| US 7,555,366 B2 | ||
| Thermal overload protection | ||
| Janne Kuivalainen, Vaasa (Finland); and Peter Österback, Vaasa (Finland) | ||
| Assigned to ABB Oy, Helsinki (Finland) | ||
| Appl. No. 10/587,574 PCT Filed Feb. 01, 2005, PCT No. PCT/FI2005/000066 § 371(c)(1), (2), (4) Date Jul. 31, 2006, PCT Pub. No. WO2005/074089, PCT Pub. Date Aug. 11, 2005. |
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| Claims priority of application No. 20040154 (FI), filed on Feb. 02, 2004. | ||
| Prior Publication US 2007/0121259 A1, May 31, 2007 | ||
| Int. Cl. G05D 23/00 (2006.01); G05B 11/01 (2006.01); G01R 19/00 (2006.01); G01K 1/08 (2006.01); G06F 11/30 (2006.01); H02H 5/04 (2006.01); H02H 7/08 (2006.01) | ||
| U.S. Cl. 700—299 [700/22; 700/33; 700/292; 702/64; 702/132; 702/184; 361/24; 361/25] | 7 Claims |
| 1. A device for thermal overload protection of an electrical device, particularly an electric motor, the device comprising
a current meter configured to measure at least one load current supplied to the electrical device;
a processor system configured to calculate a thermal load on the electrical device on the basis of said at least one load
current, and
a switch device disconnecting a current supply when the thermal load reaches a given threshold level,
said processor system employing 32-bit fixed-point arithmetic and being configure to scale the measured current into unit
values to a range of 0 to Y, wherein Y represents Y/100% of a nominal current and is a real number greater than 0, and to
calculate the thermal load using a mathematical equation that, together with its operands, is programmed into the processor
system structured such that a result or a provisional result never exceeds the 32-bit value,
wherein the mathematical equation is
 wherein
Θk=current calculated thermal load
Θk−1=previous thermal load
ΔT=interval for thermal load calculation
R=cooling factor of electrical device
C=trip-class factor
i=measured current.
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