LMG Test Suite

Harmonic emissions

Modern electrical and electronic equipment can inject significant harmonic components into the public supply system. The scope of the IEC 61000-3-2 and IEC 61000-3-12 standards, is the limitation of these harmonic emissions in order to improve electromagnetic compatibility and voltage quality in the grid.

IEC EN 61000-3-2

This standard refers to equipment under test (EUT) with input current of maximum 16 A per phase. Some general requirements include that the power input of the EUT may be connected to 220/380 V, 230/400 V or 240/415 V systems operating at 50 or 60 Hz.

Classification of equipment

A key part of the standard is the classification of the equipment under test. Electrical devices are distinguished into 4 classes. Some examples of Class A, B, C and D equipment include:

Class A: balanced 3-phase equipment, household appliances, non-portable electric tools
Class B: portable electric tools
Class C: lighting equipment
Class D: personal computers, television receivers, refrigerators and freezers

Further equipment not specified as belonging to Class B, C or D is classified as Class A equipment.

According to each equipment class, different limits and test conditions may apply. The LMG Test Suite foresees selection of the proper equipment class in the test settings, with references to the paragraphs of the standard where the corresponding limits and procedure are described.

Measurement circuit

The measurement circuit based on the EN IEC 61000-3-2 Figure A.2 for carrying out compliance tests for 3-phase EUT with the LMG600 looks like this:

The power source that the circuit employs must comply with the requirements described in §A.2. For single phase measurements the same circuit applies if the 2 of 3 phases are ignored. In the software, operation of 1 or 3 phase EUT is clearly selectable.

Test procedure

The LMG600 power analyzer is designed to perform measurements of harmonics according to the EN IEC 61000-4-7 standard. It is the user’s task to control the type test conditions in Annex B according to the nature of the EUT and select the applicable limits. These are given to LMG Test Suite as inputs before the test. During the test, the LMG Test Suite carries out the measurement procedure described in §6.3.2 of EN IEC 61000-3-2 and applies the corresponding conditions and limits to the measurement.

At the same time, besides the measurement of the harmonic currents, the instrument measures the voltage at the EUT connection terminals and the software checks whether this complies with the requirements of §A.2. The software can carry out the tests either with grouping of harmonics or without, therefore supporting both newer and older versions of the standard. Lastly, the software can plot certain current harmonics over time. Although this measurement is not required by the standard, it is very helpful in discovering the causes of harmonic emission on certain orders that might lead to non-compliance.

Test report

According to the standard, the test report may be based on information supplied by the manufacturer to a testing facility, or be a document recording details of the manufacturer’s own tests. It includes all relevant information for the test conditions, the test observation period, and, when applicable for establishing the limits, the active power or fundamental current and power factor.

IEC EN 61000-3-12

This standard refers to equipment under test (EUT) with input current exceeding 16 A and up to 75 A per phase, intended to be connected to public low-voltage distribution systems of nominal voltage up to 240 V (1-ph 2-3 wires) or 690 V (3-ph, 3-4 wires) and nominal frequency of 50 or 60 Hz.

Measurement circuit

The EN IEC 61000-3-12 standard uses the same measurement topology as the one previously given in EN IEC 61000-3-2 Figure A.2.

The power source that the circuit employs must comply with the requirements described in §A.2. For single phase measurements the same circuit applies if the 2 of 3 phases are ignored. In the software, operation of 1 or 3 phase EUT is clearly selectable.

The LMG Test suite carries out the compliance tests according to the requirements for direct measurement in §7.2.

The standard foresees also a method based on calculation by validated simulation for determination of conformity, which may be used in case the requirements of direct measurement are not met. This alternative method lies partly outside the scope of the LMG600 and the LMG Test Suite software. The power analyzer and software can be used to determine the validation reference as described in §7.3.a, to which the following simulations will be compared.

Test procedure

The LMG600 in cooperation with the LMG Test Suite, measures the harmonic currents as explained in §4.2.2 of the standard. This involves determining the smoothed 1.5s RMS for individual time windows, as defined in EN IEC 61000-4-7, as well as calculating the arithmetic average of the DFT time window values over the entirety of the observation period.

