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

By clyde March 7th, 2025 19 views

41.Why can't ordinary fuses replace blown primary fuses in voltage transformers?

Using a 10kV voltage transformer as an example, the rated current of the primary fuse is 0.5A. Fuses filled with quartz sand have better arc-quenching performance and higher breaking capacity, while also limiting short-circuit currents. Ordinary fuses cannot meet the required breaking capacity.

42.Why must the secondary sides of voltage transformers and current transformers be grounded?

The secondary-side grounding of voltage transformers and current transformers is for protective grounding. If insulation between the primary and secondary sides fails, high voltage from the primary side could transfer to the secondary side, posing a threat to personnel and equipment safety. Therefore, the secondary side must be grounded.

43.What does the nameplate FKL-10-2×750-6 represent?

FKL-10-2×750-6 represents the nameplate of an aluminum cable split reactor with a rated reactance of 6%, a rated voltage of 10kV, and two branches with a rated current of 750A each.

44.What are the functions of shunt reactors and series reactors?

Shunt reactors: Compensate for the capacitive charging current of lines, limit system voltage rise, and suppress operational overvoltages, ensuring reliable operation of the line.
Series reactors: Restrict short-circuit currents and maintain a higher residual voltage on the busbar. Series reactors in capacitor banks can suppress higher harmonics and reduce reactance.

45.What are the characteristics of single-bus sectionalized wiring?

Single-bus sectionalized wiring reduces the impact range of bus faults and improves power supply reliability. When one section of the bus has a fault, the sectionalizing circuit breaker automatically trips under the coordination of relay protection, isolating the faulty section while maintaining normal power supply to the non-faulty bus. For critical users, power can be supplied from different sections to ensure uninterrupted power supply.

46.What are the disadvantages of double-bus wiring?

Double-bus wiring has the following disadvantages:
(1) Complex wiring and operations, increasing the risk of misoperation during switching operations.
(2) A large number of bus isolating switches and a more complex structure for the distribution device, leading to poorer economic efficiency.

47.What is the function of a fault recorder?

A fault recorder automatically and accurately records changes in various electrical quantities before and after a fault occurs in the power system. Analyzing and comparing these electrical quantities helps in accident analysis, determining whether protection devices have operated correctly, and enhancing the safe operation level of the power system.

48.What are the main components of an oil-immersed transformer?

The main components of a transformer include: core, windings, tank, conservator, breather, explosion-proof vent, radiator, insulating bushings, tap changer, gas relay, thermometer, and purifier.

49.What is the compensation degree of an arc suppression coil? What is residual current?

Compensation degree: The ratio of the difference between the inductive current and the capacitive current of the arc suppression coil to the grid's capacitive current.
Residual current: The remaining current flowing through the ground point after the inductive current of the arc suppression coil compensates for the capacitive current.

50.Does the arc suppression coil carry voltage during normal operation when the neutral point is grounded through it?

During normal operation, due to the imbalance of three-phase-to-ground capacitances in the lines, there exists a certain voltage between the network neutral point and ground. The magnitude of this voltage is directly related to the degree of capacitance imbalance. Under normal conditions, the voltage generated at the neutral point should not exceed 1.5% of the rated phase voltage.

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

79 Key Professional Knowledge Areas in Electrical Engineering （51-60）