Here we provide you with frequently asked questions with possible answers
Battery replacement - how long does the battery buffer in the meter last?
The measuring instruments of Camille Bauer Metrawatt AG carry the option of a UPS. This UPS buffers the supply voltage for up to 5×3 minutes during a short-term power failure, so that no measurement data is lost during this short time. The buffer is installed as a rechargeable battery and recharges itself again and again. The charging status can be queried via the display in the device. Under normal conditions, the battery can be expected to have a lifespan of 3-5 years. After this time, replacement can be considered as a preventive measure.
I have a PQ problem - what do I need to do?
In case of a suspected PQ, caused e.g. by sudden switch-off of systems, failures in LED lighting, humming in audio systems, sudden loss of energy, failure of transformers, etc., it is recommended to deal with the control circuit (PDCA) of the Demand Side Power Quality (DSPQ). This requires, of course, that professional know-how is available. Experts such as Certum Sicherheit AG (CH), Camille Bauer Metrawatt AG (global), DV-Group (FR), PQ-Professionals GmbH (DE), Tecotec (Vietnam), Power Quality Thailand, etc. are at your disposal. Depending on the severity of the symptoms and the complexity of the plant, the experts will analyse the current situation, carry out measurements, prepare reports, analyse measurement data and, together with the data and the customer, localise the possible cause and make suggestions for remedying the disturbances.
Please note, however, that it is quite possible that there is no problem with the power quality and yet symptoms still appear. This can be caused, for example, by improper cable routing. It can also happen that symptoms and disturbances are detected, but the cause remains hidden at the time of the search for the disturbance, despite a high volume of measurements. Network quality is dynamic and subject to the context of a highly complex infrastructure.
Can the measuring device also measure transients
Transients are extreme voltage fluctuations (several kV) in a very short time, combined with a clear change in the sinusoidal curve. In order to detect fast transients, measuring instruments with a very high sampling rate are required. Often, transients are confused with a rapid voltage change, however, which according to IEC61000-4-30 Ed. 3 Class A are already detected (RVC = Rapid Voltage Change). For this reason, according to the definition IEC61000-4-30 Ed. 3 according to class A, fast transient detection is optional and also associated with extremely high acquisition costs for such measuring devices.
Rogowski coils or current transformers?
First of all, it should be noted that it depends on the type of measurement as well as the respective access to the measurement object. Furthermore, it depends on the PQI used in each case which measuring sensors can be physically connected at all.
Rogowski coils are often used for mobile measurements, as they have a wide current bandwidth and can be applied around a conductor extremely easily. Nevertheless, it is important to ensure that the respective conductors are as centred as possible in the coil in order to achieve a good measurement result. In individual cases, Rogowski coils are also used for stationary measurements.
Current transformers are available in various designs. These include, on the one hand, the design. Z. E.g. as closed conversion converters, in which the conductor must be led through the closed core. On the other hand, folding transformers are often used in existing installations to avoid installation without physically separating the conductor from its terminal (subject: disconnection).
A further but essential feature is the respective accuracy classes. Especially in the case of mains quality, it makes no sense to use particularly cheap converters with low accuracy to the detriment of the accuracy, since as a rule the PQI are rather more expensive to purchase. In addition, care must be taken to use specifically designated transducers that continue to measure accurately in the appropriate harmonic bandwidths.
The conclusion is that any measurement system is only as good as the worst link in the measurement chain.
Rogowski coils or current clamps
Basically, both sensor technologies are always appropriate when disconnection is not possible or also when space conditions do not permit current transformers. Most of the time, both technologies are used for mobile measurements, i.e. for so-called measurement campaigns. Depending on the manufacturer and type of device, it may vary which measurement sensors can be physically connected to the respective PQI, or which signal form can be connected at all.
Rogowski coils are often used for mobile measurements, as they have a wide current bandwidth and can be applied around a conductor extremely easily. But care should be taken to ensure that the respective conductors are as centred as possible in the coil in order to achieve an optimum measurement result.
