Pressure Relief Valves for Transformer: The Ultimate Guide

The pressure relief valve is a type of pressure protection device for transformers. When a serious fault occurs inside the transformer, the oil decomposes and generates a large amount of gas. Since the transformer is essentially a sealed vessel, and the connecting pipe to the conservator has a relatively small diameter, relying solely on this pipe cannot effectively and rapidly reduce the pressure. This would cause a sharp rise in pressure inside the tank, which could lead to the rupture of the transformer tank. The pressure relief valve opens in a timely manner, discharging part of the transformer oil to reduce the pressure inside the tank. Once the pressure in the tank drops, the pressure relief valve automatically closes to maintain the tank's seal.

 

 

Our company produces pressure relief valves in a variety of models, calibers, and opening pressures. The product models range from the YSF4 series to the YSF16 series; the main oil injection calibers include Φ25mm, Φ50mm, Φ80mm, and Φ130mm; opening pressures include 15kPa, 25kPa, 35kPa, 55kPa, 70kPa, 85kPa, and 138kPa. In addition to conventional electrical alarm signals, the products can also be added with electrical alarm signal functions for computers, enabling dual-channel electrical signal output. They can also convert pressure value changes into 4~20mA analog output and can be equipped with the RS485 communication protocol.

 

Features of our pressure relief valves: built-in electrical switch, high safety and reliability, good three-proof performance (moisture-proof, mold-proof, salt-fog proof), and convenient wiring. We can also provide customized services for adaptation temperature, special environments, contact capacity, outlet methods, wiring methods, etc., according to customer requirements.

 

 

The pressure relief valve features a straightforward operating logic with fully passive pressure relief and automatic reset, operating under three distinct working states:

 

Normal Operation: Sealed pressure retention, blocking ingress of air and impurities

 

Overpressure Activation: Rapid pressure relief When faults such as short circuits or electric arcs occur inside the transformer, insulating oil vaporizes from heat exposure, causing a sharp surge in pressure within the tank. Once the pressure hits the valve's preset actuation value, high internal pressure overcomes spring tension to lift the valve disc. The valve opens instantly to expel high-pressure gas and insulating oil from the tank, swiftly bringing down internal tank pressure.

 

Pressure Dropback: Automatic reset After tank pressure falls to a safe threshold (below the reset pressure value), spring force regains control and pulls the valve disc shut automatically, restoring full tank sealing. No manual intervention is required, ensuring reliable tightness for subsequent transformer maintenance and trial operation.

Internal Structure of Pressure Relief Valve

Installation Location and Quantity

The valve body is generally installed on the tank cover or side wall, with the number configured according to the gradient of the total oil volume. During type selection, the oil level must also be taken into account to ensure the valve can open in time at the "deflagration front" under all operating conditions.

 

 

When an internal fault such as a short circuit, electric arc, or severe overheating occurs in the transformer, the insulating oil decomposes rapidly. Gases like hydrogen and methane expand dozens of times in volume in an instant, and the pressure inside the tank can exceed 0.1 MPa in just tens of milliseconds. Without effective pressure relief, the steel tank will rupture in a split second, followed by a catastrophic chain reaction including explosions, fires, and impacts that endanger the power grid and personnel safety.

 

The pressure relief valve is the last line of safety defense designed specifically for this "life-or-death moment", stopping an explosion within just 0.001 seconds.

 

Core Functions of Pressure Relief Valve

 

1.Prevent tank rupture and eliminate safety accidents

This is its primary function. Instant high pressure generated by internal transformer faults far exceeds the mechanical bearing capacity of the tank. The pressure relief valve opens rapidly to release pressure, preventing tank deformation, cracking, oil spraying and fire hazards, and safeguarding the safety of equipment and operation & maintenance personnel.

 

2.Protect the transformer main body and reduce fault losses

By quickly releasing abnormal high pressure, it prevents high pressure from damaging core components including transformer windings, iron cores and tank welds. It minimizes the scope of fault damage and cuts equipment maintenance costs and repair complexity.

 

3.Coordinate with oil pressure surge protection to build dual protection

It perfectly complements the oil pressure surge protection mentioned earlier: the oil pressure surge protection actively trips circuit breakers to cut off fault sources and curb pressure rise at the source; the pressure relief valve passively releases pressure to handle instantaneous high pressure. Acting as primary and secondary measures (one active, one passive), they form a complete pressure safety protection system for transformers.

 

4.Sealing protection to maintain insulating oil performance

It provides tight sealing during normal operation, isolating air and moisture from entering the transformer tank. This stops insulating oil from moisture absorption and oxidative deterioration, preserves the insulating properties of oil, and extends the service life of the transformer.

 

 

• During daily patrols, inspect the valve exterior for oil seepage, oil leakage, damage and rust;
• Verify the signal device functions properly, check for false alarms and unreset action signals;
• Inspect that valve mounting bolts and connecting components are tightly fastened without loosening or displacement;
• Calibrate the valve actuation pressure value regularly to guarantee sensitive and reliable pressure relief and reset performance.

 

 

Flange Base / Mounting Flange

Function: Provides fixed connection, withstands pressure, and achieves a sealed interface with the transformer tank.

 

Diaphragm / Pressure Relief Disc Assembly

Function: The core pressure-relief actuation element, which is the key component determining the opening pressure.

 

Spring Mechanism, disc-type only

Function: Provides preload force, sets the opening pressure, and enables automatic reset.

 

Sealing Gasket / O-Ring

Function: Prevents transformer oil leakage and ingress of external moisture, ensuring the integrity of the tank seal.

 

Protective Cover / Deflector

Function: Protects against external mechanical damage, directs the oil-gas jet, and prevents secondary accidents.

 

Alarm Contact / Microswitch

Function: Outputs an electrical signal when the pressure relief valve operates to trigger background alarm.

 

 

 

 

Model description

 

Description: D- means with directional injection, K- means with electrical signal, SK (or KK) - means with dual electrical signal, J- means with mechanical signal, TH- means for hot and humid zone area, TA- means for dry tropical zone, T- means for dry and hot and humid zone area, B- means with blocking device.

 

 

Installation position: on the tank cover, on the lift seat or on the upper side wall of the tank;

 

Environmental requirements: -30℃ ~ 50℃; Working environment requirements: -30℃ ~ +115℃.

 

YSF Series pressure relief valves with diameters of 25mm and 50mm

 

YSF Series pressure relief valve with a diameter of 50mm

 

YSF Series pressure relief valves with diameters of 80mm and 130mm

 

 

YSF Series pressure relief valves with diameters of 80mm and 130mm

 

YSF Series directional injection pressure relief valve with a diameter of 50mm

YSF Series directional injection pressure relief valve with diameters of 80mm and 130mm

 

 

YSF Series directional injection pressure relief valve with a diameter of 130mm

 

YSF Series directional injection pressure relief valve with a diameter of 130mm

 

 

Ready to specify the right pressure relief valve for your transformer project?

 

Contact our engineering team today for a personalized consultation, free technical datasheet, and competitive quotation. Whether you need standard catalog models or fully customized OEM solutions, GNEE is your trusted partner for transformer safety components that perform when it matters most. 

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