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Harmonic analysis is carried out to identify the level of harmonic distortion on a network, that contains harmonic polluting sources, such as inverters and variable speed drives. The analysis is carried out to standard such as ENA G5.5, ENA G5.4, IEC 61000-3 and IEEE-519, and are used to determine individual levels of voltage and current harmonic distortion and the Total Harmonic Distortion (THD) on key busbars and identify any resonance points. Use and generation of harmonic impedance loci can sometimes be beneficial for these studies, but in other scenarios can lead to overly conservative results and unnecessary harmonic filters.
It is important to note that traditional ENA G5.4 and ENA G5.5 studies only assess the harmonics at the point of connection / common coupling, and it is often beneficial to extend the scope to consider the actual distortion levels on other key busbars within the system. Studies are usually carried out in DIgSILENT Powerfactory or ETAP using a simplified balanced loadflow method, but it is also possible to carry out unbalanced analysis, to consider harmonic cancellation and the behaviour in the positive negative and zero sequence networks. In some very advanced cases it is also possible to use EMT analysis to identify the true level of harmonics in the network.
Voltage disturbance studies cover a wide range of phenomena including, transformer energisation, battery storage power swings and ramps, motor starting, site trips and voltage flicker. Within the UK these are covered by the ENA P28 standard, whilst within Europe Where necessary these studies can be used to accurately size any pre-insertion resistors (PIRs) to reduce the magnitude of the volt dip for transformer energisation or specification of Soft Starters or a VSD for motors.
BESS units are of great interest during voltage disturbance studies, as they have dynamic behaviour and frequency power swings that can produce significant disturbance on the host network. It is therefore critical to correctly assess how the BESS will respond, to frequency disturbances, and if operating the BESS in voltage control mode is beneficial to the network.
Voltage unbalance studies are carried out routinely on LV networks that contain a large number of single phase loads, but are sometimes also necessary on HV systems as well. Some specific networks require large single phase loads such as rail traction supplies and large welding supplies, but also many renewables also contain a significant number of single phase loads that can cause an unbalance of the main generation system is inactive.
Contact: Craig McGlone
Phone: 01305 300 210
Aurora Power Consulting are a leading independent power systems consultancy. We provide specialist power systems analysis services using software such as DIgSILENT, ETAP, PSCAD, EMTP-ATP, CDEGS and XGSLab.
