| 摘要 |
1450567 Electric motor protective systems CANADIAN GENERAL ELECTRIC CO Ltd 11 Oct 1973 [12 Jan 1973] 47578/73 Heading H2K A protective arrangement connected to an electric motor has both an analogue circuit 14 simulating the thermal characteristic of the conductors of the motor and a temperature detecting means 16 in heat transfer relation with the motor windings and providing voltage signals to detector circuits 35, 36. Resistance 15 represents the thermal resistance of the insulation between the windings and detector means 16 and the capacitor circuit 14 is charged before switching on through the resistor 15 to an extent dependent on the motor temperature detected at 16. On switching on if the motor is stalled the capacitor voltage rises sharply and after reduction in a voltage divider 3, allowing for the higher thermal rating on inrush current, the detectors 35, 36 are operable through a diode 33. Continuous overload is detected by the combined effect of the charging current through 15 and the output of the measuring circuit through a diode 40. The charging current is provided by current transformers 44, 45, 46 feeding step-up transformers 47, 48, 49 producing voltages rectified at 50, 51, 52, across a capacitor 54 providing an amplifier 57 with a voltage proportional to the line currents. The amplifier 57 controls a transistor 59 in circuit with a Zener diode 62 and a variable resistor 64 and provides for a two slope characteristic (Fig. 5, not shown) relating the motor current and charging current. |
