Method for controlling the power of a turbine plant and device for implementing the method

TECHNICAL AREA

The present invention relates to the field of power plant technology. It relates to a method of controlling the power of a thermal power converting to turbo-electric power, which turbo group on a common shaft a turbine powered by the thermal power and driven by the turbine, includes electrical power to a grid-emitting generator, In which method determines the output from the generator electrical power and the thermal power for the turbine is controlled in dependence on the measured electrical power.

The invention further relates to a device for carrying out the method, comprising a power controller for controlling the thermal power for the turbine, and first means which compare an output power of the turbo group with a predetermined power value and pass a difference value as a control signal to the power controller.

STATE OF THE ART

The usual way to regulate the output power of a gas turbine, is the output at the output terminals of the associated generator electrical output power P_G to measure, the measured value with a given power value (setpoint) P_C and the resulting difference signal ΔP = P_G-P_C as a control signal to pass to a power regulator, which regulates the thermal performance of the gas turbine.

An exemplary circuit diagram for such a known power control is shown in FIG. The power of a turbine group 10 consisting of a gas turbine plant 15 and a generator 16 is regulated. The gas turbine plant 15 comprises the actual turbine 11, a combustion chamber 12, a compressor 13 and a controllable inlet 14 for the combustion air, which usually consists of adjustable inlet guide vanes (FIGS.<u>V</u>ariable <u>I</u>Nlet <u>G</u>uiding <u>V</u>anes VIGVs). Turbine 11 and generator 16 sit on a common shaft 17 whose rotational frequency f is measured by means of a rotary frequency generator 25. The generator 16 outputs the generated electric power P_G to a network 18, usually a three-phase system, from. The electric power P_G of the generator 16 is in a subtractor 19 with a predetermined power value P_C and the difference value .DELTA.P is supplied to a power regulator 20, which in turn via the controllable inlet 14, the amount of the combustion air supplied to the compressor 13, and the mass flow dm_fc/ dt of the combustion chamber 12 supplied fuel controls.

The specified power value (setpoint) P_C results from the sum P_ct= P_C* + .DELTA.P_ct from a reference power value P_C* and a correction value ΔP_ct, The correction value ΔP_ct in turn comes from a characteristic generator 23, the case of a deviation of the measured rotational frequency f of a rotational frequency setpoint f_C in accordance with the difference .DELTA.f formed in a subtracter 24 and a predetermined characteristic .DELTA.P_C= K (Δf) outputs a corresponding correction value. In addition, a rise limiter 21 is provided which limits the rate of change of the control signal.

It has now been found that the control circuit shown in Fig. 1 can lead to a potentially dangerous behavior of the gas turbine when strong (positive or negative) accelerations of the shaft occur. In this case, the measured (electrical) output power is P_G Turbo group no longer a measure of the thermal power P produced_T the gas turbine 15, which is determined by the mass flows of the combustion air and the fuel, but also contains a significant amount of kinetic power. The resulting inequality between the measured output power and the generated thermal power may cause the power control to initiate (in itself unwarranted) changes in the mass flows of the combustion air and fuel that are hazardous to the gas turbine itself and / or the stability of the connected network can.

In addition, when the generator switch opens, the measured electric power P falls_G at the generator to zero, since no power flow takes place in the network. In this case, too, a disparity results between the measured output power and the generated thermal power, and the power control receives incorrect information about the thermal state of the gas turbine resulting in undesirable performance of the power controller.

The fundamental cause of the problems mentioned becomes clear when one sets up the following power equation for the rotor of the gas turbine:<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>(1) P</mtext></mrow><mrow><mtext>G</mtext></mrow></msub><msub><mrow><mtext> = P</mtext></mrow><mrow><mtext>T</mtext></mrow></msub><msub><mrow><mtext> - P</mtext></mrow><mrow><mtext>kin</mtext></mrow></msub><mtext>.</mtext></mrow></math><img file="EP0903469B1_D0001.tif" /></maths> where P_T the effective thermal output of the gas turbine means and<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext>(2) P</mtext></mrow><mrow><mtext>kin</mtext></mrow></msub><msup><mrow><mtext> = 4π</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><mtext>.theta..sub.F (df / dt)</mtext></mrow></math><img file="EP0903469B1_D0002.tif" /></maths> the kinetic power of the shaft is, with the moment of inertia θ of the shaft, the rotational frequency f of the shaft and the rotational frequency change (acceleration) df / dt of the shaft. It is clear from the equations (1) and (2) that the measurement of the electric output power P_G generally not directly a measure of the thermal power to the gas turbine, but is a measure of the total power at the shaft, and the kinetic power, which is delivered or absorbed at a deceleration or acceleration of the shaft includes.

