GRID ISLANDING STUDY
High voltage post or High voltage tower
Grid Islanding Studies – Process industries are usually parallel their in-house generator with grid to increase the reliability of the power supply. Some of the advantages of paralleling in-house generator with the grid are to meet extra load requirement, to export extra generated power, to cater fluctuating load, to support momentary heavy load or motor starting. Though there are several advantages, one should keep in mind that the power system may collapse and may lead to plant shut down if proper measures are not taken against the grid disturbance.
The process of disconnecting the plant from grid in case of grid disturbance is called grid islanding scheme. Grid islanding will be generally followed by load shedding or generation shedding depending on the amount of load and generation in the islanded system. Grid islanding is also applicable for the micro grid systems.
Grid islanding study requires dynamic modelling of the system and transient stability simulations. The study results provide the data for finalizing optimum protection settings for grid islanding relay. The study provide recommendation on load shedding. The software’s used for grid islanding study is ETAP, DigSilent Powerfactory, PSCAD or PSS/E.
WHY GRID ISLANDING STUDY?
- To assess the performance of the plant during grid disturbance.
- To compute the protection settings for grid islanding relay for various elements such as under/over frequency, under/over voltage, rate of change of frequency df/dt(ROCOF), vector shift.
- To assess the requirement of load shedding after the grid islanding and to recommend the load shedding scheme (frequency based or intelligent load shedding).
HOW GRID ISLANDING STUDY? (METHODOLOGY)
- Collection of inputs (SLD, equipment parameters – Voltage kV rating, Power MVA rating, Impedance, System fault level, X/R ratio, dynamic parameters of equipment for transient stability simulations etc.)
- Modelling in study software.
- Carry out the transient stability simulations for various system configurations (normal and contingency configuration)
- Assess the performance of voltage and frequency variations.
- Provide recommendation on protection settings for grid islanding relay and load shedding relay.
- Submission of detailed report.
OUTCOMES OF GRID ISLANDING STUDY
- Detailed report explaining the input data, system configuration, observations and recommendations
- System performance during disturbance.
- Recommendation on protection settings of grid islanding relays.
- Recommendation on load shedding scheme.
REFERENCE STANDARDS
- IEEE Std 399 Recommended Practice for Industrial and Commercial Power Systems Analysis
- IEEE Standard 1110 Guide for Synchronous Generator Modeling Practices and Applications in Power System Stability Analyses
- IEEE Std 421 Recommended Practice for Excitation System Models for Power System Stability Studies