JPS623284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of steam turbine bearing oil supply in a thermal or nuclear power plant.

In steam turbine bearings, in order to reduce the friction loss caused by shaft rotation and remove the heat generated by friction, oil is supplied by a bearing oil supply device, and the drained oil whose temperature has risen is cooled by an oil cooler and then recycled again. A continuous lubrication method is used for oil supply, but in order to form an oil film of appropriate thickness on the bearing surface, the oil supply temperature must be increased in accordance with the increase in the rotational speed of the steam turbine for the following reasons. It is necessary to lower the oil supply temperature in accordance with the decrease in speed.

That is, assuming that the oil supply temperature is constant, as the number of rotations increases, the formation of an oil film on the bearing surface becomes easier, but friction loss tends to increase approximately in proportion to the third power of the number of rotations. Therefore, the optimum oil supply temperature at which oil film formation is possible and friction loss is small increases almost in proportion to the increase in rotational speed.

Therefore, in order to maintain the oil supply temperature that satisfies the above conditions, the bearing oil supply temperature control device includes an oil cooler, an oil temperature control valve that controls the flow rate of cooling water to the oil cooler, and an oil supply temperature transmitter. It is generally configured with a temperature controller.

The details of this prior art will be explained using drawings.
As shown in FIG. 1, the steam turbine oil supply system pumps oil from an oil storage tank 47 using an oil supply pump 46, a main oil pump 49 connected to the shaft of a turbine 43, and a booster pump 51 (the oil is pumped up when the turbine speed is at a predetermined speed). As shown in FIG. 4, the oil is sucked up by the main oil pump 49 until the turbine speed reaches a predetermined speed, as shown in FIG. After being cooled by the cooling water supplied through the control valve 48, the cooling water is supplied to the bearing 45, and the bearing 4 is cooled.
At the same time as the lubrication valve 5 is operated, heat due to friction is removed, and the oil itself is heated and returned to the oil storage tank 47. 50,
52 is a check valve.

As shown in FIGS. 1 and 2, the turbine bearing oil supply temperature control device measures the oil supply temperature using an oil supply temperature transmitter 1 provided at the oil outlet of the oil cooler 42 and transmits the same to the oil supply temperature controller 28. The turbine rotation speed is detected by the turbine rotation speed transmitter 2 and transmitted to the oil supply temperature setting device 22.
calculates the optimum oil supply temperature for the rotational speed as shown in Fig. 5, and sends the signal to the temperature controller 2.
8 is transmitted to the temperature controller 28 as a temperature setting signal. The temperature controller 28 is the oil supply temperature transmitter 1.
Using the signal from the oil supply temperature setting device 22 as a feedback signal and the signal from the oil supply temperature setting device 22 as a setting signal, a proportional+integral operation or a proportional+integral+differential operation is performed, and the output control signal is transmitted to the drive section of the control valve 48. In this way, the bearing oil supply temperature can be adjusted by the oil supply temperature controller 2.
The control valve 48 is controlled by the control signal 8, and the amount of cooling water in the oil cooler 42 is adjusted to control the temperature to match the rotational speed.

In the case of such conventional control methods, the temperature setting signal is a setting signal commensurate with the rotation speed,
Since this is a feedback control that compares the measured value and the set value and adjusts the opening degree of the control valve 48 based on the deviation, the timing t ₁ is determined as shown in FIG.
When the rotation speed a shown in A increases or decreases in a stepwise manner, such as at the time of starting T ₁ from time t ₂ to time t ₂ or at time T _{3 of stopping after time t 3} , at the time of cold star shown in B, Or, during the hot start shown in C, the proportional operation of the controller 28 cannot follow the changes in oil supply and set temperature and the required opening degree of the control valve 48, and the actual oil temperature is c, d relative to the optimum oil temperature b.
As shown in the figure, it rises too much or falls too much. In order to prevent such a phenomenon from occurring, increasing the proportional gain to increase sensitivity and speed up the response has the disadvantage that control becomes unstable at T ₂ during normal operation. (However, the oil supply temperature at the cold start shown in Figure 3B is much lower than the optimum oil temperature, but this is because this turbine bearing oil supply temperature control system uses an oil cooler to cool it. For,
At the time of a cold start, the oil is in the oil storage tank 47, so this phenomenon occurs because the oil itself sent to the oil cooler 42 is below the optimum oil temperature, as shown in Figure 7i. (Figure j shows the inlet oil temperature at the time of a hot start), this phenomenon is unavoidable unless measures are taken such as installing an oil heater. Also in the present invention, which will be described later, the oil supply temperature at the time of a cold start is the optimum oil temperature. Regarding the fact that it does not match the temperature, this will be excluded from the explanation. ) The object of the present invention is to control the bearing oil supply temperature of a steam turbine in all operating conditions, from during turning of the steam turbine, to startup, during load operation, and during shutdown.
An object of the present invention is to provide a temperature control method that automatically controls bearing oil supply temperature to always keep it in an optimal state and facilitates the operation of a steam turbine.