The type test conditions (Annex A) and applicable limits (Tables 2 to 5) must be controlled and properly selected by the user. These are given as inputs to the test settings. The software then carries out the test according to the given test conditions and determines compliance by applying the limits as described in §4.2.5

Test report

The test report shall contain all information relevant to the determination of the reference current, the used short circuit ratio, the minimum required short circuit ration and the applied table, as well as test conditions and observation times.

Flicker disturbance

Scope of the EN IEC 61000-3-3 and EN IEC 61000-3-11 standards is the limitation of voltage fluctuations and flicker disturbances inducted into the public low voltage power grid. Such voltage fluctuations are a result of current changes on the network impedance, coming from the equipment under test (EUT).

IEC EN 61000-3-3

This standard applies to EUT with input current no greater than 16 A per phase. The EUT is meant to be connected to low-voltage public power grids with line-to-neutral voltage between 220 and 250 V and frequency of 50 Hz.

Measurement circuit

Figure 1 of the standard shows the flicker measurement circuit. Using the LMG600 the measurement setup looks like this:

The voltage source G must fulfil the requirements of §6.2, while the measuring equipment must carry out the measurement according to the EN IEC 61000-4-15 standard. The network impedance is (0.24 + j0.15) Ω on the phase conductors and (0.16 + j0.1) Ω on the neutral.

For single phase measurements the same circuit applies if the 2 of 3 phases are ignored. In the software, operation of 1 or 3 phase EUT is clearly selectable.

Test procedure

Flicker is evaluated using the voltage change characteristic ΔU_hp(t) at the terminals of the EUT as described in §4.1 of the standard. From the ΔU_hp(t), the LMG600 deducts the basic values for flicker evaluation:

• Short-term flicker severity: P_st
• Long-term flicker severity: P_lt
• Maximum steady state voltage change: d_c
• Maximum absolute voltage change: d_max
• Maximum time duration during the observation period that the voltage deviation d(t) exceeds the limit for d_c: T_max

The user shall make sure that before each test the general conditions of §6.6 as well as the EUT-type conditions of Annex A are applied. The LMG Test Suite allows for the selection of the type of the EUT as described in Annex A and applies the according test conditions and limits during each test.

IEC EN 61000-3-11

The EN IEC 61000-3-3 standard describes also further methods for flicker evaluation besides the flicker meter, such as simulation or analytical approach. These alternative methods are out of the scope of the LMG600 and the LMG Test Suite. In any case, for flicker evaluation, measurement is always the reference method.

The EN IEC 61000-3-11 applies to electrical and electronic equipment with rated current up to 75A, meant to be connected to low-voltage public power grids with line-to-neutral voltage between 220 and 250 V and frequency of 50 Hz.

The EUT in this standard is subject to conditional connection, meaning that the EUT is not necessarily evaluated using the reference impedance as defined in the EN IEC 61000-3-3. This also covers devices with rated current up to 16 A that fail to meet the limits when tested according to the EN IEC 61000-3-3. In such cases these devices may be retested according to the EN IEC 61000-3-11 standard.

Measurement circuit

The test setup is given by Figure B.1 of the standard and is generally identical to the one described in above in EN IEC 61000-3-3 with the only difference that the value of the network impedance depends on the test and measurement procedures explained in §6.

Test procedure

The LMG600, as an EN IEC 61000-4-15 flicker-meter, follows the voltage change characteristic ΔU_hp(t) from which the basic values for flicker are extracted:

• Short-term flicker severity: P_st
• Long-term flicker severity: P_lt
• Maximum steady state voltage change: d_c
• Maximum absolute voltage change: d_max
• Maximum time duration during the observation period that the voltage deviation d(t) exceeds the limit for d_c: T_max

For EUT with rated current up to 16 A the same test conditions specified in Annex A of EN IEC 61000-3-3 are to be applied. To equipment rated above 16 A apply the general test conditions of §6.6 of EN IEC 61000-3-3. Furthermore, different conditions and limits apply to EUT that is switched manually. The correct application of the test conditions depends on the user, who shall also give them as inputs to the test setup in the LMG Test Suite. Depending on the above, the software will carry out the corresponding procedure to determine conformity.

