Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-10-30
2003-02-11
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S536000
Reexamination Certificate
active
06518772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a method and a related device for the detection of damage in the insulation of electrical components, particularly of lines and cable harnesses. The detection is effected by applying a voltage between at least one supply lead of an electrical structural element or a conductor of a line and an external counter-electrode or a further conductor of the structural element and/or of the cable harness, and pre-discharges or discharges are detected electrically, optically, acoustically and/or chemically.
Electric lines consist of a conductor and an insulation and can, as required, be provided with an enclosure, a shield and a jacket. The conductor is the conducting component of an electric line. The protective enclosure (wrapping) of a line improves the mechanical resistance or the stability against liquids. A shield is a conductive wrapping of the line for the purpose of reducing electrostatic or electromagnet disturbances. A jacket is the outer enclosure of one or more shielded or non-shielded lines.
For service in vehicles, electrical plants and equipment, lines can assembled to a prefabricated cable harness. Cable harnesses are individually made line bundles, equipped with plugs, such bundles being made from several lines mainly by hand. Depending on the application, these are provided with a wrapping for protection against physical or chemical influences.
High requirements are demanded from cable harnesses with regard to their reliability. This applies in particular for applications in aviation and aerospace. The electrical network system in aircraft and spacecraft consists of power sources, consumers, safety equipment and cable harnesses. The latter serve as the connections of the consumers with the generators of electric power and they serve the purpose of conductive transmission of electric signals.
The number of required electric circuits of electrical network systems is high, in which case a high packing density is necessary in each individual bundle. Modem insulation materials, specially developed for aviation and aerospace applications, allow extremely thin insulation layer thicknesses. However, these are very sensitive to mechanical influences. In order to avoid faults in the insulation as well as a resulting failure of the insulating ability, the manufacture of the lines is performed on a high quality level. Non-homogeneities in the structural build-up, cracks, crushes/bruises, scraping/grazing of the insulation, which are often attributable to lack of care during pre-assembly and installation of the cable harnesses, are unacceptable and are not to be allowed.
2. Description of the Related Art
In order to achieve a high level of reliability of the applied cable harnesses, safety analyses (production tests) are carried out even during the fabrication phase of the cable harness. In order to recognise dangerous weak points resulting from assembly-related faults in the cable harnesses at individual lines, comparatively high test voltages are required in this case. In order to avoid damage to any electrical or electronic structural elements possibly installed in the cabling, or to any utilities connected to the line system and which are partially highly sensitive to overvoltage, the energy input at the test object must be, however, limited. This restricts the applicability of previously known test methods. The applied test voltages have only a short effect time in order to avoid pre-discharges in non-critical zones and a limited amplitude, so that a flashover can only take place at a weak point (testing according to DIN EN 2283; Edition: 1996-03, Aviation and Aerospace; testing of cabling of aircraft; identical with the European standard EN 2283: 1996). For this reason and in this manner, only certain faulty arrangements can be detected with not too large a distance between the faulty line, the test electrode and the corresponding counter-electrode.
With a local test, meaning, a test of a line or a cable harness in an installed condition after repair, maintenance or alteration to the installed object in which a cable harness is laid, another fact to be considered is that one is restricted in any event with regard to the applied test voltage.
In other cases there are no lines or cable harnesses to be tested but, instead, individual structural elements, especially such which react sensitively to overvoltages or which are arranged in critical areas. It would therefore, for example, be desirable to be able to inspect electric sensors installed in fuel tanks for their filling level monitoring under local conditions with regard to their voltage endurance.
The discharge functions observed here for the purpose of determining a fault in the insulation are based on the effect of gas discharges so that the necessary disruptive discharge voltage U
d
is dependent on the product of the electrode distance a and the pressure p of the prevailing gas atmosphere. As the latter influence variable, however, is extensively constant due to the ambient air and the atmospheric pressure, U
d
~a applies in the area which is relevant here. U
d
, as mentioned above, is limited. For this reason, the concept of “out-testing” of faulty insulation fails with an unfavorable location of the fault, e.g., on the side facing away from the counter-electrode, so that no reliable measurement-technical detection of such weak points has been possible up to the present.
SUMMARY OF THE INVENTION
The invention is based on the task assignment of stating a method and a device with which, while using a minimum of electric energy, a non-destructive testing is made possible for the purpose of detecting assembly-related or operationally related weak points in the insulation of individual structural elements, separate lines or lines within a cable harness.
In accordance with the invention, the problem is solved by the characteristics of the claims
1
,
11
and
12
. Purposeful developments are the subject-matter of the Subclaims.
The invention is based on the principle of complete or partial substitution of the gaseous dielectric air in the zone of the test object with a testing gas having a reduced disruptive discharge voltage compared with air. By means of gas admixtures (e.g., inert gases such as helium, argon) to the main gas (air) or its complete substitution, the volume ionisation already begins at lowered field strength.
Compared with pure air, a larger number of charge carriers occurs at the same voltage. Even at comparatively smaller test voltages, this assists an increased current flow, by means of which a reduction of the disruptive discharge voltage U
d
is achieved. This principle is applied for the “low-level-energy” determination of an insulation fault. For this purpose, for example, the increased current flow during the inception discharge or the early intrusion of the test voltage, e.g. in the zone of its maximum, can be evaluated.
A test according to the method, where a cable harness is concerned, refers to various phases in its life cycle:
(a) after manufacture of the line bundle before installation into the installation object;
(b) after installation of the line bundle into the installation object;
(c) after repair, maintenance or alteration at the line bundle or at the installation object.
The solution according to the invention allows the reduction of the test voltage (direct or alternating voltage) as required for the fault recognition, so that:
unfavorable fault configurations can also be detected with a comparatively low voltage amplitude,
the energy required for the discharges at the fault location can be reduced,
a danger of overvoltages at voltage-sensitive components, if any, can be avoided,
as a result of the reduced discharge energy at the fault location, the danger of damage to neighboring “healthy” insulations is reduced,
to an increasing extent, the performance of subjective visual inspectional tests according to DIN EN 3475-201, Edition: 1993-02 (aviation and aerospace; electric lines for aircraft—test method, part
Hanson Josef
Milkovic Nikola
Birch & Stewart Kolasch & Birch, LLP
Kerveros J
Oda Christine
WEE-Electrotest Engineering GmbH
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