The most characteristic feature of the present invention for achieving this purpose is that the temperature control valve is controlled by the turbine rotation speed, the oil temperature at the inlet of the oil cooler, the temperature difference between the cooling water at the outlet and outlet of the oil cooler, and the differential pressure signal at the outlet and outlet of the temperature control valve. It is characterized by performing feed forward control of the opening degree. Further, by adding conventional feedback control to this control, it becomes possible to control the oil supply temperature more accurately.

That is, in the present invention, the optimum oil supply temperature is approximately proportional to the rotational speed of the steam turbine, as shown in FIG. It is a function of the oil temperature at the inlet of the cooler and the temperature difference between the cooling water at the outlet and outlet of the oil cooler, and the opening degree of the control valve that controls the amount of cooling water is determined by the required amount of cooling water, the differential pressure at the outlet and outlet of the control valve, and the C _V value characteristics of the control valve. By calculating each of the above-mentioned signals, the optimum opening of the control valve for controlling the optimum oil supply temperature is determined, and this opening signal is used to directly control the opening of the control valve. This is a method of controlling the oil temperature, that is, feed-forward control, which makes it possible to control the optimum oil supply temperature even in operations that are close to step changes such as starting and stopping the turbine.

Next, the theoretical basis for performing the above control according to the present invention will be explained mathematically. In addition, the meaning of each symbol in each formula described below is as follows.

Q _W : Required amount of cooling water T _WI : Oil cooler inlet cooling water temperature T _WO : Oil cooler outlet cooling water temperature △T _W : Oil cooler inlet and outlet cooling water temperature difference (=T _WO - T _WI ) n: Turbine temperature difference Rotation speed n _B : Turbine rated rotation speed T _OI : Oil cooler inlet oil temperature T _OO : Oil cooler outlet oil temperature T (n): Optimal oil temperature at rotation speed n f (T _OI ): Oil cooler inlet Function of oil temperature Q _O : Oil supply amount Q _OB : Oil supply amount at turbine rated rotation Q _A : Oil supply pump delivery flow rate Q(n): Oil supply amount to the bearing at rotation speed n C _V : Required C _V of the control valve Value △P _V : Differential pressure at the entrance and exit of the control valve O _P : Required opening degree of the control valve C _Vnax : Fully open C _V value of the control valve k ₁ , k ₂ , k ₃ , k ₄ : Coefficient C: Constant Steam turbine rotation speed The relationship between n and the amount of heat generated is
As shown in FIG. 6, the heat generated in the bearing 45 is exchanged with cooling water in the oil cooler 42. Regarding heat exchange between the cooling water and oil of the oil cooler 42, equation (1) holds true.

Q _W・(T _WO −T _WI )=k ₁・Q _O・(T _OI −T _OO )……(1) Therefore, the cooling water amount Q _W is given by equation (2).

Q _W =k ₁・(T _OI −T _OO )・Q _O /(T _WO −T _WI ) =k ₁・(T _OI −T _OO )・Q _O /△T _W ……(2) Optimum oil supply temperature T(n) is a function of the rotation speed n, has the characteristics shown in FIG. 5, and is given by equation (3).

T(n)=k ₂・n/n _B +c...(3) Oil cooler outlet oil temperature T _OO is the optimum oil supply temperature T
(n). In equation (2), (T _IO −
If the term of T _OO ) is f(T _OI ), then T _OO = T
When controlled by (n), equation (4) is established.

f(T _OI )=T _OI −T _OO =T _OI −T(n) ………(4) The amount of oil supplied Q _O is a function of the rotation speed n, and the fourth
The characteristics are shown in the figure. That is, the turbine rotation speed is approximately
When it is 80% or more, the oil supply is sent through the main oil pump 49 as shown in f, and the oil supply amount at that time is
It is given by equation (5).

