuum of the condenser 10 during normal operation of the steam turbine power plant. Non-condensable gas and minute air leakage inside the condenser 10 are discharged to the outside by the air extraction device 21 from the body 10 through the extraction air pipe 20. On the other hand, when the pressure transmitter 28 detects that the degree of vacuum in the condenser 10 has reached the first high vacuum level (for example, 735 mmHg) equal to or higher than the rated vacuum level, the pressure transmitter 28 is connected via the pressure regulator 27. When the condenser vacuum adjustment valve 25 is given an open command to be opened, and the first high vacuum degree is exceeded and the second high vacuum degree (eg, 740 mmHg) is reached, the condenser vacuum adjustment valve 25 is fully opened. In this way, the valve opening is controlled. The opening degree of the condenser vacuum adjustment stop valve 26 is also controlled in conjunction with such a condenser vacuum adjustment valve 25. On the other hand, when the degree of vacuum is lowered due to the malfunction of the degree of vacuum control in the condenser 10, the pressure switch 29 interlocks with the condenser vacuum adjustment valve 25 in order to avoid a vacuum extremely low trip. The condenser vacuum adjustment stop valve 26 is forcibly closed with priority over (protective interlock).

以上が予め設定された最高負荷（１００％）と最低負荷（例えば３０％）の範囲で運転が行われる第１運転である。 The above is the first operation in which the operation is performed in the range of the preset maximum load (100%) and minimum load (for example, 30%).

次に、上記第１運転中に最低負荷を引下げて運転することの要求があった場合の第２運転について、図４及び図５に基づいて説明する。 Next, the second operation when there is a request to reduce the minimum load during the first operation will be described with reference to FIGS. 4 and 5.

図３に示す通常運転モードでの第１運転をしているとき（図５のＳ１０）に、通常運転モードで定めた最低負荷３０％を、さらに引下げて例えば２５％となるように、最低負荷運転の変更指示があった場合（図５のＳ１１）には、２５％の最低負荷運用モードの切替えを手動あるいは自動的に行う（図５のＳ１２）。この切替えにより、例えば５０％負荷以下である４８％負荷から要求された２５％負荷の間を真空度可変設定範囲となるように前記復水器真空調整弁２５を開いて復水器１０内へ空気を流入させて真空度を低下させる（図５のＳ１３）。そして、変更要求があった２５％の最低運用負荷に達したら、復水器真空調整弁２５の開状態を維持する（図５のＳ１４）。このように、復水器１０の真空度を低下させることで、ボイラ１への給水流量を多くすることができ、設定された最低負荷をさらに引下げることができる。 When the first operation in the normal operation mode shown in FIG. 3 is performed (S10 in FIG. 5), the minimum load is set so that the minimum load 30% determined in the normal operation mode is further reduced to, for example, 25%. When there is an operation change instruction (S11 in FIG. 5), the 25% minimum load operation mode is switched manually or automatically (S12 in FIG. 5). By this switching, for example, the condenser vacuum adjustment valve 25 is opened and placed in the condenser 10 so that the vacuum degree variable setting range is between the 48% load, which is 50% load or less, and the required 25% load. Air is introduced to lower the degree of vacuum (S13 in FIG. 5). Then, when the minimum operating load of 25% at which the change request has been made is reached, the condenser vacuum adjustment valve 25 is kept open (S14 in FIG. 5). Thus, by reducing the vacuum degree of the condenser 10, the feed water flow rate to the boiler 1 can be increased, and the set minimum load can be further reduced.

このように、最低負荷の引下げ要求があった場合、復水器真空度調整装置２２の復水器真空調整弁２５を開いて復水器１０の真空度を低下させることで、ボイラ１への給水流量を多くすることができるので、引下げた最低負荷での運転が可能となるのである。 In this way, when there is a request for lowering the minimum load, the condenser vacuum adjustment valve 25 of the condenser vacuum degree adjusting device 22 is opened to lower the vacuum degree of the condenser 10, so that the boiler 1 can be reduced. Since the feed water flow rate can be increased, the operation at the reduced minimum load becomes possible.

このように、最低負荷の引下げ要求に応じた運転中に、当所設定された通常運転範囲での運転に復帰する要求があった場合には、復水器真空調整弁２５を閉じて空気抽出装置２１を駆動させ、復水器１０内の空気を抽出して所定の真空度に戻すことで復帰することができる。この復帰運転が本発明による第３の運転になる。 In this way, when there is a request to return to the operation within the normal operation range set in this place during the operation in response to the request for lowering the minimum load, the condenser vacuum adjustment valve 25 is closed and the air extraction device is closed. It can be restored by driving 21 and extracting the air in the condenser 10 to return it to a predetermined degree of vacuum. This return operation is the third operation according to the present invention.

