company news about The Role and Status of the Hydro turbine Governor in Hydropower Stations

The Role and Status of the Hydro turbine Governor in Hydropower Stations

When electricity is in operation, it is necessary to constantly maintain the balance between the power supply and the load. Additionally, ensuring the good quality of electric energy is an important task in the power production process. The main indicators for measuring the quality of electric energy are generally voltage and frequency, followed by the waveform. Deviations in frequency will seriously affect the normal operation of power users. For electric motors, a decrease in frequency will cause the motor speed to drop, thereby reducing productivity and affecting the motor's service life; conversely, an increase in frequency will cause the motor speed to rise, increasing power consumption and reducing economy. Especially in certain industrial sectors with strict speed requirements (such as textiles, papermaking, etc.), frequency deviations will greatly affect product quality and even lead to defective products. In addition, frequency deviations will have more serious impacts on the power plant itself. For example, in thermal power plants, for centrifugal machinery such as boiler feedwater pumps and fans, their output will drop sharply when the frequency decreases, forcing the boiler's output to be significantly reduced or even triggering an emergency shutdown of the boiler. This will inevitably further reduce the power output of the system, leading to a further decline in system frequency. Moreover, when operating at a reduced frequency, the turbine blades will develop cracks due to increased vibration, thus shortening the turbine's service life. Therefore, if the trend of a sharp decline in system frequency cannot be stopped in a timely manner, it will inevitably cause a vicious cycle and even lead to the collapse of the entire power system.

According to the regulations of China's power sector, the rated frequency of the power grid is 50Hz, and the allowable frequency deviation for large power grids is ±0.2Hz. For small and medium-sized power grids, system load fluctuations can sometimes reach 5% to 10% of their total capacity; even for large power systems, load fluctuations often reach 2% to 3%. The continuous change of the power system load leads to fluctuations in system frequency. Therefore, the basic task of turbine regulation is to continuously adjust the output power of the turbine-generator set and maintain the unit's rotational speed (frequency) within the specified rated range.

In summary, the hydro turbine governor is an important auxiliary device for the turbine-generator set in hydropower stations. It coordinates with the station's secondary circuit and computer monitoring system to complete tasks such as starting and stopping the turbine-generator set, increasing or decreasing loads, and emergency shutdown. The turbine governor can also work with other devices to complete tasks such as automatic generation control, group control, and regulation according to water levels. In addition, when a fault occurs in the power grid, it cooperates with the circuit breaker tripping to quickly and stably complete the load rejection process, protecting the turbine unit and enabling it to restore the rated speed as soon as possible.

In conclusion, the basic tasks of the turbine governor are summarized as follows:
◆ Normal operation of the unit
◆ Ensuring the safe operation of the unit
◆ Reasonable distribution of loads among parallel units

Types of Hydro Turbine Governors

Classified by the number of controlled objects, they can be divided into single-adjusting governors and double-adjusting governors.

• Generally, single-adjusting governors are used for various fixed-blade units of reaction turbines(such as Francis turbine). The controlled object is only the guide vanes, and the water flow through the turbine blades is controlled by adjusting the opening of the guide vanes.

• Double-adjusting governors are used for various reaction-type variable-blade units (such as Kaplan turbine). The controlled objects are guide vanes and runner blades. The output of water flow to the turbine is controlled by adjusting the opening of the guide vanes and the angle of the runner blades. In general, variable-blade units have coordinated control between guide vanes and runner blades.

In addition, impulse turbines have more controlled objects, which are classified as another type of "multi-nozzle and multi-deflector" or "multi-nozzle & one-deflector" governors, specifically designed for impulse turbines. The control objects of the governor vary according to the number of nozzle needles and deflectors of the impulse turbine.

2. Hydro Turbine governors are generally mechatronic products as a whole, and their mechanical execution parts adopt hydraulic control. Classified by electro-hydraulic conversion methods, they can be divided into digital, stepping, and proportional-digital governors. Generally, digital and proportional types are combined.

• Digital governors use solenoid valves to control the on/off of the valve with digital pulses, achieving the effect of controlling the servomotor's on/off.

• Stepping governors use current to drive the stepping motor to rotate forward or reverse, generating vertical displacement, and coordinate with the pilot valve and main distribution valve to control the servomotor's on/off.

