Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1995-11-16
1997-11-04
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Switching systems
Condition responsive
307125, 307139, 361 24, 361 28, 361 23, H01H 3500
Patent
active
056843429
ABSTRACT:
A starter comprising a contactor with an overcurrent relay provides an appropriate cooling interval for each of multiple classes of a load, such as a motor. An analog equivalent of a digital I.sup.2 t value calculated by a microcomputer in the overload relay is maintained by an external capacitor. When the microcomputer loses power following a trip, the capacitor discharges through a resistor at a rate selected to mimic cooling of the associated class of the load. Restart of the load is prevented until the appropriate interval, represented by the time required for the voltage on the capacitor to decay to a common reset value, has expired. The capacitor is charged to a voltage proportional to the I.sup.2 t trip value for the particular class of the load, which for all classes is below the forward drop of the clamping diodes on the microcomputer inputs to prevent discontinuities in the timing.
REFERENCES:
patent: 4796142 (1989-01-01), Libert
patent: 5303160 (1994-04-01), Winter et al
patent: 5539601 (1996-07-01), Farag et al.
patent: 5579194 (1996-11-01), Mackenzie et al.
Early Michael G.
Innes Mark Edmund
Eaton Corporation
Kaplan Jonathan S.
Shoop Jr. William M.
Vande Zande Larry G.
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