In medium voltage distribution networks, ring main units (RMUs) play an irreplaceable central role. It not only undertakes the tasks of power distribution, load switching and line connection, but also provides reliable protection for power lines, transformers and other equipment. When the power grid has faults such as overload and short circuit, it can quickly isolate the fault section and ensure the continuous power supply of the non-fault area, which can be called the "flexible hub" of the power system. Today, let's explore how to choose the right ring main unit.
General principles for selection of ring main units
In order to ensure the safety and stability of ring main units under normal operation, maintenance, short circuit and overvoltage and other working conditions, the following factors should be considered when selecting:
Normal operating conditions: including voltage, current, frequency and mechanical load. For example, it is necessary to ensure that the rated voltage and current of the ring main unit match the actual needs of the connected circuit.
Short-circuit conditions: including short-term withstand current, peak withstand current, breaking current, etc. These parameters directly determine the performance of the ring main unit in response to short circuit faults.
Environmental conditions: Factors such as temperature, humidity, altitude, earthquakes, and dust will affect the operating status of the ring main unit. For example, in high-temperature, high-humidity or high-altitude environments, special attention should be paid to the protection level and insulation performance of the product.
Voltage resistance: including insulation level. The higher the insulation level, the more effectively the ring main unit can prevent leakage and short circuit accidents, and ensure the safety of equipment and personnel.
Action performance and protection characteristics: There are differences in the operating characteristics of different power equipment. The action performance of the ring main unit load switch, the matching degree of fuse protection characteristics, and the coordination with the relay protection device will affect the selection results.
Normal working requirements of ring main units
To ensure the stable operation of the ring main unit, the rated voltage of the equipment should be determined according to the actual operating voltage of the power grid to ensure that it is consistent with the nominal system voltage of the circuit. At the same time, the rated current of the ring main unit should not be less than the continuous working current of the circuit to avoid long-term overload operation.
Short-circuit stability of ring main units
Short-circuit stability is a key indicator to measure the reliability of ring main units, and the following needs to be verified:
1. General requirements for short-circuit stability verification,
2. Thermal effect effect of short-circuit current,
3. Special verification of short-circuit stability.
Epilogue
Choosing the right ring main unit is not an easy task, but as long as you master these selection principles and work requirements, you can make a reasonable decision. The ring main unit is the core component of the medium voltage distribution network, and its performance is directly related to the safety and stability of the entire power supply system.