To achieve even better or more precise measuring results, it is recommended to work with measuring clamps. But it should be noted that measuring clamps are not as flexible to use as Rogowski coils due to their mechanical nature. But here again, the space required at the ladders plays a central role. In addition, high-quality measuring clamps have a significantly higher price than a simple Rogowski coil. If the price is decisive and a measuring clamp is nevertheless preferred, less powerful measuring clamps can also be useful.
When does a mobile measurement or a stationary measurement make sense?
Mobile measurements, also known as measurement campaigns, are always useful when no stationary measurement is available. They are used either to evaluate the network quality under defined conditions (e.g. recurring measurement, power runs in data centres, etc.) or also to localise faults. It is important to know that the measurement over a defined period of time always represents a snapshot and can change over time due to various influences. For this reason, a stationary measurementis advantageous for the detection of problems and trends, as it continuously records data and reports deviations regardless of the defined time period.
When and where is EN50160 relevant
EN50160 defines the network quality agreed between the supplier and the consumer at the transfer point, the so-called Point of Common Coupling (PCC), and thus forms a binding legal basis. The EN50160 is a purely statistical observation over time and is documented using an undefined reporting format. According to the PCC, the consumer himself is responsible for his network infrastructure, the so-called In-Plant-Coupling (IPC). This means that EN50160 is no longer relevant for the various IPCs. Most interferences, in fact, are generated on the consumer side due to poor network quality and are also received there. Therefore, power quality instruments (PQI) according to class A or S are useful at the IPCs to capture and record the actual events in order to track down the causes within the infrastructure in case of problems.
What does PQ mean
PQ stands for Power Quality and is actually a subchapter of the EMC standards and defines specific limit values that must not be exceeded in the network. In this regard, there are clear IEC standards that define the network quality. In the market, however, the topic of network quality can be interpreted individually by the application, the market segment and the user. Therefore, power quality issues are often already settled with harmonics, EN50160, etc. It is therefore advisable to carefully consider which application and which benefits should be brought together in the context of network quality. From this the budget that is to be used for the measure(s) can be determined.
What is the benefit of a metrologically certified measuring device?
In general, metrology is the study and science of measurement, of systems of measurement and their units. It is responsible for the definition of internationally accepted units of measurement, the realisation of units of measurement through scientific methods, and the establishment of traceability chains through the determination and documentation of measured values and their accuracies, and the dissemination of this knowledge. And especially through the traceability of the units of measurement to a so-called original measure, it can be ensured that measurements are carried out precisely by means of a metrologically certified device. These are particularly important when it comes to the comparability of measurement data, e.g. in a legal case or also for repeat measurements. Certifications or simply tests with self-declaration outside metrology with specific accreditation are to be questioned. Or would you trust a scale in the supermarket that has not been officially calibrated?!
What is the difference between class A and class S?
Measuring instruments according to IEC 61000-4-30 Class A provide measured values that are comparable across measuring instruments and manufacturers. For legal certainty in terms of comparability of measurement data, it is recommended to use metrologically certified measuring instruments. Another advantage is that the relevant measurement data are “quasi-calibrated” by the certified type test. It is also an advantage to have a metrologically certified energy measurement in order to obtain correct energy data, as this is also significantly influenced by the grid quality.
IEC 61000-4-30 class S power quality analysers are intended for basic / advanced power quality analysis and provide useful monitoring data. Instruments that meet the Class S performance requirements are used for statistical power quality surveys and contractual applications where there are no potential disputes, i.e. no comparable measurements are required. The accuracy and performance requirements for class S are less stringent than for class A and thus also set lower in price. They are often used in industrial and utility engineering, the area of so-called demand side power quality at the IPC (In-Plant-Point-of Coupling) e.g. in data centres, the semiconductor industry, airport infrastructure, food and beverage industry, metal and aluminium industry, cement industry, etc.