The network impedance is a key parameter to the test. The decision between using the reference impedance Z_ref or the selection of a test impedance Z_test lies on the user. Depending on the user selection of network impedance, the LMG Test Suite will either use the directly measured flicker properties, or adapt them according to §6.2.3 to the Z_test If the calculated values meet the limits of §5, then compliance with that standard may be declared.

In case the aforementioned limits are still not met, the procedure of §6.3 is carried out, using the maximum permissible system impedance Z_syst to evaluate the flicker properties as described in §6.3.2.

Standby Power

Environmental concerns that were considerably amplified the past 20 years have made clear that it is of major importance to reduce any energy waste. An undeniable source of that waste is the variety of modern electronic devices that consume energy while being connected to the mains but not operating under their primary function. Typical examples include LED indicators of a device’s off state, digital clocks on ovens and microwaves, or internal electronic circuits being on a standby state for remote switch-on commands or sensor inputs.

The present day, the number of electronic devices that implement such low-power functions is estimated to billions, leading to an estimation of the yearly energy consumed in the range of tens of TWh.

The European Commission decided in 2008 to limit the energy consumption of energy using products (EuP), under the Ecodesign Directive 2005/32/EC. The directive provides consistent EU-wide rules for improving the environmental performance of products. The Commission Regulation 1275/2008 definesthe limits for power consumption in off and passivestandby modes. As of 2013, the following limits apply:

• Maximum power consumption in off mode: 0.5 W
• Maximum power consumption in a passive standby mode without information display: 0.5 W
• Maximum power consumption in a passive standby mode with information or status display: 1 W

These limits are therefore design specifications for electrical and electronic products meant to comply with the EU regulations. As a result, the development phase of any new product requires reliable measurement of its power consumption in low ranges. The International Electrotechnical Commission specifies the methods of low power measurement in the IEC 62301 standard. The European EN 50564 published by Cenelec, derives from IEC 62301 but extends its scope to cover a wider range of household and office equipment. The EN 50564 is the only one applied for CE marking. Given the above, in the following paragraphs emphasis will be given to the EN 50564 standard.

The ZES ZIMMER solution, uses the LMG600 for the accurate power measurement in combination with the LMG Test Suite for carrying out the tests according to the standards, applying the limits and reporting the results.

Common issues in lower power measurement

Measurement of low power is not a simple matter. A detailed analysis of the challenges in low power measurement can be found in our Application Note 112: Measurement of standby power and energy efficiency.

Even for high end power analyzers it is often a challenge to detect and measure correctly the fast pulses/spikes that appear in low power modes. Moreover, such sudden current jumps make it hard for a user to select the appropriate current range. The influence of low power factors makes the situation even more complicated. The cause of low power factors in low power states is not only the non-sinusoidal currents that are commonly present in these modes, but also the use of EMC-capacitors that can lead to significant phase angles between current and voltage. The problem is more or less the same: low power must be measured using a much higher current scale. The low active power that is of interest is actually transferred through a current much higher than necessary, resulting from the high apparent power that is present.

It is therefore important that an instrument that measures low power must provide current ranges with high crest factors. This way, the uncertainty error can remain relatively small when a small current scale is used instead of a higher one, while the current spikes do not lead the instrument in an out-of-range state. Naturally, auto range selection is in this case out of the question, as it can lead to inacceptable measurement gaps. Further appearance of gaps in the measurement can be blamed to limited data processing and transfer capabilities of the instrument as well as to DC-offset compensation errors. In this case, high processing power and high quality components is what makes a high-accuracy instrument.

