, a professional manufacturer dedicated to power equipment R&D and production, has rich experience in the design, production and maintenance of oil-immersed transformers, especially in the fault diagnosis and handling of fully sealed oil-immersed distribution transformer. This article will detail the working principle, alarm causes and scientific handling methods of transformer gas protection, providing practical guidance for relevant practitioners.
I. Working Principle of Transformer Gas Protection
Gas protection uses a gas-sensitive relay (also called Buchholz relay) that responds to gas status to protect the transformer from all internal tank faults. These faults include: multi-phase short circuit inside the tank, inter-turn short circuit of windings, short circuit between windings and iron core or shell, iron core faults, internal bushing faults, internal winding breakage, insulation degradation, oil level drop or leakage, poor contact of tap changers, or poor welding of conductors, etc. integrates advanced gas protection technology into its fully sealed oil immersed distribution transformer, effectively improving the fault response speed and protection reliability of the equipment.
Inside the gas protection relay, there is a sealed float at the upper part and a metal baffle at the lower part, both equipped with sealed mercury contacts. Both the float and the baffle can rotate around their respective axes. The signal circuit is connected to the upper opening cup, and the trip circuit is connected to the lower baffle. There are two types of gas protection actions: 1. Light gas action: only sends a signal without tripping; 2. Heavy gas action: trips and sends a signal.
When the transformer is in normal operation, the gas relay is filled with oil. The float is immersed in the oil and in an upward position, with the mercury contacts open; the baffle hangs down due to its own weight, and its mercury contacts are also open.
When a minor fault occurs inside the transformer, gas is generated at a slow speed. On the way to the oil conservator, the gas first accumulates in the upper space of the gas relay, causing the oil level to drop. The float descends accordingly, closing the mercury contacts-that is, the signal circuit contacts of the upper opening cup in the gas relay close, turning on the delayed signal. This is the "light gas" protection signal action.
When a serious fault occurs inside the transformer, a large amount of gas is generated, causing an instantaneous sudden increase in pressure inside the tank. A strong oil flow is generated to impact towards the oil conservator. The oil flow impacts the baffle, which overcomes the resistance of the spring and drives the magnet to move towards the reed contact, closing the mercury contacts-that is, the trip circuit contacts of the lower baffle in the gas relay close, turning on the trip circuit and tripping the circuit breaker. This is the so-called "heavy gas" protection action. The heavy gas action should immediately cut off all power supplies connected to the transformer to avoid accident expansion and protect the transformer. This protection logic is also fully applied to the fully sealed oil immersed distribution transformer produced by VKE Transformer, ensuring the safe and stable operation of the equipment in various working conditions.
II. Causes of Transformer Gas Protection Action
1. Causes of Light Gas Protection Action
Minor internal faults of the transformer, such as inter-turn and inter-layer short circuits of the transformer, local overheating faults of the iron core, internal winding breakage, insulation degradation, and oil level drop.
Poor welding of transformer winding joints, which causes heating and generates a small amount of gas due to excessive contact resistance.
Sudden drop in ambient temperature or long-term oil leakage of the transformer body, resulting in the oil level being lower than the light gas float of the gas relay.
Air intrusion into the transformer due to improper sealing of the oil filtering, oil filling or cooling system.
Faults in the secondary signal circuit of the gas relay, including water ingress in the gas relay junction box, short circuit due to insulation damage of the signal cable, and short circuit of terminal block contacts.
2. Causes of Heavy Gas Protection Action
Serious internal faults of the transformer body, such as multi-phase short circuit of windings inside the tank, short circuit between windings and iron core or shell, iron core faults, and internal bushing faults.
Poor contact or breakage of the tap changer.
Transient short-circuit fault in the vicinity of the transformer.
