Some cases have been reported recently where the operation of static electricity meters for active energy has been influenced by various equipment generating disturbances in the frequency range of 2–150 kHz. This matter has been discussed at both WELMEC and CENELEC TC13 meetings since the end of 2010. NMi recently developed a new test setup for immunity investigation of electromagnetic disturbances in the frequency range of 2–150 kHz and their effect on static electricity meters.
Background
Electric energy meters, marked with CE and M and assessed according to the applicable harmonized standard, have under certain circumstances turned out not to be immune to specific types of electromagnetic disturbances. The disturbances are usually caused by common types of electronic equipment in households and light industries. The results of the disturbances are abnormal meter registering values.
As the meters are used for invoicing, it causes customers to be charged the wrong amounts by electricity companies.
Injections of current
The disturbances are a specific type of conducted high frequency current “wavelike phenomenon” in the frequency range 2–150 kHz. Although the disturbance is not constantly present in the power network it cannot be defined as transient. The bandwidth can vary from narrowband PLC-signals to larger bandwidths, such as switching frequencies from power supplies and broadband noise.
The disturbances, apart from intended signalling, can be described as injections of current into the distribution net by third party auxiliary equipment or electric devices close to the meter (“upstream or downstream” in relation to the meter). Examples of such equipment are PV inverters, frequency converters, heat pumps, domestic electronic equipment, automatic garage doors, refrigerators and dimmers.
It should be emphasized that in cases where meters have been influenced, these disturbances have caused abnormal meter register values during exposure, but the meters are not damaged permanently when exposed.
Approaches of Notified Bodies, Utilities and WELMEC
Some Notified Bodies demand that MID module B & D show conformity in the 2–150 kHz range otherwise no more meters are allowed to be placed on the market! Some Utilities are saying that they will not purchase any meters that are not immune to this electromagnetic disturbance.
WELMEC 11 states that manufacturers have to declare and prove that their meters are immune to this electromagnetic disturbance in the frequency range of 2–150 kHz.
NMi’s simulation test setup
Although no basic EMC standards are available yet for this problem and CENELEC discussion is still ongoing, NMi has developed a simulation test setup (see diagram below) to address the issue even though the final test to be proposed by the IEC in the near future may be different from NMi’s test. Backed with a positive test result of this simulation test, manufacturers can show Notified Bodies and Utilities that their Watt-hour meters are immune to this electromagnetic disturbance in the frequency range of 2–150 kHz.
If you are interested in such a test, please contact us for further details and a proposal.
Please click here for a schematic drawing of the new test setup.
