How to select contactors in Distribution Cabinet according to load characteristics
Publish Time: 2024-11-05
In Distribution Cabinet, the selection of contactors is crucial, and load characteristics are the key factors in determining contactor selection.
First, consider the type of load. For resistive loads, such as electric furnaces, incandescent lamps, etc., the current is relatively stable and easy to control. When selecting a contactor, the rated current parameters of the contactor are mainly determined based on the rated current of the load. Generally, a contactor with a rated current close to or slightly larger than the rated current of the load can be selected. For example, for a 10A resistive load, a contactor with a rated current of 10-12A can be selected.
For inductive loads, such as motors, transformers, etc., a large impact current will be generated at the moment of starting and stopping. In this case, the connection and disconnection capacity of the contactor needs to be considered. Generally, a contactor that can withstand the impact of the motor starting current (usually 5-7 times the rated current) should be selected. At the same time, attention should also be paid to the action time and release time of the contactor to ensure reliable operation during the start and stop of the motor. For example, for a 5kW three-phase asynchronous motor with a rated current of about 10A, a contactor with a rated current of 40-50A should be selected to cope with the starting shock.
When the capacitive load is connected to the power supply, a large charging current may be generated. For such loads, a contactor with inrush current suppression function should be selected. For example, in the compensation capacitor cabinet, a specially designed capacitor contactor can effectively limit the charging inrush current through a built-in current limiting resistor and other mechanisms to protect the contactor contacts and other circuit components.
In addition, the load's working system cannot be ignored. For loads with long-term continuous working system, the heating of the contactor is an important consideration. It is necessary to select a contactor with good heat dissipation performance and long-term rated current. For loads with intermittent cycle working system, the selection of the contactor should be adjusted according to the load's on-off ratio to ensure that the contactor will not be damaged prematurely during frequent operation, and to ensure the reliable operation of the distribution cabinet and the safe and stable operation of electrical equipment.
