Insulator failures strain India’s transmission grid

The reliability of India’s vast and complex power transmission network, a critical artery for the nation’s economic growth, has come under intense scrutiny following a disturbing trend of failures in a seemingly inconspicuous but vital component: the insulator. These devices, which silently perform the dual task of electrically isolating high-voltage conductors from grounded steel towers and mechanically supporting them, are failing at an alarming rate, triggering forced outages and threatening grid stability. The issue, which came to a head with major supply disruptions to Mumbai in July 2025, has prompted a comprehensive national review. The resulting report, “Report of the Committee on Addressing Insulator Failures on Transmission Lines,” lays bare a systemic problem that demands an immediate and coordinated overhaul of specifications, manufacturing, and maintenance practices.

Trigger event and committee formation
Grid Controller of India Limited (Grid-India) flagged a surge in transmission outages in 2025, linking them to widespread polymer insulator failures. These failures led to the tripping of key 400 kV lines supplying the Mumbai Metropolitan Region on July 30 and 31, causing multiple outages and grid stress.

In response, the Central Electricity Authority (CEA) set up a Technical Committee on October 29, 2025, chaired by Member (Power System) V. K. Singh. The committee was tasked with analysing the root causes of these failures and recommending corrective measures.

Data trends and monsoon correlation
The committee’s findings, based on two detailed meetings held on December 19, 2025, and February 12, 2026, paint a picture of a systemic issue rather than a series of sporadic events. A deep dive into the 2025 failure data from various utilities reveals compelling and concerning trends. PGCIL reported 79 line outages due to insulator failure in their inter-state transmission system, with a staggering 82% occurring during the rainy season. MPPTCL documented 155 outages, noting that of the 176 cumulative composite insulator failures recorded between 2015 and 2025, nearly 39% occurred in the single year of 2025. MSETCL reported 241 incidents, and GETCO logged 274, with composite insulators accounting for 91% of their failures. A consistent and undeniable pattern emerged from every utility’s data: the monsoon period is the crucible in which insulator weaknesses are exposed, with failure rates correlating strongly with environmental stress from heavy rain, lightning, and pollution.

Performance gap between insulator types
The analysis identifies a clear divergence in the performance and failure mechanisms of the two primary insulator types. Porcelain and glass insulators, made from inorganic materials, offer a long and proven track record, often exceeding 30 to 40 years of service life with predictable, gradual degradation. Their primary vulnerability is their hydrophilic surface, which attracts water and necessitates frequent washing or the application of Room Temperature Vulcanizing (RTV) silicone coatings to perform reliably in polluted or coastal environments. When they fail, issues like de-capping, flashover, and shattering are common.

Composite or polymer insulators, consisting of a fiber-reinforced plastic (FRP) core with a hydrophobic silicone rubber housing, are a newer technology lauded for their light weight and superior pollution performance. However, their in-service performance has deviated sharply from a claimed lifespan of 25 years. The committee’s report and utility data indicate that failures are frequently occurring in early-to-mid-life stages, sometimes within two to five years of commissioning. The failure modes for composite insulators are more complex and insidious, including brittle fracture of the FRP core, tracking and erosion, loss of hydrophobicity, sheath damage, and a particularly concerning phenomenon called “flash-under,” where electrical discharge travels along the interface between the FRP core and the silicone housing. A critical finding from PGCIL’s root cause analysis was that many failed insulators were able to pass the standard tests that were in place at the time of manufacture, confirming that the previous technical specifications and testing protocols were insufficient.

Root causes of composite insulator failures
The committee’s investigation pinpointed a nexus of causes behind these premature composite insulator failures. Environmental stress is a primary aggressor, with contamination from fertiliser dust and pesticides combining with monsoon wetting to create a conductive layer that triggers leakage currents and dry-band arcing. Electric field stress concentration near the high-voltage end fittings, often due to improperly designed or absent grading and corona rings, was identified as another major factor. Incompatibility between the insulator and various hardware configurations across different utilities was also observed to exacerbate localized corona-induced erosion. Fundamentally, the committee noted a critical sensitivity to manufacturing quality, highlighting that issues such as marginal raw material quality, improper bonding at the rod-housing interface, and non-uniform molding can create latent defects that only manifest under the combined stress of high voltage and harsh weather.

