Section News

Watch Again | IEEE Power and Energy Webinar – Under Frequency Load Shedding and Islanding: Main Causes of Erratic Operations by Julie Zambrano, Power Systems Operations and Electrical Protections Specialist

This event was co-hosted by IEEE PES WIP UK&I Chapter, and IEEE PES Student Branch Chapters at:

  • University of Birmingham
  • University of Manchester
  • University of Sheffield
  • University College Dublin
  • Imperial College London
  • University of Strathclyde


Automatic under frequency load shedding and islanding, as with any other protection scheme, could fail leading to a blackout. In general, the failures are related to implementation and setting update issues, but frequency calculation algorithm and how the frequency is being measured also affect the scheme performance, resulting in partial or total loss of the system load.

Since the frequency is obtained from voltage, there are two aspects to consider: which voltage phase, or combination of it, is used as a reference for the calculation and where the relay is located, since local voltage is affected by transient phenomena that may occur in the system and each phase and busbar is not affected equally.

Depending on the manufacture of the relay, different responses can be obtained with the same settings.  During major events not just frequency but also voltage may vary, leading to power oscillations and disconnection of the corresponding load set.

About the Speaker

Julie Zambrano, electrical engineer with experience in the operation and simulation of electrical Power systems and protection systems. In 2008, she obtained a master’s degree in electrical engineering, and in 2015, she completed a Diploma in Protection Systems.

Julie spent nearly a decade between supporting the activities in the Control Centre, in Caracas, and working as protection engineer for the maintenance area.

Currently, Julie works as Protection Engineer, where she performs power flow, short circuit and coordination studies. At the end of 2022, Julie published her first book: Analysis of Failures in Power Systems.