fault signal to interface 30 which in response to the fault signal applies a control signal to contactor 32 the control signal de energizes the coil of contactor 32 to open the contacts of contactor 32 and remove power to motor 34 by way of modification circuit 28 may be programmed to detect motor 34 problems based upon direct and quadrature currents i qs e and i ds e which are aligned with the stator flux vector in particular an analysis of induction motor characteristics will show that motor problems unrelated to mechanical torque loads e g eccentric air gaps misalignment broken rotor bars etc will have effects generally limited to the direct axis current i ds e thus if i ds e is estimated from i qs e rather than measured directly the estimated value of i ds e i ds e will not include the effects of motor problems upon determining i ds e this value can be compared to the actual value of i ds e to produce a fault signal as discussed above turning now to the calculation of i ds e based upon i qs e this calculation can be performed based upon the following equation equ14 where u03c9 is.