Standardisation of failure reporting
In response to these detailed findings, the CEA committee has recommended a multifaceted and comprehensive set of actions that go far beyond simple specification tweaks. A cornerstone of the reform is the standardization of failure reporting. The report includes a standard format, detailed in Annexure-IX, which requires utilities to capture granular data on each incident, from GPS coordinates and pollution classification to the specific failure mode and batch traceability. This data will feed into a centralized database, enabling evidence-based decision-making, batch-level defect tracking, and the creation of an early warning system for systemic issues. The implementation timeline for this is set for June 2026.

Design upgrades for composite insulators
The most significant technical reforms target composite polymer insulators. The report mandates a series of design improvements, including increasing the minimum silicone rubber sheath thickness from 3 mm to 5 mm and specifying a minimum shed root thickness of 6 mm to improve resistance to tracking, erosion, and mechanical damage. It specifies that the glass transition temperature for the FRP rod must be increased to a minimum of 140 degrees centigrade to maintain mechanical strength under high-temperature service conditions. The silicone rubber itself must have a water absorption rate of less than 0.25% to prevent moisture uptake that degrades hydrophobicity. A critical design change is the requirement for an over-moulding design on end fittings to prevent moisture ingress at the most failure-prone interface between the metal and the polymer.

Stricter testing and validation requirements
To verify these improved designs, the committee has dramatically raised the bar on testing. Several new tests are to be mandated as part of the technical specification. A 5000-hour accelerated ageing test, as per IEC 62730, will be required to simulate long-term field conditions. The recovery of hydrophobicity test will now involve a 100-hour corona exposure to ensure the silicone rubber can genuinely recover its non-wetting properties after severe electrical stress. An ozone resistance test will be introduced to check for degradation from atmospheric ozone. Crucially, a 100% Dry Power Frequency Test with thermovision scanning is recommended during manufacturing to detect internal bonding failures and hotspots invisible to standard inspection. The report also highlights the indispensability of properly designed grading and corona rings, making them mandatory at specific voltage levels, with their design to be validated through project-specific Electric Field Modelling (EFM) to ensure hardware compatibility.

Enhancements for porcelain insulators
For the mature technology of porcelain insulators, the recommendations focus on enhancing performance in polluted environments through the use of factory-applied RTV silicone coatings and special shed profiles, including semiconducting glazed insulators. The report suggests that porcelain insulators with RTV coatings be considered on the same competitive platform as composite insulators, allowing each technology to compete on its merits. It also recommends mandating the Power Arc Test as per IEC 61467 for 400 kV lines and above to ensure the string can withstand fault currents without catastrophic shattering.

Lifecycle management and monitoring framework
Beyond design and testing, the report emphasizes the importance of lifecycle management, issuing model guidelines for storage, handling, and installation. It notes that improper practices, such as storing composite insulators without rodent protection or damaging the sheath during conductor stringing, can create defects that lead to premature failure. A condition-based monitoring framework is also prescribed, recommending pre-monsoon thermovision scanning and drone-based UV corona camera inspections for all composite insulator strings on 400 kV and 765 kV lines, followed by post-monsoon follow-ups on lines with a failure history.

Lifecycle cost approach and procurement reforms
Summing up the philosophy of the report, the committee stressed that decisions on insulator selection must be based on total lifecycle costs, factoring in not just the initial purchase price but also long-term operation, maintenance, and replacement expenses. The report also urges utilities to consider area-specific features like coastal and desert conditions when designing tenders. To ensure quality, it recommends that tenders mandate a proven field performance record of at least five years in tropical monsoon climates and include an extended performance warranty.

Implementation roadmap and expected impact
The way forward, as envisioned by the committee, is a holistic and standardized approach. By mandating centralized failure databases, strengthening technical specifications with globally benchmarked tests, enforcing quality assurance through detailed manufacturing quality plans, and institutionalizing condition-based maintenance, the aim is to close the gap between the claimed and actual service life of insulators. The successful implementation of these measures, with key deadlines set for December 2026, is expected to usher in a new era of resilience for India’s transmission network, ensuring that this critical backbone can withstand the nation’s diverse and punishing climatic conditions while reliably powering its growth.