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Independent Renewable Energy

Consulting Engineers

Case Study - Anaerobic Digestor Generator            Client: Chynoweth Farm

Chynoweth Farm Partners had begun construction of a 30kW anaerobic digester (AD). The aim was to develop an AD plant to be genuinely on farm using only waste products from the farm and not require bought in or specially grown feedstock.
A 30kW permanent magnet generator, robust gas engine, as used on USA/Canadian oil fields and DC/AC inverters had already been purchased but there was no electrical design.
Redcotec undertook the complete electrical design for control of the engine, generator and the connection to the national grid. Due account had to be taken of the characteristics of this type of generator and their abilities to produce overvoltage and sustain electrical fault currents.
Redcotec designed and oversaw the manufacture and installation of the control panel and grid connection relay. It was found that speed governor on the engine was not sufficiently sensitive to control the engine speed in the event of a sudden loss of the mains connection. This could allow the generator to overspeed and damage the inverters. A modification to the controls was implemented to provide two stage monitoring of the generator output linked to the AD gas valve. This now provides good regulation of the generator speed during normal operation and a safety cut-out to protect the engine, generator and inverters in the vent of a component failure. A prominent DC voltmeter allows the generator voltage to be easily checked.
Successful commissioning of the scheme was witnessed by Redcotec personnel and the system was approved by Western Power Distribution for connection to the national grid.
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