The Principle of How to Select China Circuit Breakers

Promulgator : TAIXIDate : 2019-03-02Views : 228

      China Circuit Breaker is a kind of equipment to control current interruption. It is mainly used to protect the circuit and equipment. If there are overload, short circuit, undervoltage and other faults in the circuit, the circuit breaker can quickly cut off the power supply to protect the safety of the line, load and related equipment. China circuit breakers are widely used in mechanical and electrical equipment and circuits, but with the different ability of the protected object to withstand overload current, the protection characteristics of the selected China circuit breakers are different, so how to select the appropriate China circuit breakers becomes very important.

      How to Select China circuit breakers
      According to their use, China circuit breakers can be divided into distribution circuit breakers, motor protection circuit breakers, household protection circuit breakers, leakage circuit breakers and so on. According to their different protection characteristics, this paper introduces how to select suitable circuit breakers so as to select circuit breakers as a basis. 
      1. Selection of Circuit Breakers for Distribution
      Distribution circuit breakers are generally used in low-voltage power grid for distribution of electricity, including power supply circuit breakers and load branch circuit breakers. When choosing such circuit breakers, special attention should be paid to the following selection principles:
      1)The allowable carrying capacity of the line is not less than the setting value of the long delay action current of the circuit breaker. If wire and cable are used, the setting value of long delay action current of circuit breaker can be 80% of the allowable current of wire and cable. 
      2)The starting time of the motor with large starting current in the circuit is not more than three times the return time of the setting value of the delay action current. 
      3)Instantaneous current setting value I1:I1=1.1 (Ijx+klkIedm). Among them: KL is the impulse coefficient of the starting current of the motor, generally KL = 1.7~2; Iedm is the rated current of a large motor.
      2. Selection of Motor Protected Circuit Breakers
      The motor has two characteristics: first, the starting current is usually several times the rated current; second, it has a certain overload capacity. Therefore, when choosing circuit breaker to protect motor, we must pay attention to these two characteristics of motor. In order to ensure the reliable operation of motor, we should pay attention to the following points when choosing circuit breaker:
      1) The rated current of the motor is used to determine the setting value of the long delay action current of the circuit breaker. 
      2) The return time of setting value of 6 times long delay action current of circuit breaker is the actual starting time of motor. 
      3) Instantaneous action current setting value of circuit breaker: cage motor should be 8-15 times the rated current of tripper; winding motor should be 3-6 times the rated current of tripper.
      3. Choice of household protective circuit breakers
      Circuit breaker is usually used as main power protection switch or branch line protection switch in household power supply. If the line or household appliances are short-circuited or overloaded, the circuit breaker can automatically trip and cut off the power supply, thus effectively protecting these devices from damage and reducing the accident to a minimum.
      In the family, unipolar (1P) is usually used as branch protection, and bipolar (2P) circuit breaker is used as general power protection. It is very important to choose the rated capacity current of circuit breaker in family, because if the rated current of circuit breaker is too large, when the line or household appliances are short-circuited or overloaded, the circuit breaker can not automatically trip and cut off the power supply. If the selection is too small, the circuit breaker is easy to trip frequently, causing unnecessary power outages, affecting normal life and causing unnecessary trouble.
      Generally, the specifications of general miniature circuit breakers are distinguished by rated current, mainly 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A, etc.
      1) Values of branch currents
            (1) Electrical nameplates for pure resistive loads indicate that power is directly divided by voltage.
            Formula: I = Power/200v;
            For example, for a 200 W bulb, branch current I = 200W/220V = 0.9A
            Resistive load electrical appliances include light bulbs, electric heaters, fans, electric frying pans, electric heaters, electric irons, electric blankets, rice cookers, vacuum cleaners, electric water heaters, air conditioners, etc.
            (2) The calculation of inductive load is slightly complicated, considering the power consumed and the power factor, etc. In order to estimate easily, I give a simple calculation method. For the general inductive load, the branch current I = 200W/220V = 0.9A and the double is 0.9*2 = 1.8A according to the specified load, for example, the branch current I = 200W/220V = 0.9A and the double is 0.9*2 = 1.8A. 0.3A more than exact value 1.5A.
Inductive electrical appliances include TV sets, washing machines, fluorescent lamps, refrigerators, fluorescent lamps, etc.
      2) Total load current is the sum of branch currents.
Knowing the branch current and total current, we can choose the specifications of branch circuit breakers and gate circuit breakers, or check whether the specifications of the designed electrical components meet the safety requirements; in order to ensure safety and reliability, the rated working current of the electrical components should generally be greater than the maximum load current required by two times; in addition, when selecting the electrical components, we should also take into account the future increase of electricity load. Additional possibilities leave a margin for future demand.
      4. Selection of Leakage Circuit Breakers
Leakage circuit breakers are generally divided into two poles, three poles and four poles, which are used in different circuits. Only the correct choice and use can play its due role, so when choosing leakage circuit breaker, we should pay attention to the following five points:
      1) The rated current of the overload tripper is greater than the maximum load current of the line.
      2) The ultimate breaking capacity of the circuit breaker is greater than the maximum short circuit current of the circuit.
      3) The leakage current to be protected by the line shall be less than the specified leakage protection current of the circuit breaker.
      4) Normal operating voltage and current of line equipment are less than rated voltage and current of circuit breaker.
      5) Shorter interruption reaction time can protect circuit and equipment.
      Sometimes it is difficult to judge whether to choose quadrupole circuit breaker or not in application. In this paper, the principles to be followed for choosing quadrupole circuit breaker are put forward. Quadrupole circuit breaker should be selected in the following circumstances:
      1) According to the regulation of IEC 465.1.5, the switching circuit breaker between the normal power supply and the standby generator;
      2) Quadrupole circuit breaker should be used in double power supply conversion circuit breaker with leakage protection. Two upper circuit breakers have leakage protection, and the lower power supply converts to the circuit breaker.
      3) Power switching circuit breakers between two different grounding systems;
      4) Power line breaker of IT system;
      5) Circuit breakers used in IT systems when neutral lines are drawn out.