尚、復水器１０の真空度の低下させるため一例として、４８％負荷〜２５％負荷の間を真空度可変設定範囲となるように前記復水器真空調整弁２５を開いて復水器１０内へ空気を流入させるようにしたが、蒸気タービン発電プラントの容量や構成機器によっては、前記真空度可変設定範囲が４８％負荷〜２５％負荷以外になることは当然である。 In order to lower the vacuum degree of the condenser 10, as an example, the condenser vacuum adjustment valve 25 is opened so that the vacuum degree variable setting range is between 48% load and 25% load. Although air is allowed to flow in, the vacuum degree variable setting range is naturally other than 48% load to 25% load depending on the capacity of the steam turbine power plant and the components.

本発明による蒸気タービン発電プラントの一実施の形態を示すブロック図。1 is a block diagram showing an embodiment of a steam turbine power plant according to the present invention. 図１に示された復水器真空度調整装置の詳細図。FIG. 2 is a detailed view of the condenser vacuum degree adjusting device shown in FIG. 1. 図１に示された蒸気タービン発電プラントの通常運転モードにおける復水器真空度設定図。The condenser vacuum degree setting figure in the normal operation mode of the steam turbine power plant shown in FIG. 図１に示された蒸気タービン発電プラントの最低負荷引下げ後の運転モードにおける復水器真空度設定図。The condenser vacuum degree setting figure in the operation mode after the minimum load reduction of the steam turbine power plant shown in FIG. 図１に示された蒸気タービン発電プラントの最低負荷引下げ運転を示すフローチャート。The flowchart which shows the minimum load reduction operation | movement of the steam turbine power plant shown in FIG.

符号の説明Explanation of symbols

１…ボイラ、２…高圧タービン、３…中圧タービン、４Ａ，４Ｂ…低圧タービン、５…発電機、８…ボイラ再熱器、１０…復水器、１１…冷却器、１４…低圧供給水加熱器、１６…脱気器、１７…ボイラ給水ポンプ、１８…第２高圧給水加熱器、１９…第１高圧給水加熱器、２０…抽出空気配管、２１…空気抽出器、２２…復水器真空度調整装置、２３…空気吸込み口、２４…空気吸込み管、２５…復水器真空調整弁、２６…復水器真空調整止弁、２７…圧力調整器、２８…圧力発信器、２９…圧力スイッチ。 DESCRIPTION OF SYMBOLS 1 ... Boiler, 2 ... High pressure turbine, 3 ... Medium pressure turbine, 4A, 4B ... Low pressure turbine, 5 ... Generator, 8 ... Boiler reheater, 10 ... Condenser, 11 ... Cooler, 14 ... Low pressure feed water Heater, 16 ... deaerator, 17 ... boiler feed pump, 18 ... second high pressure feed water heater, 19 ... first high pressure feed water heater, 20 ... extraction air piping, 21 ... air extractor, 22 ... condenser Vacuum adjustment device, 23 ... Air suction port, 24 ... Air suction pipe, 25 ... Condenser vacuum adjustment valve, 26 ... Condenser vacuum adjustment stop valve, 27 ... Pressure regulator, 28 ... Pressure transmitter, 29 ... pressure switch.

Claims

復水器を備えた蒸気タービン発電設備と、前記復水器内から抽出空気配管を介して空気を抽出する空気抽出装置と、この空気抽出装置の上流側の前記抽出空気配管に接続され前記復水器の真空度を調整する復水器真空度調整装置とを有する蒸気タービン発電プラントにおいて、前記復水器真空度調整装置は、予め設定された最高負荷と最低負荷の範囲で運転中に、最低負荷の引下げ指令があると、前記復水器内に空気を注入して前記最低負荷より低負荷での運転が行われるように構成されていることを特徴とする蒸気タービン発電プラント。 A steam turbine power generation facility equipped with a condenser, an air extraction device for extracting air from the condenser through an extraction air piping, and the extraction air piping upstream of the air extraction device and connected to the condenser In a steam turbine power plant having a condenser vacuum degree adjusting device for adjusting the vacuum degree of a water vessel, the condenser vacuum degree adjusting device is operating in a range of preset maximum load and minimum load, A steam turbine power plant configured to perform operation at a lower load than the minimum load by injecting air into the condenser when a minimum load reduction command is issued.

