Essais Current Zero
Current zero (CZ) se rapporte au phénomène d'interruption de courant dans les disjoncteurs de forte puissance. Aujourd'hui il semble économiquement improbable que des circuits haute tension puissent être interrompus par d'autres moyens que l’arc électrique.
Tous les disjoncteurs fonctionnent sur le principe de lames de contact s'écartant l’une de l’autre, entraînant la formation d’ un arc électrique entre les contacts. Le paramètre normalisé Current Zero est un indicateur de la pression, de la température, de la densité ionique, de l'écoulement de plasma, etc.
Les mesures Current Zero sont employées pour comprendre le phénomène d’arc électrique et pour identifier les paramètres prépondérants pour obtenir une interruption réussie du courant. Pour en savoir plus au sujet des matériels et logiciels de HBM Genesis High Speed pour les mesures Current Zero.
Besoins en matériel pour l'essai Current Zero
En utilisant la technologie de la conversion numérique isolée par fibre optique pour les essais Current Zero, 4 conditions principales doivent être réunies :
- Résolution verticale
- Bande passante
- Immunité contre les coupures rapides
- Immunité contre les champs magnétiques
Solution HT 6600 homologuée pour les mesures normalisées Current Zero
Les essais d’homologation ont été menés au laboratoire Haute Puissance KEMA de Arnhem en Hollande, un des organismes référents en termes d'essais Haute Puissance. Etant donné l'absence de normes et de méthodes d’étalonnage unanimement reconnues, KEMA a décidé d’établir un programme d’essais dédié, basé sur l'expérience acquise en en dix ans de mesures du Current Zero.
- Current Zero and Acceptance Testing FAQ
What does “Current zero (CZ)” mean?
Current zero (CZ) refers to the interruption phenomena in high power circuit-breakers. Today it seems improbable that high voltage circuits could be interrupted economically by other means than the electric arc.
What are the current zero measurements used for?
All circuit-breakers are working based on contacts moving away from each other, thus creating an electrical arc between the contacts. The current zero phenomena is an indicator for the pressure, temperature, ion density, plasma flow, etc. Current zero measurements are used to understand the phenomena
of the arc and to identify the dominant parameters for a successful interruption of the current.
Who is interested in current zero measurements?
Current zero measurements are performed by researchers to understand
and improve the descriptive mathematical model of the arc. With the
knowledge of the dominant parameters, it becomes feasible to improve
the circuit-breaker design and to reach even higher interruption capability.
International Standards and Acceptance Testing
Does an international standard exist for CZ measurements?
No, CZ measurements are a research tool to understand the phenomena. The international standards for circuit-breakers cover the test procedures and requirements for the final product.
What is acceptance testing used for?
Acceptance testing is normally used to verify the published specifications of a product by a third party test house. The external test house uses its expertise to act as an independent authority between buyer and seller.
Who defines what to test?
Mainly the buyer specifies, which of the published specifications of the product he wants to have verified. The external test house will use international standards and procedures where applicable, combined with experience from the past.
Hardware Requirements for a Current Zero Measurement System
Why is the vertical resolution so important?
A high dynamic range of the input is required because for example currents in the order of 100mA should be measured immediately after the interruption of many tens of kA of short circuit current.
Why is the required bandwidth so important?
Although the mains frequency is most of the time only 50Hz or 60Hz, the relevant processes occur on a sub-microsecond scale.
Why is immunity against fast transients so important?
Very severe electrical transients arise both in current as well as in
voltage during the switching process.
Why is immunity against magnetic fields so important?
A fiber optic digitizer should be placed as close as possible to the test object to keep the analogue cables as short as possible and so to get the best possible measurement results.
What were the criteria to meet the acceptance test performed on the isolated digitizer 6600?
A fiber optic digitizer needs to deliver at least the same performance in terms of signal quality as the existing KEMA system (comparison with known system). In terms of electromagnetic immunity, the system needs to withstand the transients and the magnetic fields and operate undisturbed and uninterrupted.
Acceptance testing results
How relevant are the results of the acceptance test?
The acceptance test is designed to verify the proper operation under the most severe conditions in a high-power lab. Passing this worst case scenario implies that the operation under less severe conditions should not cause any significant problems.
Why are the conditions in a high-power HV lab most severe?
The worst electromagnetic conditions are seen in high-power laboratories testing high-voltage circuit-breakers, as here the highest voltages and the highest currents occur at the same time. Here the highest amount of energy is used.
What is different in MV and LV labs?
In MV and LV tests, the currents and voltages are lower, means there is less engery used to perform the tests. Overall, all components are exposed to less stress.
Acceptance test report
Is the acceptance test report available?
Yes, the test report can be downloaded from the HBM webpage
at www.hbm.com/power in the Current Zero section.
What do I gain from this acceptance test?
The gain from the acceptance test is the confidence, that the
GEN DAQ isolated digitizer 6600 HV was tested in the most
severe environment and passed.
Can I trust this acceptance test?
The test was performed at the KEMA High Power lab in Arnhem in the
Netherlands, one of the leading experts in terms of High Power testing. Given the absence of standards and generally accepted calibration methods against which to test, KEMA decided to set up a dedicated test program, based on experience gained in ten years of current zero measurements.
Why does the report not mention HBM?
The product was tested in 2007 by KEMA. At that time, the
6600HV was sold under the LDS brand name (see also the
document: Brand change to HBM Genesis HighSpeed) on the
webpage www.hbm.com/power in the Current Zero section.
- Solution validée par le KEMA
- Matériel pour essais du current zero
- Conçus pour les applications Hautes Puissances