Circuit short-circuit consequences and short-circuit calculation purposes - Database & Sql Blog Articles

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

Single chip microcomputer STM32L151CCU6

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

SMD aluminum electrolytic capacitor

After a short circuit occurs in the power supply system, the impedance of the circuit is much smaller than that during normal operation. The short-circuit current usually exceeds the normal operating current by several tens of times up to hundreds of times, which has the following serious consequences:
1. A huge short-circuit current passes through the conductor, which generates a large amount of heat in a short time, forming a very high temperature, which easily causes the device to overheat and be damaged.
2. Due to the electrodynamic effect of the short circuit current, a large amount of electric power is generated between the conductors. If the electric power is too large or the equipment structure is not tough enough, it may cause mechanical deformation or even damage of the electrical equipment, which further expands the accident.
3. When the short circuit occurs, the system voltage suddenly drops, which has a great impact on the user. For example, as an asynchronous motor of the main power equipment, the electromagnetic torque is proportional to the square of the terminal voltage. A large drop in voltage will cause the motor speed to decrease or even stop running, causing loss to the user. At the same time, the voltage drop can cause lighting load such as sudden darkening of the electric lamp and extinguishing of some gas discharge lamps, which affects normal work, life and learning.
4. When an asymmetric short circuit occurs in the system, sufficient magnetic flux generated by the magnetic effect of the asymmetric short-circuit current can induce a large electromotive force in the adjacent circuit. This may cause strong interference to nearby communication lines, railway signal systems, and other electronic equipment and automatic control systems.
5. When a short circuit occurs, it will cause a power outage accident and bring losses to the national economy. And the closer the short circuit is to the power supply, the larger the range of power outages.
The most serious consequence of a short circuit is the loss of synchronization between the power plants operating in parallel. Destruction of the system is stable, eventually causing the system to collapse, forming a regional or regional power outage.
The purpose of short-circuit calculation is mainly as follows:
(1) In order to select and verify electrical equipment such as circuit breakers, disconnectors, fuses, transformers, busbars, porcelain bottles, cables, overhead lines, etc. These include calculating the three-phase short-circuit inrush current and the inrush current effective value to verify the electrical power stability of the electrical equipment, and calculating the steady-state effective value of the three-phase short-circuit current to verify the thermal stability of the electrical equipment and the current-carrying conductor, and calculating the three-phase short circuit. Capacity to verify the breaking capacity of the circuit breaker, etc.
(2) For the calculation of the relay protection device.
When considering the correct and reasonable installation of the protection device, when verifying the sensitivity of the protection device, it is necessary to calculate not only the three-phase short-circuit current value in the short-circuit fault branch, but also the distribution of other branch short-circuit currents; The maximum short-circuit current value that may occur in the circuit, and the minimum short-circuit current that may occur in the minimum operating mode; not only the three-phase short-circuit current but also the two-phase short-circuit current or the single-phase ground current as needed. .
(3) When selecting the electrical connection with the design system, the short-circuit calculation can provide a basis for technical comparison of different schemes and determination of whether to limit the short-circuit current.