Power quality measurement IEC 61000-4-30

In our previous content we talked about the IEC 61000-4-30 standard and concluded what is actually common for carrying out measurements and what is a construction characteristic, inherent to the manufacturer of analyzers. Here we will talk about its annexes. 

In terms of page count, the annexes are almost half of the standard itself, and provide important and rich details when applying measurement techniques, using qualified tools.

IEC 61000-4-30 Power Quality Measurement Procedure :

We have reached the first annex of the standard! This part presents the concepts for performing a class A measurement, and my friends, some of the information here must be in your report and others you must know before generating a report or measuring something.

It elucidates, in short:

• Installation precautions;

• Transducers;

• Transient voltages and currents;

• Rapid voltage variations;

• Current;

• Voltage sag characteristics;

Let’s take a look at the super summary of each of these items…

Installation precautions

This section mentions the IEC61010 standard, which deals with the safety of inspection and measurement equipment. Rules and precautions for temporary or permanent installation, connection of cables and voltage and current test leads, access to live parts, instrument accommodation, grounding, and interference.

There are countless precautions that aim to ensure the safety of people, the installation, the equipment, and the measurement, because we want the result to be correct! This is the only subject for a new article! I believe that reading this is mandatory for everyone, and preparing a checklist exploring and ensuring that all the numerous requirements have been met is also mandatory.

Transducers

The standard explains the need to use these, since adjustments to voltage levels, or even the use of current sensors to collect signal samples, are widely used. We are talking about both the equipment's own accessories, such as Rogowski coils and test leads, as well as shunt-type derivations, and CTs and TPs (most common) for leveling and adjusting measurement levels and limits.

In this case, knowledge of the linearity and frequency response of the transducer is essential for an analysis so that we can understand the behavior of some phenomena and extrapolate uncertainties, that is, if there is a transducer, it must be known and its uncertainties must be mentioned and considered in the analysis.

A current transformer, for example, varies in accuracy class, ratio, material, section, etc., and generally the cutoff frequency varies from 1 to a few kilohertz, which affects, for example, the phase response when close to the cutoff frequency. This must be taken into account when evaluating an oscillatory transient and dimensioning filters, for example.

Such consideration would affect the dimensioning of a filter. It is important that the report considers the existence of the transducer and mentions it, so that the reader can be led to a conclusion, having an overview of the measured system.

Transients and rapid changes and dips

The standard goes into more detail regarding the measurement of transients and rapid voltage changes, which are transitions between two permanent regimes, and voltage dips (which are more common in everyday life). Note that, as with almost everything in electrical engineering, analyses in Permanent Regime and Transient Regime are different. Here the standard addresses issues such as saturation, cutoff and operating frequencies, exclusion of transducers, among other aspects more specific to equally peculiar situations. In summary, answer these two questions before measuring:

• Do the signal levels utilize the full scale of the instrument?

• Is the operating frequency suitable for the measured signal?

If the answers are yes, the equipment and transducer are suitable for the measurement.

Fortunately, most manufacturers make the equipment limits for their transducers clear, so it is important to adopt tools and accessories with known, tested and published data, obviously. This way, the system can be evaluated in its entirety, compatible sensors can be grouped together and, of course, some conclusion can be reached.

The standard cites the phenomena, classifies them, names them and draws attention to the care required when measuring, however, do not expect to see more precise analysis guidelines (How to measure, what to measure with, interpret or conclude).

Current

I would like to make a big reservation and draw attention to a detail that may have gone unnoticed: Up until now we have only talked about VOLTAGE! So yes! A device can be class A without measuring current, so the standard treats current measurement as something useful, but in a complementary manner, under the responsibility of each manufacturer, to ensure the same standard of precision previously indicated in the parameters defined and explicit at the beginning of this publication.

It mentions acceptable limits and uncertainties, but does not describe tests. Therefore, evaluate and be careful to use equipment that also follows the class rigor in current measurement, whether in magnitude, phase, uncertainty, etc. Note that the Power Factor, for example, requires such a measurement, but is not even mentioned in this standard. This also applies to current harmonics, inrush assessment, etc. PRODIST module 8, for example, treats this parameter as mandatory, therefore, it is desirable that a device meets this and other measurement needs as well, such as the RE8000 from Embrasul.

