Clear control requirements
Control object: First, determine the type of electrical equipment to be controlled, such as motors, lighting systems, heating equipment, etc. If it is to control the motor, you also need to consider factors such as the type of motor (asynchronous motor, synchronous motor), power, speed, starting method (direct start, step-down start, soft start), etc. For example, for high-power motors (over 11kW), you may need to use step-down start or soft start, so you need to choose an electrical control cabinet with corresponding starting control functions.
Control function: Determine the required control functions, such as start, stop, forward and reverse, speed regulation, timing control, automatic interlocking control, etc. If it is used for an automated production line, it may be necessary to have a complex interlocking control function, that is, the start and stop sequence between the equipment needs to be carried out according to a certain logical relationship. For example, in a packaging production line, the packaging machine motor can only start after the conveyor belt motor is started. In this case, an electrical control cabinet that can realize interlocking control is required, and PLC (programmable logic controller) is usually used to achieve such a function.
Control accuracy: For some equipment with high control accuracy requirements, such as high-precision temperature control equipment, speed control motors, etc., it is necessary to consider whether the electrical control cabinet can meet the accuracy requirements. For example, in a precision injection molding machine, the temperature of the heating cylinder needs to be accurately controlled, and the error range may be required to be within ±1°C, which requires the selection of an electrical control cabinet with a high-precision temperature controller.
Consider the use environment
Ambient temperature and humidity: If the electrical control cabinet is installed in an environment with high or low temperature, or in a place with high humidity, it is necessary to select a control cabinet with corresponding protective measures. For example, in a high temperature environment (such as a metallurgical plant), it may be necessary to select a control cabinet with a heat dissipation device (such as a fan, radiator) to ensure that the internal electrical components are within the normal operating temperature range; in a humid environment (such as a sewage treatment plant), it is necessary to select a control cabinet with a higher protection level and moisture-proof function, such as a product with a protection level of IP54 or above, to prevent moisture from entering the cabinet and damaging the electrical components.
Dust and corrosive substances: In dusty environments (such as cement plants and mines), select an electrical control cabinet with good sealing to prevent dust from entering. For environments with corrosive gases (such as chemical plants and electroplating plants), the control cabinet should have anti-corrosion function. The cabinet material can be stainless steel or cold-rolled steel plates with special anti-corrosion treatment, and the internal electrical components also need to have a certain degree of corrosion resistance.
Electromagnetic interference and explosion-proof requirements: In some places with strong electromagnetic interference (such as large substations and near communication base stations), it is necessary to select electrical control cabinets with good electromagnetic compatibility (EMC) to avoid electromagnetic interference affecting the transmission of control signals and the normal operation of equipment. If it is in an environment with flammable and explosive gases or dust (such as gas stations and flour mills), you must choose an explosion-proof electrical control cabinet. This control cabinet is specially designed and manufactured to prevent internal sparks from causing explosion accidents.
Evaluate electrical performance
Rated voltage and current: The rated voltage and current of the electrical control cabinet must meet the requirements of the electrical equipment controlled. Factors such as the operating voltage range and starting current of the equipment should be considered. For example, for a three-phase AC motor, its operating voltage is generally 380V, and the starting current may be 4-7 times the rated current. Therefore, the rated voltage of the electrical control cabinet should include the voltage level of 380V, and the rated current should be able to withstand the starting current and normal working current of the motor, and a certain margin should be left (generally recommended margin is 20% – 30%) to cope with possible overload conditions.
Short-circuit protection and overload protection capabilities: Reliable short-circuit protection and overload protection are essential functions of electrical control cabinets. Short-circuit protection can be achieved through fuses or circuit breakers. When a short circuit occurs in the circuit, the fuse melts or the circuit breaker trips quickly, cutting off the circuit and protecting electrical components and equipment. Overload protection can use thermal relays or circuit breakers with overload protection functions. When the equipment is overloaded for a long time, it can act in time to avoid damage to the equipment due to overheating. When choosing an electrical control cabinet, it is necessary to understand whether the type, action characteristics and protection range of its short-circuit protection and overload protection devices meet the requirements.
Power factor and efficiency: Power factor is an important indicator to measure the efficiency of electrical energy utilization of electrical equipment. For some places with high requirements for power quality (such as large factories and data centers), electrical control cabinets with higher power factors should be selected to reduce reactive power loss. The efficiency of the electrical control cabinet is also very important, which reflects the loss of the control cabinet during the power conversion and control process. A control cabinet with higher efficiency can reduce energy consumption and operating costs.
Pay attention to the cabinet structure and size
Cabinet structure strength and stability: The structure of the cabinet must be able to withstand the weight of the internal electrical components and possible external impact. Generally, a frame structure or a box structure is adopted. The cabinet with a frame structure has high strength, which is convenient for installing large electrical components and internal wiring; the box structure is relatively compact and has good sealing. The thickness of the steel plate of the cabinet is also a factor in measuring the structural strength. Usually, the thickness of the steel plate of the cabinet shell should not be less than 1.5mm to ensure sufficient strength and stability.
Protection level and sealing: As mentioned earlier, the protection level is divided according to the cabinet’s ability to protect against solid foreign matter and water. Choose a cabinet with a suitable protection level according to the use environment. At the same time, the sealing of the cabinet is also very important. Good sealing can prevent dust, moisture, etc. from entering the cabinet. Check the sealing of the cabinet to see whether the sealing strip between the cabinet door and the cabinet is intact, and whether there are sealing measures for the cabinet’s vents, wire inlets and other parts.
Size and installation method: The size of the electrical control cabinet should be determined according to the installation space and the number of internal electrical components. Make sure that the cabinet has enough space to install electrical components and is easy to operate and maintain. At the same time, consider the installation method of the cabinet. Common installation methods include wall-mounted, floor-standing, and embedded. Wall-mounted is suitable for places with smaller spaces, floor-standing is suitable for large control cabinets and heavier equipment, and embedded can make the cabinet better integrated with the surrounding environment and save space.
