A gas-steam combined cycle unit FCB operation method of a self-provided power plant

Abstract

This invention discloses a method for operating a gas-fired combined cycle (FCB) turbine unit in a self-owned power plant, comprising: 1) setting the gas-fired combined cycle turbine unit of the self-owned power plant according to FCB operation requirements; 2) when a distribution network fault occurs, the unit disconnection control device issues a tripping command to enter FCB operation mode; 3) after receiving the FCB start signal, the gas-fired combined cycle turbine unit of the self-owned power plant enters FCB operation mode; 4) after the grid fault is cleared, it performs islanded operation and reconnects to the grid. This invention addresses the problem of drastic changes in unit parameters during sudden grid faults, where the gas-fired combined cycle turbine unit itself has low plant load, insufficient to maintain stable turbine operation, leading to abnormal turbine shutdowns and equipment damage, and reduces fuel consumption during restart, thus minimizing economic losses. While ensuring safe and stable unit operation, it also solves the public welfare problem of heat interruption caused by abnormal shutdowns.

Description

Technical Field

[0001] This invention belongs to the field of power generation technology, specifically relating to a method for operating a gas-steam combined cycle (FCB) unit in a self-owned power plant. Background Technology

[0002] With rapid economic and social development, gas-fired combined cycle (GC-C) units, compared to traditional coal-fired power plants, address both power generation and heating needs, thus placing higher demands on the units' reliability and continuous operation. However, during grid faults, the unit parameters of power plants undergo drastic changes. Due to the loss of auxiliary power, the unit equipment may become uncontrollable, easily escalating the accident and causing equipment damage. Furthermore, without a starting power source, the power plant can only passively wait for grid restoration, prolonging the restoration time. In recent years, accidents caused by power outages leading to wear on unit journals and bearings have increased. Therefore, improving the grid's self-healing capabilities and rapidly restoring grid power supply to ensure the power plant's auxiliary power supply is particularly important for the power system during grid faults. The FCB (Fast Cut Back) function refers to the automatic control function used to maintain unit operation while maintaining auxiliary power supply during normal operation, provided the unit is disconnected from the grid due to an external grid fault, instantly shedding all grid-side power loads without shutting down the generator. This is also known as islanded operation. Currently, gas generators are mainly used in China to realize the FCB function. However, there is a lack of a method to realize FCB operation in a power plant with a gas-steam combined cycle unit in a self-owned power plant for the purpose of using a gas-steam combined cycle unit in a self-owned power plant.