Important terminologies

Transient: Phenomenon or a quantity that varies between 2 consecutive steady-state states during a time interval, when compared to the time scale of interest.

Surge: It is a transient voltage wave, propagated along a line or circuit, characterized by a rapid increase, followed by a slower decrease.

Rapid voltage change: Rapid transition of the effective voltage between 2 steady-states. (Note that there is only a shift from the broader term “transient” to a “voltage transient”, defining the quantity that was encompassed in the definition of transient).

Inrush: It is a transient energizing current.

Interharmonic Frequency: Any frequency that is not an integer multiple of the fundamental frequency.

Measurement of electrical power quality:

Recommendations for application

Here we can divide and already direct 2 large classes of application.

Measurements with a contractual purpose or possible contractual purpose

For these, class A, because we are talking about compliance with something agreed between the parties. Here, it is very common to link to PRODIST and to more than one module of this, since PRODIST establishes rules for specific measurements, thresholds, and also for aspects of service, reimbursement, etc. The standard even states that “a standard must be the starting point”: PRODIST, for example. Remember, this standard discusses techniques, not limits. Further on, the standard also talks about how to configure the equipment to measure, depending on the phenomenon. Here I emphasize that IEC and PRODIST are in agreement, because they require similar configurations. I strongly recommend that these two standards be cited in audits for such purposes: IEC 61000-4-30 and PRODIST, as many as the necessary modules.

Measurements for statistical purposes and studies

Class S. Here the standard also mentions “consumers and supply network”, however, it understands that it may be a continuous and in fact statistical assessment, including indicating the need to increase the measurement class for any deviation parameter in S. I emphasize that I think this is unlikely (opinion). Class S, within the current Brazilian regulatory scenario, meets the overwhelming majority of cases with flying colors. It is common, within what I have already evaluated within my years of experience here at Embrasul, to see widespread use of class S equipment by numerous engineers and companies. Class S analyzers meet almost complete internal assessments at the coupling point, including at the point, delivering a complete PRODIST analysis, as is the case with the RE7000 and its siblings 7080 and 7040 .

Class A equipment, such as the RE8000 energy analyzer , covers legal situations of verification, such as those mentioned in the standard, but is also indicated for commissioning plants, laboratories, sensitive and/or complex loads, among others. In other words, both classes are suitable for numerous applications, and for restricted applications, there is a more specific guideline. Therefore, whenever you are going to perform a measurement or campaign, use a tool according to the situation and problems to be solved. The overwhelming majority of applications are not mentioned in the standard. And if necessary, our application team can help with this.

Priority of Quantities

Embrasul equipment performs measurements of the evaluated parameters simultaneously, across its entire line. However, not all equipment has this capacity, therefore, the standard defines the measurement priorities, which are:

1. Electrical parameters (V, I, P, Q, S, DPF, TPF, etc.);

2. Voltage dips/swells;

3. voltage harmonics;

4. current harmonics;

5. imbalance;

6. transient;

7. Flicker;

8. Voltage and current interharmonics;

9. communication of voltage signals through the network.

In other words, the standard prioritizes continuous aspects present in a permanent regime, to the detriment of transient events, if there is a need for consecutive, not simultaneous, measurement.

Integration of Quantities

For each of the parameters mentioned above, the standard addresses an integration time, or rather, a recommended aggregation: 10s, 10 min, 2h, 3s, 200ms, among others. And here I draw attention to the fact that, unlike PRODIST, which requires 1008 valid records in 10 minutes, IEC61000-4-30 addresses each parameter individually, with multiple simultaneous integrations.

It is even possible to see, throughout the standard, that PRODIST also has similarities with IEC 61000-4-30, since its rules are similar to those of some parameters, such as: Magnitude of supply voltage, which understands that the aggregation must be performed in 10 minutes for the same period of one week.

I would like to point out that not all equipment has such a capacity for multiple aggregations, therefore, for full service and to be able to support and comply with the choice recommended in this standard, the equipment used must allow such capacity, otherwise, one or limited aggregations may not allow a simultaneous study of all parameters, requiring consecutive measurements, respecting the priority of the quantities, but also extending the measurement period.

