Power Quality Monitoring

tChapter 7Project description – BankThe problem:In banks, insurance companies and other commercial buildings, increasing powerproblems with reference to harmonics, flickers, voltage peaks and similar effects haveoccurred in the past years. Network perturbations are often transported into the buildingfrom the medium voltage network.The reason for internal power problems is the large number of PCs and switched modepower supply units which are used. Due to the widely branched 5-conductor networks,so-called “stray” currents can occur in ground wires. These are caused by incorrect grounding.These particularly lead to problems in data networks because they proceed incables.Flickering can lead to discomfort, headaches and tiredness among the members of staff.These disturbances are certainly not welcome because working in these types ofbuildings is made more difficult and may even become impossible without safecommunication options. European norms have existed for several years for theassessment of network perturbations.EN50160 regulates the power quality which must be provided by the energy supplier.The EN61000-2-4 provides the opportunity to measure the power quality within abuilding.The task:The power quality must be checked in a large bank at the feeders in accordance withEN50160 and at the sub-distributions in accordance with EN61000-2-4. Furthermore,the reasons for frequent problems in the data cables had also to be identified. Theemployees in building services should have access to the data at all times. Intranet wasprovided as the communication medium.The solution:A total of 39 x UMG 511 were installed in the feeders and all important distributionsfor communication, such as in the server rooms etc. An important feature is the fourthcurrent and voltage input on the instrument. Due to the installation of the fourthcurrent transformer in the protective earth conductor, stray currents could be trackeddown. Potential differences due to incorrect grounding were identified using a separatemeasurement with the bridge between N and PE.The existing grounding errors could, therefore, be corrected. Obviously all of the datawith reference to the power quality and all current related data were stored in the 256MB memory of the UMG 511. The GridVis software could be used to read the data atany time. An Ethernet TCP/IP interface was available for this purpose.The reasons for the frequent loss of communication in the data network were found andimportant knowledge about the power quality was gained. The producers of harmonicscould, therefore, be tracked down. Materials such as electronic controls or server supplyunits, which were previously destroyed due to network perturbations, could be protectedwith suitable power filters.Furthermore, the monitoring of the power quality from the energy supplier was madepossible in accordance with EN50160. A pleasing side-effect is the control of energypurchases or the power utility meter.t225