RU2251625C1 - Method of and device for starting gas-turbine set - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: proposed group of inventions is designed for starting stationary single-shaft gas-turbine sets with barring gear with electric motor and overrunning clutch consisting of gas turbine and synchronous turbo generator whose shafts are mechanically coupled. According to proposed method of starting of gas-turbine set with barring gear with electric motor and overrunning clutch in which synchronous turbogenerator is used as barring motor mechanically coupled with shaft of gas turbine, current from starting frequency converter is supplied to stator winding of barring motor. At beginning of starting, voltage is changed proportionally to frequency, and when gas turbine comes to self-propelled mode, current from starting frequency converter is cut off and, according to invention, starting begins at induction mode of said turbogenerator and during period of starting torque of turbogenerator is found by values of output power and voltage of starting frequency converter, and current is supplied to field circuit of brushless synchronous exciter installed on shaft of turbogenerator proportional to turbogenerator torque at constant value of shaft, and initial rate of frequency rise is chosen to provide coming of said exciter to current supply mode after release of overrunning clutch. With overrunning clutch released, frequency rise rate is increased to provide self-synchronization of turbogenerator, and after self-synchronization, starting is continued at synchronous mode of turbogenerator. In gas turbine set starting device including starting frequency converter whose output is connected to leads of stator winding of synchronous turbogenerator whose shaft is coupled with shaft of gas turbine, accortoding to invention, device contains brushless synchronous exciter whose shaft is coupled with shaft of said turbogenerator, field current setter and drive torque meter. Field winding of said exciter is connected with output of field current setter to create positive feedback. First input of field current setter is connected to data output of drive torque meter, and second input of field current setter is connected to constant shift current source.

EFFECT: improved reliability of starting, reduced cost of equipment used for starting of gas-turbine set.

3 cl, 1 dwg

Description

The claimed group of inventions is intended primarily for starting stationary single-shaft gas turbine units having a shaft-turning device with an electric motor and an overrunning clutch and consisting of a gas turbine and a synchronous turbogenerator, the shafts of which are mechanically connected.

The inventive method solves the problem of accelerating the rotor of a gas turbine unit by an accelerating motor, from the moment the rotor moves off to the moment the starting frequency converter is turned off. As an accelerating electric motor, a synchronous turbogenerator is used (hereinafter referred to as “turbogenerator”), equipped with a brushless synchronous exciter (hereinafter referred to as “exciter”). On the specified time interval, it is necessary to sequentially perform:

- moving the rotor - smoothly overcome the moment of dry friction in the bearings,

- acceleration of the rotor to a speed corresponding to the uncoupling of the cams of the freewheel of the shaft-turning device,

- acceleration of the rotor to a speed set for ventilation of the flow path of a gas turbine,

- time delay (for ventilation of the gas turbine flow path) while maintaining a constant speed,

- accompaniment by the starting converter of the frequency of ignition of the combustion chamber from the moment of ignition of the fuel to the output of the turbine in self-propelled mode, after which it is turned off the current of the starting converter of frequency.

During the start-up of the gas turbine unit, it is required to comply with the specified torque limits of the accelerating engine. In particular, a worm gear with an overrunning clutch can transmit power in only one direction. Therefore, in the first two sections of the start-up schedule of the unit, the accelerating engine should not change the sign of torque. On the other hand, the accelerating engine in the last two sections of the start-up schedule should have a sufficient maximum torque, providing the required amount of margin of static stability of the engine.

There is a method of starting a gas turbine unit using a turbogenerator as an accelerating engine (E.A. Krutyakov, P.A. Pavlov, M.V. Pronin, Algorithms for the operation of thyristor starting devices for turbogenerators and synchronous motors manufactured by AO ила Elektrosila Сбор, Collection ″ Elektrosila ″, No. 40, 2001, pp. 53-59), adopted by us for the prototype. In this method, the accelerating engine is used only in synchronous mode, performing the following sequence of operations. To determine the initial position of the stationary rotor of the accelerating engine, current pulses are supplied to various pairs of machine phases. The position of the rotor relative to the axis of the stator field is determined by the magnitude of the amplitude of the voltage pulses on the rotor winding. The ratio of the amplitudes of the pulses allows you to determine the position of the rotor. Then, the current from the starting source of the excitation current is supplied to the rotor circuit and the start is started by applying voltage to the stator circuit from the frequency converter, setting the previously required initial phase (in accordance with the position of the rotor). Thus, the acceleration engine is synchronized with the power source (starting frequency converter). At the start of a start, the voltage is changed in proportion to the frequency. In common with the prototype is the fact of using a turbogenerator connected mechanically to the shaft of the gas turbine as an accelerating engine. The current from the starting frequency converter is supplied to the stator winding of the turbogenerator, and at the beginning of the start, the voltage is changed proportionally to the frequency, and when the turbine enters the self-propelled mode, the current of the starting frequency converter is turned off.

