Abstract A circuit is shown useful to protect dynamoelectric machines from overtemperature conditions. The circuit comprises first and second tuned circuits coupled to the power lines of the dynamoelectric machine along with an oscillator for injecting a selected frequency signal in the line and a detector for detecting the signal when the tuned circuits are resonant. A thermally responsive switch comprising an electromechanical bimetal switch or a solid state PTC or NTC switch is adapted to be disposed in heat conductive relation with the dynamoelectric machine and is electrically coupled to one of the tuned circuits so that the temperatures below a selected level the switch will be in one state, e.g. a low impedance state, precluding resonance while at temperatures above the selected level the switch will be in an opposite state, e.g. a high impedance state, permitting resonance. A detector particularly useful for detecting the above-mentioned signal is shown to comprise a three legged E-I transformer core on one leg of which is disposed a shunt winding. The shunt winding is coupled to a frequency selective device such as a capacitor. A sensing winding is disposed on the center leg and a power supply line is trained through the core so that it forms two turns and causes opposing flux in the center leg of the transformer.
Detection apparatus comprising a three legged E-I transformer core, a shunt winding disposed on the first leg, frequency selective means electrically coupled to the shunt winding, signal sensing means inductively coupled to the second leg and a carrier signal line trained through the core forming two turns, one turn disposed between the first and second legs and the second turn disposed between the second and third legs.
Claim 2
Dependent Claim
67 words
Detection apparatus comprising a three legged E-I transformer core, a shunt winding disposed on the first leg, frequency selective means electrically coupled to the shunt winding, signal sensing means inductively coupled to the second leg and a carrier signal line trained through the core forming two turns, one turn disposed between the first and second legs and the second turn disposed between the second and third legs.
Claim 3
Dependent Claim
53 words
Detection apparatus according to claim 1 in which a second carrier signal line is trained through the core forming two turns, one turn of the second carrier signal line disposed between the first and second legs and the second turn of the second carrier signal line disposed between the second and third legs.
Claim 4
Dependent Claim
15 words
Detection apparatus according to claim 1 in which the frequency selection means is a capacitor.
Claim 5
Dependent Claim
20 words
Detection apparatus according to claim 3 in which the signal sensing means comprises a winding disposed on the second leg.