It is common for analyzers and meters to have the capacity to integrate one or two aggregations. It is not trivial in the market for a device to have all the different aggregations per parameter simultaneously, as is possible in the RE8000 .

Below we present the main recommendations regarding these aspects:

Industrial Frequency	1 week	10 second aggregation
Supply Voltage Magnitude	1 week	10 minute aggregation
Flicker	1 week	10 minute aggregation
1 week	Aggregation 2 hours (Plt).
Voltage Dips	1 year	not informed
Interruptions	1 year	not informed
Source Voltage Imbalance	1 week	Aggregation of 10 minutes and/or 2 hours
Harmonic Voltages	1 week	10 minute aggregation
1 week	Aggregation 150/180 cycles
Interharmonic Voltages	1 week	10 minute aggregation
1 week	Aggregation 150/180 cycles
Communication Signals in Power Grid Voltage	1 week	not informed

Such periods and aggregations may seem strange, but remember that a consideration must be made before measuring. Such values ​​can and should vary according to the objective, and must comply with the reference standard. It is the famous saying: “A case for each case”, defining an absolute rule for any application is not possible.

A good strategy, when in doubt, is to use longer measurement periods, with shorter integrations. This strategy allows integrations for longer periods, and ensures that there is no lack of records due to purges, etc. In short, if you use an integration of 200ms, it is possible to reintegrate it for 10 minutes.

The opposite is not true. As for the measurement time, you need 1 week, or 1008 10-minute recordings. Add 2 more days or make it 14, so that you can choose a convenient and useful window for measurement, avoiding the problem of missing recordings.

Comparison of Results

As we move towards the end of this content, the standard also mentions how to compare and present the results and contractual limits. Note that this is a statistical analysis, and for each parameter a specific selection is necessary, that is, do not use this for all and any parameters. The standard addresses each method for each parameter specifically, but to make it easier and more compilable, I bring the methodology it presents, and the reader classifies what is useful for each parameter.

• Number or % of values ​​during measurement that exceeded the limit either above or below;

• Peak values ​​(at the same or different interval);

• Weekly Probability values ​​95% or 99%, expressed in magnitude;

• Number of consecutive values ​​exceeding limits;

• Number of deviations from nominal.

For each of the electrical parameters and phenomena, these methods may or may not make sense, so to provide a good basis for your report, check the parameter and the comparison method exactly, so that your analysis complies with this standard. But don't limit yourself to that! It is advisable to err on the side of excess. Always show as much data as is necessary for the reader to fully understand. The standard presents the minimum required. 

As a matter of interest, PRODIST, in module 8, also presents a methodology.

Decision factors

There are decision factors that are not explicit in the standard. Here are some:

Location

At what point on my diagram do I measure? Here, an expert analysis is necessary because factors such as feasibility, cost, proximity to the load, among others, affect this choice and can vary from case to case. Therefore, keep in mind the implications of error, environment, access of people, and other variables not explicitly stated here or in the standard, which can affect the campaign/measurement.

Objectives

They depend on the reason for the event, and based on this, parameters, integration time, equipment, cost, thresholds, and validation and purges are defined, that is, campaigns allow greater power of choice and decision, but the standard mentions precautions such as “Gather as much documentation as possible”

• Change logs;

• Knowledge of disturbing loads and operating regimes;

• Problem details

• Search for coincidences (We may have to take simultaneous measurements at different points to prove something by inference and inspection).

See, the standard gives us the precautions we must take before taking on a measurement, campaign, study, and how to gather information that helps us reach some conclusion, after all, that is what we are looking for, a conclusion for something.

Campaign preparation

Finally, we come to the end of this standard. I bring some points mentioned in the standard, which are important when carrying out the study to conclude this content. And if you are interested in further studying this, purchasing and reading it is recommended and available in the ABNT catalog, available through a simple Google search.

• Set the number of phases and the reference voltage;

• Define the current measurement and its ranges and transducers;

• Define interpretable thresholds and monitoring period;

• Characterization of the measured point with maximum information about it;

• Define statistical analysis indicators (%, max, min, avg…) to condense a large number of values;

• Define the analysis and comparison references for each parameter with a confidence level greater than or equal to 95%;

• Point out contractual compliance and operator/consumer requirements;

• In results, perform the counting and tabulation of events;