[0003] Defects and shortcomings of existing technology: When a temporary fault occurs in the power grid connected to a gas-steam combined cycle unit, it will cause drastic changes in the unit parameters, leading to abnormal shutdowns and damage to the unit equipment. Gas-steam combined cycle units themselves have relatively low plant loads, and the low loads are insufficient to maintain the stable operation of the turbine unit, resulting in unplanned turbine shutdowns. Furthermore, restarting the unit will consume a large amount of fuel and time, causing huge economic losses. On the other hand, it can easily cause public welfare problems such as heat supply interruptions due to abnormal shutdowns. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for operating a gas-fired combined cycle (FCB) unit in a self-owned power plant. The purpose is twofold: firstly, to solve the problem of instantly disconnecting all external power supply loads from the external grid when a fault occurs in the power grid connected to the gas-fired combined cycle unit of a self-owned power plant, without shutting down the unit, thus maintaining the power plant's self-consumption power. After the grid fault is cleared, the unit can quickly and effectively connect to the external grid to supply power to the system, carrying its own plant power load. Secondly, to ensure the waste heat boiler remains operational, effectively solving the problem of heating interruptions affecting people's livelihoods.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A method for operating a gas-fired combined cycle (FCB) unit in a self-owned power plant includes the following steps: 1) Configure the gas-steam combined cycle units of the self-owned power plant according to the FCB operating requirements; 2) When a grid fault occurs, the unit tripping control device issues a tripping command to enter FCB operation mode; 3) After receiving the FCB start signal, the gas-steam combined cycle unit of the self-owned power plant enters the FCB operation state, which includes two modes: Mode 1 refers to the gas turbine unit and the steam turbine unit entering the FCB operation state simultaneously. The external load of the gas turbine unit is supplied by the gas turbine unit side. The gas turbine unit control system TCS and the steam turbine unit control system DCS disconnect the load automatic control mode and switch the control mode from constant pressure control to frequency control mode. At the same time, the high-pressure side bypass and low-pressure side bypass of the steam turbine are set to constant pressure control state. The high-pressure side bypass and the low-pressure side bypass are opened, and the power generation load follows the plant power load and the external load. The demand for the load gradually reaches a stable state; Mode 2 refers to the gas turbine unit entering the FCB operating state, the steam turbine unit tripping, and at the same time, the gas turbine unit's external load fast-switching device receives a switching command, the external load is switched from the power supply side of the gas turbine unit to the power supply side of the other grid, the external load circuit breaker MCB is tripped, and the waste heat boiler bypass is opened; Mode 1 and Mode 2 are in sequential control logic. After the gas-steam combined cycle unit of the self-owned power plant receives the FCB start signal, it enters the FCB Mode 1 operating state. If the unit frequency exceeds the limit and the unit parameters cannot operate stably within the set time, the unit enters the FCB Mode 2 state; 4) Reconnect to the grid after islanding operation following grid fault clearance. This refers to the self-owned power plant's gas-steam combined cycle unit achieving synchronous grid connection through generator outlet circuit breakers GCB1 and GCB2. After the grid fault is cleared, the self-owned power plant's gas-steam combined cycle unit achieves synchronous grid connection through the main transformer high-voltage side circuit breaker THCB at synchronization point 3 after the islanding operation stabilizes. Since the self-owned power plant's gas-steam combined cycle unit's FCB operating state in step 3) includes two modes, if the self-owned power plant's gas-steam combined cycle unit operates stably in mode 1, the sequential control logic skips mode 2 within a set time and enters the pre-connection state at synchronization point 3 after the grid fault is cleared; otherwise, the sequential control logic is executed. The concurrent parallel point 1 is the gas generator outlet circuit breaker GCB1, and the concurrent parallel point 2 is the steam turbine generator outlet circuit breaker GCB2.

[0006] A further improvement of this invention is that step 1) of setting up the gas-steam combined cycle unit of the self-owned power plant according to the FCB operating requirements includes four aspects: a) The gas-steam combined cycle unit of the self-owned power plant adopts a 3-synchronous parallel point design; b) Modify the trip output of the gas turbine and steam turbine generator protection; c) The external loads other than the load of the gas-steam combined cycle unit have automatic grid and power supply switching functions; d) All equipment in the gas-steam combined cycle unit is interlocked in accordance with the FCB operation requirements.

[0007] A further improvement of the present invention is that, in step 2), when a grid fault occurs, the generator tripping control device issues a tripping command to enter the FCB operating state, which means that when the main transformer high-voltage side circuit breaker THCB is in the open position, the external load circuit breaker MCB is in the closed position, and the generator outlet circuit breaker is in the closed position, the FCB operating state is triggered.

[0008] A further improvement of this invention is that the target value for the frequency control mode of the gas-steam combined cycle unit of the self-owned power plant is 50Hz.

[0009] A further improvement of the present invention is that the tripping of the generator output circuit breakers GCB1 and GCB2 for the generator out-of-step protection and generator frequency protection of the gas-steam combined cycle unit is changed to the tripping of the main transformer high-voltage side circuit breaker THCB.