Q _O = k ₃・Q _OB・(n/n _B ) ³ ...(5) On the other hand, when the rotation speed n is less than about 80%, Fig. 4 e
As shown in the figure, oil is supplied by an oil supply pump 46, and the amount of oil supplied is given by equation (6).

Q _O =Q _A ...(6) The amount of oil supplied by equations (5) and (6) is regarded as a function of the rotation speed n and is expressed by equation (7).

Q _O =Q(n) ...(7) By substituting equations (4) and (7) into equation (2), equation (8) is established.

Q _W = _k1 ·f(T _OI )·Q(n)/△T _W ...(8) The required C _V value of the control valve 48 for this required amount of cooling water Q _W is determined by equation (9).

The required opening degree R _P of the control valve 48 for the required C _V value of the control valve 48 is expressed as (10) if the C _V value characteristic of the control valve 48 is a linear characteristic as shown in a in FIG. 11.
It is given by Eq.

O _P =C _V /C _Vnax (10) When formulas (8) and (9) are substituted into formula (10), formula (11) is established.

As is clear from equation (11), the required opening degree O _P of the temperature control valve 48 is determined by the difference between the turbine rotation speed n, the oil cooler inlet oil temperature T _OI , and the oil cooler inlet and outlet cooling water temperature difference ΔT _W
and the differential pressure between the inlet and outlet of the temperature control valve 48 ΔP _V .

An embodiment of the oil supply temperature control method according to the present invention, which is constructed based on such a theoretical background, will be described in the eighth section.
This will be explained with reference to FIGS. The steam turbine bearing oil supply system shown in FIG. 8 is different from the one shown in FIG. The difference is that a differential pressure transmitter 6 at the inlet and outlet of the control valve 48 is added. Also, the difference between the oil supply temperature control device shown in FIG. 9 and the one shown in FIG. An oil supply temperature difference calculator 24 that calculates the deviation between the setting signal of the oil supply temperature setting device 22 for setting the temperature and the inlet oil temperature signal from the oil cooler inlet oil temperature transmitter 5, and a temperature difference and a cooling water temperature difference transmitter. A cooling water amount calculator 25 that calculates the amount of cooling water from the cooling water temperature difference signal from the cooling water temperature difference signal from the cooling water amount calculator 21 and the oil supply amount signal from the oil amount calculator 21, and a cooling water amount signal obtained by the cooling water amount calculator 25 and a control valve. Required C _V value calculator 26 that calculates the required C _V value of the control valve 48 from the differential pressure signal from the inlet/outlet differential pressure transmitter 6
and a valve opening calculation unit 23 which calculates the valve opening according to the characteristics shown in FIG. 11a from the output signal of the calculation unit 26.
An addition/subtraction computing unit 27 is added that performs addition/subtraction on the output signal of the computing unit 23 and the output signal of the oil supply temperature controller 28, and the opening degree of the control valve 48 is adjusted using the output signal of the addition/subtraction computing unit 27. It is configured as follows.

The operation of this device will be explained below. The output signal of the turbine rotation speed transmitter 2 is transmitted to the oil supply amount calculator 21, where the calculations of equations (5) and (6) are performed to obtain the oil supply amount signal shown in FIG. 4.

The oil supply temperature setting device 22, as in the conventional case,
(3) is calculated and transmitted to the oil supply temperature difference calculator 24 and the oil supply temperature controller 28. Oil supply temperature difference calculator 2
4 calculates equation (4) based on the signal from the oil cooler inlet oil temperature transmitter 5 and the signal from the oil supply temperature setting device 22, and transmits the result to the cooling water amount calculator 25.

The cooling water amount calculator 25 calculates the formula (8) based on the above two signals, that is, the oil supply temperature difference signal and the oil supply amount signal, as well as the signal from the cooling water temperature difference signal generator 4.
The required amount of cooling water _QW is determined and transmitted to the required C _V value calculator 26, which receives the signal from the control valve inlet _differential pressure transmitter 6 and the above-mentioned cooling water amount calculator 25. Based on the signal, equation (9) is calculated to obtain the required C _V , and this C _V value is transmitted to the valve opening degree calculator 23 .

