Starting the turbine
The steam turbine is used according to all the requirements specified in the instructions by the manufacturer
The instructions contain rules compiled by specialists to avoid dangerous situations: rules for technical operation, fire safety requirements and safety precautions for maintenance and repair of equipment.
According to the above materials, local instructions are compiled at all power plants: rules for using the turbine, rules for starting, stopping and taking it into repair. Actions in case of possible malfunctions and the procedure for their elimination (for example: replacement of spare parts of steam turbines, equipment modernization, restoration of working surfaces of parts and units of steam equipment), which are mandatory for study before starting work.
Problems that prevent turbine startup
Despite the variety of turbine designs, differences in their circuits and auxiliary equipment, there is a general list of frequently encountered breakdowns that must be eliminated before starting.
Startup is prohibited in the event of:
- Absence or malfunction of the main device, including sensors of the thermal process of the turbine and its mechanical condition (vibrometer, pressure gauge, tachometer, etc.);
- Faulty lubrication system (low oil level or level indicator), malfunction of the oil cooler, oil line, etc.;
- Faulty circuit protection system, and cessation of steam supply. In this case, the entire protection chain is checked, starting with sensors and ending with actuators (shutoff valve, reheating, etc.);
- If there are faults in the control system;
- In case of a fault in the shaft-turning device. In this case, the steam supply may cause the rotor to bend.
Preparing for start-up
The method of starting the turbine varies depending on its temperature. Start-up at a temperature below 150 degrees Celsius is considered "cold". At least three days are allocated for such a start after stopping. Start-up from a temperature above 400 degrees Celsius is considered "hot". If the turbine temperature is between cold and hot, it is considered a start from a warm state.
The main rule of any start is the maximum possible speed from the condition of reliability (not to damage).
The main difference in the start of non-block turbines (with cross-coupling) is the use of steam with nominal parameters.
The process of working with a turbine
Using a steam turbine installation, if shortened, consists of starting, loading and stopping.
Starting a turbine
The entire start of a turbine is divided into three stages:
- preparatory;
- turning up to full speed;
- synchronization (connection to the network) and supplying the load.
During the preparatory period, the general condition of all devices and other equipment of the turbo plant is checked, the presence of unfinished work and the operation of the alarm are checked. Heating the steam pipeline and each bypass pipe takes 1-2 hours. During this time, water is prepared for supply to the condenser. The oil pumps are checked except for the main one (on the shaft), the starting and shaft-turning apparatus are started. The protection and adjustment system is tested when closing the main steam valve, the absence of pressure near the stop valve is checked. The vacuum build-up process is started, the control mechanism is set to the minimum position, automatic safety is started and the drains in the turbine housing are opened.
The rotor is set in rotation by opening the control valve, or the GPP bypass with the control valves fully open.
Initially, low speeds (400-800) are maintained in the turbine, during which time thermal expansion, seals, bearings and other devices (oil, temperature, pressure) are checked.
The critical frequency must be passed at speed, therefore, after checking all the parts in a normal situation, a turn is made, while the turbine must be constantly audible. The temperature difference between the lower and upper parts of the cylinder should be no more than 30-35 degrees Celsius, and between the stud and the flange no more than 20-30 degrees Celsius. The next inspection is carried out when the turbine reaches the threshold of 3000 revolutions per minute, the protection system, the control system are checked, a trial run of the manual and remote shutdown function is carried out. The device checks the smoothness of the movement of the control valves, the safety machine for supplying oil to the striker is started for a test, the mechanism for increasing the speed is checked.
After the procedures are carried out and if there are no conflicts in the starting system, the signal "Attention! Ready!" is displayed on the main panel. The generator is connected to the grid and loads the turbine according to the standards specified in the instructions.
Starting with backpressure is carried out in two ways:
After disconnecting the pipeline with backpressure, the turbine is started together with the release of steam, the exhaust is transferred to this collector after the steam pressure in the outlet pipe exceeds the backpressure steam pipeline (collector).
A similar option can be used to start warming up the turbine (after warming up the steam pipeline) from the exhaust ("tail").
The GPP bypass produces a push on the rotor, which allows the turbine with backpressure to start working according to the electrical schedule even at low load after starting the generator in the grid. When all devices and elements reach a load of 15% of the standard, the pressure regulator is turned on and the turbine is transferred to work in accordance with the thermal schedule.
The main difference between backpressure turbines is the absence of a condenser.