This results in the following undesirable behavioral patterns of performance regulation:

1.

Thermal discharge during a release of kinetic power

In this case, the rotor (the shaft) is braked sharply. This typically occurs when the gas turbine is synchronized with a network that is subject to a sharp drop in frequency. As a result of this drop, the rotor releases a large amount of kinetic power, resulting in a sudden increase in the measured output P_G leads. If the setpoint P changes_C not essential, the power control reduces the thermal power P_Tto measure the measured output power P_G as close as possible to the setpoint P_C to keep. However, this is exactly the wrong answer of the control system, because a drop in frequency in the network is a sign of increased power consumption. Rather, gas turbines that have sufficient power reserve should increase rather than reduce thermal power to help stabilize the grid. In addition, the thermal discharge of the gas turbine due to the release of kinetic power can lead to a flame extinguishing, which further exacerbates the already existing power deficit of the network. Overall, this behavior seriously jeopardizes network stability.

Second

Thermal charge during a load shedding

Considered here is the situation of a gas turbine running synchronously to a stable grid at constant speed and with a certain power (eg 160 MW thermal power). Since the velocity of the wave is constant (df / dt = 0, P_kin= 0), the total measured electric power is P_G according to equation (1) identical to the thermal power P_T, Now, when the generator switch opens, the measured electric output power P falls_G to zero. As a result, the power controller receives a signal representative of 0 MW output power, although the thermal power is actually unchanged (160 MW in the example). The power controller is thereby erroneously caused to increase the thermal power by an amount required by the power command value. Theoretically, this allows the thermal power to be twice the power set point P_C increase. As soon as the generator switch opens, the rotor is heated by the thermal power P_T accelerated. The fall of the signal P_G and the resulting increased thermal power of the gas turbine will increase the acceleration of the shaft so that the shaft may reach a speed limit.

EP 0742356 A2 describes a method for setting a main controlled variable during operation of a gas turbine group. As the main controlled variable can serve for example, the generator power or the rotational frequency of the rotor after this solution. A nominal value of the selected main controlled variable is compared with a measured value of the main controlled variable, and a required main differential difference is distributed hierarchically via a management to at least one cascade. In the case of a gas turbine group with sequential combustion, it is possible by means of the management to preferably proceed in this way, that first the potential of a first power temperature cascade, which sets the fuel mass flow in the first combustion chamber, is exhausted until reaching a maximum turbine inlet temperature, and then the potential of a second power-temperature cascade for the second combustion chamber is exhausted, and thereafter that of the power-pressure cascade. The distribution of the main rule difference to independent cascades precludes mutual interaction of the cascades. Through the series connection of main variable speed controller and size controller within the cascades, the size controller is always responsive. This makes the regulation fast and safe with regard to the exclusion of mutual influences. Nevertheless, with a limitation to the mentioned main variables power and rotational frequency, the aforementioned disadvantages can not be reliably excluded.

A method for protecting a turbomachine from a dangerous increase in the rotor frequency during a load shedding is described in SU 1149037 A based on the operation of a steam turbine plant. This method is based on three output quantities, the measured generator electric power N_∋, the rotational frequency n of the rotor and the effective mechanical turbine power N_T, which indirectly by the measured pressure parameters p₁; p₂; p₃ the process steam and unspecified coefficients K₁; K₂; K₃ in an adder (1) is determined by calculation. From the mechanical turbine power N_T and the generator power N_∋ is in the subtractor (3) in accordance with the equation N_T-N_∋= I^·n^·dn / dt, where I symbolize the moment of inertia of the rotating mass of the rotor and dn / dt its acceleration, the kinetic power I^·n^·dn / dt of the rotating rotor calculated. An adder (6) combines the signals corresponding to the rotational frequency and the kinetic power. As soon as the sum of these signals exceeds a predetermined limit value (comparator (7)), a warning signal is output to the logic module (12) by pulse shaper (8). In a second, independent cascade, the generator power N_∋ via comparators (9) and (10). As soon as N_∋ over a predetermined period of time falls below a target value, in particular falls to zero, pulse generator (11) outputs a warning signal to the logic module (12). If alarm signals at the logic module (12) are simultaneously emitted from both cascades, then a protective signal is triggered which causes the shut-off of the steam supply to the turbine. This method is not designed as a power control of a turbo group, but as a method of protecting turbo sets from mechanical overstress during load shedding. By determining the parameters rotor frequency and electrical generator power as well as calculation of the kinetic rotor power, dangerous situations due to mechanical overstressing should be reliably detected and prevented in time by blocking the power supply to the turbine.

PRESENTATION OF THE INVENTION

It is an object of the invention to provide a method for power control of a turbo group, which avoids the disadvantages described and the thermal performance is regulated so that both instability of the network by the turbo group as well as an overload of the turbo group are reliably avoided.

