Magnetostrictive Amorphous Wire as an Alternative Means of Frequency Measurement for Micro Hydro Power Plants

Robert Agyare Ofosu, Keren Kanuthu Kaberere, John Ndichu Nderu, Stanley Irungu Kamau, Erwin Normanyo

Abstract


This paper presents Magnetostrictive Amorphous Wire (MAW) as an alternative means of frequency measurement for Micro Hydro Power Plants (MHPPs).  In essence, the operation of the frequency sensor is based on Large Barkhausen Jump (LBJ) which refers to the sudden reversal or change of magnetization when the magnetic flux reverses. Due to LBJ, MAW generates very sharp and stable voltage spikes which are induced in a pickup coil wound around the MAW. The frequency measured is basically the number of voltage spikes recorded per second.  In a Micro Hydro Power Plant an Electronic Load Controller (ELC) together with a frequency sensing transducer are used in place of the speed governor to control the frequency of the supply as the load changes. This is due to the fact that the speed governor is very expensive. The frequency sensing element of the ELC measures the generator frequency so as to serve as the basis for the ELC to take appropriate control action to keep the frequency constant by diverting excess power to the damper load when the consumer load changes. Some of the conventional sensors used as frequency sensors are tachogenerators and shaft encoders. However, these sensors are not reliable and very expensive. There is therefore the need for a more accurate and reliable sensor as means for frequency measurement. This is achieved in this paper using MAW. In this work a comparison of the frequency sensing systems of a MHPP was done using MAW and digital tachometer. From the results obtained, it was observed that the MAW sensor was able to measure the frequency effectively with high accuracy when compared to the frequency measurement from the tachometer. It is therefore recommended that MAW should be used as frequency sensor to the ELC to control the frequency of a MHPP since it is cost effective and provides accurate measurement of the frequency.


Keywords


Magnetostrictive Amorphous Wire; Micro Hydro Power Plant; Synchronous Generator

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