B, the number of turns of the primary and secondary windings of an ideal transformer is n, and the primary winding is connected to an AC power supply with a voltage of U, then the output terminal voltage is Un, while the input power of the motor is UIn, the power of the bulb is I2R=U2n2R, and the input power is equal to the output power of UIn+U2n2R ... Therefore, B is wrong;
C, the input power of the motor is UIn, and the power consumed by the coil resistance of the motor is I2r, so the mechanical power of the motor D is UIn-I2r ... Therefore, C is correct;
D, because the voltage across the secondary coil is Un, if the electric fan is stuck due to mechanical failure, the secondary coil loop can be regarded as a pure resistance loop, and the equivalent resistance of the loop is R+rRr, so the current in the secondary coil is URrn(R+r), and the current through the primary coil is U(R+r)n2Rr, and D is correct;
So choose: CD