      Quadrupole circuit breakers are generally not required or prohibited in the following cases:
      1) Quadrupole circuit breakers are not generally required in TN-S and TN-C-S systems; 
      2) Quadrupole circuit breakers are strictly prohibited in TN-C systems.
      Selection Principle of Circuit Breaker
      1. The rated voltage of the circuit breaker ≥ the rated voltage of the line.
      2. The rated current of the circuit breaker ≥ the calculated load current of the circuit.
      3. The rated current of the circuit breaker tripper ≥ the calculated load current of the circuit.
      4. The ultimate breaking capacity of circuit breaker ≥ the maximum short-circuit current in the circuit.
      5. The instantaneous (or short delay) tripping setting current of the automatic switch at the end of the line is not less than 1.25 times of the single relative ground short circuit current.
      6. The rated voltage of undervoltage tripper of circuit breaker = the rated voltage of line.

      Notices for Selection of China Circuit Breakers
      There are many ways to buy China circuit breakers on and off the line, but for such large devices, most people should go to physical stores to see the goods and determine their quality. They believe that the warranty, delivery and return of physical stores are more convenient, which is also an important reason for their purchase here. We can choose any way to buy, but how to choose? Will it fall into a misunderstanding? It's not easy to choose a good product. Let's follow the editor.
      It's tragic to choose the most important thing that suits you when purchasing, and not to spend the last money on the contrary. The purchase rate of this product is not low, but you need to have a goal, clear what you want to buy, performance requirements to be well-informed, and really use its functions.
      We need to carefully observe the quality of the products when we choose and buy them. We can't have some physical injuries, scratches, etc. We need to look carefully, otherwise it's hard to find them. You can try to observe from different angles, horizontal and vertical visual angles, and tilt angles. Or to observe in different light, to ensure that there is no omission before you can rest assured, to avoid some merchants "fish eyes mixed beads".
      After checking, as a user, we should experience the function of circuit breaker. If not, how can we know whether it is good or not? In its use, some functions will be greatly discounted if they are repeatedly used. If they are used more times, it will not be guaranteed that its elasticity will be good or its sensitivity will be reduced. Through the test of related functions, test one by one, put some of the main functions on trial. In the selection, we should be absolutely sure, ask the manufacturer about the situation, and be prepared beforehand.
      Delivery also needs attention. Whether the merchant delivers the goods to his door or picks them up by himself, you need to ask clearly how to guarantee if something goes wrong. Ask how long it will last and so on. All these questions need to be answered one by one. Otherwise, it will be you who will suffer.
      Finally, when purchasing China circuit breakers, we need to check the invoice information to see whether the models are the same, because the brand models are very close, but the price gap is too far, especially for foreign investors, it is always good to pay attention to them. If the price you buy is too high or the quantity is too large, then the invoice should be paid more attention, otherwise you will encounter a lot of trouble when repairing and returning the goods. In addition, we need a guide to buy a business card. In case of problems, manufacturers, shopping malls and guides can find it and solve the problem more quickly.