Industrial electric heating furnaces – Arc furnace device
Reexamination Certificate
2003-03-24
2004-10-26
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Arc furnace device
C373S104000, C219S503000
Reexamination Certificate
active
06810069
ABSTRACT:
TECHNICAL FIELD
This description relates to detection and clearance of faults in an electrical system.
BACKGROUND
Conventional power systems exist to provide electrical power. In such a power system, faults may occur that are dangerous to users of the system, and that cause damage to the system that may be expensive and/or time-consuming to correct. For example, a power system that experiences a current short-circuit, such as an arc current, may cause a fire or explosion, or otherwise damage itself and related equipment and operators. In particular, very high voltage power systems, such as those that include a high-voltage power transformer, may experience such faults.
When faults are quickly and accurately detected, they may be eliminated by corrective measures, such as an activation of a circuit breaker and, if necessary, subsequent repair of the power system. In this way, damage from the fault may be minimized.
SUMMARY
According to one general aspect, an electrical protection system includes a first Rogowski coil positioned along a first conductor and operable to measure a first current in the first conductor and output a first signal, where the first conductor is part of an electric arc furnace (EAF) system, and a protection device operable to use the first signal in determining that a fault exists in the EAF system.
Implementations may include one or more of the following features. For example, the first conductor may be associated with a primary winding of a transformer of the EAF system. In this case, the first Rogowski coil is located outside of a vault housing the transformer.
The first conductor may be associated with a secondary winding of a transformer of the EAF system. In this case, the first current is output from the secondary winding, and the first Rogowski coil may be located within a vault housing the transformer. Also, the first conductor may include a conducting arm attached to an electrode of the EAF system.
A second Rogowski coil may be positioned along a second conductor of the EAF system and may be operable to measure a second current in the second conductor and output a second signal. In this case, the first conductor may be associated with a primary winding of a transformer of the EAF system and the second conductor may be associated with a secondary winding of the transformer. Also, the protection device may include a differential relay.
The differential relay may determine that the fault exists based on the first signal and the second signal, and the differential relay may determine that the fault exists between the first Rogowski coil and the second coil. A third Rogowski coil may be positioned along a third conductor of the EAF system and may be operable to measure a third current in the third conductor and output a third signal.
In this case, the differential relay may determine that the fault exists between the second Rogowski coil and the third Rogowski coil, or may determine that the fault exists between the first Rogowski coil and the third Rogowski coil.
A table containing a first winding ratio of a transformer of the EAF system at a first position of an operating tap of the transformer and a second winding ratio of the transformer at a second position of the operating tap also may be included. In this case, the protection device may be operable to determine whether the first winding ratio or the second winding ratio is associated with a present position of the operating tap, and may be further operable to scale a magnitude of the first signal based on the present position.
According to another general aspect, a first current is measured in a first conductor using a first Rogowski coil, where the first conductor is part of an electric arc furnace (EAF) system, a first signal is output from the first Rogowski coil, the first signal is input at a protection device, and the fault is determined to exist in the EAF system, based on the first signal.
Implementations may include one or more of the following features. For example, a second current in a second conductor of the EAF system may be measured using a second Rogowski coil, a second signal may be output from the second Rogowski coil, and the second signal may be input at the protection device, which may include a differential relay.
In this case, the fault may be determined to exist in the EAF system between the first Rogowski coil and the second Rogowski coil, based on the first signal and the second signal. Also, a third current may be measured in a third conductor of the EAF system using a third Rogowski coil, a third signal may be output from the third Rogowski coil, and the third signal may be input at the protection device.
In the latter case, the fault may be determined to exist in the EAF system between the second Rogowski coil and the third Rogowski coil, based on the second signal and the third signal. Also, the fault may be determined to exist in the EAF system between the first Rogowski coil and the third Rogowski coil, based on the first signal and the third signal.
In the latter case, the first conductor may be associated with a primary winding of a transformer of the EAF system, and the second conductor and the third conductor may be associated with a secondary winding of the transformer.
According to another general aspect, an electrical protection system includes a first Rogowski coil positioned to measure a first current at a first location of an electrical arc furnace (EAF) system and output a first signal, a second Rogowski coil positioned to measure a second current at a second location of the EAF system and output a second signal, and a protection device operable to input the first signal and the second signal and determine that a fault exists within the EAF system based on the first signal and the second signal.
Implementations may include one or more of the following features. For example, the protection device may be include a differential relay. Also, the protection device may be further operable to open a circuit breaker associated with the EAF system upon determination of the fault.
The details of one or more implementations set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.
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Bishop Martin T.
Kojovic Ljubomir A.
Fish & Richardson P.C.
Hoang Tu Ba
McGraw-Edison Company
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