This method of starting a gas turbine unit has the following disadvantages:

- starting with any (arbitrary) initial phase of the stator field is impossible both because of the instability of the synchronous motor at a low frequency, and the high probability of failure of the shaft-turning mechanism,

- requires a pulse shaper and a device for supplying test pulses to the stator winding,

- a device is required for measuring the magnitude of the voltage pulses induced in the rotor winding,

- to ensure smooth starting of the rotor and subsequent smooth acceleration, it is necessary to set the phase of the voltages supplied to the stator circuit, depending on the current angular position of the rotor, while it is possible to determine only the initial position of the rotor.

An accelerating motor operating in synchronous mode, at a low frequency of the supply voltage, is unstable and can create alternating torque. The swings of the rotor of the accelerating engine at start, accompanied by a change in the sign of torque, can cause jamming of the worm pair of the shaft-turning mechanism.

At the beginning of the start-up of the unit, the cams of the overrunning clutch of the shaft-turning device are not pulled to the fully disengaged state by centrifugal force and, when the accelerating engine has a positive torque, operate in the slip mode. When the sign of the torque changes, the cams of the accelerating clutch, after selecting the play, begin to work against the stop.

Under these conditions, even a brief change in the sign of the torque of the accelerating engine can cause the worm pair of the shaft-turning mechanism to jam and damage the worm.

A more favorable outcome is also possible when, in order to avoid damage to the worm, the pins of the overrunning clutch are cut. In any case, jamming of the shaft-turning mechanism transfers the gas-turbine unit from the operating state to the repair state.

A device for starting a single-shaft gas turbine unit is known (E.A. Krutyakov, P.A. Pavlov, M.V. Pronin, Algorithms for the operation of thyristor starting devices for turbogenerators and synchronous motors manufactured by AO "Electrosila", Collection "Electrosila", No. 40, 2001 g., pp. 53-59), adopted as a prototype. The device comprises a turbogenerator connected mechanically to the shaft of the gas turbine, a starting frequency converter, the output of which is connected to the terminals of the stator winding of the turbogenerator. The turbogenerator is used in a synchronous electric motor mode when the rotor circuit is powered by a static excitation current source.

The prototype has the following elements in common with the claimed device:

- starting frequency converter, the output of which is connected to the stator winding of the turbogenerator, connected mechanically with the shaft of the gas turbine.

The prototype device has the following disadvantages:

- requires a powerful starting source of excitation current,

- a change in the sign of the torque of the accelerating engine can cause jamming of the worm pair of the shaft-turning mechanism and damage to the worm.

- the brush apparatus with a large magnitude of the excitation current transmitted through the slip rings requires periodic maintenance and reduces the reliability of the unit.

The technical result of the proposed method for starting a gas turbine unit is that:

- provides a smooth start to the movement of the rotor when starting the unit,

- the asynchronous mode of operation of the accelerating engine in the initial part of the start-up schedule ensures smooth rotor acceleration to a speed corresponding to the disengagement of the overrunning clutch cams (in this case, the cams slip without causing breakage, and after disengaging, the cams are moved to a safe position).

- self-synchronization of the accelerating engine, performed after uncoupling the cams of the overrunning clutch, provides the possibility of further acceleration of the rotor in a more advantageous (at this stage) synchronous mode of the accelerating engine,

- after the self-synchronization of the accelerating engine, it is possible to maintain a high power factor, in particular Cosφ = 1.

- significantly reduces the likelihood of an unsuccessful start-up of gas turbines.

The technical result of the inventive device for the frequency start-up of a gas turbine unit is that:

- significantly reduces the magnitude of the current control excitation in comparison with the prototype,

- a brushless synchronous exciter, structurally combined with an accelerating synchronous electric motor, provides a smooth transition from asynchronous to synchronous operation of the accelerating electric motor, while there is no need for a powerful (and used only when starting the unit) excitation current source of the accelerating motor.

