Let symmetrical breaking current = I. Circuit breakers breaking capacity is the rated RMS value of current that a CB can break at the rated voltage. Question 3: Why we need Icu and Ics and how Icu is different from Ics? Electrical calculators provides powerful automation tools to boost your productivity. BREAKING CAPACITY OF CIRCUIT BREAKER =SQRT(3) x V x I x 10-6 V is supply voltage I is circuit breaker capacity answer appears in MVA. Generally circuit breaker rating are defined in terms of breaking and making capacity. For making practical design another term Ics is used. Answer: The European industrial standards involve the use of k factor as 100%. It is mandatory to procure user consent prior to running these cookies on your website. Electrical calculators is collection of tools, reference tables, formulas and electrical reference tables which helps you boost your productivity. Therefore, making Current must be higher than the Breaking Current. have several parameters the manufacturer sets. The current breaking capacity corresponds to a certain voltage, so an electrical apparatus … Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. Question 4: What do you mean by Ics = 100 % Icu or Ics = 100 % Icn? We also use third-party cookies that help us analyze and understand how you use this website. 55 × Symmetrical breaking capacity, Where 2.55 is obtained by multiplying 1.8 by √ 2. Electrical calculators is collection of tools, reference tables, formulas and electrical reference tables which helps you boost your productivity. Find the making current. This category only includes cookies that ensures basic functionalities and security features of the website. This website uses cookies to improve your experience. These cookies will be stored in your browser only with your consent. We also use third-party cookies that help us analyze and understand how you use this website. Where 1.732 = √3 represents a multiplier for three phase circuits, Where M = Mega (A prefix representing 106). Answer: Icu is maximum fault current that could prevail in case of extreme menacing faults. Making and breaking capacity diffrent from each other. CO represents closing operation time which is immediately followed by an opening operation without any intentional time delay. B.C is always expressed in terms of MVA. A = Short-circuit current. So as to equate both equations: Ics = Icu. 1. First, circuit breakers (every kind, fuses, resettable, self resettable, etc.) It is maximum fault current that a CB should be able to interrupt. Practically there exist very small chances for occurrence of such faults. Breaking capacity (B.C) = 1.732 * V * I * 10-6. This website uses cookies to improve your experience while you navigate through the website. The prospective short-circuit current which can occur under short circuitconditions should not exceed the rated breaking capacity of the apparatus, otherwise breaking of the current cannot be guaranteed. Answer: Ics means service breaking capacity. Where k represents a percentage number eg 10%, 20%, 25%, 50%, 75%, or 100%. You also have the option to opt-out of these cookies. Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. Necessary cookies are absolutely essential for the website to function properly. Electrical calculators provides powerful automation tools to boost your productivity. This is the maximum current that the device can carry without opening. But opting out of some of these cookies may have an effect on your browsing experience. We'll assume you're ok with this, but you can opt-out if you wish. This website uses cookies to improve your experience while you navigate through the website. It can be very high such as of the order 5000 A in case of CB or even 5,00,000 A in case of MCCB. Where 1.732 = √3 represents a multiplier for three phase circuits. Where √ 2 is used to convert RMS symmetrical to peak and 1.8 is used for doubling effect of maximum symmetry. Solution: B.C = 1.732 * 33 kV * 50 A * 10-6 = 2.85 MVA. 55 × Symmetrical breaking capacity Where 2.55 is obtained by multiplying 1.8 by √ 2 Where √ 2 is used to convert RMS symmetrical to peak and 1.8 is used for doubling effect of maximum symmetry. Ics is the rated short-circuit breaking capacity. Example 2: Repeat the above example problem for I = 50 A, V = 33 kV. For example, if a circuit breaker has an Ics of 10,000 Amperes and an Icu of 20,000 Amperes: Any fault below 10kA will be cleared with no problem. One, and an important one, is the Hold Current. These cookies will be stored in your browser only with your consent. t = 0.3 sec for circuit breaker. A circuit breaker has symmetrical breaking current capacity of 25,000 A (rms). t’ is time between two operations which is necessary to restore the initial conditions and/or to prevent undue heating of conducting parts of circuit breaker.
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