Configuration of Lightning Arrestor With Fuse Drop Out in a Distribution Transformer

Hi Halifa, My name is Kevin from South Africa. Our utility has been using your idea for years and there are a number of problems with the it : 1. Many nuisance fuse operations. More than the nuisance surge arrestor SEF when the surge arrestor is in parallel. 2. In higher lightning dense areas. High rates of transformer failure. This is because the surge arrestor needs to operate through the fuse which is a weaker device in terms of current carrying capacities. This leads to multiple single phasing on the system. 3. Voltage differentials are high when the fuse blows. This is because the fuse cuts the surge arrestor off from the overhead line. The surge arrestor can then not perform its duty of high current discharge to earth and on the casing of the transformer. 4. There is a device called a transformer Combi unit which holds the surge arrestor and fuse in a parallel connection, with the surge arrestor directly connected on the overhead line and bonded to the transformer casing. Lightning will flow firstly through the surge arrestor protecting the fuse and the transformer by keeping the voltage differential equal. That is the big key. 5. The surge arrestor always needs to be connected between two solid connections and not via a fuse which inhibits its original function and design. 6. My experience as a distribution line lightning consultant , which covers pole-mounted transformers is that the surge protection should also be done higher up on the line via Firewall drop out surge arrestors and should not only rely on the surge arrestors only at the transformer. And then as previously mentioned one should never "hide the surge arrestor behind the weaker fuse, because of the 1% of the surge arrestors which malfunction on sensitive earth fault. Rather eliminate the 99% nuisance fuse blows, causing single phasing and transformer failure due to nuisance fuse rupturing. A fuse cannot deal with lightning the way the lightning arrestor can. 7. Utilize the live line surge arrestor which can be replace "live" from ground via a link stick. These surge arrestor devices never need an outage for maintenance because they disconnect themselves from the network and drop out like a fuse. To improve SAIDI and SAIFI you need to implement these Live Line Technology devices available in the market. 8. The transformer comb unit for pole mounted transformer surge protection is being used widely by utilities like Eskom, Botswana, DRC, Eritrea, Namibia, and Swaziland and they are seeing brilliant results. 9. The drop out surge arrestor is a very popular device as it deals with lightning higher up on the overhead line, eliminating the majority of the lightning surges which usually travel down a distribution line, sometimes for kilometers. Kind regards, Kevin Risi