What is a Water Turbine?

The role of water turbine sets is to rivers, lakes, etc. located in the high places with potential energy of water flow to the low places, through the turbine into the mechanical energy of the turbine, the turbine and promote the generator to generate electricity, will be converted to mechanical energy into electrical energy.

Water Turbine Basics

The turbine generator in a hydroelectric generator set is driven by the hydraulic turbine. The rotational speed of the generator determines the frequency of the output alternating current (AC), so stabilizing the rotor speed is essential to ensure the stability of the frequency. Closed-loop control can be adopted to control the turbine speed, that is, to take the frequency signal samples of the alternating current, and feedback them to the control system that controls the opening and closing angle of the turbine guide vane to control the turbine's output power, in order to stabilize the speed of the generator.

Water Turbine Component

Hydraulic generator set is an energy conversion device to realize the conversion of water potential energy into electric energy, which is generally composed of hydraulic turbine, generator, governor, excitation system, cooling system and power station control equipment.

• Hydraulic turbine: The commonly used hydraulic turbine has two types: impact type and counterattack type.
• Generator: most of the generators are synchronous generators with low rotational speeds, generally below 750r/min, and some of them are only a few tens of rpm; because of the low rotational speeds, the number of magnetic poles is more; the structural dimensions and weights are larger; there are two types of installation forms for hydro generator sets, namely vertical and horizontal.
• Speed regulation and control device (including governor and oil pressure device): The function of governor is to regulate the rotational speed of hydraulic turbine to ensure that the frequency of output power meets the requirement of power supply, and to realize the operation of the unit (start-up, shutdown, speed change, load increase, load decrease) and safe and economic operation. For this reason, the performance of governor should meet the requirements of fast operation, sensitive response, rapid and stable, convenient operation and maintenance, etc. It also needs reliable manual operation and accidental shutdown device.
• Excitation system: Hydro generator is generally electromagnetic synchronous generator, through the control of DC excitation system can be achieved by voltage regulation, active power and reactive power regulation and other control to improve the quality of the output power.
• Cooling system: The cooling of small hydro generator mainly adopts air cooling to ventilate the system to the generator stator, rotor and core surface for cooling. However, with the growth of stand-alone capacity, the stator and rotor heat load continues to increase, in order to increase the generator output power per unit volume at a certain speed, large-capacity hydroelectric generators use the stator and rotor windings directly water-cooled; or stator windings cooled with water, while the rotor is cooled with a strong wind.
• Power station control equipment: Power station control equipment is mainly based on microcomputer, to realize the hydroelectric generator grid, voltage regulation, frequency regulation, power factor adjustment, protection and communication and other functions.
• Braking device: Rated capacity over a certain value of hydroelectric generator are equipped with braking device, its role is in the generator shutdown process, when the speed is reduced to 30% ~ 40% of the rated speed, the implementation of continuous braking of the rotor, in order to avoid the thrust bearings due to the destruction of the oil film under the low-speed and burn the axial tile. Another function of the braking device is to jack up the rotating parts of the generator with high-pressure oil before installation, maintenance and starting. The braking device uses compressed air for braking.

Control Technology

Hydro generator set automatic control system undertakes the following tasks: automatic parallelism of hydro generator sets, automatic adjustment of excitation, frequency and active power, reactive power compensation, automatic control of auxiliary engines, automatic operation of hydro generator sets, automatic protection, etc., of which the frequency and power control is the main one.

Small hydroelectric generator sets convert water energy into electric energy and supply it directly to the load or integrate it into the power grid for the load to use. For the load, not only requires safe and reliable power supply, but also requires high quality of power supply, that is, the voltage and frequency of the power should be rated value, and small fluctuations. This is very important for off-grid appliances, so reliable off grid power supply is needed.

Generator voltage, frequency or grid voltage, frequency stability depends on the balance of reactive and active power in the generator or grid, respectively. Where the cause of frequency fluctuations is the imbalance between the generator input power and output power, synchronous generator issued by the frequency of electrical energy and its rotational speed of the relationship between the f = np / 60, in the generator pole logarithm P is unchanged, the frequency f by the rotational speed of the n decision. When the load of the generator increases, the mechanical torque input to the generator is less than the electromagnetic torque output, the motor speed decreases, which causes a decrease in the frequency of the electrical energy, and vice versa the frequency will increase. And the fluctuation of voltage is mainly caused by the change of load size and the change of load nature (change of active and reactive power). The basic task of hydro generator set control is to continuously adjust the active and reactive power output of the hydro generator set according to the changes in the load, and to maintain the unit speed (frequency) and output voltage within the specified range. The control of hydro generator set frequency is realized by the turbine governor, while the stabilization of terminal voltage can be completed by the generator excitation regulator. The regulation of the two is relatively independent and has little influence on each other.