[0010] A further improvement of this invention is that the waste heat boiler tripping is interlocked in one direction with the power plant gas turbine tripping, the power plant gas turbine tripping is interlocked in two directions with the gas generator outlet circuit breaker GCB1 tripping, the steam turbine tripping is interlocked in two directions with the steam turbine outlet circuit breaker GCB2 tripping, the main transformer high-voltage side circuit breaker THCB tripping is not interlocked with the gas turbine outlet circuit breaker GCB2 tripping, and the main transformer high-voltage side circuit breaker THCB tripping is interlocked with the FCB start-up mode.

[0011] The present invention has at least the following beneficial technical effects: This invention proposes a gas-steam combined cycle (FCB) operation method for self-owned power plants. This method enables the FCB unit to instantly shed all power supply load to the grid during external grid failures, allowing both the gas turbine and turbine generator units to simultaneously enter islanded operation. This addresses the issue of drastic changes in unit parameters during sudden grid failures, where the FCB unit's own plant load is low and insufficient to maintain stable turbine operation, leading to abnormal turbine shutdowns and equipment damage. It also reduces fuel consumption during restart, minimizing significant economic losses. Furthermore, while ensuring safe and stable unit operation, this method also solves the public concern of heat supply interruptions caused by abnormal shutdowns. Attached Figure Description

[0012] Figure 1The main wiring diagram for implementing FCB function in a gas-steam combined cycle unit of a self-owned power plant includes a gas generator unit, a steam turbine generator unit, a gas generator outlet circuit breaker GCB1, a steam turbine generator outlet circuit breaker GCB2, a voltage transformer PT02 on the GCB1 side, a voltage transformer PT04 on the GCB2 side, a medium-voltage side external load circuit breaker MCB, a plant service transformer AT, a main transformer MT, a main transformer high-voltage side circuit breaker THCB, a main transformer high-voltage side voltage transformer PT05, a 220kV busbar, and a 220kV busbar voltage transformer PT06. The gas generator unit includes a gas generator, generator terminal voltage transformer PT01, and generator protection devices. The steam turbine generator unit includes a steam turbine generator, generator terminal voltage transformer PT03, and generator protection devices. The generator frequency protection and generator out-of-step protection tripping outputs are changed from generator output circuit breaker GCB tripping to main transformer high-voltage side circuit breaker THCB tripping. Gas generator output circuit breaker GCB1 is synchronization point 1, and voltage transformer PT02 and generator terminal voltage transformer PT01 provide the synchronization voltage required for synchronization point 1. Steam turbine generator output circuit breaker GCB2 is synchronization point 2, and voltage transformer PT04 and generator terminal voltage transformer PT03 provide the synchronization voltage required for synchronization point 1. Main transformer high-voltage side circuit breaker is synchronization point 3, and main transformer high-voltage side voltage transformer PT05 and 220kV bus voltage transformer PT06 provide the synchronization voltage required for synchronization point 3.

[0013] Figure 2 This diagram illustrates the interlocking logic for implementing FCB (Fuel Cell Buffer) functionality in a gas-fired combined cycle (GCCB) unit of a self-owned power plant. It includes waste heat boiler tripping, GCCB turbine tripping, generator outlet circuit breaker (GCB) tripping, main transformer high-voltage side circuit breaker (THCB) tripping, and FCB start-up mode. The interlocking logic is as follows: boiler tripping is directed unidirectionally to the GCCB turbine tripping in the self-owned power plant; GCCB tripping is directed bidirectionally to the generator outlet circuit breaker (GCB); canceling THCB tripping is directed bidirectionally to the generator outlet circuit breaker (GCB); and THCB tripping is directed unidirectionally to the FCB start-up mode.

