Annual inspections can extend the useful life of high-voltage equipment while ensuring the safe and reliable operation of the electrical grid. Standardized tests, such as those recommended by The Institute of Electrical and Electronics Engineers, can assess the health of high-voltage transformers located in substations while preventing service instability and outages.
The Importance of Periodic Maintenance and Testing
Initial quality checks completed in the factory ensure that the equipment meets performance requirements. With fast track power systems, tests are completed off-site during assembly. For conventional projects, tests are performed during the last stages of installation. These results provide a baseline that can measure changes in capacity and output.
One test is not enough to assess the condition of transformers. Multiple tests are required to check each component. This provides an accurate picture of the equipment’s overall health. Inspections can pinpoint problems before they cause outages. That way, transformers can be repaired or refurbished.
The Cost of Delaying Maintenance
Safety and reliability are impacted every time regular maintenance is delayed or canceled. Strategies that focus on short-term cost cutting typically involve larger long-term expenses. To avoid legal and financial challenges, high-voltage companies must develop and execute effective maintenance plans. Each part of substations benefit from maintenance, but it is especially important for transformers to be inspected and tested.
Substation and Transformer Tests
Advanced testing equipment delivers accurate results quickly, so there is minimal downtime. Testing windows can be coordinated between engineers and project managers to determine the ideal time for taking equipment off line. The following inspections and tests should be performed annually.
- The fluid inside an oil-filled power transformer must be tested to measure its dielectric strength. Extreme temperatures decrease the fluid’s insulation potential. Test samples should be taken from the bottom of the tank. The oil level should also be checked.
- The transformer turns ratio (TTR) is one of the most important tests. It measures the ratio between the high- and low-voltage sides of the transformer to ensure that the unit is increasing or decreasing the voltage as expected.
- Winding resistance tests detect insulation damage, which is a common cause of transformer failure. Winding resistance is measured between the bushings. On- and off-load tests can pinpoint a number of problems.
- Excitation current and dissipation factor tests measure the insulation in transformers and other equipment. Testing devices are designed to reduce electrical noise and magnetic interference caused by nearby equipment.
- A variety of portable test equipment is available for analyzing insulation resistance (IR) and dielectric frequency response (DFR). These tests measure moisture content, oil conductivity and tan/delta dissipation at high-interference sites.
- Sweep frequency response analysis (SFRA) is a newer test that detects internal faults to identify possible mechanical damage.
- Infrared thermography can be used to scan substations for leaks, excessive heat and trouble spots.
These tests are intended for routine checkups. If a problem is reported, additional tests can be performed to determine the cause. Different protocols are used during fabrication and maintenance. Each component should be visually inspected in the field too. Everything from the exterior finish to the surge arresters must be thoroughly examined. Here are a few of the items that should be checked during an inspection.
- Gaskets
- Tanks
- Gauges
- Control wires
- Connections
- Terminals
- Nameplates
Regular maintenance is essential for protecting individual transformers, local substations and the greater power grid. Equipment rentals and service contractors eliminate the need to purchase specialized testing equipment and to pay for annual certifications and calibration. Mobile testing vans can travel to high-voltage substations anywhere. If additional maintenance is required, it can be completed on-site as well. For more information about transformer maintenance and field testing, call Equisales Associates at 713-733-3999.