the KK1800A 3500V fast turn-off thyristor  has become the best items  of  the Spring festival of 2017 in our company, the main reason for it is that our factory can produce this kind of items with withstand voltage value close to 3500V , so with so kind of high withstand voltage wth kk thyristor , the circuit inside induction heating system will  not create the counter electromotive force that will breakdown the thyristor with withstand voltage as high as 3500V