Low voltage distribution cabinet plays a key role in distributing electric energy and controlling circuits in power systems. The selection and sensitivity optimization of its short-circuit protection device are crucial and directly related to the safe and stable operation of the system.
First of all, the selection of short-circuit protection devices needs to take into account multiple factors. For distribution cabinets with smaller rated currents, fuses may be a simple and effective choice. They have inverse time delay characteristics and can quickly melt and cut off the circuit when the short-circuit current is too large. For low voltage distribution cabinets with larger capacity and higher protection selectivity requirements, circuit breakers should be used. Circuit breakers can achieve long delay for overload, short delay for short circuit and instantaneous action protection. Their breaking capacity should be determined according to the short-circuit current level of the system where the distribution cabinet is located, ensuring that the fault current can be reliably cut off when a short-circuit fault occurs to prevent the accident from expanding.
In terms of sensitivity optimization, the short-circuit current value should be accurately calculated. This requires accurate grasp of the electrical parameters of the distribution cabinet, such as the internal resistance of the power supply, the line impedance, and the equivalent impedance of the connected load. The action current setting value of the protection device is determined by short-circuit current calculation. Generally speaking, the action current of the protection device should be less than the minimum short-circuit current that may occur when a short circuit occurs at the end of the protected line, so as to ensure that the short-circuit fault can be detected in time and the protection action can be triggered in any case, so as to avoid the protection refusal to operate due to insufficient sensitivity, resulting in equipment damage and power outage accidents.
At the same time, taking into account the changes in the system operation mode, such as grid structure adjustment, load increase and decrease and other factors, an adaptive protection strategy should be adopted. For example, the system parameters are monitored in real time by an intelligent controller, and the action parameters of the protection device are automatically adjusted according to the operating conditions to ensure that high sensitivity can be maintained under different operating conditions.
In addition, the action time of the protection device also needs to be optimized. For a multi-level protection system, in order to achieve the selective coordination of the upper and lower protections, the action time of the upper protection should be greater than the action time of the lower protection, to avoid over-tripping, ensure the accuracy and selectivity of fault removal, and minimize the scope of power outage.
Attention should also be paid to the coordination between the protection device and other components of the distribution cabinet. For example, the connection with the busbar, cable, etc. should be firm and reliable to reduce the contact resistance, prevent local overheating or excessive voltage drop caused by poor connection, and affect the normal operation and sensitivity of the protection device.
The selection and sensitivity optimization of short-circuit protection devices for low-voltage distribution cabinet is a systematic project. It is necessary to comprehensively consider electrical parameters, operating conditions, protection coordination and other factors. Through precise calculation, reasonable selection, intelligent control and system coordination, it is ensured that the short-circuit protection device can operate quickly and accurately to ensure the safe and stable operation of the low-voltage distribution system.
