Transformer Protection System

Transformer Protection System

Now we will explain the components and systems of the protection section. First, we need to classify the emergency protection system:

Classification:

(1) Power Disconnection Device: Disconnects the faulty transformer from the power grid.

(2) Pressure Relief Device: Discharges oil and gases generated by the decomposition of oil-paper insulation caused by the accident.

(3) Fire Extinguishing Device: Extinguishes the fire after a transformer fire.

2. Composition

(1) Power Disconnection Device. The information feedback mechanism of the power disconnection device is relay protection, and the actuator is a circuit breaker. After the gas relay or differential protection operates, the circuit breaker is activated to disconnect the transformer from the power grid.

(2) Pressure Relief Device. In the past, the pressure relief device used a safety vent; now it uses a pressure relief valve. The safety vent uses glass as an explosion-proof membrane. When the oil pressure in the oil tank exceeds the pressure that the glass can withstand, the glass is broken and the oil is discharged. The pressure relief valve uses a spring to apply a certain pressure to the valve plate. When the oil pressure on the valve plate exceeds the rated pressure of the spring, the pressure relief valve opens and the oil is discharged. As the oil flow rate increases, the pressure on the valve plate decreases, and the valve plate opening degree decreases. Therefore, after the pressure relief valve actuates, the amount of oil discharged is small and cannot cause a rapid and significant decrease in the pressure inside the oil tank.

Each transformer is equipped with only one safety vent. The number of pressure relief valves installed is determined by the rated capacity of the transformer.

3. Fire Extinguishing Devices. The fire extinguishing devices used in transformers are as follows:

1) Water Spray Fire Extinguishing Device. The water spray fire extinguishing device consists of pipes, valves, nozzles, and fire alarm sensors installed around the transformer. After the sensor receives a fire signal, the water spray fire extinguishing device automatically (or manually) sprays.

2) Nitrogen-Fired Fire Extinguishing Device. The nitrogen-fired fire extinguishing device consists of a nitrogen cylinder, pipes, valves, detectors, and a control box. When the detector detects a fire, the detector melts, the contacts close, and a signal is emitted. The drain valve automatically opens, draining a certain amount of oil. Then, the valve connected to the oil tank connection pipe closes, creating space at the top of the tank. The nitrogen cylinder automatically opens, injecting nitrogen from the bottom of the tank. The nitrogen lowers the oil temperature at the top of the tank, covering the flames and extinguishing them.

3) Foam Fire Extinguishing System. This system consists of a large steel cylinder mounted on a cart. Fire-extinguishing foam is placed inside the cylinder, and in the event of a fire, it is sprayed onto the flames to extinguish them.