Fault analysis during the use of distribution cabinets

Release time:

2022-05-29

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Abstract

The disadvantages caused by the impact of ambient temperature on low-voltage electrical appliances in distribution cabinets include components such as fuses, AC contactors, residual current devices, capacitors, and measuring instruments. These low-voltage electrical appliances are designed and manufactured according to GB1497 "Basic Standards for Low-Voltage Electrical Appliances," which stipulates the normal operating conditions: the upper limit of ambient air temperature should not exceed 40°C. The average ambient air temperature over 24 hours should not exceed 35°C; the lower limit of ambient air temperature should not be lower than -5°C or -25°C. The distribution cabinets in rural power grid renovation work outdoors, where they are not only exposed to direct sunlight causing high temperatures but also generate heat during operation. Therefore, during the hot summer months, the internal temperature of the cabinet can reach above 60°C, significantly exceeding the environmental temperature limits set for these appliances, leading to failures due to overheating of electrical components inside the distribution cabinet. Failures caused by product quality issues arise during rural power grid renovations due to the large number of required distribution cabinets and short construction periods. The manufacturers of distribution cabinets face urgent demands for low-voltage electrical appliances in large quantities, resulting in a lax approach to product quality. Consequently, some products experience failures shortly after being put into operation. For instance, certain types of AC contactors may fail shortly after the distribution cabinet is commissioned due to burnt-out coil circuits. Failures caused by improper selection of electrical appliances in the distribution cabinet occur because the capacity selection for AC contactors during manufacturing is not very appropriate. Identical capacity AC contactors are used for different outgoing circuits without considering the imbalance of three-phase loads. As a result, some outgoing contactors' current ratings were not upgraded by one level based on normal selection criteria, leading to instances of AC contactor burnout during high-temperature summer operations.

The disadvantages caused by the impact of ambient temperature on low-voltage electrical appliances. The low-voltage electrical appliances in the distribution cabinet consist of fuses, AC contactors, residual current protective devices, capacitors, and measuring instruments. These low-voltage electrical appliances are designed and manufactured according to GB1497 'Basic Standards for Low-Voltage Electrical Appliances', and corresponding regulations have been made regarding their normal working conditions: the upper limit of the surrounding air temperature does not exceed 40°C.

 

The average value of the surrounding air temperature over 24 hours does not exceed 35°C; the lower limit of the surrounding air temperature is not lower than -5°C or -25°C. The distribution cabinets for rural power grid transformation work outdoors, where they are not only exposed to direct sunlight causing high temperatures but also generate heat during operation. Therefore, during the hot summer season, the temperature inside the cabinet can reach above 60°C, which greatly exceeds the environmental temperature regulations for these electrical appliances, leading to failures caused by overheating of electrical components inside the distribution cabinet.

Failures caused by product quality issues. During the rural power grid transformation, due to the large number of required distribution cabinets and short construction period, manufacturers faced urgent demands for low-voltage electrical appliances in terms of supply time and quantity. This led to a phenomenon where product quality requirements were not strict, resulting in some products failing shortly after being put into operation. For example, some types of AC contactors burned out their coil shortly after the distribution cabinet was put into operation, rendering them inoperable.

Failures caused by improper selection of electrical appliances in the distribution cabinet. Due to inappropriate selection of AC contactor capacity during manufacturing, contactors with the same capacity were used for different outgoing circuits without considering the imbalance of three-phase loads. As a result, some outgoing contactors did not have their current ratings increased by one level based on normal selection types, leading to cases of AC contactors burning out during operation in high summer temperatures.

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