The object is achieved in a method of the type mentioned above in that the thermal power of the turbine from the output from the generator electrical power P_G and the kinetic power of the shaft is controlled such that in addition to the electric power P_G the rotational frequency f of the shaft is determined, and from the rotational frequency f and the temporal change df / dt of the rotational frequency f in accordance with the equation P_kin = 4π^{2 ·}θ^·f^·df / dt (where θ symbolizes the moment of inertia of the rotating mass) the kinetic power P_kin the wave is determined, the kinetic power P_kin the electric power P_G is added up, and the sum of the electric power P_G and the kinetic power P_kin with a given power value P_C is compared, and thereby determined difference value ΔP to a power regulator (20) for controlling the thermal power P_T the turbine (11) is passed. By including the electric power of the generator and the kinetic power of the shaft in the power control, an undesirable behavior of the control, especially in cases of load shedding and instability of the network, can be safely avoided. It is possible to determine with a single rotary encoder on the shaft in a simple manner, the kinetic power of the wave at any time safely and accurately.

Basically, the electrical power can be measured at the terminals of the generator. Another, independent of the generator type of measurement is according to a second preferred embodiment of the invention, characterized in that the rotation frequency of the shaft and the torque acting on the shaft measured to determine the electrical power delivered by the generator and the electric power is calculated from these quantities ,

In the determination of the kinetic power of the wave, the moment of inertia θ of the wave enters. In principle, the moment of inertia can be calculated or determined experimentally. A particularly simple method of determination results, if according to a further preferred embodiment of the invention for determining the moment of inertia θ of the shaft in a stationary operation of the turbo group at a time set the electric power by disconnecting the generator from the grid to zero and the rotational frequency and spin present at this time the wave is measured, and if the value of the moment of inertia θ of the shaft is chosen to be that according to the formula P_kin = 4π²θf (df / dt) calculated kinetic power P_kin equal to the measured electric power P_G at the time of the separation is.

An inventive apparatus for performing the method for controlling the power of a thermal power into electric power converting turbo group, which turbo group at least on a common shaft driven by the thermal power turbine and driven by the turbine, electric power P_G to a grid-emitting generator and a power controller for controlling the thermal power for the turbine comprises, characterized by first means which an output power of the turbo group with a predetermined power value P_C compare and a difference value .DELTA.P as a control signal to the power controller for controlling the thermal power P_T for the turbine, second means for measuring the rotational frequency f of the shaft, third means, which from the measured rotational frequency f and the temporal change df / dt of the rotational frequency f in accordance with the equation P_kin = 4π^{2 ·}θ^·f^·(df ​​/ dt) (where θ symbolizes the moment of inertia of the rotating mass (17)) determine the kinetic power of the shaft (17), and fourth means (30) which determine the electric power (P_G) and the kinetic power P determined by the third means (26, .., 29)_kin add and forward as output of the turbo group (10) to the first means (19).

A preferred embodiment of the device according to the invention is characterized in that the third means comprise a differentiator, a multiplier and an amplifier with an adjustable amplification factor.

According to the invention, the method is applied to a turbo group, which comprises a steam turbine or a gas turbine, or to a combined cycle power plant, which comprises a gas turbine and a steam turbine connected behind the gas turbine.

Further embodiments of the invention will become apparent from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic diagram of a power control for a gas turbine according to the prior art; and</dd><dt>Fig. 2</dt><dd>the circuit diagram analogous to Fig. 1 with additional consideration of the kinetic power of the shaft according to a preferred embodiment of the invention.</dd></dl>

WAYS FOR CARRYING OUT THE INVENTION

In Fig. 2 is in a to Fig. 1 a schematic diagram of a power control for a gas turbine 15 is shown, which is based on a preferred embodiment of the method according to the invention. The gas turbine plant 15 with its parts 11, .., 14, the shaft 17, the generator 16 connected to a network 18, and the control loop formed from the elements 19, .., 25 are substantially the same, as shown in FIG. 1, and therefore also provided with the same reference numerals. A change from FIG. 1 results in that the measured electric power P_G from the generator 16 not directly to the subtractor 19 with the predetermined power setpoint P._C but that to the electric power P_G first in an adder 30, the kinetic power P_kin is added.

