The design of a 5 kW microhydro generating set

In rural areas of many countries, the supply of electricity has always been scarce due to the relative isolation from the national electricity distribution system. In New Zealand for example, many high country farm houses rely almost entirely on diesel generating sets for power. This method of power generation costs more than urban electricity supply. However, a recent advance in control technology, and a new turbine concept have shown that very small hydro power schemes also known as microhydro, can now produce urban quality electricity at a cost not much greater than urban supply. Through research and testing a 5 kW microhydro generating set was developed. The design of the micro hydro generating set involves the utilisation of the latest control technology, and proprietary components. The single most important contribution to the development of the microhydro generating set was the use of an electronic load governor with the run-of-the-river principle which results in constant flow operation of the turbine. This eliminates the need for a precision speed governor and accurate turbine flow control and thus greatly simplifies the turbine design. A malfunction protection system and a load management system have also been incorporated to allow maximum utilisation of the power output without risk of damage to the generating equipment. The use of a Delphi electronic load governor in conjunction with a brushless, self excited and self regulated synchronous generator have produced a stable electrical output of 5 kW at 230 V, 50 Hz, AC, when using an appropriate flywheel to provide shaft inertia to dampen out electrical transients. It was found that shaft inertia of four times that recommended by the governor manufacturer, was required. One of the simplest turbines is a centrifugal pump operating in the reverse mode. Tests have shown that centrifugal pumps perform exceptionally well as power recovery turbines, with efficiencies similar or in some cases even greater than that for the pumping case without any modification. Consequently, the combination of well established mechanical and control hardware, simplifies the design and installation of a microhydro scheme to a technical task rather than one requiring the expertise of a design engineer. A set of five machines was designed, covering the range of heads and flows most commonly encountered in hilly isolated areas. The operating conditions cover heads ranging from 30 m to 150 m and flows ranging from 30 l/s to 10 l/s respectively