The claimed solution also allows to reduce the cost of starting equipment for a gas turbine unit.

To achieve the specified result in the method of starting a gas turbine unit, mainly for units with a shaft-turning device with an electric motor and an overrunning clutch, a synchronous turbogenerator mechanically coupled to the turbine shaft is used as an accelerating engine, current is supplied from the starting frequency converter to the stator winding of the accelerating engine, and at the beginning of start-up, the voltage is changed proportionally to the frequency; when the turbine enters the self-propelled mode, the current of the starting frequency converter is turned off, with According to the invention, the start is started in the asynchronous mode of the named turbogenerator, during the start, the torque of the turbogenerator is determined from the output power and voltage of the starting frequency converter, a current proportional to the torque of the turbogenerator with a constant bias value is supplied to the excitation circuit of the brushless synchronous exciter installed on the shaft of the turbogenerator , the initial rate of frequency rise is chosen so that the output of the brushless synchronous pathogen to the current output mode occurred after the freewheel clutch disengages, after the freewheel clutch disengages increase the rate of frequency rise, providing conditions for the self-synchronization of the turbogenerator, and after self-synchronization, the start is continued in synchronous mode of the turbogenerator.

To optimize the mode of the frequency converter according to current and optimize the mode of the accelerating motor in terms of stability in the present method (claim 2), the excitation current is set once during holding in constant frequency mode before ignition of the fuel, and the coefficient of positive feedback of the exciter current calculated torque according to the condition of zero reactive power, and a constant value of the bias is selected such that it provides the required margin stability of the accelerating engine.

To exclude the influence of the excitation current on the torque of the accelerating motor operating in an asynchronous mode, in the inventive method (paragraph 3 of the formula), the excitation current of the pathogen is switched on after the overrunning clutch is disengaged.

The inventive device is intended to implement our proposed method of starting a gas turbine unit. To achieve this result, in the start-up device of the gas turbine unit, including the starting frequency converter, the output of which is connected to the stator winding of the synchronous turbogenerator, the shaft of which is connected to the shaft of the gas turbine, according to the invention, the device further comprises a brushless synchronous exciter, the shaft of which is connected to the shaft of the synchronous turbogenerator, a master the excitation current and a torque meter of the drive, and the excitation winding of the above pathogen is connected to the output of field current sensor to create positive feedback, the first input of the field current generator is connected to the information output of the drive torque meter, and the second input of the field current generator is connected to a bias DC source.

The starting frequency converter preferably comprises a rectifier connected by its input to the supply network, and the output to the capacitors of the DC link. The indicated capacitors are connected to the output of the frequency converter through an independent (autonomous) inverter. Autonomous inverter provides smooth pulse-width control of the frequency and amplitude of the output voltage.

The invention and the possibility of their technical implementation is illustrated by the drawing, where are indicated:

1-compressor

2 - gas turbine,

3 - gear

4 - shaft-turning device

5 - accelerating engine (turbogenerator),

6 - brushless pathogen,

7 - circuit current excitation brushless pathogen,

8 - drive current excitation,

9 - power circuit of the accelerating engine,

10 - starting frequency converter,

11 - power frequency converter,

12 - offset current excitation

13 - output of the computer torque.

The inventive method of frequency starting a gas turbine unit is as follows.

Start start with the asynchronous mode of the accelerating engine. The stator winding of the accelerating motor is supplied with current from the starting frequency converter, and at the beginning of starting the voltage is changed proportionally to the frequency.

In the initial stage of start-up, the magnetic flux generated by the stator current (at a very low frequency) penetrates deep into the array of the rotor barrel, and the current in the rotor winding relative to the current induced in the rotor barrel is small. For this reason, the rotor moves uniformly, and during one revolution of the rotor (relative to the stator field) the slip changes little. Under these conditions, the torque of the accelerating engine in a first approximation is proportional to the slip.

During the start-up, the torque is calculated from the values of the power and frequency of the supply voltage, while the current is proportional to the calculated torque of the accelerating engine with a constant offset value in the excitation circuit of the pathogen located on the shaft of the accelerating engine.