[0014] Figure 3 This diagram illustrates the FCB startup logic module for a gas-steam combined cycle unit in a self-owned power plant, including the closed position of the medium-voltage side external load circuit breaker MCB, the open position of the main transformer high-voltage side circuit breaker THCB, the closed position of the generator outlet circuit breaker GCB, the AND logic module, and the FCB startup mode. Detailed Implementation

[0015] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0016] This invention provides a method for operating a gas-fired combined cycle (FCB) unit in a self-owned power plant, comprising the following steps: Step 1 involves setting up the gas-steam combined cycle unit of the self-owned power plant according to the FCB operating requirements, including three aspects: a) The gas-steam combined cycle unit of the self-owned power plant adopts a 3-synchronous parallel design; b) Modify the trip output of the gas turbine and steam turbine generator protection; c) The external load of the gas-steam combined cycle unit has an automatic switching function between the grid and the unit's power supply; d) All equipment in the gas-steam combined cycle unit is interlocked according to the FCB operating requirements.

[0017] (1) The gas-steam combined cycle unit of the self-owned power plant adopts a three-synchronous parallel point design: such as Figure 1 As shown, during normal startup of a gas-steam combined cycle unit, the gas-steam combined cycle unit of the self-owned power plant is connected to the grid through the gas generator outlet circuit breaker GCB1 (synchronization point 1), and the steam turbine generator outlet circuit breaker GCB2 (synchronization point 2). If grid instability exceeds limits, the unit disconnection control device will first automatically disconnect the high-voltage side circuit breaker THCB (synchronization point 3) of the main transformer of the gas-steam combined cycle unit, and the gas-steam combined cycle unit of the self-owned power plant will enter FCB operation mode. When the grid system fault is cleared, if the unit needs to be reconnected to the grid from islanded operation, it needs to be reconnected by closing the main transformer high-voltage circuit breaker THCB.

[0018] (2) Modify the trip output of the gas turbine generator protection: such as Figure 1 As shown, conventional gas-steam combined cycle units in self-owned power plants set the trip output of generator frequency abnormality protection and out-of-step protection to the generator output circuit breaker GCB of the gas-steam combined cycle unit in the self-owned power plant. However, this setting cannot meet the requirements of FCB operation. In this invention, the trip output of generator frequency abnormality protection and out-of-step protection is set to the high-voltage side circuit breaker THCB of the main transformer of the gas-steam combined cycle unit in the self-owned power plant.

[0019] (3) The external load of the gas-steam combined cycle unit has an automatic switching function between the power grid and the unit's power supply. For example... Figure 1 As shown, when the gas-steam combined cycle unit of the self-owned power plant is operating normally, the external load is powered by the unit side. When the unit enters FCB state mode 1 and operates stably, the external load is still powered by the unit side. When the unit is about to enter FCB state mode 2, the external load switching device HST quickly switches the power supply of the external load from the unit side to the grid side.

[0020] (4) Interlock all equipment in the gas-steam combined cycle unit of the self-owned power plant according to the FCB operating requirements; such as Figure 2 As shown, the waste heat boiler trips with unidirectional interlocking, the power plant gas turbine trips, the power plant gas turbine trips with bidirectional interlocking, the gas generator outlet circuit breaker GCB1 trips, the steam turbine trips with bidirectional interlocking, the steam turbine outlet circuit breaker GCB2 trips, the main transformer high-voltage side circuit breaker THCB trips without interlocking, the gas turbine outlet circuit breaker GCB2 trips, and the main transformer high-voltage side circuit breaker THCB trips with interlocking FCB start mode.

[0021] like Figure 3 As shown, step 2, when a grid fault occurs, the generator tripping control device issues a tripping command to enter the FCB operating state, which means that when the main transformer high-voltage side circuit breaker THCB is in the open position, the external load circuit breaker MCB is in the closed position, and the generator outlet circuit breaker is in the closed position, the FCB operating state is triggered.

