79 Key Professional Knowledge Areas in Electrical Engineering （11-20）

By Milly March 4th, 2025 20 views

【11.What are the differences between the values indicated by energy meters and power meters?】

A power meter indicates the instantaneous amount of electric power generated, transmitted, and consumed by equipment during operation. In contrast, an energy meter accumulates and displays the total amount of electrical energy generated, transmitted, and consumed over a specific period of time.

【12.What are the requirements for batteries in parallel battery banks?】

In parallel-connected batteries, the electromotive forces (EMFs) of all batteries should be equal; otherwise, batteries with higher EMF will discharge into those with lower EMF, creating circulating currents within the battery bank. Additionally, the internal resistances of all batteries should be the same; otherwise, batteries with lower internal resistance may experience excessive discharge currents. Batteries with significantly different conditions (e.g., new vs. old) should not be connected in parallel.

【13.What is the function of a central signaling system?】

The central signaling system monitors the operation of electrical equipment in substations. Based on the fault characteristics of the equipment, it generates audible and visual signals to promptly inform operating personnel, enabling them to quickly investigate, make accurate judgments, and take appropriate actions, thereby ensuring the safe operation of the equipment.

【14.Why does an electric tester still indicate voltage on a cable line shortly after it has been de-energized?】

A cable line acts like a capacitor. Even after being de-energized, residual charges remain on the line, resulting in a potential difference relative to ground. If tested immediately after de-energization, the electric tester will still indicate voltage. Therefore, the line must be fully discharged before verifying that it is de-energized and grounding wires can be installed.

【15.What is internal overvoltage?】

Internal overvoltage occurs due to operations, faults, or other causes that suddenly change the state of the system, leading to a transition from one stable state to another. During this transition, dangerous overvoltages may occur, which are caused by oscillations and accumulation of electromagnetic energy within the system. These overvoltages are referred to as internal overvoltages.

【16.What is the function of the grading ring at the top of a 220kV surge arrester?】

The grading ring ensures uniform voltage distribution across the surge arrester after installation.

【17.What is protective grounding? What are its advantages?】

Protective grounding involves connecting the non-electrified metal parts of equipment to the system through a conductor under normal conditions. This method ensures personal safety and prevents electric shock accidents.

【18.What is the difference between the neutral point, zero point, and neutral line?】

The common connection point where the three-phase windings' terminals (either the start or end points) are connected together is called the neutral point of the source. When the neutral point is properly connected to a grounding system, it is referred to as the zero point. The conductor extending from the zero point is called the neutral line (or zero line).

【19.What is the role of the DC system in a substation?】

The DC system in a substation provides reliable DC power for control systems, signaling, relay protection, automation devices, and emergency lighting. It also supplies reliable operating power for various operations. The reliability of the DC system is crucial for the safe operation of the substation, serving as a critical guarantee for its safe functioning.

【20.What terminal voltage should each battery maintain during normal float charging to ensure full charge?】

To maintain each battery in a fully charged state during float charging, the terminal voltage of each battery connected to the DC bus should be maintained at 2.15V.

79 Key Professional Knowledge Areas in Electrical Engineering （1-10）

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