At a low shaft speed, the brushless synchronous exciter does not produce the current required to transfer the accelerating motor to synchronous mode.

The initial rate of frequency rise is chosen so that the overrunning clutch disengages before the pathogen enters the current output mode. Overrunning clutch cams disengage under the action of centrifugal force, and overrunning clutch disengages. The brushless synchronous exciter starts to smoothly increase the rotor current of the accelerating engine, and after self-synchronization of the accelerating engine, its operating conditions in synchronous mode are ensured. In this case, the torque of the accelerating engine is increased in accordance with the intended acceleration schedule.

Before igniting the fuel, a time delay is carried out at a constant speed, used to ventilate the turbine working path before fuel is supplied.

The starting frequency converter is turned off after ignition of the fuel and the turbine enters self-propelled mode.

The second claim provides a method in which the adjustment of the excitation current is performed once during holding at constant frequency before ignition of the fuel.

In this case, the coefficient of positive feedback of the exciter current is selected according to the calculated torque according to the condition of zero reactive power. Thus, at zero bias, the purely active power of the accelerating engine is provided, and a constant value of the bias increases the excitation current so as to provide some over-excitation of the accelerating engine. Thus, the required margin of static stability of the accelerating engine is selected.

To increase reliability during the transition of the motor to asynchronous mode, the current is supplied to the exciter circuit after the overrunning clutch is released (third paragraph of the formula).

The inventive device operates as follows.

The field winding of the brushless exciter is connected to the output of the field current generator to create positive feedback on the torque of the accelerating engine. An additional direct bias current in the exciter circuit increases the excitation current and, thus, the safety factor of the static acceleration of the accelerating engine.

The first input of the drive excitation current is connected to the information output of the drive torque. This provides a drive current of a brushless exciter linearly dependent on the drive torque. The second input of the excitation current generator is connected to a DC bias source. The amount of displacement provides some over-excitation of the accelerating engine, desirable to create a margin of static stability.

The system parameters are chosen so that the overrunning clutch disengages at a rotational speed lower than that required for self-synchronization of the accelerating engine.

To this end, the third claim provides an additional opportunity to turn on the excitation current of the pathogen after disengaging the freewheel.

Claims (4)

1. The method of starting a gas turbine unit mainly with a shaft-turning device with an electric motor and an overrunning clutch, in which a synchronous turbogenerator is used as an accelerating engine, mechanically coupled to a gas turbine shaft, current is supplied from the starting frequency converter to the stator winding of the accelerating engine, and at the beginning of starting the voltage change proportionally to the frequency, when the gas turbine enters the self-propelled mode, the current of the starting frequency converter is turned off, characterized in that the starting they are installed in the asynchronous mode of the named turbogenerator, the torque of the turbogenerator is determined during the start by the values of the output power and voltage of the starting frequency converter, a current proportional to the torque of the turbogenerator with a constant bias value is supplied to the excitation circuit of the brushless synchronous exciter installed on the shaft of the turbogenerator, the initial pace the frequency rise is chosen so that the output of the named pathogen to the current output mode occurs after the overrunning clutches s, after disengaging the freewheel clutch, increase the rate of frequency rise, providing the conditions of the self-synchronization of the turbogenerator, and after the self-synchronization, the start is continued in the synchronous mode of the turbogenerator. 2. The method according to claim 1, characterized in that the adjustment of the excitation current is performed once during exposure in the constant frequency mode before ignition of the fuel, while the coefficient of positive feedback of the excitation current of the brushless synchronous exciter is selected for a certain torque according to the condition of zero reactive power, and a constant displacement value is selected such that it provides the required margin of static stability of the turbogenerator. 3. The method according to claim 1, characterized in that the current is supplied to the excitation circuit of the brushless synchronous pathogen after the overrunning clutch is disengaged. 4. A start-up device for a gas-turbine unit, including a start-up frequency converter, the output of which is connected to the stator windings of a synchronous turbogenerator, the shaft of which is connected to the gas turbine shaft, characterized in that the device further comprises a brushless synchronous exciter, the shaft of which is connected to the shaft of the named turbogenerator, a master the excitation current and a drive torque meter, wherein the field winding of said exciter is connected to the output of the field current generator for positive feedback of the building, the first input of the excitation current set point included in data output meter drive torque, and the second input of the excitation current setter connected to a source of DC bias current.