The black material is considered as carbon deposition,which is formed by oily-liquid medium fission product(mainly carbon black) covering inside crack during the discharge process of pulse current.

• 认为这些黑色覆盖物为脉冲电流在放电过程中,油性液体介质裂变产物(主要为碳黑)涂覆在裂纹内部形成的积碳。