What is the difference between a surge arrester of a 100 MVA generator connected to 13.8 KV and a surge arrester connected on a distribution circuit feeder connected to the same voltage level?
Do I need the short circuit current for selection a proper Surge Arrester?
The following answer is based on the assumption that the arrester is connected directly between the generator terminals and earth (100 MVA), between generator and generator-breaker (13.8 kV) and the generator neutral point is directly earthed.
The continuous operating voltage (Uc) of the surge arrester should be selected in such a way that the power frequency voltage-versus-time characteristics of the system are covered by the temporary overvoltage (TOV) capability of the surge arrester. The highest TOV at the generator terminals occurs if the loaded generator is suddenly disconnected from the grid with maximum load rejection.
Therefore the Uc of the arrester should be selected according to the formula provided here: Application Guidelines- Overvoltage protection (page 57, 9.6: Generator connected to a lightning endangered MV line)
For maximum lifetime of the generator insulation, a surge arrester with the lowest protection characteristic should be used. Therefore a heavy duty surge arrester of line discharge class 4 can be used for this application. We recommend the surge arrester type POLIM-H of class 4 (station heavy duty), as this type has the best protection level. Read more about POLIM-H here.
Surge arresters in a distribution network are mostly used to protect distribution transformers from transient overvoltages caused by lightning. The TOV determining the Uc of an arrester in a distribution network is the power frequency overvoltage occurring during possible fault conditions. Please refer: Application Guidelines- Overvoltage protection (page 26, 3.6: Temporary overvoltage. A distribution class surge arrester is sufficient for this application.
Short-circuit tests of surge arresters are conducted in order to show that an arrester failure does not cause violent shattering of the arrester housing. The short-circuit current of the Generator is not a dimensioning criteria for the surge arrester.
High Voltage Products
If you want to purchase a product, need any pricing information or need help or support from ABB, please contact your local partner.