Torque and speed estimation for line-start IM using dot-cross Products of current and voltage vectors

The IM has been adopted widely as the driving sources of the industrial machine and the plants. That reason is that IM is robust and easy to drive. A typical line-start drive system is a motor operated valve arranged to the power plants, the chemical plants. These valves are used for application that energy supply is shut down in an emergency. So, the IM which makes valve operate is connected to 3-phase power supply directly and used. Because of this, the drive system heart of an IM has very high reliability. However, mechanical deterioration is problem. Routine inspections are carried out to those valves and reliability is secured. A conventional failure diagnosis is the examination which motor operated valve is disassembled regularly. However, conventional method has some risks. So, it is hoping to judge trouble possibility easily from the torque and the speed. If torque and speed sensors are set around the IM, torque and speed can be measured easily. However, the permanent establishment of the sensors is difficult because the movement environment is very severe. We wish that the torque and speed information for failure diagnosis is estimated by using current and voltage sensors put near switchboard. This paper presents torque and speed estimation method for Line-start IM. We use the dot-cross products of current and voltage vectors. The current and voltage vectors are measured with the switchboard which supplies a power supply to IM. As for the proposal technique, the torque and speed estimation of IM not only in the static state but also in the transient state is possible. Furthermore, we cope about the electric parameters as follows. The stator resistance value is measured. The values of leakage inductance, mutual inductance and rotor resistance are identified. Proposed estimation methods are verified by results of experiment.