復水器を備えた蒸気タービン発電設備と、前記復水器内から抽出空気配管を介して空気を抽出する空気抽出装置と、この空気抽出装置の上流側の前記抽出空気配管に接続され前記復水器の真空度を調整する復水器真空度調整装置とを有する蒸気タービン発電プラントにおいて、前記復水器真空度調整装置は、予め設定された最高負荷と最低負荷の範囲で運転中に、最低負荷の引下げ指令があると、前記復水器内に空気を注入して前記最低負荷より低負荷での運転が行われるように構成されており、また前記空気抽出装置は、前記最低負荷より低負荷での運転が行われるときに、予め設定された最高負荷と最低負荷の範囲で運転する指令があると、前記復水器内の空気を抽出するように構成されていることを特徴とする蒸気タービン発電プラント。 A steam turbine power generation facility equipped with a condenser, an air extraction device for extracting air from the condenser through an extraction air piping, and the extraction air piping upstream of the air extraction device and connected to the condenser In a steam turbine power plant having a condenser vacuum degree adjusting device for adjusting the vacuum degree of a water vessel, the condenser vacuum degree adjusting device is operating in a range of preset maximum load and minimum load, When there is a command to lower the minimum load, air is injected into the condenser so that the operation is performed at a lower load than the minimum load. It is configured to extract air in the condenser when there is a command to operate in a range between a preset maximum load and minimum load when operation at a low load is performed. Steam turbine power generation plan .

復水器を備えた蒸気タービン発電設備と、前記復水器内から抽出空気配管を介して空気を抽出する空気抽出装置と、この空気抽出装置の上流側の前記抽出空気配管に接続され前記復水器の真空度を調整する復水器真空度調整装置とを有する蒸気タービン発電プラントの運転方法において、予め設定された最高負荷と最低負荷の範囲で運転する第１運転と、この第１運転中に、最低負荷の引下げ指令があると、前記復水器真空度調整装置によって前記復水器内に空気を注入して前記最低負荷より低負荷で運転する第２運転とで運転することを特徴とする蒸気タービン発電プラントの運転方法。 A steam turbine power generation facility equipped with a condenser, an air extraction device for extracting air from the condenser through an extraction air piping, and the extraction air piping upstream of the air extraction device and connected to the condenser In a method for operating a steam turbine power plant having a condenser vacuum degree adjusting device for adjusting a vacuum degree of a water vessel, a first operation that operates in a range between a preset maximum load and a minimum load, and the first operation. If there is a command to lower the minimum load, the operation is performed in the second operation in which air is injected into the condenser by the condenser vacuum degree adjusting device and the operation is performed at a load lower than the minimum load. A method of operating a steam turbine power plant.

復水器を備えた蒸気タービン発電設備と、前記復水器内から抽出空気配管を介して空気を抽出する空気抽出装置と、この空気抽出装置の上流側の前記抽出空気配管に接続され前記復水器の真空度を調整する復水器真空度調整装置とを有する蒸気タービン発電プラントの運転方法において、予め設定された最高負荷と最低負荷の範囲で運転する第１運転と、この第１運転中に、最低負荷の引下げ指令があると、前記復水器真空度調整装置によって前記復水器内に空気を注入して前記最低負荷より低負荷で運転する第２運転と、この第２運転中に、前記第１運転に復帰する指令があると、前記空気抽出装置を駆動して前記復水器内の空気を抽出して前記第１運転に復帰する第３運転とで運転することを特徴とする蒸気タービン発電プラントの運転方法。 A steam turbine power generation facility equipped with a condenser, an air extraction device for extracting air from the condenser through an extraction air piping, and the extraction air piping upstream of the air extraction device and connected to the condenser In a method for operating a steam turbine power plant having a condenser vacuum degree adjusting device for adjusting a vacuum degree of a water vessel, a first operation that operates in a range between a preset maximum load and a minimum load, and the first operation. If there is a command for lowering the minimum load, a second operation for injecting air into the condenser by the condenser vacuum degree adjusting device and operating at a lower load than the minimum load, and this second operation If there is a command to return to the first operation, the air extraction device is driven to extract the air in the condenser and to operate in the third operation to return to the first operation. Features of steam turbine power plant operation Law.