Q & A on common knowledge in electrical industry

How many kinds of reactive power sources are there in the power system?

The reactive power sources in the power system include:
1. Synchronous generator
2. Adjustable camera
3. Parallel compensation capacitor
4. Series compensation capacitor
5. Static compensator

What is the purpose of current transformer?

The current transformer changes the large current into small current according to a certain proportion, provides the current for various instruments and relay protection, and isolates the secondary system from the high voltage. It not only ensures the safety of personnel and equipment, but also simplifies and standardizes the manufacture of instruments and relays, and improves economic benefits.

Why should a group of lightning arresters be installed between the power capacitor and its circuit breaker?

The installation of lightning arrester can prevent the possible operation overvoltage of power capacitor during pulling and closing operation and ensure the safe operation of electrical equipment.

What are the connection modes of current transformer?

The wiring mode of current transformer includes two-phase V-shaped wiring and two-phase current difference wiring using two current transformers; There are three-phase Y-shaped wiring, three-phase △ shaped wiring and zero sequence wiring using three current transformers.

Why must the secondary side of voltage transformer and current transformer be grounded?

The secondary side grounding of voltage transformer and current transformer belongs to protective grounding. Because if the insulation of the primary, secondary and secondary sides is damaged, the high voltage on the primary side will be connected to the secondary side, which will threaten the safety of personnel and equipment, so the secondary side must be grounded.

What are the functions of shunt reactor and series reactor?

The line shunt reactor can compensate the capacitive charging current of the line, limit the rise of system voltage and the generation of operating overvoltage, and ensure the reliable operation of the line.
Bus series reactor can limit short-circuit current and maintain high residual voltage of bus. The capacitor bank series reactor can limit high-order harmonics and reduce reactance.

What are the characteristics of the wiring mode of single bus section?

Single bus section wiring can reduce the influence range of bus fault and improve the reliability of power supply. When a section of bus fails, the section circuit breaker will trip automatically with the cooperation of relay protection to remove the fault, so as to keep the normal power supply of non fault bus. For important users, power can be obtained from different sections to ensure uninterrupted power supply.

What are the disadvantages of double bus connection?

Double bus has the following disadvantages:
Wiring and operation are complex, and misoperation is easy to occur during switching operation
2. There are many bus disconnectors and the structure of power distribution device is complex, so the economy is poor

What is the compensation degree of arc suppression coil and what is residual current?

The ratio of the difference between the inductance current and the capacitance current of the arc suppression coil and the capacitance current of the power grid is called the compensation degree. After the inductive current of the arc suppression coil compensates the capacitive current, the residual current flowing through the grounding point is called residual current.

When the neutral point is grounded through the arc suppression coil, does the arc suppression coil have voltage during normal operation?

During normal operation of the system, due to the unbalance of three phase to ground capacitance of the line, there is a certain voltage between the network neutral point and the ground, and the voltage value is directly related to the unbalance of capacitance. Under normal conditions, the voltage generated by the neutral point shall not exceed 1.5% of the rated phase voltage.

Why does the battery discharge itself?

The main reason for the battery self discharge is that the electrode plate contains impurities, forming a local small battery, and the two poles of the small battery form a short circuit circuit circuit, resulting in the battery self discharge. In addition, due to the different density of the battery electrolyte, the electromotive force on the upper and lower plates is unequal, which will also cause the self discharge of the battery.

Why charge and discharge the battery regularly?

Regular charge and discharge, also known as checking charge and discharge, is to conduct a large charge and discharge reaction on the material of the electrode plate of the floating charge battery after a certain period of time to check the battery capacity, find the aging battery and maintain it in time to ensure the normal operation of the battery. Regular charge and discharge is generally no less than once a year.

What is the unbalanced current of transformer? What are the requirements?

The unbalanced current of transformer refers to the current difference between the windings of three-phase transformer. In three-phase three wire transformer, the unbalance degree of each phase load shall not exceed 20%. In three-phase four wire transformer, the neutral line current caused by unbalanced current shall not exceed 25% of the rated current of low-voltage winding. If the above provisions are not met, the load shall be adjusted.


Post time: Aug-12-2021