Individual properties during the start-up of units are tied to the difference in the thermal schemes of block and non-block units. The start-up of a block unit is carried out with a sliding system of parameters, in this case, during the start-up process, the steam parameters can constantly change, and sometimes reach the nominal value even at a low load.
Turbine load
In this case, the main task of turbine maintenance workers is to ensure the specified loads, and maintain guarantees of reliability, safety and cost-effectiveness of the work. The maximum or minimum permissible load for the turbine can be found in the relevant sources.
Special attention is paid to parameters that, if changed above the permissible limit, can threaten the stable operation of the unit (rotor extension/shift, vibration state, etc.).
The steam parameters, both from industrial overheating and in the turbine, the oil sensor, the heating of the bearings, and the seals are under constant control.
The instructions for safe use also indicate the vacuum, the feed and cooling water temperature sensor, the increase or decrease in the condenser temperature - which directly affects the efficiency of the work. According to the table, a decrease in the feed water temperature by 1 degree Celsius increases the specific heat consumption by 0.01%.
Salts from the steam can be carried into the flow part of the turbine. This reduces the efficiency of the process and leads to a deterioration in the reliability of the blade apparatus, which affects the entire turbine as a whole. To avoid this, periodic steam cleaning is recommended. However, this is a very responsible and therefore undesirable operation.
Stable operation of the turbine directly depends on the thoroughness of control, frequency of checks and adjustments. Constant inspection of each unit and element in the chain allows you to avoid unexpected surprises during operation.
In accordance with the PTE, at certain times, the strikers of the safety and speed increase machines are periodically checked, the tightness of the stoppers is checked, the regulating and check valves are diagnosed. A complete check of the above is carried out after installation work, and 2 times during major repairs (before and after). The stop and adjustment valves according to the standard may not have absolute tightness, but their parallel closure should not allow the rotor to rotate.
Turbine stop
If the turbine is stopped in hot reserve, the metal temperature should be maintained at the highest possible position. When placing the turbine in long-term reserve or in case of major or current repairs, a shutdown with subsequent cooling is performed.
Before any shutdown, according to the instructions, the turbine is unloaded in accordance with the instructions of the head of the estimate. The regulated selection and regeneration is disconnected.
After reducing the load to 10-15% of the total standard load, after receiving permission via the shutdown button, the steam supply directly to the turbine is stopped. To avoid high heating of the "tail", the closure of the stop and control valve is checked in a short time, the negative power of the wattmeter is checked to avoid power consumption from the network. The generator is disconnected from the network.
If there is a load according to the wattmeter, disconnection from the network is prohibited. In this case, the GPP is closed, the valves on the extraction are tightened and the valves are tapped, after the steam supply to the turbine stops, the turbine is disconnected from the network.
During the unloading process, the rotor should be monitored, preventing it from reaching critical limits. The rotor runout curve is recorded. The standard is 20-40 minutes. In case of deviation of more than 2 minutes, it is necessary to find the cause of the change.
Following the rotor, the shaft turning device is immediately turned off, operating until the temperature drops below 200 degrees Celsius.
Emergency shutdown of the turbine
In case of an emergency, you should act according to the list of possible emergency situations, all provisions of which are prescribed in the emergency instructions. According to it, measures are taken to eliminate the sources of the problem and their consequences.
In the process of eliminating the emergency, you should focus on the main indicators of the unit's operation:
- Rotation speed and load sensors;
- Fresh steam and reheating;
- Condenser (vacuum in it);
- Vibration frequency;
- Shift along the axis and the position of the rotor relative to its housing;
- Oil and oil pressure in the lubricant (at the inlet and drain).
The emergency response instructions define options for emergency shutdown under different circumstances.
In the event of an emergency shutdown, the first thing to do is to stop the supply of fresh steam, and after making sure that it has stopped, send a signal to the main control panel "Attention! The machine is in danger!" The next step is to disconnect the generator from the network. It is extremely important to close the gas processing plant and its bypass together with the selection.
The subsequent shutdown activities are carried out in a standard manner.
If it is necessary to stop the rotor quickly (for example, with a sharp jump in the oil level, water hammer, high vibration frequency, etc.), the vacuum is broken.
In the case of a stop with a vacuum break, the rotor stops in 15 minutes, while with a standard procedure it takes 32-35 minutes. It should be taken into account that when the vacuum is broken, the exhaust pipe is heated, which is why the vacuum should be broken only in a case specified by the emergency instructions.