[0022] Step 3 describes the self-owned power plant's gas-steam combined cycle unit entering FCB operation mode after receiving the FCB start signal. This includes two modes. Mode 1 refers to the gas turbine and steam turbine simultaneously entering FCB operation mode. The external load of the gas turbine is supplied by the gas turbine side. The gas turbine control system (TCS) and the steam turbine control system (DCS) disconnect the automatic load control mode and switch the control mode from constant pressure control to frequency control mode (target value 50Hz). At the same time, the high-pressure side bypass and low-pressure side bypass of the steam turbine are set to constant pressure control mode, and the high-pressure side bypass and low-pressure side bypass are opened. The power generation load follows the plant's auxiliary power load. And the demand for external loads gradually reaches a stable state; Mode 2 refers to the gas turbine unit entering FCB operation state, the steam turbine unit tripping, and at the same time, the gas turbine unit's external load fast switching device receives a switching command, the external load is switched from the power supply side of the gas turbine unit to the power supply side of the grid on the other side, the external load circuit breaker MCB is tripped, and the waste heat boiler bypass is opened; Mode 1 and Mode 2 are in sequential control logic. After the gas-steam combined cycle unit of the self-owned power plant receives the FCB start signal, it enters the FCB mode 1 operation state. If the unit frequency exceeds the limit and the unit parameters cannot operate stably within the set time, the unit enters the FCB mode 2 state.

[0023] like Figure 1 As shown, step 4, which involves waiting for the grid fault to be cleared before reconnecting to the grid after islanding operation, generally refers to the following: the voltages collected by the gas turbine generator terminal voltage transformers PT01 and PT02 are compared, and synchronous grid connection is achieved through the generator terminal GCB1 circuit breaker (synchronous connection point 1); the voltages collected by the steam turbine generator terminal voltage transformers PT03 and PT04 are compared, and synchronous grid connection is achieved through the generator terminal GCB2 circuit breaker (synchronous connection point 2). After the grid fault is cleared, once the islanding operation of the gas-steam combined cycle unit of the self-owned power plant is stable, synchronous grid connection is achieved through the main transformer high-voltage side circuit breaker THCB at synchronous connection point 3. Since the FCB operation state of the self-owned power plant gas-steam combined cycle unit in step 3 includes two modes, if the self-owned power plant gas-steam combined cycle unit operates stably in mode 1, the sequential control logic skips mode 2 within a set time and enters the pre-connection state at synchronous connection point 3 after the grid fault is cleared; otherwise, synchronous connection at synchronous point 3 is executed according to the sequential control logic.

[0024] Example The present invention discloses a gas-steam combined cycle (FCB) operation method for a self-owned power plant. The method was tested on a 189MW gas-steam combined cycle unit. By simulating the disconnection of the high-voltage side switch THCB of the main transformer, the gas-steam combined cycle unit was prompted to enter the FCB mode. Various parameters of the unit were monitored. The gas turbine unit was able to smoothly transition to the self-owned power supply mode, and the unit parameters were good. This verifies the applicability of the FCB operation method for a self-owned power plant gas-steam combined cycle unit.

