YBD2 series change一pole multi一speed flameproof three phase asynchronous motor is designed on the basis of YB2 series flameproof motors.It uses the simplex winding polarity reversal method to realize the speed transformation. Different poles offer relative speed. YBD2 series motor are suitable for mechanical equipments which required speed regulation， mainly used in coal，oil and natural gas，petrochemical and chemical industries，usually used to drive pumps，fans，compressors and other transmission machinery. YBD2 series motor could marked as Exd I、Exd II AT4 or Exd II BT4. Exd I is applied in the non一excavation working condition and coal mine with methane or coal dust，Exd II AT4 and Exd II BT4 are applied in the condition of explosion一proof gas compound with Factory II type，Grade A&B， temperature T1，T2，T3 and T4.