III. Inspection and Handling Methods After Gas Protection Action
The action of gas protection will either send a light gas protection action signal (minor case) or trip the transformer switch through heavy gas protection action (major case), causing the transformer to stop running immediately and affecting the reliability of power supply. VKE Transformer reminds that scientific and standardized handling after gas alarm is crucial to reducing equipment damage and ensuring power supply recovery. The specific handling methods are as follows:
1. Inspection and Handling Methods for Light Gas Protection Signal Action
During the operation of the transformer, when the light gas protection action signal is sent, the substation operation personnel should first reset the sound signal, closely monitor the changes of transformer current, voltage and temperature, and immediately conduct an external inspection of the transformer. Whether there is gas accumulation in the gas relay after the gas protection signal action is the most basic principle to distinguish the cause of the signal action. Gas cannot be generated by the gas signal action caused by secondary circuit faults and oil level drop. Therefore, when there is no gas accumulation in the relay, the cause should be judged step by step.
First, inspect the transformer body and cooling system for oil leakage. If there is oil leakage, immediately report to the superior dispatching and competent leaders and take leakage plugging measures; if not, judge whether the oil level drops due to sudden ambient temperature drop. At this time, it is necessary to observe whether the oil level indicator of the transformer oil conservator is normal and whether the oil channel is blocked. If it is abnormal, take corresponding measures. If it is not caused by the above reasons, the possibility of secondary signal circuit fault is high, and the secondary circuit defects must be inspected and eliminated.
If no abnormal phenomenon is found after the external inspection, the gas in the transformer should be collected, and the nature of the gas should be verified by oil chemical personnel. If necessary, take an oil sample for gas chromatography analysis to judge the nature, development trend and severity of the fault. According to the analysis conclusion, take continuous monitoring operation or shutdown treatment. For the fully sealed oil immersed distribution transformer, VKE Transformer recommends that professional and technical personnel be arranged to conduct regular gas detection and oil quality analysis to prevent minor faults from developing into major hazards.
2. Inspection and Handling Methods for Heavy Gas Protection Action
If the operating transformer sends a heavy gas protection action trip signal, the possibility of internal faults of the transformer should be considered first. The handling of such transformers should be very cautious. At this time, immediately check the accident message on the background computer to understand the accident situation, record the protection action situation, accident time and the voltage and current fluctuation when the transformer trips, reset the background accident alarm sound, and then conduct an on-site external inspection of the faulty main transformer.
Check whether the switches on each side of the main transformer are in the open position, check whether the oil temperature, oil color and oil level are normal, whether there is gas in the gas relay, whether the oil level is normal, whether the pressure relief device is activated, and whether there is oil injection and smoke emission. Check whether the main transformer shell is deformed and whether the welding seam is cracked and oil injected. On the background computer and measurement and control screen, check whether the voltage of each level of bus PT is normal and monitor the operation status of the load on each side. If there is overloading, contact the dispatching in time to reduce the load, contact the dispatching to open the isolating switch of each side switch of the main transformer to form an obvious disconnection point to isolate the faulty main transformer, and contact the dispatching to apply for converting the faulty main transformer to body maintenance.
If the gas protection action is caused by internal faults of the main transformer, notify the oil chemical personnel to collect gas samples, oil samples from the relay and oil samples from the body for gas chromatography analysis respectively. If all the above inspections are normal, check whether the insulation of the DC system is grounded and whether there is any fault in the secondary circuit to judge whether the protection is misoperated or the circuit breaker is misoperated. If it is determined that the misoperation is caused by the secondary circuit, the heavy gas protection can be withdrawn under the condition that the differential overcurrent protection is put into operation, and the transformer can be commissioned with no load and closely monitored.
IV. Conclusion
The gas alarm of oil-immersed transformers is an important early warning signal for internal faults. Correctly understanding the working principle of gas protection, mastering the causes of alarm and scientific handling methods are the key to ensuring the safe and stable operation of transformers. As a professional power equipment manufacturer, high-quality fully sealed oil immersed distribution transformer and perfect after-sales service. We remind all users that regular maintenance and inspection of transformers, timely handling of gas alarm signals, and standardized operation can effectively extend the service life of transformers and avoid economic losses caused by faults. If you have any questions about transformer fault diagnosis and handling, you can contact VKE Transformer for professional technical support at any time.