The valve opening degree calculator 23 calculates the expression (10) and calculates the opening degree O.
_P is determined and transmitted to the addition/subtraction calculator 27.

The signal from the oil supply temperature controller 28 of the feedback controller similar to the conventional one is transmitted to the addition/subtraction calculator 27, which performs addition/subtraction calculations with the valve opening degree signal from the valve opening degree calculator 23, and generates a control signal. is transmitted to the control valve 48 after fine adjustment. As a result, the bearing oil supply temperature can always be maintained at an optimal state, and as shown in Fig. 10, stable control of the oil supply temperature g during a cold start and the oil supply temperature h during a hot start without hunting or overshoot can be achieved. can.

In the above embodiment, the differential pressure at the inlet and outlet of the control valve 48 was measured, but in a plant where the pressure at the inlet of the control valve is always constant, the pressure difference cannot be substantially determined by measuring only the pressure at the outlet of the control valve. Since it involves measurement, it can be adopted. In addition, the characteristics of the control valve 48 include a linear characteristic as shown in a in FIG. 11, a rapid opening characteristic b, and an equal ratio characteristic c. If you change it according to
Control valves with various characteristics can also be used as they have the same effect as when using a valve with linear characteristics.

In the above embodiment, since the conventional feedback control is added to the correction control, more accurate control operation is possible.

As described above, according to the present invention, it is possible to maintain the oil supply to the bearings in an optimal state in all operating conditions from the turning of the steam turbine to the startup, load operation, and stoppage of the steam turbine. The driving operation becomes easier.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing a conventional steam turbine bearing oil supply system, Figure 2 is a system diagram showing a conventional oil supply temperature control system, Figure 3 is a characteristic diagram of oil supply temperature and optimum oil supply temperature according to the conventional technology, and Figure 4 is a system diagram showing a conventional steam turbine bearing oil supply system. The figure is a characteristic diagram of the steam turbine rotation speed and the oil supply flow rate to the bearing, Figure 5 is the characteristic diagram of the steam turbine rotation speed and the optimum oil supply temperature, and Figure 6 is the characteristic diagram of the steam turbine rotation speed and the calorific value of the bearing. , FIG. 7 is a characteristic diagram of oil cooler inlet oil temperature, optimum oil supply temperature, and steam turbine rotation speed at the time of starting a steam turbine, and FIG. 8 is a system diagram of a steam turbine bearing oil supply device showing an embodiment of the present invention. Fig. 9 is a system diagram of a steam turbine bearing oil supply temperature control device showing an embodiment of the present invention, Fig. 10 is a characteristic diagram of the oil supply temperature according to the present invention, and Fig. 11 is a diagram showing the opening degree of the control valve and C _V
FIG. 3 is a characteristic diagram showing the main relationships among values. 1... Oil supply temperature transmitter, 2... Turbine rotation speed transmitter, 4... Cooling water temperature difference transmitter, 5... Oil cooler inlet oil temperature transmitter, 6... Control valve outlet/outlet differential pressure transmitter, 2
1... Oil supply amount calculator, 22... Oil supply temperature setting device, 23
...Valve opening degree calculator, 24...Oil supply temperature difference calculator, 25
...Cooling water amount calculator, 26...Required C _V value calculator, 2
7... Addition/subtraction calculator, 28... Oil supply temperature controller, 42...
Oil cooler, 43...turbine, 45...bearing, 48...
Temperature control valve.

Claims (1)

[Claims] 1. In controlling the oil supply temperature by cooling the oil supply to the steam turbine bearing with an oil cooler and adjusting the amount of cooling water to the oil cooler with a control valve, the turbine rotation speed and the oil 1. A turbine bearing oil supply temperature control method, characterized in that feedforward control of the opening degree of the control valve is performed based on a cooler inlet oil temperature difference, a cooling water temperature difference at an oil cooler outlet and outlet, and a differential pressure between the control valve inlet and outlet. 2. Claim 1 further includes feedback control for correcting the opening degree of the control valve based on the deviation between the oil supply temperature at the outlet of the oil cooler and the set temperature set based on the turbine rotation speed. A turbine bearing oil supply temperature control method characterized by: