What is insulation coordination?
Insulation coordination selects and assesses equipment insulation withstand levels against the overvoltages relevant to an electrical system. The study considers the network, equipment characteristics and protective measures, such as surge arresters, using an agreed design basis.
The primary objective of insulation coordination is to maintain the reliability and safety of electrical power systems. By coordinating the insulation levels, the following benefits can be achieved:
1. Protection Against Overvoltage:
The assessment compares the relevant overvoltage cases with equipment withstand and protective-device characteristics. The included lightning, switching or other overvoltage cases should be stated in the study basis; the study does not guarantee that insulation failure can never occur.
2. Enhanced System Reliability:
Insulation failures can lead to equipment damage, system downtime, and potential blackouts. Through insulation coordination, the probability of insulation failures is reduced, resulting in improved system reliability and availability.
3. Extended Equipment Lifespan:
Adequate insulation coordination helps to prevent premature ageing and degradation of equipment due to electrical stress. By properly selecting insulation levels, the equipment’s lifespan can be extended, reducing the need for frequent replacements and lowering maintenance costs.
4. Improved Safety:
Insulation failure can create hazards, but insulation coordination should not be treated as a complete personnel-safety assessment. The applicable design, installation, earthing, protection and operating responsibilities must be addressed separately. IEC 60071-1 itself does not cover requirements for human safety.
5. Compliance with Standards and Regulations:
The applicable standards, editions, equipment requirements and local criteria must be agreed for the Project. The IEC 60071 series is relevant to insulation coordination within its defined scope; completing a study alone does not demonstrate compliance with every regulatory or equipment requirement.
What does an insulation coordination study involve?
1. Transient Overvoltage Analysis:
The study begins with an assessment of the potential transient overvoltage that can occur in the power system. These overvoltage can result from lightning strikes, switching operations, or other transient events. By understanding the types and magnitudes of these overvoltage, appropriate insulation levels can be determined.
2. Selection of Insulation Levels:
Based on the transient overvoltage analysis, suitable insulation levels are selected for each component of the power system. This includes transformers, circuit breakers, cables, surge arresters, and other equipment. The insulation levels are typically defined in terms of voltage ratings or impulse withstand levels.
3. Coordination of Insulation Levels:
Once the insulation levels are selected, the coordination between different equipment is assessed. The goal is to ensure that the insulation levels are appropriately coordinated to avoid insulation failures and flashovers. This involves considering the voltage withstand capabilities of the equipment in relation to the potential overvoltage they may experience.
4. Evaluation of Insulation Coordination Measures:
The study evaluates the effectiveness of insulation coordination measures such as surge arresters, voltage grading techniques, insulation materials, and insulation clearances. These measures help enhance the insulation performance and protect against overvoltage.
Insulation coordination studies are essential for maintaining the integrity, reliability, and safety of electrical power systems. By carefully selecting and coordinating insulation levels, the risk of insulation failures and associated consequences can be minimized, leading to improved system performance and reduced downtime.
What should the study report contain?
The agreed report should identify the network and equipment assessed, the input basis, overvoltage cases, equipment withstand characteristics, surge-protection assumptions, findings and recommendations. It should also state data gaps and exclusions. Model files, equipment selection or implementation support are included only where agreed in the scope.
See ETPL’s Insulation Coordination Study service for inputs, process and deliverables. Use the Power System Study Input Checklist to organise available network records.
