Quality seal for power quality analysers

Class A certification (IEC 61000-4-30):

Quality seal for power quality analysers

For a long time the quality of the power supply was synonymous for supply security, i.e. the absence of noticeable interruptions. Electronic loads, such as IT systems or industrial controls need far more, for example, because harmonics, transients, etc. can cause significant damage. As a result, the German Federal Court of Justice stipulated that power distributor operators are subject to product liability. A comprehensive analysis and documentation of the power quality with a certified process is even more important.

A growing group of service providers and consumers is involved in determining the power quality: network operators are confronted with a – rather pleasant – increasing number of renewable energy producers. The consumers, especially in the commercial and industrial sector, are concerned with their numerous embedded systems and controls throughout the various range of applications. Here, they must also recognise that they sometimes cause the faults themselves. Frequency converters, energy savers par excellence, are only one example for non-linear loads that can cause severe problems. But even a very trivial asymmetric load in the three-phase network can cause trouble.

The German Product Liability Act also applies to electricity

The topic gained more relevance by a decision handed down by the German Federal Court of Justice from February 2014 (reference number: VI ZR 144/13). In the opinion of the German Federal Court of Justice, electricity is a product according to §2 of the German Product Liability Act (ProdHaftG). As a result, the distribution system operators are liable if electrical equipment is damaged due to poor power quality. The court expressly rejected an exemption from liability through the Low Voltage Grid Connection Ordinance (NAV). The power utility is liable, irrespective of culpability. The network operator must keep the voltage and frequency as constant as possible so that standard consumer devices and power distribution and generation plants can operate properly. 

Of course, continuous monitoring with sufficient granularity is required for the analysis as well as the verification and the documentation of the power quality.

Searching for the responsible

Regardless whether you want to hold the "culprit" accountable or force him to pay for resulting damage or take proactive measures to detect and mitigate fault sources: you need reliable and documented measured values that stand up in court in case of doubt. In this case, the recordings of the power quality analysers, like the ones Janitza electronics GmbH has been developing and selling for many years, provide valuable assistance. Thanks to comprehensive analysis tools and various documents, they offer extensive and detailed insight into an electrical system. In addition to the basic values, such as voltage levels, frequency and curve form, above all they record any kind of fault (image 1). This may include flicker effects or also temporary voltage drops, such as for example, those typical when systems do an automatic reclosing after short circuits caused by arcs. 

Another classic example includes harmonics. They are caused by non-linear loads and can significantly damage the function of other devices. Unlike basic oscillation in three phase systems, all harmonics that are divisible by three (triple harmonics) do not neutralise each other in the neutral conductor. In fact, they accumulate. This can result in an unacceptably high current load on the neutral conductor. The frequency converters specified above are the typical "harmonic producers". Overvoltages are also widespread in switching operations.

Standardised measuring procedures for power quality

Clearly, these effects can only be recorded at a considerable effort and the chronological resolution and a high measurement accuracy of the power quality monitoring device play a key role in the documentation. The measurement methods play a vital role, especially in areas where power quality or limiting faults are key contractual components. The contractual partners must then agree on the voltage characteristics as well as the measurement methods and the quality of the measurement devices that determine these factors (image 2).

Image 1: The event recording includes the mean, minimum and maximum value as well as the start and end time. With longer events, the waveform is also included at the beginning and end of the result.
Image 1: The event recording includes the mean, minimum and maximum value as well as the start and end time. With longer events, the waveform is also included at the beginning and end of the result.

Otherwise, it would extremely tempting to generously overlook possible faults using less efficient PQ monitoring devices. Even if assume the best of intentions, it would be difficult to compare instruments from different manufacturers over the long term. In the absence of binding standards, they each developed their own procedures for analysing a measurement. The user thus not only has to work with the actual measurement but he may also have to deal with the measurement algorithms and procedures of the manufacturers. In order to provide legal certainty, the suppliers and customers must conclude pages and pages of agreements concerning the measurement devices to be used in the contract.

Image 2: Principle of a power quality monitoring with the watchdog function, 3-fold responsibility
Image 2: Principle of a power quality monitoring with the watchdog function, 3-fold responsibility

Fortunately, the IEC 61000-4-30 Class A standard was established several years ago. It provides detailed specifications that a power quality monitoring device must meet so that the results can also be consulted in case of disputes. The standard defines the necessary parameters, suitable measurement methods, accuracy and bandwidths. This makes it possible to easily reproduce and compare results of class A power quality monitoring devices from different suppliers and devices.

