The product is used in indoor system of 50HZ and rated voltage of 10-15.5KV.It cannot be used independently,instead it must be connected in series together with oil-immersed transformer protection backup fuse to offe an overall protection against indoor electric system.the products are tested by national high-voltage electric fac-ilities Quality Suppervising and Testing center,and they are in accordance with GB15166.2and 1EC282-2.