One of the stated aims of the Electricity North West R&D Strategy is to research new techniques to manage Electricity North West's ageing asset base and one of the most significant items of substations plant is the On-Load Tap Changer (OLTC). It is estimated that the population on the UK distribution network is around 5000 and many different designs exist with a number of variations within the internal mechanism but all essentially provide the same function, to momentarily divert the load current being carried by a transformer to allow a physical change to made to the number of turns in the transformers winding thereby changing the output voltage.
OLTCs, like many mechanical devices with stored energy mechanisms, are subjected to regular and repetitive low level mechanical stresses which over time can lead to stress and fatigue fractures that cannot easily be detected during routine maintenance and inspections. These fractures can eventually lead to catastrophic failure of the OLTC mechanism, in many instances whilst the OLTC is being switched between tap positions and is at its moment of maximum mechanical loading. It has been reliably estimated that across the UK there are up to five OLTC failures per year and at least one of these failures will lead to the loss of the transformer in addition to the OLTC.
This project has taken a very early OLTC monitoring prototype developed under the SuperGen Amperes Project and made some minor modifications to facilitate data handling and retrieval and extended the monitoring to 25 OLTCs. The system will use the same type of opto-acoustic unit as the initial trial for data capture but will employ an embedded PC connected to Electricity North West's iHost system via GSM to remotely download the recorded data. Liverpool University will be responsible for data management and will also develop software algorithms that will interrogate the data highlighting trends of increasing vibration or acoustic energy emission that could indicate an incipient failure.