[0025] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method of operating a gas-steam combined cycle unit of a self-contained power plant (FCB operation), characterized in that, Includes the following steps: 1) Configure the gas-steam combined cycle units of the self-owned power plant according to the FCB operating requirements; 2) When a grid fault occurs, the unit tripping control device issues a tripping command to enter FCB operation mode; 3) After receiving the FCB start signal, the gas-steam combined cycle unit of the self-owned power plant enters the FCB operation state, which includes two modes: Mode 1 refers to the gas turbine unit and the steam turbine unit entering the FCB operation state simultaneously. The external load of the gas turbine unit is supplied by the gas turbine unit side. The gas turbine unit control system TCS and the steam turbine unit control system DCS disconnect the load automatic control mode and switch the control mode from constant pressure control to frequency control mode. At the same time, the high-pressure side bypass and low-pressure side bypass of the steam turbine are set to constant pressure control state. The high-pressure side bypass and the low-pressure side bypass are opened, and the power generation load follows the plant power load and the external load. The demand for the load gradually reaches a stable state; Mode 2 refers to the gas turbine unit entering the FCB operating state, the steam turbine unit tripping, and at the same time, the gas turbine unit's external load fast-switching device receives a switching command, the external load is switched from the power supply side of the gas turbine unit to the power supply side of the other grid, the external load circuit breaker MCB is tripped, and the waste heat boiler bypass is opened; Mode 1 and Mode 2 are in sequential control logic. After the gas-steam combined cycle unit of the self-owned power plant receives the FCB start signal, it enters the FCB Mode 1 operating state. If the unit frequency exceeds the limit and the unit parameters cannot operate stably within the set time, the unit enters the FCB Mode 2 state; 4) Reconnect to the grid after islanding operation following grid fault clearance. This refers to the self-owned power plant's gas-steam combined cycle unit achieving synchronous grid connection through generator outlet circuit breakers GCB1 and GCB2. After the grid fault is cleared, the self-owned power plant's gas-steam combined cycle unit achieves synchronous grid connection through the main transformer high-voltage side circuit breaker THCB at synchronization point 3 after the islanding operation stabilizes. Since the self-owned power plant's gas-steam combined cycle unit's FCB operating state in step 3) includes two modes, if the self-owned power plant's gas-steam combined cycle unit operates stably in mode 1, the sequential control logic skips mode 2 within a set time and enters the pre-connection state at synchronization point 3 after the grid fault is cleared; otherwise, the sequential control logic is executed. The concurrent parallel point 1 is the gas generator outlet circuit breaker GCB1, and the concurrent parallel point 2 is the steam turbine generator outlet circuit breaker GCB2.

2. The FCB operation method of a gas-steam combined cycle unit of a self-provided power plant according to claim 1, characterized by, Step 1) Setting up the gas-steam combined cycle unit of the self-owned power plant according to the FCB operating requirements includes four aspects: a) The gas-steam combined cycle unit of the self-owned power plant adopts a 3-synchronous parallel point design; b) Modify the trip output of the gas turbine and steam turbine generator protection; c) The external loads other than the load of the gas-steam combined cycle unit have automatic grid and power supply switching functions; d) All equipment in the gas-steam combined cycle unit is interlocked in accordance with the FCB operation requirements.

3. The FCB operation method of a gas-steam combined cycle unit of a self-provided power plant according to claim 1, characterized by, Step 2) When a grid fault occurs, the unit disconnection control device issues a trip command to enter the FCB operating state. This means that when the main transformer high-voltage side circuit breaker THCB is in the open position, the external load circuit breaker MCB is in the closed position, and the generator output circuit breaker is in the closed position, the unit is triggered to enter the FCB operating state.

4. The FCB operation method of a gas-steam combined cycle unit of a self-provided power plant according to claim 1, characterized by, The target frequency for the frequency control mode of the gas-steam combined cycle unit of the self-owned power plant is 50Hz.

5. The FCB operation method of a gas-steam combined cycle unit of a self-provided power plant according to claim 1, characterized by, The tripping of the generator output circuit breakers GCB1 and GCB2 for the generator out-of-step protection and generator frequency protection of the gas-steam combined cycle unit will be changed to the tripping of the main transformer high-voltage side circuit breaker THCB.

6. The FCB operation method of a gas-steam combined cycle unit of a self-provided power plant according to claim 1, characterized by, Waste heat boiler tripping is a unidirectional interlocking event; power plant gas turbine tripping is a unidirectional interlocking event; power plant gas turbine tripping is a unidirectional interlocking event; gas generator outlet circuit breaker GCB1 tripping is a unidirectional interlocking event; steam turbine tripping is a unidirectional interlocking event; steam turbine outlet circuit breaker GCB2 tripping is a unidirectional interlocking event; main transformer high-voltage side circuit breaker THCB tripping is not interlocked; gas turbine outlet circuit breaker GCB2 tripping is a unidirectional interlocking event; main transformer high-voltage side circuit breaker THCB tripping is an interlocking event in FCB start-up mode.

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