Ferro Resonance Study

Ferro resonance or nonlinear resonance is a type of resonance in electric circuits which occurs when a circuit having a nonlinear inductance is fed from a source that has series capacitance, and the circuit is subjected to a disturbance such as opening of a switch. It can cause severe overvoltage and overcurrent in an electrical power system and can pose a risk to transmission and distribution equipment and to operational personnel. It can also damage the equipment and components, such as the transformer, the cable, the switch, the surge arrester, etc. Ferro resonance can also affect the power quality and stability of the system, causing harmonics, core saturation, waveform distortions, flickers, voltage fluctuations and cause transformer temperature rise, noise and vibration.

A ferro resonance study is performed to understand and mitigate the risks associated with ferro resonance in electrical power systems. Ferro resonance is a complicated electrical phenomenon which has long been a problem for power utilities.

Why perform Ferro Resonance Study?

Besides proving mitigation techniques, researchers have also concentrated their efforts to predict or confirm ferro resonance occurrence in susceptible networks. The Ferro Resonance Study is performed to provide recommendations to facility owners, EEORs and PEs on how to protect the equipment/personnel, perfect system performance and ensure system reliability in compliance with the Codes and Standards as mentioned below.

• IEEE Standard C57.137-IEEE Guide for Acceptance and Maintenance of Insulating Oil in Equipment - Provides guidelines for the acceptance and maintenance of insulating oil in transformers, which is relevant to ferro resonance studies involving transformers.
• IEEE Standard C57.12.90-IEEE Standard Test Code for Liquid Immersed Distribution, Power, and Regulating Transformers - Defines standard procedures for conducting tests and liquid immersed transformers, including those that might be involved in ferro resonance scenarios.
• ANSI C84.1-Electric Power Systems and Equipment-Voltage Ratings (60 Hz) - Establishes standard voltage ratings and tolerances for systems and equipment in power distribution, which may affect ferro resonance considerations.
• IEEE Standard 141-IEEE Recommended Practice for Electric Power Distribution for Industrial Plants (Red Book) - Supplying guidelines for the design and operation of electric power distribution systems, including recommendations for avoiding and mitigating ferro resonance.
• IEEE Standard 242-IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (Buff Book) - Offers recommendations for protection and coordination of power systems, including guidance on protective devices that can help mitigate ferro resonance.

Ferro Resonance Results and Identifying Issues

The method for performing a ferro resonance study can vary depending on the type, size, and complexity of the power system, as well as the codes and standards that apply to the system. Following are the steps to perform ferro resonance study:

• Define System Parameters and Select Test Conditions such as system configuration, voltage levels, equipment ratings, design criteria, nonlinear inductance, the series capacitance, the switching operation.
• Model the system using electrical drawings, simulate events and analyze the results. Figure out the risk and impact of ferro resonance on the power system, such as the overvoltage and overcurrent levels, the equipment damage and failure, the power quality and stability issues.
• Develop Mitigative Strategies - Propose and implement the strategies for preventing or reducing ferro resonance in the power system, such as the selection and installation of appropriate equipment and devices, such as surge arresters, reactors, filters, the modification and optimization of the system configuration and parameters, such as the cable length, the transformer tap, the grounding resistance, etc., the application and coordination of protection and control schemes, such as the differential protection, the overvoltage protection, the reclosing scheme, etc.

Qualified PEs and EITs/Professional Engineers:

Providing engineering recommendations about the causes of exceptions, the integrity of the system, or recommendations for corrective actions requires knowledge and skills beyond those of power systems engineering. Our team of certified professional engineers have the expertise to investigate optimal/abnormal scenarios and provide innovative engineering solutions for your power system. We collaborate closely with our clients to accurately study, model, simulate, validate, and recommend solutions to optimize your power system.

AllumiaX, LLC provides independent consulting and third-party engineering support by presenting comprehensive deliverable reports backed by the latest industry standards and best practices. Analysis is performed based on industry-leading software: SKM, ETAP and Easy Power and proven results based on accurate modelling and calculations. The reports are expected to include the following deliverables:

• A comprehensive and accurate electrical model of the facility.
• A background and context of the study, the system description, the design criteria, codes, and standards.
• Overvoltage and overcurrent waveforms, the frequency spectrum, the mode of ferro resonance sources their characteristics and severity.
• Drawings showing the design and installation of the equipment and devices for ferro resonance prevention or mitigation.
• Performance and compliance reports of the equipment and devices for the ferro resonance prevention or mitigation, such as the surge arresters, reactors, filters.
• Test reports and certificates can be obtained by conducting field tests, such as the impulse tests, the switching tests, the noise test.

What is the customer/client responsible for?

At AllumiaX, we evaluate the potential risks and severity in case of overvoltage and undervoltage conditions and recommend the best-in-the-market practices to our customers for a safe, regulated, dependable, and well-designed power system. A customer who chooses not to perform the ferro resonance study misses out on a huge value proposition.

Customers should help develop a list of equipment to be evaluated via onsite data collection for the existing facility or by providing updated one-line, BOMs and cutsheets for all equipment in the facility.

What to Expect?

Ferro Resonance Study will be in 100% compliance with the latest IEEE and NEC standards. Study outcomes and recommendations are expected to improve the following areas in your facility:

• Protect the equipment and personnel
• Ensure System Reliability
• Avoid Insulation Damage
• Improve System Safety
• Optimize System Performance
• Compliance with Standards
• Prevent Operational Issues
• Design Validation