JPS5818567A - Operation of hydraulic turbine - Google Patents

Abstract

PURPOSE:To prevent an accident to occur by the resonance of hydraulic turbine runners by providing a moderate decrease ratio of revolving speed of the hydraulic turbine with respect to opening of a guide vane when the hydraulic turbine is driven up to a speed which stands below a rated speed of the hydraulic turbine and exceeds a critical limit of resonance. CONSTITUTION:When a hydraulic turbine is driven in a parallel operation mode of a system, a speed governor of the turbine detects frequencies of the system. Opening of a guide vane is regulated on the basis of variation of the frequencies and a prefixed speed decreasing ratio so as to control the output power of the hydraulic turbine. Characteristic lines of normally decreased revolving speeds are cut off at points P1-P3 which stand below a rated speed Vd and exceed the critical limit (Vc) of resonance to reduce respective speed decreasing ratio in the range of revolving speeds at P1-P3, hence preventing the revolving speeds of a main engine from being induced into the critical zone Vc of resonance during parallel operation of systems. Since an accident caused by the resonance of runners of the hydraulic turbine is prevented, and safe and reliable operation may be ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a water turbine or a pump-turbine, and particularly relates to a method of operating a water turbine when the natural frequency of the runner is less than or equal to the excitation frequency equivalent to the rated rotational speed of the launch. .

When the turbines are running in parallel, the turbine governor detects the frequency of the system. The output of the water turbine is adjusted by adjusting the opening degree of the guide vane in accordance with this frequency change and a preselected speed droop rate. The speed droop rate is selected depending on the operating method of the water turbine, etc., and is usually uniquely set to an arbitrary value of about 3 to 10 inches.

Incidentally, in recent years, water turbines, especially pump water turbines, have become faster and faster, and there are cases where they are operated at a rated rotational speed that exceeds the natural frequency of the water turbine runner. In other words, since the excitation frequency is expressed as a linear function of the runner's rotational speed, as the rotational speed of the launch accelerates from stop to the rated rotational speed (equivalent to fv, o), as shown in Figure 1, the excitation frequency increases. The vibration frequency fK also increases, and eventually exceeds the launch natural frequency (lower limit f□, upper limit f.2) and reaches the vibration frequency fvco equivalent to the rated rotational speed.

The problem here is that while the water turbine is operating in parallel, the excitation frequency is in the runner's natural frequency region, that is, in the resonance danger zone V.
This is the resonance when entering c. When the launch resonates, it generates vibrations with large amplitudes, and the stress at that time reaches several times the design value, creating a dangerous situation that can lead to runner destruction. However, conventional operating systems have the drawback of not providing sufficient protection against this phenomenon.

That is, as shown in Figure 2, when the turbines are operating in parallel, the turbine governor detects the frequency of the system and adjusts the guide vanes according to the pre-selected speed droop rate as the frequency changes. The opening degree is adjusted and the output of the water turbine is adjusted, but if the above-mentioned resonance danger zone VC is close to the rated rotational speed V of the main engine, as shown in Fig. 2,
There is a possibility that the rotational speed of a water turbine operating along the speed droop characteristic line falls into the resonance danger zone Vc region.

In the prior art, sufficient consideration has not been given to such drawbacks.

The purpose of the present invention is 1. The present invention aims to eliminate the drawbacks of the prior art described above and provide a safe and reliable method of operating a water turbine.

The key point of the present invention is to provide a bending point at any rotational speed below the rated rotational speed of the main engine and above the resonance danger zone, and to reduce the rate of speed droop in the rotational speed region where the bending is expected. The aim is to prevent the main engine from entering the resonance danger zone during system parallel operation.

An embodiment of the invention is shown in FIG.

For normal speed droop rate characteristics, at any rotational speed below the rated rotational speed v6 and above the resonance danger zone VC, we have established drooping rate bending points P, ~P3, and below the bending points P1~P3. By reducing the rate of speed droop in the rotational speed region, the main engine will not enter the resonance danger zone during system parallel operation, allowing safe and reliable operation.

The rotational speed at the turning points (P, -P3) is detected by a speed relay, and the speed droop rate below the turning points CP1-P3) can be electrically switched to an arbitrary constant value.

In the above-mentioned embodiment, the bending point of the speed droop rate was one point for every one of the speed droop rate characteristics, but if necessary, two or more bending points could be set, and the result would be the same as described above. You can get the following effect.

According to the present invention, accidents caused by resonance of a water turbine launch can be prevented, and a safe and reliable method of operating a water turbine can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an excitation frequency characteristic diagram, FIG. 2 is a conventional velocity drooping rate characteristic diagram, and FIG. 3 is a velocity drooping rate characteristic diagram of the present invention.

Claims (1)

[Claims] 1. In controlling a water turbine equipped with a water turbine runner and a guide vane, when the water turbine reaches a rotation speed that is below the rated rotation speed and above the resonance danger zone, the drooping rate of the rotation speed of the water turbine with respect to the guide van opening degree is gradually set. A method of operating a water turbine characterized by: