| 主权项 |
1. A method for evaluating the temperature of a contactor, which contactor comprises:
power contacts movable to and from open and closed positions, respectively, at least one actuating coil, control means of voltage applied to the actuating coil,
a processing unit designed to act on the control means of the voltage applied to the actuating coil, andmeasuring means of electric current flowing in said at least one actuating coil; said method, comprising:
sending a closing order from the processing unit which applies a voltage V1 to terminals of the actuating coil enabling an electric current to flow in the coil up to a first reference value I1;sending a drop-out order from the processing unit to the control means thereby fixing a drop-out voltage at the terminals of the actuating coil; setting a reference value of one of (a) an electric current I2 flowing in the actuating coil, or (b) a time elapsed DT, alter a drop-out order is sent;
and if electric current (a) is the set reference value, then measuring the time elapsed DT for the electric current to reach said set reference value after a drop-out order is sent,or if time elapsed (b) after a drop-out order is sent is the set reference value, then measuring the second electric current I2 flowing in the actuating coil at said set reference value of elapsed time;the processing unit determining the operating temperature of the actuating coil-after a drop-out order has been sent by: determining the value of the resistance Rcoil of the actuating coil from the first and second reference values of the electric current and the elapsed time, said resistance of the actuating coil being expressed in the equation:
(I2+Ucoil/(Rcoil+Reps))/(I1+Ucoil/(Rcoil+Reps))=exp(−DT×Rcoil/Lcoil)wherein:I1 is the first reference value of the electric current,I2 is the second value of the electric current,DT is the elapsed time,Ucoil is equal to the coil voltage,Reps is equal to the sum of the additional resistances present in the electronic circuit, andLcoil is the inductance of the coil; and wherein, the temperature Tbob of the actuating coil is expressed in the equation:
Tbob=Tinit+(Rbob/Rinit−1)/α,wherein:α is the thermal coefficient of the electric resistance, andRinit is equal to a resistance of the coil at an initial temperature Tinit; and voltage Ucoil applied to the coil by the control means is maintained in a range between voltage V1 corresponding to the first reference value I1 of the electric current, and a voltage V2 corresponding to the second value I2 of the electric current, which range correlates to a corresponding range of operating temperatures. |
