Functions and Selection of Transformer Pressure Relief Valves: A Detailed Guide to the YSF Series Safety Protection System
Date: June 11, 2026, 02:12:02
- pressure relief valveFeatures: Pressure relief valves are essential safety devices for oil-filled transformers and non-sealed electrical equipment. When a fault inside the transformer causes the tank pressure to rise abnormally, the pressure relief valve automatically opens to rapidly release the pressure, preventing the tank from deforming, cracking, or even exploding. Once the pressure drops to a safe level, the valve automatically closes and remains sealed to prevent external air and moisture from entering.
- Scope of Application: Not limited to transformers—pressure relief valves are also suitable for various types of oil-filled electrical equipment, including prefabricated substations, hermetically sealed transformers, high-voltage switchgear, power capacitors, reactors, and on-load tap changers.
- Key Selection Parameters: Nominal diameter (determines the relief rate), opening pressure (determined by the equipment's design pressure), installation method (flange connection size), and whether it features directional oil injection
1. Operating Principles and Structural Features of Pressure Relief Valves
At the heart of a pressure relief valve is a valve disc preloaded by a spring. During normal operation, the valve disc is held tightly against the seat by the spring force, maintaining a seal. When the internal pressure of the equipment rises above the opening pressure—which corresponds to the product of the spring’s preload and the valve disc’s area—the valve disc is pushed open, and the internal pressure is rapidly released through the valve orifice. When the pressure drops below the spring’s return force, the valve disc automatically returns to the seat and re-establishes the seal.
A key feature of the YSF series pressure relief valves is their built-in electrical switch design—the signal switch is housed inside the valve body, which not only protects the switch from external environmental factors but also ensures accurate electrical signal output when the valve operates. With excellent protection against dust, water, and corrosion, and convenient wiring, these valves are suitable for outdoor substation environments.
The directional oil-injection type features a deflector at the valve outlet that controls the direction of the oil jet when the valve is opened, preventing high-temperature oil from being sprayed toward personnel or nearby equipment, thereby enhancing safety.
2. Comparison and Selection of Models with Different Bore Sizes
| Nominal Size | Pressure relief capacity | Compatible Devices | Application Scenarios |
|---|---|---|---|
| φ25 mm, φ50 mm | smaller | Small distribution transformers, prefabricated substations | The equipment has a low oil level, so there is limited room for pressure to rise. |
| 80 mm, 130 mm | larger | Large main transformers and reactors | The equipment contains a large volume of oil, and in the event of a malfunction, it produces a large amount of gas, requiring rapid pressure relief through a large-diameter valve. |
When selecting a model, a larger diameter generally provides greater pressure relief capacity; however, compatibility with the equipment’s flange connections must also be considered. Large transformers are typically equipped with large-diameter pressure relief valves, or even multiple valves installed in parallel, to ensure timely pressure relief even under the most severe fault conditions.
3. andGas RelayDivision of Responsibilities for Protection
Both pressure relief valves and gas relays are safety protection devices for oil-immersed transformers, but they differ in the objects they protect and their operating logic: Gas relays detect gases and oil flow generated by internal transformer faults—in the event of a minor fault, gas accumulation triggers a light gas alarm, while in the event of a severe fault, oil surges trigger a heavy gas trip. Pressure relief valves, on the other hand, respond directly to increases in internal tank pressure—they open to relieve pressure when the pressure exceeds the set value, serving as the final line of defense against tank explosions.
The relationship between the two can be understood as follows: gas relays provide protection based on chemical and fluid signals indicating a fault, while pressure relief valves provide protection based on the physical consequences of a fault (increased pressure). In a large transformer, both are typically installed together, each performing its own specific function.
4. Installation and maintenance
4.1 Installation Location— The pressure relief valve is installed on the top of the transformer tank; the flange mounting surface must be kept level to ensure that the valve disc is subjected to uniform force. The deflector of a directional spray type must be oriented toward a safe direction (away from inspection walkways and adjacent equipment).
4.2 Signal Wiring——The internal signal switch outputs an electrical signal when the valve operates, which is connected to the transformer protection circuit or the monitoring system. After wiring is complete, a test operation should be performed to verify that the signal circuit is functioning properly.
4.3 Regular Inspections—It is recommended to inspect the valve seat seal annually to ensure it is intact, check for any signs of oil leakage, and verify that the signal switch contacts are functioning properly. Since pressure relief valves are normally closed and remain inactive for long periods, the rubber seals are prone to deterioration, which can lead to poor sealing performance.
5. Frequently Asked Questions FAQ
5.1 Q: Does the pressure relief valve reset automatically after it activates?
A: Yes. In the YSF series pressure relief valves, when the tank pressure drops below the spring reset value, the valve disc automatically returns to its seat and re-seals; manual reset is not required. However, after the relief valve has actuated, the cause of the pressure increase should be investigated, and operation should not resume until the fault has been confirmed to be resolved.
5.2 Q: How should I handle oil leakage from a valve?
A: Oil leakage is usually caused by aging rubber seals or foreign objects between the valve disc and seat, resulting in an improper seal. Minor oil leakage should be documented and included in the maintenance schedule; severe oil leakage requires immediate replacement of the seals or the entire valve.
5.3 Q: What is the difference between a pressure relief valve and a burst disc?
Answer: A burst disc is a single-use safety device—it must be replaced after a burst. A pressure relief valve, on the other hand, can operate repeatedly and resets automatically. Modern oil-immersed transformers generally use pressure relief valves instead of burst discs.
5.4 Q: How many pressure relief valves are required for a transformer?
A: It depends on the transformer's oil capacity and design. Small transformers typically have one, while large transformers may have two or more installed in parallel. The specific number should be determined by the transformer's design drawings.
Disclaimer: The content of this article is for technical exchanges and reference only, and does not constitute any form of procurement commitment or contract offer. Product technical parameters, configuration programs and prices are subject to the actual signed contracts and technical agreements.
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