Power System Analysis is an essential part of any electrical design process, as it validates that the design is safe and will work as expected. This may seem obvious, but it is surprising how many companies overlook these studies and then find themselves having to undertake expensive remedial works on site, which could have been easily avoided at the design stage through proper validation.
Aurora are highly experienced in power system studies, and have undertaken a wide range complex studies for many large clients and on many complex plants. At Aurora we use a number of industry leading software packages including ETAP and DIgSILENT for main power system studies, and EMTP-ATP, EMTP-RV and PSCAD for more detailed electromagnetic studies.
Correct protection settings of relays are of vital importance to any electrical system, as it ensure that should a fault occur, only the faulted item of equipment is removed form service, and the healthy equipment is kept on line. If the protection study has not been coordinated correctly and there is insufficient grading margin, a simple LV fault can trip a whole HV substation. Aurora has experience of undertaking a wide range of protection grading studies from simple over current earth fault coordination studies for a Ring Main Unit, up to configuring complex differential protection schemes and investigating nuisance protection trips. We specialise in undertaking difficult studies, and using the ETAP or DIgSILENT software package we can simulate faults on any part of the network and confirm the exact operating sequence and times for the protective devices. Aurora can also help specify and set-up differential protection schemes for transformers, switchgear, cables etc. where appropriate. We also have AMTECH Protect HV for carrying out simple studies, when this approach is requested by a Client.
Within the UK, the new ENA G99 standard (and corresponding National Grid Code), stipulates a range of power system studies that must be carried out prior to the connection of generators to the UK electrical system. The level of studies required, depend on the generator rating, and connection voltage. At present there are four main categories – Type A Generators (<1MW) do not require any special analysis; Type B Generators (>1MW and <10MW) which require a Fault Ride Through (FRT) study, Limited Frequency Sensitive – Over (LFSM-O) study, and a basic reactive power flow study. Type C Generators (>10MW and <50MW), that require a full spread of studies including Reactive Power Flow, Reactive Power Stability, FRT, LFSM-O, LFSM-U and FSM-O. Type D Generators (>50MW and/or connected at 110kV and above), are more or less identical to Type C generators. Aurora are experienced in these complex studies, and can accurately simulate the dynamic response of the system to upstream faults. Studies are carried out using DIgSILENT Powerfactory.
Arc flash studies are becoming increasingly important, as they can help ensure that operational personnel are adequately protected, and provided with suitable PPE, for any switching duties. These studies are typically carried out to IEEE 1584 and look at the typical busbar clearances, working distance, fault levels and protection operating time to identify the total incident energy in Cal/cm2, to ensure it is within safe operating limits, and what level of PPE is required. Studies can be carried out using either ETAP or DIgSILENT as required.
As more and more power systems contain harmonic polluting sources, such as inverters and variable speed drives, the need for harmonic analysis has been dramatically increasing. Aurora has experience of a wide range of harmonic analysis techniques and are familiar with IEC 61000-3, IEEE-519 and ENA G5/4 (now G5/5) approaches; and can undertake both stage 2 and stage 3 assessments as part of ENA G5/4. As part of Aurora studies approach, we will examine the individual levels of harmonic distortion and the Total Harmonic Distortion (THD) on the system and key busbars, as well as identify any resonance points in the system. Where necessary Aurora can suggest suitable modifications to the power system design, or specify suitable mitigation measures such as harmonic filters and power factor correction equipment. Studies can be carried out using either ETAP or DIgSILENT as required.
Transformer inrush studies are becoming increasingly demanded by utility companies and are often of key importance in remote rural areas, where the power system is weak and energising a large transformer at the wrong time can cause a significant voltage sag on the network. Aurora can undertake these power system analysis studies by creating a detailed electromagnetic model using the PSCAD, EMTP-ATP or EMTP-RV software packages, which allow a full frequency domain analysis. Where necessary these studies can be used to accurately size any pre-insertion resistors (PIRs) to reduce the magnitude of the volt dip.
Aurora can undertake loadflow studies for a wide range of operational scenarios, to validate how the system performs during planned and unplanned outages and standby conditions. As part of the loadflow analysis we will examine equipment loading, power system losses and the voltage profile of the system to identify correct tap settings and ranges as well as identify the need for any reactive power compensation equipment to improve the power factor.
Aurora has experience of a wide range of short circuit study approaches, and are familiar with IEC 60909, IEC 61363, ENA G74 and the ANSI C37 standard. 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 and the issues relating to asymmetrical duty of circuit breakers due to high X/R ratios. Using either the ETAP or DigSilent package we can also calculate the asymmetrical, peak and DC component experienced by circuit breakers and identify increased fault duty any delayed current zeros.
The presence of any large motors on an electrical system is of key interest to a DNO, as their starting can cause voltage disturbance and flicker problems on the nearby electrical system. Aurora can undertake simple static motor starting studies to identify the initial voltage sag, but we can also carry out more complex dynamic motor starting evaluations which consider the motor and load behaviour and dynamic response of any generators on the system. Using the ETAP or DigSilent software packages, we can model DOL starts, star-delta starters, auto transformers, resistance starters, or electronic soft-starters.
Transient and Dynamic stability studies are most frequently associated with island power systems and embedded generators, and are used to measure voltage stability, frequency stability in relation to faults, loss of main supplies, generation and load acceptance and rejection. These studies are useful for identifying any the need for load shedding systems, fast differential protection schemes or other form of power system compensation. Studies can be carried out using either ETAP or DIgSILENT as required.