Infrared thermography represents an electronic method enabling the visualization of thermal energy. This capability has earned its recognition as one of the most versatile and efficient tools for condition monitoring available today. Through thermal imaging, maintenance engineers at substations can significantly enhance their ability to foresee equipment failure and strategize corrective actions proactively, thus mitigating the risks of costly shutdowns, equipment damage or personnel injuries.
Infrared Thermography (IR) involves acquiring and analyzing thermal data using non-contact thermal imaging devices.
The intensity of infrared radiation emitted by objects primarily depends on their temperature. IR thermography detects emitted radiation in the infrared range of the electromagnetic spectrum. This corresponds to wavelengths longer than the visible light portion of the spectrum, as shown in figure 1. Thermal imaging can therefore be utilized to detect defects in EHV Substations like overheated joints due to loose contact or corrosion at contacts, which may not be visible through eyes. An infrared camera generates a thermogram or infrared image, depicting the thermal radiation emitted by objects in the scene according to their temperatures.
Typically, the standard image is grayscale, with hotter objects appearing white and gradually transitioning through shades of gray until reaching black, which signifies the coolest temperature in the scene. Optionally, colorization can be applied, with yellows and reds typically representing hotter objects, while violet and blue hues denote cooler items.
Infrared Condition Monitoring
The passage of current through an electrical system generates a small amount of heat due to electrical resistance. The thermal energy produced by an electrical component is directly proportional to the square of the current passing through it, multiplied by the component’s resistance (known as I2R Loss). Heat losses increase with the current, unbalanced loads, or overloads. As an electrical component deteriorates, its resistance rises, leading to greater heat generation. Consequently, as the component’s temperature increases, its resistance further escalates.
Heat or thermal energy serves as one of the primary indicators of the condition of operating equipment. It is a natural byproduct of all types of work, whether electrical, mechanical, or chemical. Failure to control thermal energy can lead to problems in various types of equipment, including electrical, mechanical, or process-related systems.
Infrared condition monitoring is a technique that can detect impending failures by analyzing the thermal distribution and temperature variations on a component’s surface. Defects usually change the surface’s thermal profile due to alterations in the component’s heat generation and heat transfer properties.
Significance of Temperature
Temperature serves as one of the initial observable indicators of equipment condition. Heat, also known as thermal energy, is a natural byproduct of various types of work, including electrical, mechanical, or chemical processes, particularly in abnormal conditions. The thermal characteristics of electrical equipment installed in substations can provide valuable insights for diagnosing issues and forecasting equipment reliability.
Applications of Infrared Thermography Inspection to Sub- Station Equipments
Loose connections, poor contacts, unbalanced loads, or overloading can lead to overheating of electrical joints in substation equipment, creating localized hot spots that may disrupt system operations significantly. Therefore, it’s crucial to promptly identify these hot spots to prevent potential breakdowns in the system.
Effective planning is essential for successful electrical substation inspection. One straightforward method involves starting from the top and working down, or initiating the inspection from one end of a line and systematically scanning to the other end. To ensure thoroughness, begin by inspecting Power Transformers and all high-voltage structural equipment, such as Structure-Mounted Potential Transformers (PTs), Current Transformers (CTs), air break switches, bus connections, and substation line terminations.
Case Studies
Thermography inspection of 315 MVA ICT & 100 MVA Power Transformers
The thermal images of 315 MVA ICT and 100 MVA Power transformers are depicted in Fig.2 and Fig.3 respectively. In both transformers bushing clamp temperature was observed high i.e. 75°C and 115°C respectively, which clearly indicates loose bushing clamps. Immediately it was rectified by tightening of clamps after taking transformers shutdown.
Thermography Inspection of Generator Step up Transformer
The thermal image of GT transformer is depicted in Fig.4, where a substantial temperature rise of 160°C on the surface of the Isophase-to-Low-Side bushing was detected by an infrared thermal imaging camera.
The elevated temperature of 160°C on the bushing compartment’s surface indicates internal heat generation within the compartment. The likely cause of this heat was suspected to be a high resistance connection between the low side bushing and the isophase. Due to considerable heat required to elevate the surface temperature to 160°C, concerns arose regarding the potential for a catastrophic transformer failure. The customer was suggested to attend this problem immediately in concern with transformer manufacturer.
Thermography Inspection of CT, Circuit Breaker, Wave Trap and Isolator Contacts
Through thermographic inspection, localized hotspots resulting from loose joints, corrosion of metallic parts in components can be detected such as Current Transformers (CT) (Figure 5), Circuit Breakers (Figure 6), Wave Traps (Figure 7), Isolator Contacts (Figure 8). This enables to prevent any abnormalities in system operation by promptly taking corrective measures.
Electrical Predictive Maintenance Schedule
Predictive maintenance schedule can be planned based on the rise of temperature of the various elements of substation as per Table 1.
Core Studies and Findinds from IR Thermography
Infrared thermography is one of the most effective and cost-efficient non-destructive condition monitoring techniques available to utilities today. These surveys identify areas with abnormal temperature conditions, diagnose real problem areas, and determine their level of severity in electrical systems. Infrared Thermographic (IR) inspections are the most preventive measure that a business can implement.
Faults can be assessed in two ways, and it’s important to distinguish between the severity of a finding (of fault) and its impact. Severity measures the seriousness of a finding based on thermal temperature thresholds, while impact considers potential equipment damage costs (including related property damages) and the potential disruption or downtime the facility might experience. Both perspectives are essential for fully assessing each finding.
Benefits of Thermography
This technology is applied either independently or alongside other techniques and testing instruments. The advantages of assessing equipment health before conducting maintenance are significant compared to breakdowns or preventive maintenance measures. Some advantages of Infrared Condition Monitoring encompass failure detection, minimized downtime, decreased maintenance expenses, enhanced reliability, greater equipment and process availability, and improved performance. Additionally, thermography can furnish insights to instigate equipment enhancements, operational improvements, and process adjustments.
Conclusion
Infrared thermography serves as an invaluable predictive maintenance tool, aiding in the detection of issues within utility generating stations and their transmission and distribution systems. Its integration into predictive maintenance programs helps prevent emergency restorations, identifies additional issues for routine maintenance consideration, mitigates component deterioration to extend their life cycle, and validates the quality of work conducted while highlighting any subpar practices.
These advantages collectively lead to reduced utility maintenance expenses and inventory, heightened system reliability, increased utility and customer revenues, and enhanced customer retention. Moreover, infrared thermography facilitates the determination of equipment and facility maintenance priorities, bolsters operational safety, and contributes to a more robust bottom line.
Lakshmi Narain Giri is a Post Graduate in Electrical Engineering with specialization in Power Electronics and Drives. Currently he is working as an Engineering-Officer in CPRI Noida. He possesses eighteen years of experience in the fields of High Voltage Testing, EHV Substation Equipment Condition Monitoring and Third-Party Inspection of Power Transformers.
Gangeshwar Singh is a graduate Electrical Engineer. Currently he is working as an Engineering-Officer at the High Voltage Testing Laboratory in CPRI Noida. He has four years of experience in the field of Testing and Certification of High Voltage and Ultra-High Voltage equipment.
Satish Kumar is a graduate engineer. Currently he is working as an Engineering-Officer at High Voltage Testing Laboratory in CPRI Noida. He holds thirty years of experience in the field of Testing and Certification in high voltage.
Manoj Kumar Jaiswal is a Graduate in Electrical Engineering. Currently he is the Unit Head and Joint Director of CPRI Noida. He owns thirty years of experience in the fields of Testing, Certification and Consultancy in High Voltage, Ultra-High Voltage, Energy Meters, LED and Cables.
