Common Electrical Equipment Questions and Answers

Why is a ZnO surge arrester installed between the power capacitor and its breaker?
A ZnO surge arrester is installed to prevent overvoltage caused by switching operations, thereby ensuring the safe operation of electrical equipment.

What is the difference between an energy meter and a power meter?
A power meter indicates the instantaneous power output or consumption, while an energy meter records the total energy produced, transmitted, or consumed over a specific period.

What are the requirements for batteries in parallel connection?
Batteries connected in parallel must have equal electromotive forces (EMF); otherwise, batteries with higher EMF will discharge into those with lower EMF, creating internal circulating currents. Additionally, each battery should have the same internal resistance to avoid excessive discharge currents. Batteries of different ages should not be used in parallel.

What is the function of the central signaling device?
The central signaling device monitors the operation of electrical equipment in substations and issues audio and visual alarms based on fault characteristics. This helps operators quickly identify issues, make accurate judgments, and ensure the safe operation of the equipment.

Why might a power cable still show voltage after disconnection?
Power cables act as capacitors and store residual charge after disconnection, which can create a potential difference with the ground. This residual voltage must be discharged before confirming that the cable is de-energized.

What is internal overvoltage?
Internal overvoltage occurs when a system undergoes a sudden change (due to operations, faults, or other reasons) and transitions from one stable state to another. During this transient process, dangerous overvoltage may arise due to oscillations and energy accumulation within the system.

What is the role of the equalizing ring on a 220kV valve-type surge arrester?
The equalizing ring ensures uniform voltage distribution across the arrester.

What is protective grounding, and what are its advantages?
Protective grounding involves connecting the normally non-energized metal parts of equipment directly to the system ground. This method ensures personal safety by preventing electric shocks.

What is the function of a high-voltage circuit breaker?
High-voltage circuit breakers can interrupt and close load and no-load currents under normal conditions. In case of system faults, they work with protective devices to quickly interrupt fault currents, preventing accidents and ensuring the safe operation of the system.

What is the function of a high-voltage circuit breaker?
(Note: This question is repeated with question 9.)
High-voltage circuit breakers can interrupt and close load and no-load currents under normal conditions. In case of system faults, they work with protective devices to quickly interrupt fault currents, preventing accidents and ensuring the safe operation of the system.

What should be the terminal voltage of each battery in a float charging system?
To maintain a fully charged state, each battery in the system should have a float charge voltage of 2.15V per cell.

Why is a DC insulation monitoring device necessary?
A prolonged ground fault in a DC system is not permitted, as another ground fault in the same pole could cause malfunctions in signaling, protective relays, and control circuits. Additionally, if both poles become grounded, it could result in a short circuit.

What is float charging?
Float charging involves using two charging units: a primary charger and a float charger. The float charger compensates for the self-discharge of the battery, keeping the battery bank fully charged.

What is the function of a wave trap (blocking device)?
A wave trap is an essential high-frequency communication component for carrier communication and high-frequency protection. It prevents high-frequency currents from leaking into other branches, minimizing high-frequency energy loss.

What are the phenomena observed during system oscillation?
During system oscillation, the following phenomena occur: