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November 11, 2020
The drive system couples the turbine to the generator. At one end, it allows the turbine to spin at its optimum RPM. At the other, it drives the generator at the RPM that produces correct voltage and frequency. The most efficient and reliable drive system is a direct, 1:1 coupling between the turbine and generator. This is possible for many sites, but not for all Head and Flow combinations. In many situations it is necessary to adjust the transfer ratio so that both turbine and generator run at
their optimum, but different, speeds. These types of drive systems can use either gears, or pulley and belts, all of which introduce additional efficiency losses into the system. Belt systems tend to be more popular because of their lower cost. Your turbine manufacturer can provide valuable guidance about matching turbine and generator RPM, and suggest options Belt drive coupling between turbine and generator. if a direct, 1:1 coupling is not possible.
The generator converts the rotational power from the turbine shaft into electrical power. Efficiency is important at this stage too, but most modern, well-built generators deliver good efficiency. There can be big differences in the type of power generated, however. DC (Direct Current) generators can be used with very small systems, but typically are augmented with batteries and inverters for converting the power into the AC (Alternating Current) power required by most appliances.
AC generators are normally used in all but the smallest systems. Common household units generate 120VAC (volts AC) and 240VAC, which can be used directly for appliances, heaters, lights, etc. AC voltage is also easily changed using transformers, which makes it relatively simple to drive other types of devices or transmit over long distances. Depending on your power requirements, you can choose either single-phase or three-phase AC generators in a variety of voltages. One critical aspect of AC power is frequency, typically measured as cycles per second (cps) or Hertz (Hz). Most household appliances and motors run on either 50Hz or 60Hz (depending on where you are in the world), as do the major grids that interconnect large power generating stations. Frequency is determined by the rotational speed of the generator shaft; faster rotation generates a higher frequency.
Electronic Load Governors
An electronic load governor works by automatically adjusting the load so the generator always turns at exactly the right speed. In effect, it is always slowing the generator down just enough to produce correct voltage and frequency. Electronic load governors constantly monitor voltage or frequency, adding or subtracting electrical loads as necessary to compensate for human usage. For example, let’s say our system has a Design Load of 5kW. To maintain proper voltage and frequency, power
consumption from the system must always be 5,000 watts. If a person switches off a 1,500 watt stovetop burner, the governor will sense the rising frequency and compensate by switching on a different 1,500 watt load (such as a baseboard heater)
to maintain total load at 5kW. In this example, the governor must have direct control over 5,000 watts of load, so that it can provide total Design Load in the event all human-controlled loads are switched off. In addition to managing ballast loads, this Load Management Governor Moreover, it must be able to control can prioritize up to 8 additional devices. loads in small increments (perhaps 100 watts) to compensate for light bulbs, small appliances, etc. to keep the frequency exact. An electronic load governor is highly effective for small systems up to about 12kW. It uses two or more “ballast” loads, which can be any purely resistive device such as a heater. Excess power is shunted to the ballast loads, and a variable electronic switch can regulate the amount of power being directed to the ballast (much as a dimmer switch can regulate power to a light bulb). In this way, the electronic governor can make small-wattage adjustments even though the ballast loads themselves may be quite large.