Basic Electrical knowledge Q & A (especially for beginners)

Name explanation:
1. Three-phase alternating current (AC): An electric power system consisting of three AC circuits with the same frequency, equal potential amplitude, and Mutual Difference of 120 °.
2. One-time device: the device directly related to power generation and distribution is called one-time device. Including various high voltage circuit breakers, isolating switches, busbars, power cables, voltage transformers, current transformers, reactors, lightning arresters, arc suppression coils, parallel capacitors, and High Voltage Fuses.
3. Secondary equipment: Auxiliary Equipment that monitors, measures, controls, and protects a single device. Such as various relays, signal devices, measuring instruments, wave recording devices, telemetry, remote communication devices, various control cables, and small busbars.
4. High-voltage circuit breaker: Also known as high-voltage switch, it can not only cut off or close the no-load current and load current in the high-voltage circuit, but also when the system fails, through the action of the protective device, cut off the overload current and short-circuit current. It has a well-developed Arc Extinguishing structure and sufficient cut-off capability.
5. load switch: the construction of the load switch is similar to that of the classified isolation switch, but a simple arc extinguishing device is installed. It also has an obvious disconnection point, with a certain degree of cut-off capability, can be operated with load, but cannot directly disconnect the short-circuit current, if needed, it depends on the High-Voltage Fuses connected with it.
6. Air Circuit Breaker (automatic switch): It is a low-voltage switch that uses a manual (or electric) switch and uses a lock to keep the switch position. The trip mechanism acts on the switch and has an arc extinguishing device, it is widely used in AC and DC units below V. When overload, short circuit, and voltage decrease or disappear in the circuit, the circuit can be automatically cut off.
7. Cable: cables consist of core wires (conductive parts), plus insulation layer and protective layer.
8. busbars: Electrical busbars are the access devices that collect and distribute electric energy. They determine the number of devices in the Power Distribution Device and indicate how to connect generators, transformers, and lines, and how to connect to the system to complete the transmission and distribution task.
9. Current Transformer: The instrument converter is an instrument that converts large current into small current.
10. Transformer: a static electrical device used to change the AC voltage of a certain value to another type or multiple types of AC voltage with the same frequency.
11. High-Voltage electroscope pen: it is a tool used to check whether high-voltage network power distribution equipment, overhead cables, and cables are charged.
12. Ground Wire: it is an important tool to ensure the staff when voltage occurs on the equipment and lines that have been powered off. According to ministerial provisions, the grounding wire must be made of bare copper cables larger than 25mm 2.
13. Notice Board: used to warn people not to be close to the equipment and charged part, instruct the staff to prepare a work place, and remind them to take safety measures, and notice board prohibiting the power-on of a certain device or line. It can be divided into warning, allow, prompt, and deny.
14. Cover bar: to prevent staff from accidentally touching the screen guard of charged equipment, there are two types of temporary and permanent blocks.
15. Insulation ROD: it is also called a linker rod, insulation rod, and Operation rod. Insulation rod consists of three parts: Work head, insulation rod and grip. It is used for closed or in-position high-voltage isolating switch, mounting and dismounting the portable grounding wire, as well as measurement and testing.
16. Xtep voltage: if there is a potential difference between the two points on the ground with a horizontal distance of 0.8 m, when the human body is in contact with the two points, the voltage will bear on the human body. This voltage is called Xtep voltage. The maximum cross-Step Voltage occurs between the grounding body and the grounding body at a horizontal distance of 0.8 m from the grounding body.
17. phase sequence: it refers to the order in which the instantaneous values of alternating current (AC) pass through zero values from negative values to positive values.
18. Power Grid: a power grid is a part of the power system. It is a unified network composed of various substations (sites) and transmission and distribution lines of different voltage levels.
19. Power System: The power system is part of the power system. It consists of generators and power distribution devices in power plants, boost-up and step-down substations, transmission and distribution lines, and electrical equipment of users.
20. Power System: power plants, substations, and the electrical equipment of users. The power system is connected by an electric network and a thermal network (or a hydraulic system.

1. What is the purpose of relay protection?
A:

① When the power grid encounters a fault that is sufficient to damage the equipment or endanger the safe operation of the power grid, the protected equipment will be quickly detached from the power grid;

② The abnormal operation of the power grid and abnormal status of some equipment can be promptly issued with an alarm signal for rapid processing and recovery;

③ Realize automation and automation of the power system and automatic control of industrial production.
2. What is the basic principle of the relay protection device?
Answer: when the power system fails, the basic features are sudden increase of current, sudden decrease of voltage, and change of the phase angle between current and voltage. Various relay protection devices seize these features, based on the changes in these physical quantities, different physical quantities, such as the internal and external faults, are protected by the difference between the normal and the fault, and the overcurrent protection is implemented when the reaction current increases, low-voltage protection with reduced Reactive voltage, over-current protection with changes in reactive current and phase angle, and distance protection with the ratio of Reactive voltage to current.