How to choose a circuit breaker - Aerospace - Ship - [Wickway]

Circuit breakers need to be matched with circuit loads and power supply, and the selection of circuit breakers is closely related to protection timeHow to choose a circuit breakerWhat about it? We can understand that general circuit breakers are divided into two types: C-type and D-type. C-type is used for power distribution, while D-type is used for power. The type of motor load we use is D-type, while C-type circuit breakers used in professional power distribution fields are less commonly used. We will not discuss this here. If it isAviation circuit breakerThe selection of industries such as aerospace and shipbuilding will also be different.

In order to avoid the circuit breaker from malfunctioning when the load is started, we generally choose a circuit breaker that is one level higher than the motor type load when selecting and using the corresponding circuit breaker. For example, if we are using a 7.5KW motor and a current of around 15A, we should choose a circuit breaker of around 20-25A. Here is a reminder from the editor: When purchasing electrical products, we should not choose circuit breakers based on the stable current of the electrical product's operation, because many electrical appliances will have a current much greater than the working current when they are just started. Therefore, we should choose corresponding circuit breakers within the safe range. Generally, reputable electrical appliance manufacturers will provide safe recommended current values, so there is no need to worry about this. However, the rated current of the circuit breaker cannot be amplified too much. The circuit breaker will be redundant, and it will be difficult to protect it in case of a short circuit in the circuit or load.

But the above is only to ensure the normal operation of the circuit breaker during normal load start-up and operation. We should know that circuit breakers also have their own current load, and once it exceeds this range due to uncontrollable factors, the circuit breaker is likely to short-circuit and be damaged along with the electrical appliances. At this point, it is necessary to calculate the expected short-circuit current of the electrical appliance. However, it is generally difficult to obtain accurate values for calculating the expected short-circuit current of electrical appliances. Factors such as how direct current is broken and whether the current selectivity can reach the circuit breaker can affect the calculation of the expected short-circuit current. So in order to obtain more accurate data, we can achieve it by observing more samples.

Principles for selecting circuit breakers:

1. The rated voltage of the circuit breaker must be greater than or equal to the operating voltage of the circuit.

The voltage of the load or rated power supply should be greater than or equal to the rated voltage of the switch, as this is related to the safety performance of the product. A voltage higher than the rated voltage of the switch may cause a decrease in the insulation performance of the product, leading to potential accidents.

2. The rated short-circuit breaking capacity of the circuit breaker is ≥ the maximum short-circuit current that may occur in the circuit.

The short-circuit current between phase lines or between phase lines and neutral lines in the circuit is large, and the closer it is to the power distribution end, the greater the current, because the impedance of the entire short-circuit circuit is small. Therefore, it is required that the circuit breaker must have a certain short-circuit breaking capacity. When the short-circuit breaking capacity is greater than or equal to the maximum short-circuit current that may occur in the line, the switch can instantly extinguish the arc and disconnect under the action of the instantaneous release. If the rated short-circuit breaking capacity of the switch is less than or equal to the maximum short-circuit current that may occur in the circuit, the switch cannot extinguish the arc, and the high temperature caused by the arc causes the contacts to stick (short circuit), thereby damaging the distribution line and equipment.

3. The rated current of the circuit breaker is greater than or equal to the load current of the circuit.

The rated current of the load must be equal to or less than the rated current of the switch. Generally, it is less than the rated current of the switch. Considering a certain margin, the rated current of the switch is generally selected to be about 20% higher than the actual load current. Do not choose it too high. It is necessary to consider that both overload protection and short-circuit protection can be activated. If the rated current is too high, the overload protection will lose its effect. Due to the thickness and length of the line, the short-circuit current at the load end cannot reach the set action value of the instantaneous release, thus causing the short-circuit protection to fail.

4. When a single phase to ground short circuit occurs at the end of the circuit breaker, the switching action of the B, C, and D type instantaneous release devices can be activated. For different types of loads (electrical equipment), different instantaneous release devices and corresponding current level products can be selected. Select different types of instantaneous release devices and rated currents according to different load equipment. The objects of use for B, C, and D type instantaneous release devices are explained earlier. When selecting the rated current and corresponding instantaneous release device, the rated current of the load and the maximum possible short-circuit current output must be considered. The short-circuit protection can only be activated when the maximum short-circuit current is greater than or equal to the set dynamic value of the B, C, and D type instantaneous release devices.

That's all for today's sharing. If you have more questions about how to select circuit breakers, you can contact the electrical engineers at Weikewei, who will provide you with quick replies and answers.