Hanau, Germany — (METERING.COM) — March 14, 2007 – Meter components manufacturer VACUUMSCHMELZE has introduced a new range of shielded current transformers that are designed specifically for use in IEC-standard electronic electricity meters, and also comply with an array of national standards for meters that are tamper-proof against manipulation attempts using external magnetic fields.
Electronic electricity meters are increasing in popularity all over the world. Free from mechanical wear and tear, they permit remote reading, are network-enabled and support multiple tariffs. However, rising energy costs are accompanied by an increase in the number of cases where meters of this type are subjected to manipulation. External magnetic fields can be used to influence the measuring circuit and reduce the power consumption registered. Although obtaining large permanent magnets with high magnetic induction was extremely difficult in the past, today such magnets are relatively easy to find.
The current transformers in the new X151 range, which also features integrated shielding, are meters that are largely proof against manipulation attempts using DC magnetic fields of permanent magnets, which can generate air induction levels exceeding 300 mT. Integrated shielding has the benefit that shielding of the entire meter – a complex procedure involving high space requirements – is unnecessary, thus enabling compact meters to be designed that feature high immunity against external magnetic fields.
The basic design principle used in VACUUMSCHMELZE current transformers itself offers the benefit of ultra-low sensitivity to magnetic alternating current fields, owing to their annular symmetry. The IEC Standard 62053-21 specifies the maximum permissible additional error for an electronic Class 1 meter as 2% at a test field strength of 0.5 mT in ambient air at normal operating frequency.
Since the current transformer cores have no air gap, magnetic fields in the specified strength exert no more than a negligible effect on the flux within the magnetic circuit.