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The Composition And Working Principle Of The Control System Of A Hydroelectric Generating Set

November 13, 2020

The composition and working principle of the control system of a hydroelectric generating set


Governors and Controls

Governors and other controls help ensure that the generator constantly spins at its correct speed. The most common types of governors for small hydro systems accomplish this by managing the load on the generator. To illustrate, consider a hydro system without a governor. When you increase the load on the generator by switching something on, it causes the generator to work harder. Without a governor, it would slow down, lowering both voltage and frequency. Likewise, removing a load by switching something off would cause the generator to speed up, raising voltage and frequency. With no load whatsoever, the generator would “freewheel,” and run at a very high RPM (possibly causing damage). But by adding progressively higher loads, you would eventually slow the generator until it reached the exact RPM for proper voltage and frequency. As long as you maintain this “perfect” load, known as Design Load, power output will be correct. (Design Load is based on Design Flow.

When Flow drops off during dry periods, the load on your generator will need to be reduced as well.) You might be able to maintain the correct load yourself by manually switching devices on and off, but a governor can do a better job – automatically.



Load Management Systems

A load management system is an enhanced version of the electronic load governor, offering not only the ability to regulate power usage, but also the option for you to choose and prioritize how power is used. In addition to the ballast loads described above, it can directly control a wide variety of devices via relays. Small load adjustments work just like the electronic governor; the variable electronic switch regulates power to the ballast loads. When there is enough excess power, however, the load management system will control other devices in a certain priority. For example, let’s assume you’ve connected two water heaters and a room heater to your load management system. Excess power is directed first to the top priority load, your primary water heater. If there is still excess power available, it will be directed to your next priority, the room heater. If still more power is available, it will go to your backup water heater.



Now assume your well pump kicks on. It draws significant power, but probably runs for less than a minute. Power to one of the water or space heaters may be briefly interrupted while the well pump runs, and then restored when it shuts off. Obviously the brief interruption won’t have a major impact on the availability of hot water or room temperature, and the well pump always has power when it needs it. Similarly, water in your primary water heater will eventually get hot and the thermostat will switch off. The load management system will automatically compensate, moving down the priority chain until it finds a load it can turn on. Load management systems typically have six or more loads that can be prioritized and switched using relays, and their seamless operation helps facilitate normal household activities, even with relatively small hydro systems.



Emergency System Shutdown

An emergency shutdown system is an option that protects the system from overspeed, which may damage the generator. For example, if a tree falls over a power line, it may cause either a dead short (an extremely high load on the generator) or an open line (zero load) which would cause generator runaway. (A dead short may also cause runaway if it trips a breaker.) Any of these conditions are both dangerous and expensive, so an emergency shutdown system is a wise investment.Emergency shutdown usually means removing all water power from your turbine. It is important to recognize, however, that an abrupt halt to water flow could damage your pipeline. (If you’ve heard your plumbing “bang” when you’ve turned off a faucet, you get the idea.) For high-flow turbines such as Francis and Crossflow designs, water flow must be reduced gradually. Emergency shutdown of impulse turbines, such as Pelton and Turgo designs, can be very fast because the water jet can simply be deflected away from the turbine. Since the water flow doesn’t change, there are no damaging surges. There are many different techniques for managing overspeed conditions, Close-up of jet deflector in position to deflect the water jet away not all of which require an emergency from the turbine. shutdown device. Check with your turbine supplier to see which approach would be appropriate for your hydro system.


Utility Grid Interface Controls

Utility Grid connections are becoming more commonplace, but proper controls are essential for proper operation and – above all – safety. The grid interconnects very large, public utility power generation systems. It allows hundreds of megawatts of power to move around the country as regional supply and demand change. It provides automatic controls and switchgear, so that a failure in one location can be bypassed with minimal impact to consumers. Most of the time the grid works well, but as illustrated with the widespread U.S. power outage of 2003, it can be remarkably fragile as well. It is possible to interconnect a small hydro system with the utility grid. Grid connection would allow you to draw power from the grid during peak usage times when your hydro system can’t keep up, and feed excess power back into the grid when your usage is low. If you choose to do so, however, keep in mind that significant synchronization and safeguards must be in place.



Grid interconnection controls do both. They will monitor the grid and ensure your system is generating compatible voltage, frequency, and phase. They will also instantly disconnect from the grid if major fluctuations occur on either end. Automatic disconnection is critical to the safety of all parties. For example, if a tree falls on a public utility line, their grid controls will automatically shut down that portion of the line. But imagine if your hydro system continued to send power to the downed line. When the public utility line crew shows up to repair what they believe is an inactivated line, they could be in grave danger. You could face the same danger if you were unaware the grid was powering your lines. If you are thinking about connecting to the utility grid, begin by contacting your utility company to learn their policies. If you expect to sell power back to the utility, pay extra attention to the efficiency of your hydro system, because higher output and a lower cost-per-watt will go straight to your bottom line. Your turbine manufacturer can give you guidance on the most efficient design, as well as grid interconnection controls and safeguards.