At a glancePower quality is a critical parameter forthe smooth operation of all connectedloads and resources. It is often impos-sible to determine the causes of faultsafter the fact, as they frequently onlyoccur briefly, often only for fractions ofseconds. Continuous recording of thepower quality makes it easier to draw arelationship between an outage (e.g.the failure of a machine) and its cause.

Siemens PTI offers:

· Continuous monitoring and analy-sis of power quality

· Consulting services and recom-mendations for improving the grid

The Challenge:On one hand, industrial grids arethemselves a regular source of disturb-ances due to the increasing number ofpower converters. On the other, thegrowing distribution of electroniccomponents is rendering the connect-ed loads increasingly sensitive to alldisturbances in the power supply,which can range from brief voltagedrops to voltage components superim-posed on the fundamental-frequencywave.

In most cases, exact data on the dis-turbances are essential for the selec-tion and dimensioning of solutions toeliminate specific recurring sources ofinterference. Furthermore, detaileddata can help identify interferencesources outside of one's own area ofinfluence (e.g. at the utility or neigh-

boring companies) and in supportingwith having the responsible partiesimplement corresponding measures.

Our solutionMeasurements and analysesFirst, standard values are continuouslyrecorded, such as fundamental fre-quency currents and voltages, powerlevels and harmonics. These are savedwith an averaging time of a minute, forexample, and are used to provide arough overview of the electrical land-scape. In addition, triggers are set todetect abrupt changes in power qualityor transient events and to then recordthese in detail at a high sampling rate.

The combination of long-term record-ings with high-resolution snapshots ofpotentially problematic events thenyields an overall picture for the evalua-tion of power quality and for the rapidinvestigation of disturbances. One or

more highly sensitive points areequipped with measuring devices thatcontinuously record the data andtransfer them to the analyzer at regu-lar intervals.

The measured data are evaluated byexperts with many years experience inmeasurement, evaluation and resolu-tion of power quality issues. In a regu-lar short report, e.g. on a monthly ba-sis, the results of the continuousmeasurements are presented, potentialproblems are described and recom-mendations are made for further stepsto improve power quality if this provesnecessary.

Independently from this, in the eventof faults in operating equipment, ahotline can be called where a staffmember immediately examines thecorresponding data and evaluates thefault from the perspective of themeasurement results and powerquality.

Before the start of the measurements,an audit is performed in which the op-erator submits grid data to the analyz-er and explains the operational pro-cesses.

Continuous powerquality monitoring

siemens.com/power-technologies

Figure 1: Overview of interference phenomena

Over the course of the measurementsand in close cooperation with the gridoperator, relationships are derived suc-cessively between power quality andoperating processes. It is also useful ifthe grid operator maintains a log ofkey switching operations and changesin production processes or can at leastreconstruct such changes in retrospectfor a specific point in time.

Data Access – Different VariantsThere are various possibilities fordownloading the data:

· Customer provides measureddataOne variant is to connect themeasuring instruments to the op-erator's data network. The operatorthen downloads the data at regularintervals and sends them to thespecialists for analysis.

· External access to measured dataAs an alternative, the analyzer canalso be provided for external accessto the company's internal datanetwork so that they can thendownload the data themselves.

· LTE access to measured dataAccess to the measured data viathe mobile wireless network (LTE)is also possible, so that the cus-tomer's data network remainscompletely unaffected.

The optimum variant must be deter-mined based on local conditions andthe needs of the operator.

The data are treated as confidential bySiemens, are never transmitted to thirdparties and are only used for the con-tractually agreed purpose.

The costs vary depending on the num-ber of measuring points, the hardwareused and the agreed depth of service.Considering that outages in productionfacilities, for example, can quickly en-tail costs running into four or five fig-ures, continuous monitoring of powerquality pays for itself when only one ora few faults have been prevented byfast detection and elimination ofsources of disturbances.

Consulting services for powerquality issuesIf problems in power quality are de-tected and the course of events involv-ing the faults can be sufficiently recon-structed, the solution to the problem isoften only a step away.

Siemens PTI supports customers withits entire expertise in the selection of

suitable measures. In some individualcases, problems can be solved by sim-ple grid reconfigurations, for example,with absolutely no additional equip-ment or costs. In other cases, it will benecessary to replace possible disturb-ance-inducing equipment or to installfilter systems. If necessary, we canprovide support for this process up tothe design or up to the request forproposals for equipment, for example.

Example ApplicationsFailure of operating equipmentAt irregular intervals, systems, con-trols, electrical equipment or other op-erating equipment fail – the cause isuncertain. The specific failed unit isreplaced, but nobody knows when thenext failure will occur.

Figure 2: High-frequency oscillationsoften result in faults in electronic equipment(in this example: voltage in an industrial gridwith 100% power converter load – 400 V)

Voltage dropsAt irregular intervals, faults occur dueto brief voltage drops in the supplygrid, which can specifically cause vari-able speed drives to fail.

Figure 3: Voltage drops due to faults in thesupply grid often result in the failure of varia-ble speed drives (in this example: short inter-ruption after a fault in the high-voltage grid)

Damage to operating equipmentA resonance point in the grid imped-ance can result in continuous highharmonic levels that do not directlyresult in disturbances and are thereforenot detected. These result in prema-ture aging of all installed equipmentover a period of months, with a subse-quent elevated failure rate.

Figure 4: Large distortions in voltages and cur-rents are often caused by resonances in thegrid and are often not manifested until theconnected equipment is permanently dam-aged (in this example: voltage in an industrialgrid, 34.5 kV)

Inadequate power qualityDisturbances due to inadequate powerquality often occur only sporadicallyand cannot be reconstructed withpointwise measurements, as the causelies in a special combination of the gridconfiguration and/or of the operatingmode of individual operating equip-ment. Parallel simulation of the gridcan help in the detection of relation-ships of this type.

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Published bySiemens AG 2017

Energy Management DivisionFreyeslebenstrasse 191058 Erlangen, Germany

For more information, please contact:power-technologies.energy@siemens.com

AL=N, ECCN=EAR99Subject to changes and errors. The infor-mation given in this document only con-tains general descriptions and/or perfor-mance features which may not alwaysspecifically reflect those described, orwhich may undergo modification in thecourse of further development of theproducts. The requested performance fea-tures are binding only when they are ex-pressly agreed upon in the concluded con-tract.

Long-term monitoring of thepower quality makes it easier tolocalize interference phenomena.

Continuous power quality moni-toring helps to detect problemsat an early stage and to take cor-rective actions before greaterdamage occurs.

Detailed statistics over an ex-tended timeframe help as a tar-geted approach for the grid op-erator as well as in planning suit-able corrective measures.

Continuous monitoring of powerquality helps to identify thecauses for outages and to derivecorrective measures from this.