• Proportional servo valves complete electro-hydraulic conversion through proportional controllers and main distribution valves.

3. Classified by the oil pressure used, they are divided into conventional oil pressure and high oil pressure governors.

• Conventional oil pressures: 2.5MPa, 4.0MPa, 6.3MPa

• High oil pressure: generally 16MPa

The capacity of the pressure oil tank is determined by the size of the servomotor oil cavity.

Classified by the capacity of the controlled unit, they are divided into large, medium, and small governors.

Development History of Hydro Turbine Governors

Hydro Turbine governors have a long history of application in hydropower plants. As early as the late 19th century, in 1891, the German company Voith manufactured the first pure mechanical governor, namely the mechanical centrifugal pendulum-type governor, in which the opening and closing of the turbine were directly driven by a belt. With the improvement of requirements for the governor system, especially for sensitivity, a large regulating force is required for opening and closing within a short time, making hydraulic pressure necessary. This led to the development of mechanical governors with water pressure amplification and oil pressure amplification. From the late 1950s to the 1960s, mechanical-hydraulic governors reached their peak. Sweden produced electro-hydraulic governors in 1944.

China began to develop electro-hydraulic governors as early as the 1950s, and in 1961, China's first self-manufactured electric governor was put into operation at the Liuxihe Power Plant. The 1960s to 1970s were a period of large-scale development for electro-hydraulic governors.

The development of electric governors has roughly gone through several stages:

• The vacuum tube stage, where vacuum tubes were used as electrical amplifiers, and electrical frequency measurement circuits replaced mechanical centrifugal pendulums.
• Later, transistors replaced vacuum tubes, giving rise to transistor-type electro-hydraulic governors.
• In the 1970s, large-scale integrated circuit technology developed rapidly, and integrated circuit operational amplifiers were applied to turbine governors. Thus, electro-hydraulic governors gradually evolved from discrete components to integrated circuit structures.

With the development of science and technology, after microprocessors entered the market in the mid-1970s, many countries successively began to develop microcomputer governors in the late 1970s and early 1980s. The world's first digital governor was developed by Canada in the early 1970s. In 1976, Canada developed a real-time digital governor, and in 1981, the test results of an adaptive governor were published. China also started the development of microcomputer governors in the early 1980s. At the end of 1981, Huazhong University of Science and Technology began researching the "Adaptive Variable-Parameter PID Microcomputer Processor Governor for Hydraulic Turbine Generators," which featured PID parameters that automatically changed with the unit's operating conditions (water head and opening) and was a fault-adaptive governor.

Practice has proven that microcomputer governors have many advantages over analog electro-hydraulic governors:

• The software of microcomputer governors is flexibly configured, allowing control modes and strategies to be set according to the characteristics of the turbine regulation system and the specific requirements of each power plant, enabling the unit to operate efficiently, with high quality, and economically. Therefore, microcomputer governors have shown strong vitality since their emergence.
• The application of microcomputer diagnostic technology and fault-tolerant technology helps improve the reliability of governors. The communication, interface, and strong expansion functions of microcomputers enable microcomputer governors to well adapt to the requirements of computer monitoring systems in power plants.

In 1969, the American company Digital Equipment Corporation (DEC) successfully developed the "Programmable Logic Controller (PLC)". Subsequently, Japan and European countries also successfully developed and began producing programmable controllers. PLC has become the preferred product for many industrial automatic control equipment and systems due to its reliability, including a series of anti-interference measures in hardware such as photoelectric isolation, electromagnetic shielding, and analog/digital filtering, as well as system software with functions like a watchdog timer (WDT) and self-checking of hardware and software.

Turbine governors are important basic equipment for the integrated automation of hydropower plants. Their technical level and reliability directly affect the safe power generation and power quality of hydropower plants, thus influencing the power quality of all sectors of the national economy.

