Application of various types of sensors in hydropower plants

In modern automated production processes, various sensors are needed to monitor and control the various parameters in the production process, so that the equipment works in a normal state or in an optimal state, so excellent sensors are the basis of modern production.

1 Temperature detection

A temperature sensor is a device that converts the temperature into a resistance value or other electrical signal. Commonly used are platinum, copper-based thermal resistance sensors, semiconductor-based thermistor sensors, and thermocouple sensors.

The temperature sensor is not only used to detect the upper guide, thrust, lower guide, water guide bearing temperature of the hydro-generator set and the oil temperature in the four guide bearing oil grooves, but also to measure the temperature of the generator stator and rotor and to cool them. The temperature of the water in the air cooler.

In the actual work, due to the harsh environment of the four guide bearings of the hydro-generator unit, the platinum resistance wire often breaks. Therefore, the root wire of the platinum resistance needs special protection to prevent the generator set from rotating during the rotation. The impurities in it are constantly impacting. In addition, the mounting position of the panel is quite close to the position of the sensor. To prevent the measurement error caused by the wire, a three-wire connection is required.

2 Pressure detection

A pressure sensor is a sensor that converts a pressure signal into an electrical signal. According to the working principle, it can be divided into piezoelectric sensor, piezoresistive sensor and capacitive sensor. It is a general term for detecting the energy of interaction between gases, liquids, solids, etc. It also includes pressure gauges above atmospheric pressure and vacuum gauges below atmospheric pressure. The capacitance of the capacitive pressure sensor is determined by the electrode area and the distance between the two electrodes. It has recently developed rapidly due to its high sensitivity, good temperature stability and large pressure range.

Whether in the air compressor control system or the hydraulic device control system, or in the power plant maintenance or leakage drainage control system, it is necessary to install two sets of pressure sensors or even three sets of sensors that are mutually standby, mainly to be safely detected. It is measured to prevent the unit from being accidentally shut down due to the pressure drop of the pressure gas tank and the pressure oil tank. It also prevents the flooding plant from leaking water that cannot be discharged from the plant in time due to the high water level in the water collecting well.

In practical applications, the zero point of the pressure sensor is prone to drift, so periodic calibration is required. In addition, the long-term use of the sensor is prone to fatigue and the measurement signal is inaccurate and needs to be replaced periodically.

3 speed detection

The speed sensor is a kind of sensor that converts the speed signal into an electric signal. It can detect both the linear speed and the angular speed. The commonly used speed generators and pulse encoders and the gear speed measurement.

However, the gear speed measurement also has its shortcomings. First, it increases the cost of hardware and the complexity of the software. Second, due to the limitation of machining accuracy, the distance between the teeth and the teeth on the toothed disc cannot be exactly equal, or the pitch is not May be completely uniform. For high-sensitivity speed sensors, it calculates the speed by scanning the time between the teeth and the teeth. Even if the actual speed of the unit does not change, the different intervals between the teeth and the teeth will reflect the change of speed, thus generating interference signals. The third is that the proximity switch collision is easily damaged.

4 Flow detection

A flow sensor is a sensor that converts a flow signal into an electrical signal. Commonly used are electromagnetic flowmeters and flow switches.

The electromagnetic flowmeter is a meter that measures the volumetric flow rate of a conductive liquid by using Faraday's law of electromagnetic induction. The measuring channel of the electromagnetic flowmeter is a smooth straight pipe with an unobstructed flow detecting piece. It is not easy to block and is suitable for measuring liquid-solid two-phase fluid containing solid particles or fibers. It does not produce pressure loss due to the detection flow rate, and the resistance of the instrument. It is only the resistance of the pipeline of the same length, which is most suitable for large diameter water supply pipelines requiring low resistance loss. The measured volumetric flow is unaffected by fluid density, viscosity, temperature, pressure, and electrical conductivity (as long as it is above a certain threshold).

5 Detection of oil mixed water

The oil mixed water sensor is a capacitive sensor for measuring oil mixed water or oil accumulated water. It is used to detect the content of water mixed into the return tank or the leak tank in the automatic control oil system of the hydro-generator set. It can also be widely used as the detection of oil-mixed or stagnant water in the tank.

The oil mixed water sensor is placed in the measured medium. When the water is mixed with water, the medium value changes, and the sensor outputs a corresponding electrical signal. After the signal sent by the sensor is processed, the 0-100% moisture content in the oil is converted into a corresponding 4-20 mA output.