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Dynamic power system studies generally refer to any time based study. In most cases they are carried out as an RMS simulation, but for more advanced cases they can be carried out as EMT simulations. In power system analysis dynamic studies is a general catchall name, and refer to a wide range of studies, this can include motor starting, load rejection, generation rejection, small signal stability, transient stability, black starting, control system tuning and general stability studies for G99 / Grid Code compliance.
Studies can be carried out using ETAP, DIgSILENT or PSCAD as required.
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.
Sub Synchronous Oscillation (SSO) studies have been a requirement for all large power systems since the 1970s, but have usually been carried out by the network TSO, using well established techniques like Eigenvalue analysis. However, with the increasing penetration of Inverter Based Renewables (IBR) on the network, new SSO modes have been increasingly identified for resonance stability and converter stability. NESO are specifically requiring SSO studies for all grid connected renewable energy plants to the UK mainland system.
SSO studies are now typically carried out using EMT analysis techniques on individual IBR generation through a series of network perturbations to identify any specific modes or resonance points. The results of theses studies need reviewing and discussing with the host TSO, and when resonance points identified the associated controllers may need to be re-tuned.
With the increasing presence of Inverter Based Renewables (IBR) on the system, modelling, analysis and tuning of synchronous machine controllers like AVR and Power System Stabiliser (PSS), is often seen a historical issue. The reality is however, that large synchronous machines are still a key part of the system, and the use of synchronous condensers are becoming increasing important to maintain overall grid stability.
Tuning activities can be carried out for all the synchronous machine controllers such as the Automatic Voltage Regulator (AVR), Stator Current Limiter (SCL), Over Excitation Limiter (OEL), Under Excitation Limiter (UEL) and Power System Stability (PSS).
Motor starting studies are a lot less common these days, as many large motors are VSD controlled. Large VSDs are not cheap however, and can produce significant harmonics, so many industries such as oil & gas, process, and water still use a significant amount of large DOL motors, that need assessing. It should also be noted that whilst a soft starter can reduce the impact of a starting a large motor, it does not remove it entirely, and if not set correctly, motors starting against a large torque can stall.
There are two types of motor starting study possible, static and dynamic. Static studies are a simple check of the maximum voltage dip that occurs during the motor start (based on system fault level and motor LRC), whilst dynamic motor starting studies consider the motor and load dynamic responses.
Contact: Steve Sommerville
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.
