What is an oil surge relay?
An Oil Surge Relay (OSR) is an essential auxiliary device used in oil-immersed transformers to protect against potential damage during operational failures. Positioned strategically between the on-load tap changer (OLTC) tank and its conservator, the OSR ensures that any surge in oil pressure resulting from internal arcing is quickly managed. When the rate of pressure crosses a predetermined value, the relay operates to activate alarm and trip contacts, effectively safeguarding the transformer.
The OSR’s design prevents oil in the OLTC and main transformer chambers from getting mixed together, maintaining operational integrity. In extreme scenarios, such as heavy faults, the relay initiates the tripping of both HT and LT breakers, isolating the transformer to minimize damage. Proper mounting and arrangement of the OSR ensure seamless function and limit system risks, making it indispensable equipment for reliable transformer performance.
Importance of Oil Surge Relays
Oil Surge Relays (OSRs) play a critical role in ensuring the reliability of a transformer by acting as the first line of defense against sudden changes in oil flow or pressure. These devices help promptly address potential problems, like spikes in pressure, that could lead to catastrophic failures if left unchecked.
A well-maintained OSR can enhance the lifespan of the transformer by providing early indications of issues in key components such as the OLTC (On Load Tap Changer). By raising alarms and allowing operators to investigate the root cause, OSRs help reduce the risk of failures and ensure overall reliability. Their role in protecting against excessive wear and tear on the system contributes significantly to reducing maintenance efforts and extending the equipment’s service life.
Role of OSR During Tripping
When an OSR relay is triggered, it ensures the safety of the transformer by addressing issues caused by a sudden change in oil conditions. Over time, the properties of oil in the OLTC tank can become contaminated, especially after repeated tripping events. This contamination alters critical parameters of the oil, which must be tested thoroughly to assess its performance. If abnormalities are observed, actions such as filtration or complete replacement of the oil may be needed to restore optimal functioning.
My own experience highlights how regular testing and monitoring of oil properties can prevent unexpected failures. Once, we noticed significant degradation in oil after several relay operations, and timely intervention saved the system from major damage. The maintenance process includes ensuring the tank is clean and that contamination is minimized to preserve the transformer’s reliability and efficiency.
The transformer oil needs to undergo the following tests.
Testing dielectric strength with BDV
The BDV test is an important method to check the dielectric strength of transformer oil, ensuring it is free from impurities like water that can weaken its insulating properties. Conducted on-site using a kit, this test offers a quick way to assess the purity of the oil. If the strength is reduced, a breakdown in the insulation may occur, leading to potential failures. Regular testing helps maintain the performance and reliability of the transformer, ensuring its voltage-handling capabilities remain intact.
PPM Test
The PPM test is used to determine the moisture content in the transformer oil, as excessive moisture reduces the dielectric strength and increases the chances of a flashover. By analyzing the percentage of water present, this test ensures the oil’s insulating properties remain intact. Regular testing helps in knowing the results early and preventing potential damage when such issues occur.
DGA Test
The DGA test is a crucial method to identify the levels of various dissolved gases in transformer oil. When thermal or electrical stresses occur in a transformer, they produce hydrocarbon gases like methane, ethane, ethylene, acetylene, and propane, as well as hydrogen, carbon monoxide, and carbon dioxide. The concentration of these dissolved gases is measured in ppm and can be cross-checked with the IS standard for precise analysis. This process helps detect abnormalities and ensures that the transformer operates safely and efficiently.
Monitoring Oil Levels
Properly monitored oil levels are crucial for preventing a breakdown of the system’s insulation, which occurs when the level drops too low. The oil plays a vital role in maintaining the system’s performance, and ensuring it never gets below the required threshold is a task that must be prioritized.
Silica Gel Dehydrating Breather
The silica gel inside the breather plays a key role in keeping the oil conservator safe by drying the air that is drawn in when there’s a drop in load or temperature, causing the oil to contract. This gel can absorb moisture up to 20% of its weight. As it becomes saturated, its color changes from blue to pale pink, signaling it needs to be replaced. This simple yet effective design ensures the moisture in the air doesn’t affect the system’s performance.
Single Float in Oil Surge Relay
The solitary float in an oil surge relay is an essential apparatus engineered to identify irregular oil displacement in transformers. This mechanical arrangement features a buoyant element that remains stable under normal operation but reacts to increases in oil flow caused by faults like short circuits or insulation issues.
When a surge occurs, the float shifts its position, triggers a switch, and sends a signal to the protection system. This action allows the system to initiate protective measures, such as disconnecting the transformer from the power supply to prevent further damage. The smooth and reliable functioning of this protective relay is essential for avoiding critical faults and maintaining the safety of the transformer.
Difference Between Buchholz Relay and Oil Surge Relay (OSR)
The Buchholz relay and the Oil Surge Relay (OSR) serve distinct purposes in transformer protection. While the Buchholz relay is actuated by gas and primarily detects internal faults through the formation and accumulation of gases, the OSR is actuated by excessive oil surges caused by a malfunction in the On-Load Tap Changer (OLTC) chamber.
The Buchholz relay is mounted on the connecting pipe between the transformer and the conservator tank, while the OSR is installed in the pipe linking the OLTC head and the oil conservator. Buchholz reacts to low oil levels and falls due to faults, whereas the OSR triggers when the flow rate exceeds a preset value, ensuring timely protection for reactors and transformers.
