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Loadflow studies are steady state analysis calculations, that are used to validate how the system performs during normal, outages and standby conditions. As part of the loadflow analysis the system is analysed for active (MW) and reactive (MVAr) power flows, in order to identify the need for any shunt MVAr compensation equipment or power factor correction.
Studies are used to identify equipment loadings, the network voltage profile, transformer tap changer requirements, system losses, generator ratings and loadings, and for more complex DNO network outage and contingency cases are analysed in detail. Studies can be carried out in either DIgSILENT or ETAP.
Fault level and short-circuit studies (these two terms are often used interchangeably) are one of the most basic types of study carried out by Aurora. These studies are of critical importance, as they are used to select/check the suitability of switchgear and circuit breakers to meet the required fault duty. Studies can be carried out in accordance with IEC 60909, ENA G74 or IEEE C37.010, as required. As part of any short circuit study we will determine the fault levels and ensure that the selected equipment can safely interrupt any short circuit that may occur on the system.
Aurora also has a detailed knowledge of more complex short circuit scenarios considering asymmetrical duty of circuit breakers due to high X/R ratios for large complex networks with embedded synchronous machines or large super grid transformers. Studies are typically carried out in either DIgSILENT Powerfactory or ETAP.
For more complex fault studies, we can carry out assessments using RMS and EMT modelling techniques, and consider circuit breaker performance for networks with delayed current zeros using the IEC 62271-37-13 Generator Circuit Breaker standard.
Cable sizing studies can range from simple 6.6 kV or 11 kV circuits up to large 400 kV systems, and HVDC networks. Cable sizing, whilst simple conceptually can be become surprisingly complex, and incorrect assumptions about sheath currents and losses due to the use of cable ducts can have significant financial risks leading to undersized cables. In many cases the use of cyclic rating and emergency ratings can provide significant costs savings. For more complex installations, specific analysis can be carried out for HDD system, tunnel systems, special backfills and fireproof enclosures. It is also possible to carry out detail calculations of cable pulling tension and forces
Depending on the cable size, rating and route length, different bonding strategies can be considered to increase the overall cable rating. Bonding options can include solid bonding, single point bonding and full cross bonding and to determine the localized magnetic fields around the cables.
Cable analysis can be carried out using simple Excel tables for the most basic circuits up to full detailed FEM models, using Cableizer or ELEK.
Concept studies are wide ranging studies that are carried out at the earliest stages of a project, they are used to identify key equipment ratings and specification. They can either be taken as part of a validation exercise of a proposed design, or used as a basis for developing a network topology and configuration.
Well-developed concept studies seek to balance the requirements of the customer overall objectives balancing technical robustness with cost, and considering issues such as constructability and operability. Typical considerations would include determining the level of reliability needed in the system, optimising equipment ratings, confirming short circuit ratings, identify transformer impedances and tap changer requirements, and developing the design to a level to allow an accurate cost estimate to be achieved.
Network planning and reinforcement studies are a holistic approach to understanding the needs of an electrical network. They consider how a system should be designed and reinforced to meet existing and future needs, and can range from a mixture of simple load flow and short circuit studies up to a blend of complex reliability, availability, dynamic ratings and quasi dynamic studies seeking to balance technical requirements against cost.
The ultimate aim of network planning and reinforcement is to identify what technical investment is required, where it is required and when it is required.
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.