The kinetic power P_kin is calculated in a correction circuit 26 from the rotational frequency f of the shaft 17 measured on the shaft 17 in accordance with the equation (2). For this purpose, the measured rotational frequency f is given to an input of a multiplier 28 provided with two inputs. At the other input of the multiplier 28, the temporal change df / dt of the rotational frequency f is given, which is derived from the measured rotational frequency f by differentiation in a differentiator 27. The product of the quantities f and df / dt calculated in the multiplier 28 is then amplified in an amplifier 29 having the amplification factor 4π²θ. At the output of the amplifier 29, which also forms the output of the correction circuit 26, then the size P is_kin which is forwarded to the adder 30. The correction circuit 26 of the exemplary embodiment represents an analog calculation circuit which, from the measured rotation frequency f, the desired kinetic power P_kin calculated. Of course, this calculation can also be done digitally by means of a microprocessor or the like., If the input quantities are previously digitized accordingly. The measurement of the rotational frequency f is done in Fig. 2 for the sake of simplicity by means of a separate Drehfrequenzgebers 25 '. Of course, it is possible to dispense with this separate rotary frequency transmitter 25 'and to use the output signal of the rotary frequency transmitter 25 for the calculation of the kinetic power.

As already mentioned, the sum formed in the adder 30 is the electric power P_G and the kinetic power P_kin in the subtractor 19 with a predetermined power value P_C compared and the thermal power P_T decreases when the difference value .DELTA.P is positive, and increases when the difference value .DELTA.P is negative. When controlling a gas turbine plant 15 comprising a controllable inlet 14 for the combustion air, a compressor 13 for compressing the combustion air, a combustion chamber 12 for combustion of a fuel under supply of combustion air, and a turbine 11, are used to control the thermal power P_T the mass flow of the admitted combustion air via the controllable inlet 14, and the mass flow of the fuel dm_fc/ dt regulated.

In the arrangement of Fig. 2, the electric power P_G for the power control directly at the output terminals of the generator 16 removed. If it is necessary to dispense with such a measurement on the generator 16, to determine the electric power P emitted by the generator 16_G the rotational frequency f of the shaft 17 and the torque acting on the shaft 17 are measured and from these quantities the electric power P_G be calculated. As a result, for example, insulation problems on the generator side can be avoided.

For the calculation of the kinetic power, the knowledge of the moment of inertia θ of the shaft 17 is necessary, so that, for example, the amplification factor of the amplifier 29 can be adjusted accordingly. In this context, an experimental determination of θ is expedient. For this purpose, in a stationary operation of the turbo group 10 at a time, the electric power P_G by disconnecting the generator 16 from the network 18 to zero. The existing at this time rotational frequency f and spin df / dt the shaft 17 are measured and entered, for example, in the correction circuit 26. The value for the moment of inertia θ of the shaft 17 or the amplification factor of the amplifier 29 are now chosen so that the formula P according to the formula_kin = 4π²θf (df / dt) calculated kinetic power P_kin or the output signal of the amplifier 29 equal to the measured electric power P_G at the time of disconnection, the rest (due to the stationary state prevailing at that time) is equal to the thermal power P_T at this time is.

This type of determination has its background in that when the electric power P disappears_G in a stationary state (kinetic power P_kin= 0) the entire thermal power is converted into kinetic power, resulting in an acceleration of the shaft (df / dt&gt; 0). The kinetic power of the shaft 17 which can be determined from the onset of acceleration can therefore be equated directly with the thermal power at the time of separation or the electrical power, ie P_T= P_G= P_kin= 4π².theta..sub.F (df / dt). Since P_T or P_G and f and df / dt are known, the moment of inertia θ can be determined from this.

The control method described can be applied to individual turbo groups or even to a combination of several turbo groups. The turbine can - as explained in the example - be a gas turbine. But it can also be a steam turbine. In particular, the inventive method can be used in combined cycle power plants, which comprise at least one gas turbine and at least one connected behind the gas turbine steam turbine.

NAME LIST

<dl id="dl0002" compact="compact"><dt>10</dt><dd>Turbo group</dd><dt>11</dt><dd>turbine</dd><dt>12</dt><dd>combustion chamber</dd><dt>13</dt><dd>compressor</dd><dt>14</dt><dd>controllable inlet (Variable Inlet Guiding Vane (VIGV))</dd><dt>15</dt><dd>Gas turbine plant</dd><dt>16</dt><dd>generator</dd><dt>17</dt><dd>wave</dd><dt>18</dt><dd>Mains (three-phase network)</dd><dt>19.24</dt><dd>subtractor</dd><dt>20</dt><dd>power controller</dd><dt>21</dt><dd>velocity limiter</dd><dt>22.30</dt><dd>adder</dd><dt>23</dt><dd>Characteristic transmitter</dd><dt>25.25 '</dt><dd>Rotary frequency generator</dd><dt>26</dt><dd>correction circuit</dd><dt>27</dt><dd>Differentiator</dd><dt>28</dt><dd>multipliers</dd><dt>29</dt><dd>amplifier</dd></dl>