79 Key Professional Knowledge Areas in Electrical Engineering （31-40）

By clyde March 6th, 2025 23 views

31.What is the function of a transformer's oil conservator?

The oil conservator serves as a reservoir to store and replenish oil when the volume of the transformer oil expands or contracts due to temperature changes. It ensures that the oil tank remains fully filled with oil. Additionally, by installing an oil conservator, the contact between the transformer and air is reduced, slowing down the degradation of the oil. A side-mounted oil level gauge on the conservator allows for monitoring of oil level changes.

32.Why does the core of a transformer need to be grounded?

During operation, the core and other components of the transformer are within the electric field surrounding the windings. If not grounded, the core and accessories will induce a certain voltage. When this induced voltage exceeds the breakdown voltage relative to ground, discharge may occur. Grounding the core prevents internal discharges in the transformer.

33.How does a transformer's purifier work?

In operation, the temperature difference between the upper and lower layers of oil in the transformer causes the oil to circulate through the purifier. Harmful substances in the oil, such as moisture, free carbon, and oxides, are absorbed by the silica gel inside the purifier as the oil circulates. This process purifies the oil, maintaining its good electrical and chemical properties and regenerating the transformer oil.

34.What is the cooling effect of forced oil-cooling systems with and without flow guidance in transformers?

In transformers equipped with non-guided forced oil-cooling systems, most of the oil flows back through the gaps between the tank wall and the windings, with only a small portion entering the windings and core. This results in poor cooling efficiency.
In contrast, in transformers with guided forced oil-cooling systems, the cooling oil flows effectively through the core and windings via flow-guiding baffles, improving the cooling effect and reducing winding temperature rise.

35.What is the function of a thermometer? What are the measurement methods?

A thermometer measures the temperature of the top layer of oil inside the tank, monitoring whether the power transformer is operating normally. Depending on the transformer capacity, thermometers can use one of three methods: mercury thermometers, signal thermometers, or resistance thermometers.

36.What is the function of the opening and closing buffers in high-voltage circuit breakers?

The opening buffer prevents damage to the circuit breaker components caused by the significant impact force generated when the spring releases energy during the opening process. The closing buffer prevents excessive impact during closing, which could damage the bushing.

37.What is "free trip" in a circuit breaker?

Free trip refers to the ability of a circuit breaker to reliably open at any moment during the closing process if the tripping circuit is activated by protective devices. Circuit breakers with free-trip functionality ensure that short-circuit faults during closing are quickly interrupted, preventing the expansion of accidents.

38.What are the good arc-quenching properties of SF6 gas?

SF6 gas has the following excellent arc-quenching properties:
(1) High arc-column conductivity, very low arc voltage, and low arc-column energy.
(2) Rapid recovery of dielectric strength after the zero-crossing of AC current, approximately 100 times faster than air, giving it an arc-quenching capability 100 times higher than air.
(3) High insulation strength of SF6 gas.

39.What are the features of vacuum circuit breakers?

Vacuum circuit breakers have characteristics such as small contact gap, short arcing time, and minimal contact wear when interrupting fault currents. They require less operating energy and act quickly. Additionally, they are compact, lightweight, require minimal maintenance, and offer fireproof, explosion-proof, and low-noise operation.

40.What does "synchronous" mean in synchronous condensers?

When a synchronous condenser operates, the rotating magnetic field of the stator and the rotor rotate in the same direction and at the same speed. This condition is referred to as "synchronous."

79 Key Professional Knowledge Areas in Electrical Engineering （21-30）

79 Key Professional Knowledge Areas in Electrical Engineering （41-50）