Last but not least, no voltage or current meter is perfect. In other words, every volt-meter has a very high but finite internal resistance which leads to a current leak through it, and every amp-meter has very small but non-zero internal resistance that leads to a voltage drop over it. Any possible power measurement wiring will carry one of these two imperfections to the result. But for measurement of low current, a wiring is preferred where the amp-meter is connected to the load-side of the circuit. This way the power meter measures the actual current in the load and the inevitable measurement error comes from the voltage drop on the amp-meter. This error is normally very small compared to the actual voltage of the load. However, one cannot risk a current error when measuring low current. Therefore a wiring with the volt-meter on the load-side is not recommended, as the small current leak though a voltage meter would be comparable to the small current through the load.

Specifications of an accurate low power meter

There are differences in the definitions of accuracy between the EN 50564 standard and the EU 1275/2008 Commission regulation. The first only specifies the accuracy of the measurement instrument while the latter, the accuracy of the entire measurement setup. This very fact requires special attention, as the EU regulation rules, override the EN 50564 standard.

Anex B of the EN 50564 standard gives some informative guidelines on the power meter specifications. At the same time, ZES ZIMMER sets the bar high with the LMG600, providing a high-end power analyzer with one of the highest accuracies in the market. All the problems explained in the previous chapter as well as the instrument considerations described in §B.2 of EN 50564 are addressed by the LMG600 under the following specifications:

• Accurate measurement of voltage, current, real power, power factor with uncertainty of 0.025%
• Real time analysis of the measured values: true RMS, peak, crest factor, etc.
• Synchronous delivery of the measured values
• Measurement resolution of 6 decimal digits
• Accuracy specification independent of power factor
• High crest factors in low current ranges
• Lowest current range of 5 mA
• Continuous and gapless sampling at 1.2 MS/s
• Manual & auto range settings with out-of-range detection
• Accurate power averaging
• Energy integration with resolution of 5 decimal digits
• Bandwidth of 10 MHz
• Minimum cycle time and record rate of 10 ms
• Data output to PC via Ethernet
• Direct shunt current inputs

The EN 50564 standard

The methods of power measurement described in EN 50564 standard apply to electrical equipment operating in a low power mode. Rated output voltages may vary within 100-250 V AC for 1-phase devices or 130-480 V AC for other devices.

In a low power mode, the energy using product is connected to the mains but does not perform any of its primary functions. The low power mode includes one of the following states:

• Off mode: The product does not provide any function other than the indication that the product is in the off state.
• Standby mode: The product provides one or more user oriented or protective functions such as activation of other modes, status information or sensor based functions.
• Network mode: At least one network function is activated such a reactivation over a network command or network integrity communication.

There are several product types that may incorporate and one or more of low power functions into one or more main functions under different switching conditions between one another. These types are defined in detail in §A.5 of the standard.

Test procedure

A low power mode test involves several procedures that need to be carefully taken care of the user, such as preparation of the product, proper warm-up and achievement of a stable state, as well as recognizing and separating different low power states.

Furthermore, low power loads can be distinguished according to their stability to non-cyclic or cyclic, meaning that a product in a low power mode can either have a stable power consumption behavior or follow a regular sequence of power states over time. Different procedures apply for each case.

The standard describes in §5.3 three different measurement methods:

• Sampling method: The recommended method for all types of modes and necessary when the stability of the mode is under question. Involves the recording of power samples over equal time intervals and their evaluation according to §5.3.2.
• Averaging method: Is only permitted for non-cyclic loads. Includes the averaging of the power over an observation time by two ways: either by direct measurement of average power or calculation by measuring the energy and dividing it by the monitoring period, as described in §5.3.3.
• Direct meter reading method: May only be used when the power consumption of the product is proven to be stable over a sufficient observation period. The exact procedure is described in §5.3.4 of the standard.

Deciding which stability mode applies and which method should be used depends eventually on the user. The user must additionally control that the test procedure is carried out properly when it comes to wiring, energizing the product before the test and taking care of any further details that require human input. The LMG Test Suite provides all measurement methods for any stability mode that can be selected in the pre-test settings. The software evaluates the readings as each method requires and concludes to the final pass/fail results.