FPGLab & KEMA TDT-C&M join forces

The 'influence of short-time overcurrents' test, as is described in the IEC 62053 family of standards, is an integral part of the type test for every directly connected (static, mechanical or smart) kWh meter. It is an important part of the type test as the kWh meter is required to withstand all peak currents that could arise from a short-circuit fault condition within the consumer premises connected directly behind this meter, without any damage or diminished functionality to the meter itself.

Testing requirements are stringent, requiring the kWh meter to withstand a rms current of 30 times its maximum rated current for a duration of 10ms (static type meter) and a peak current of 50 times its maximum rated current for a duration of 1ms (mechanical type meter). Depending on the specific kWh meter rating, test currents of upto 8kA are required.

As a result of the migration from KEMA Quality to Dekra in 2009 this particular test became an outsourced activity for the newly inaugurated TDT C&M unit (formerly part of KEMA Quality). Relocating this particular test to one of the TDT laboraties (HVL or HPL) has also proven to be difficult as most equipment at these TDT laboratories is much too large to 'shoot' at such small 'targets'.

Now enter the Flex Power Grid laboratory! With flexibility already embedded as part of its name, the FPGlab was able to step in and provide exactly the current waveforms required for this test using its programmable converter and some current amplification transformers. At first the creation of the 1ms current pulse time seemed to be a challenge, but with minor modifications to the control software of the FPGLab converter also this current waveform can now be provided in a stable and repeatable manner.

Looking at the future, and in particular at the introduction of smart meters as integral part of the smart grid revolution, the relevance of this particular test on upcoming smart meters, especially those combined with disconnect switches is foreseen to gain importance quickly. The disconnect switch integrated with upcoming smart meters will provide the grid operator with the means to remotely connect or disconnect a consumer, to allow for pre-paid tariff structures, or if fraud is suspected, for example. However, if the switch contacts become welded shut due to (repetitive) short-time overcurrents, the disconnect functionality will be lost together with part of the added value of the meter for the grid operator.

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