Electricity: measuring and testing – Electromechanical switching device – Relay
Reexamination Certificate
1998-03-03
2001-05-01
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Electromechanical switching device
Relay
C324S424000
Reexamination Certificate
active
06225807
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of determining the remaining lifetime of contacts of switchgear, in particular contactor contacts. In addition, the present invention also relates to the respective device with an analyzer for determining and displaying the remaining lifetime.
BACKGROUND INFORMATION
In German Patent Application No. 44 27 006 (not prior art) the remaining lifetime of a contactor in the disconnection operation is derived from the time difference between the start of the armature opening movement and the start of contact opening. Using an analysis algorithm, a microprocessor determines from the time difference the momentary value of the contact spring action, which decreases due to erosion from its new value (=100% remaining lifetime) to its minimum (=0% remaining lifetime).
The time signals required to do so are detected by interrupting an auxiliary current path over the armature and yoke of the solenoid actuator and on the basis of the contact voltage at the main contacts, and are converted to defined voltage pulses.
To simplify the contact voltage measurement, it is proposed according to German Patent Application No. 1 96 03 310.1 that contact opening, specifically in a three-phase system, be performed by monitoring the voltage, specifically at an artificial neutral point. This makes it possible to switch the device for determining the remaining lifetime as an independent add on unit in the load circuit between the contactor and the electric consumer, which is connected to the contactor with only one communication line for the opening of the armature-yoke contact.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for determining the remaining lifetime independent of any modification of the contactor, specifically an armature-yoke contact, so that it can be used with any desired contactors.
This object is achieved according to the present invention with a method of the type defined in the preamble by detecting the time of separation of the armature from the yoke of the contactor solenoid actuator from the voltage on the solenoid. The increase in magnetic resistance of the magnetic circuit is advantageously detected when the magnet armature is raised. The voltage signal induced on the solenoid by the change in flux over time is used for the time measurement.
In the respective arrangement, the analyzer has means for detecting and measuring the voltage on the solenoid. These means are preferably units for signal rectification, signal contraction, signal shaping, and signal suppression and release.
The present invention is based on the following physical phenomena on disconnection of a contactor solenoid actuator: to generate the required armature closing force, a magnetic flux of a predetermined size is built up by the solenoid current in the ferromagnetic circuit. On disconnection of the control circuit, the solenoid becomes de-energized, and the magnetic flux in the closed ferromagnetic circuit decays a few milliseconds later due to remanence. The magnet armature begins to open at the moment when the magnetic closing force becomes less than the opening force, i.e., the sum of the spring forces of the contacts and the bridge carrier. When the magnet armature is raised, the magnetic resistance of the magnetic circuit increases suddenly, and the remaining magnetic flux &PHgr; (Kmagn-&PHgr;
2
) decays rapidly, and the change in flux over time induces a voltage signal on the solenoid.
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patent: 5204633 (1993-04-01), Ahladas et al.
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patent: 5629869 (1997-05-01), Johnson et al.
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patent: 5747984 (1998-05-01), Amft et al.
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patent: 44 27 006 (1996-02-01), None
patent: 44 33 209 (1996-03-01), None
patent: 196 03 310 (1997-08-01), None
patent: 694 937 (1996-01-01), None
Kenyon & Kenyon
Metjahic Safet
Nguyen Vincent Q.
Siemens AG
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