| 摘要 |
PURPOSE:To exactly detect the temperature rise of rotor by the procedure in which I<2>1 + alpha I<2>2 is obtained from positive phase current I1 and antiphase current I2 drawn from filter and its value exceeding the set value K is detected. CONSTITUTION:Since the heating of the rotor of 3-phase induction motor is proportional to the I<2>1 + alpha I<2>2 of positive phase current I1 and antiphase current I2, the value of the resistor R1 and the value of the variable resistor R5 are set up to 1 : alpha and the set value voltage V3B is determined by the variable resistor R5 and sent to the resistor R6. Since, in this case, the output of the comparator 8 is proportional to V<2>1R1 + V<2>2R5 - V3BR5, if the value of the resistor R6 is equal to R1 and thus V<2>1 + alpha V<2>2R5 - V3B > 0, the output of the comparator 8 is inversed and the thermal starting relay 14 is operated by the driver circuit 10. Since V<2>1 is proportional to I<2>1 and also V<2>2 is proportional to I<2>2, the operating zone of the thermal starting relay 14 becomes I<2>1 + alpha I<2>2 > K. |