What measuring accuracy must a measuring device have
The accuracy of the measuring instruments is subject to various standards and is usually based on IEC/EN 60688 for PQI to comply with the following basic errors: voltage, current ±0.1 %, power ±0.2 %, power factor ±0.1°, frequency ±0.01 Hz, unbalance U, I ±0.5 %, harmonics ±0.5 %, THD U, I ±0.5 %. For energy, basic faults are defined as follows: Active energy class 0.2S (IEC/EN 62 053-22), reactive energy class 0.5S (IEC/EN 62 053-24).
But attention: These are basic errors of the measuring instruments themselves. These are directly dependent on the sensors, e.g. the current transformers used. If you choose a poor accuracy class or even current transformers that are not harmonic resistant, the error in the measurement chain adds up.
What accuracy should the current transformers have
The accuracy of the measuring instruments is subject to various standards and is usually based on IEC/EN 60688 for PQI to comply with the following basic errors: voltage, current ±0.1 %, power ±0.2 %, power factor ±0.1°, frequency ±0.01 Hz, unbalance U, I ±0.5 %, harmonics ±0.5 %, THD U, I ±0.5 %. For energy, basic faults are defined as follows: Active energy class 0.2S (IEC/EN 62 053-22), reactive energy class 0.5S (IEC/EN 62 053-24).
But attention: These are basic errors of the measuring instruments themselves. These are directly dependent on the sensors, e.g. the current transformers used. If you choose a poor accuracy class or even current transformers that are not harmonic resistant, the error in the measurement chain adds up.
What is the minimum current that a Rogowski sensor can measure?
The minimum current to be measured depends on several aspects and can be far below 10A despite high nominal current specifications (e.g. 3’000A). The accuracy depends strongly on the environmental conditions. The lower the current in the line, the more sensitive the Rogowski coil is to environmental conditions such as EMC. For small currents, it is also even more important to position the coil centrically to the measured line.
How high is the deviation of the accuracy over time?
If a measuring instrument cannot be calibrated after a certain period of use, it is recommended to at least consider the error above value. The error describes the maximum permissible variation over a period of time. For this example, it is defined like this:
BASIC FAULT ACCORDING TO IEC/EN 60688:
- Voltage, current ±0.1
- Power ±0.2 %Power factor ±0.1°
- Frequency ±0.01 Hz
- Asymmetry U, I ±0.5 %
- Harmonic ±0.5 %
- THD U, I ±0.5 %
Deviation formula:
- Temperature influence 0.5 x basic error per 10 K
- Long-term drift 0.5 x basic error per year
How high does the sampling rate of a measuring device actually have to be?
According to the PQ standard, a measuring device must be able to detect harmonics up to the 50th order (2.5KHz at 50Hz). According to the sampling theorem, a sampling rate of at least twice the signal frequency is required for the detection of this signal. Means ≥5kHz at 50Hz. This is also sufficient to detect PQ events such as voltage dip or voltage rise, which are monitored on the basis of half-period values. Only if (optionally) voltage transients or disturbances in an extended frequency range are to be detected, a higher sampling rate is required. Again, this is at least twice the value of the signal or interference frequency that is still to be detected. According to the PQ standard, transient detection is an option.
How often do I have to calibrate the PQ meter?
This topic is often and intensively debated. There is no basic rule according to IEC. Although manufacturers and authorities (e.g. ESTI, etc.) issue guidelines stating that measuring instruments in regular use should be calibrated every 2-3 years. This applies, first of all, to measuring and testing technology – i.e. mobile measuring technology. In the case of stationary measurement technology, devices are normally only calibrated when they are repaired by the manufacturer, as in most cases built-in measurement technology cannot be easily removed and dispensed with. But if one attaches importance to the fact that built-in devices are also calibrated, which is usually done by government organisations or on the basis of legal requirements, then a measuring device in a 19″ rack version is recommended. This can be easily exchanged, so that even the time of calibration can be bridged by means of an exchange device. If calibration is not performed, at least the basic error (e.g. according to IEC 60688) with the permissible deviation should be kept in mind.
But attention: Calibration does not automatically mean adjustment. Please continue reading in the glossary.