The following parameters are defined:

  • Mains frequency 
  • Supply voltage 
  • Flicker, harmonics, interharmonics (some references are made to other standards) 
  • Voltage drops and excessive voltages 
  • Supply interruptions 
  • Voltage unbalance 
  • Ripple control signals 
  • Rapid voltage changes

Certified devices

Image 3: UMG 512 Class A power quality monitoring device
Image 3: UMG 512 Class A power quality monitoring device

There are a number of power quality analysers on the market; however, they are by far not all certified. Janitza already completed this step several years ago. The UMG 511 power quality monitoring device already received its Class A certificate of conformity according to IEC 61000-4-30 back in January 2011. This provides a reliable reference – even in disputes – for the documentation of the power quality for end customers and inspection authorities or for the specific analysis of faults when power quality problems occur in the energy supply. 

Its successor, the UMG 512 power quality analyser, was launched into the market in the summer 2014 (image 3). It masters all the disciplines of its field, e.g., continuous monitoring of power quality, harmonics analysis in the event of network problems, inspection of the internal supply network as per EN 61000-4-7, EN 6100-4-15, EN 61000-4-30, etc. 

The UMG 512 is designed to record the large quantities of data that occur at its high sampling rate of 25,600 Hz or during a continuous true RMS measurement. To ensure that the quantity of measured values is retained even if the data network fails, the unit is equipped with a large on-board measurement data memory with a capacity of 256 MB. This also makes it possible to implement the unit using the PLC functions via a Jasic interface, i.e. local intelligence. Together along with the alarm management included in the GridVis® software, faults can frequently be detected and remedied in advance (image 4). The large, colour graphic display is intuitive to operate and simplifies access to the many functions and measuring points. The display can present measured values and results not only in numerical format but also as bar charts and line graphs. Current and voltage can be displayed in waveform. In addition, the GridVis®-Basic software package included in the scope of supply also simplifies evaluation and documentation.

Image 4: Online and historical data is displayed via the APP integrated UMG measuring device homepage, e.g. with the optional measured value monitor here
Image 4: Online and historical data is displayed via the APP integrated UMG measuring device homepage, e.g. with the optional measured value monitor here

The communication architecture is also adjusted to the wide range of possible applications and the large data quantities. The various Ethernet protocols ensure the cost-efficient remote monitoring of critical processes, for example. As a Modbus gateway, the UMG 512 can economically connect subordinate measurement devices without an Ethernet interface. It utilises as well the BACnet protocol for use in building communication. 

In contrast to its predecessor, the device offers a new, faster A/D converter with a higher sampling rate (25.6 kHz), a temperature input, two RCM measuring inputs as well as a separate 3-pin RS485 interface with inbuilt switchable termination resistor, etc. 

However the key improvement is certainly the enhanced PQ-core: True RMS half-wave effective values for voltage, current, effective power, reactive power and frequency are simultaneously available for phase/phase and phase/ground. The event and transient recording period was extended (image 5). Events can also be displayed in waveforms. The event and transient recording period was drastically increased to 11 minutes. A pre-trigger time of one minute and a post-trigger time of ten minutes are also recorded. Half-wave effective values for V, A, kW, kvar and Hz for star and delta are available at the same time.

It also features residual current monitoring

Image 5: Graphical representation of a transient
Image 5: Graphical representation of a transient

The UMG 512 has two RCM inputs (Residual Current Monitoring), which along with the alarm management from the GridVis® software provides additional security (image 6). When continuously monitoring the residual current of an electrical system, for example, a digital output is set or an e-mail is sent if a threshold value is exceeded. As a result, the system operator can quickly respond before a protective device is triggered. This is especially important in systems that must ensure very high availability (e.g. hospital, data center …). 

Outlook

Image 6: Message before shut-down, an objective of residual current monitoring
Image 6: Message before shut-down, an objective of residual current monitoring

The UMG 512 is a highly sophisticated device that provides added security in the trading relationships between customers and suppliers thanks to the certification according to IEC 61000-4-30. Janitza is naturally developing the total package further. For example, the new device homepage offers a traffic light function that clearly indicates whether the European standard EN 50160 is met. 

Janitza is also launching new APPs to enhance user comfort: You can use the “Measured Value Monitor” App to retrieve online and historically data directly from the device without any additional software. The App “EN 50160 analysis” uses the local intelligence of the device to analyse and prepares the data. This reduces the data quantities to be transmitted so that you can also obtain significant information about your system state over less efficient communication channels, for example, in the mobile communication sector. The user thus benefits from the hardware, with extensions and improvements over the entire service life of the device.

Image 7: Heatmap, i.e. colour (traffic light principle) illustration of how good or bad the power quality was at a particular measurement point in a calendar week. This principle guarantees a quick overview of the complete supply area
Image 7: Heatmap, i.e. colour (traffic light principle) illustration of how good or bad the power quality was at a particular measurement point in a calendar week. This principle guarantees a quick overview of the complete supply area

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