Primary and secondary deep fusion circuit breakers are mainly used in the main circuit of high-voltage power systems. Their fusing characteristic curves have the characteristics of short delay and strong breaking capacity. When the short-circuit current greatly exceeds the rated current, the primary deep-fusion circuit breaker needs to act quickly to cut off the circuit and avoid the expansion of the fault. Its curve usually shows that in the large current range, the action time is extremely short and the fuse is almost instantly blown to achieve rapid protection of high-voltage equipment and lines. At the same time, due to the huge current and energy of the primary system, the circuit breaker is required to have high tolerance and stable fusing performance to ensure that the circuit can still be reliably broken under extreme working conditions.
Secondary deep-fusion circuit breakers are often used in low-voltage control, protection and measurement circuits. Their fusing characteristic curves are significantly different from those of primary deep-fusion circuit breakers. The secondary circuit current is small, and the circuit breaker sensitivity requirements are higher. Therefore, its curve has a relatively long action time when the current is small overloaded to avoid false action caused by instantaneous current fluctuations. As the current increases, the action time of the secondary deep-fusion circuit breaker gradually shortens. In the case of short-circuit current, it can also quickly cut off the circuit and protect secondary equipment. In addition, the secondary deep-fusion circuit breaker needs to have good anti-interference ability to ensure stable characteristics in complex electromagnetic environments.
Comparing the fusing characteristic curves of primary and secondary deep fusion circuit breakers, the most obvious difference lies in the operating current range and time parameters. The operating current threshold of the primary deep-fusion circuit breaker is high, and it acts quickly when breaking large currents; the operating current threshold of the secondary deep-fusion circuit breaker is low, and it has a certain delay characteristic when the small current is overloaded to improve the accuracy of protection. At the same time, the slopes of the curves of the two are different. The slope of the curve of the primary deep-fusion circuit breaker is larger, which means that the impact of current changes on the operating time is more significant; the slope of the curve of the secondary deep-fusion circuit breaker is relatively small, which reflects that its operating time changes more slowly in the small current range. These differences reflect the protection focus and performance requirements of the two in different application scenarios.
When selecting, first ensure that the rated voltage of the circuit breaker matches the voltage of the system. Whether it is the primary or secondary circuit, voltage mismatch may cause insulation failure or failure to disconnect normally. For rated current, the primary deep-fuse circuit breaker needs to be selected according to the maximum working current, short-circuit current and other parameters of the main circuit, and the model with sufficient breaking capacity and withstand current should be selected; the secondary deep-fuse circuit breaker should consider the normal operating current, load characteristics and possible overload current of the secondary circuit to ensure that the circuit breaker does not melt during normal operation and can operate reliably in the event of a fault.
According to the protection requirements of the power system, select a circuit breaker with appropriate protection characteristics. For the primary deep-fuse circuit breaker, it is necessary to cooperate with other protection equipment (such as relay protection devices and fuses) to ensure the selectivity and coordination of the action and avoid over-tripping. The secondary deep-fuse circuit breaker should be coordinated with other components in the secondary circuit (such as relays and instruments) to prevent system failures caused by mismatched protection actions. At the same time, the delay characteristics of the circuit breaker need to be considered to ensure accurate protection under different fault conditions.
Environmental factors and installation conditions also affect the selection of circuit breakers. Harsh environments such as high temperature, humidity, and dust will reduce the performance of circuit breakers, and products with corresponding protection levels need to be selected. Primary and secondary deep fusion circuit breakers are usually installed outdoors or in high-voltage switch cabinets, and dust, moisture and corrosion protection must be considered; secondary deep fusion circuit breakers are mostly installed in control cabinets, and attention must be paid to heat dissipation and electromagnetic compatibility. In addition, the size of the installation space also limits the size and structure selection of the circuit breaker, and comprehensive considerations must be made to ensure that the installation is convenient and meets the system layout requirements.