Evolution of Governor Control Laws and System Structure

The development of control laws in governors has been rapid:

• The earliest governors (mechanical types) were proportional links, forming proportional control laws, denoted by the symbol P.
• Later, most governors were designed with proportional-integral control laws, i.e., PI-type governors, where I represents the integral action.
• By the late 1950s and early 1960s, with the adoption of acceleration regulation, governors with P-I-D control laws emerged, where D represents derivative control. For example, the FRVV-10S electro-hydraulic governor produced by Sweden's ASEA and the RAPID electro-hydraulic governor by France's NEYRPIC both feature P-I-D control laws.
• In the mid-1970s, PID regulators were directly applied to turbine governors, giving rise to PID types, i.e., governors with parallel proportional (P), integral (I), and derivative (D) links. The integral action here is generated by electrical links, which clearly differs from the P-I-D governors where integral action was generated by oil pressure servos. This PID-type governor has good static and dynamic characteristics and is one of the more advanced governors.
  (Note: P-I-D represents electric governors with P, I, D control laws, including P-I-D acceleration-type governors; PID denotes electric governors with P, I, D links in parallel, embodying P, I, D control laws.)

Before the 1960s, most governors used PI control laws. After the 1970s, electro-hydraulic governors produced worldwide widely adopted PID control laws, as the introduction of speed derivative regulation software significantly improved the regulation quality of frequency control.

Research and Application of Advanced Control Laws

In recent years, with the development of microcomputer technology and control theory, research on applying advanced control laws to turbine governors has been fully launched, including: optimal control, state feedback control, adaptive control, predictive control, fuzzy control, adaptive variable-parameter control, variable structure control, sliding mode variable structure control strategies, and water pressure compensation signal control.

• The emergence of Programmable Logic Controllers (PLC) injected new vitality into turbine governor control, integrating multiple control functions, greatly enhancing control performance, and simplifying the structure of electrical control units. Practice in subsequent R&D and production proved that using PLC as the control core of turbine governors gradually became the mainstream, forming the basis for the development of various governor types by different manufacturers.
• The development and commissioning of digital valve-type governors marked the beginning of reforms in the mechanical part of governors. The electro-hydraulic conversion link (got rid of) dependence on the main distribution valve, featuring low cost, stable performance, and low requirements for oil quality, which greatly aided the rapid development of small hydropower stations thereafter.
• Impulse turbine units feature short servomotor strokes and multiple control objects. The development and commissioning of this governor accumulated experience for subsequent research on special impulse governors.
• The further development of electro-hydraulic conversion links achieved the coexistence of dual conversion modes, (mutually backup), non-interfering, allowing one link to work while the other is under maintenance. With successful operation experiences in multiple power stations, it has become the preferred product for large hydropower stations.

Performance Indicators

• Adjustment range of guide vane servomotor full closing time: 3–100 S

• Adjustment range of guide vane servomotor full opening time: 3–100 S

• Adjustment range of runner blade servomotor full closing time: 10–120 S

• Adjustment range of runner blade servomotor full opening time: 10–120 S

• Frequency adjustment range: 45–55 Hz

• Adjustment range of permanent speed droop : 0–10%

• Adjustment range of proportional gain : 0.5–20

• Adjustment range of integral gain : 0.05–10 1/s

• Adjustment range of derivative gain : 0.0–10 s

• Adjustment range of artificial dead zone: 0–±1.5%

• Speed dead zone measured to the main servomotor: ≤0.02%

• After the turbine rejects 25% load, the servomotor non-operation time: ≤0.2 s

• Non-linearity of static characteristic curve: ≤0.5%

• During 3-minute automatic no-load operation, the relative speed fluctuation of the unit: ≤±0.15%.

• After rejecting 100% rated load, the number of speed fluctuations exceeding 3%: ≤2 times; the relative value of continuous speed fluctuation of the unit caused by the governor: ≤±0.15%.

• From the moment the unit rejects load until the relative speed deviation is less than ±1%, the ratio of the regulation time to the time from load rejection to the highest speed should be ≤15 for medium/low-head reaction turbines and impulse turbines; for units supplying power to the power plant after disconnection from the grid, the minimum relative speed of the unit after load rejection should be ≥0.9.

2.4.4 Reliability of the Governor System

• Availability in automatic mode: >99.99%

• Availability in automatic + manual mode: 100%

• Mean Time Between First Failures (from on-site acceptance): ≥35,000 hours

• Overhaul interval: 10 years

• Service life before decommissioning: >20 years