Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Patent
1983-06-09
1986-12-02
Levy, Stewart J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
336174, 336232, H01F 4006, G01R 1502
Patent
active
046267786
DESCRIPTION:
BRIEF SUMMARY
The dimensions of active current sensors, which are constructed in form of inductive current comparators, are for the most essential part determined by the cross-section of the secondary winding, which is necessary in order to produce the Ampere-turn equilibrium. For a correct operating mode, current comparators with modern magnetic core materials with a high initial permeability, require only a relatively low degree of magnetic flux flow. Even if, for the measuring of higher currents the primary winding of such a transducer consists of a single winding the magnetic flux flow required for the measurement transmission is mostly higher by a multiple than is required for the core function. As a result of this, the expenditures relating to the conductor material, to the core material and power consumption for the electronics, are also correspondingly high. However, in particular when constructing static electric meters, it is necessary to keep the dimensions and the costs for the current comparators low. Several proposals for the solving of this problem are known, which by means of a resistance-shunt convey only a portion of the measuring current to the comparator. Such resistance-combinations are subject to the condition that the internal power consumption at the maximum current value has to remain within the order of magnitude of a few watts.
It follows from this, that the resistance-relationship between the main circuit and the shunt can be established only by means of well-conducting materials (for example copper, aluminum), the resistance values of which are adversely affected by large temperature coefficients. This again necessitates that for the attainment of a constant resistance-ratio the main circuit and the shunt conductor always have to have the same temperature. However, the latter cannot be achieved with simple means, since the shunt lead forms the primary winding of the current comparator and thereby cannot be in direct thermal contact with the main circuit lead.
Irrespective of the constructive difficulties in the construction of such a shunt-transducer, another aggravating difficulty persists when using this method with comparators which are also required to transmit direct-currents. As it is known, these comparators, generally in an additional winding, require an additional alternating-current signal for the generation of a magnetic flux flow modulation. Since the shunt, together with the main circuit forms a closed electric circuit with a relatively low ohmic resistance, the modulation leads to a transformation of the modulation signal in this circuit, so that the desired influence of the magnetization (for example, saturation) of the core cannot take place.
The invention has the task of creating an arrangement of an active current sensor, in the case of which the aforecited disadvantages and difficulties are practically eliminated in a simple manner.
This task is solved by the features cited in the characterizing clause of the patent claim 1.
By means of the arrangement designed according to the invention of an active current sensor with a primary reducing winding, the structural size of a current sensor can be drastically reduced, without noticeably decreasing the measuring range and the measuring accuracy, since in the case of this embodiment of a primary winding, only the difference of the currents flowing in the two conductors has to be determined, and the geometry of the winding permits both conductors to be brought in contact mechanically along their entire length between the branching points, so that both conductors always take on the same temperature.
By the inventive arrangement of a current sensor with a primary reducing winding, principle-conditioned modulation signals for the detection of direct-currents are not disturbed in a given case, since, due to the opposite winding direction of the two conductors of the reducing winding, voltages induced, at the same number of turns, by means of modulation signals in the conductors, are directed in opposite directions, and, thus, an equa
REFERENCES:
patent: 2535554 (1950-12-01), Thurston
patent: 2831164 (1958-04-01), Johnson
patent: 3111619 (1963-11-01), Gertsch
patent: 3916310 (1975-10-01), Stark et al.
patent: 4182982 (1980-01-01), Wolf et al.
patent: 4488135 (1984-12-01), Schwartz
Baker Stephen M.
Levy Stewart J.
LGZ Landis & Gyr Zug AG
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