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Abstract: choose different types of short-circuit breaking capacity of the circuit breaker to adapt to different lines expected short-circuit current (when I in the same situation) needs Breaker selection principle is: short-circuit breaker circuit breaking capacity than the expected short-circuit current.
Keywords: Breaker points Distribution Line
1 、 A different load should use different types of circuit breakers
The most common are the load distribution lines, motor and household and similar home (lighting, appliances, etc.) three categories.。 This will correspond to the distribution of protection, the protection of electrical and household and similar home-breaker protection. The three circuit breaker protection and the protection of nature is not the same. The distribution of circuit breaker, it is in categories A and B of points: A non-choice type, the selection of Class B. By choice of means breaker
Delay has been contained, short-circuit short delay instantaneous and short-circuit protection of paragraph 3. Universal (also known as the frame) circuit breakers in DW15 series, DW17 (ME) series, AH DW40 series and, in most Conventional Series B, DZ5, DZ15, DZ20, TO, TG, nitrogen, and TM30 Molded series and Universal DW15, DW17 some of the specifications contained only a lapse, the second member of transient short-circuit protection, which is a non-choice of the Class A circuit breaker. Selective protection.
当When the F points short, only around F QF2 breaker point moves, the position of not QF1 breaker action, which is selective protection (as QF1 not move, not on the failure of QF3, QF4 slip maintain electricity).
If QF2 and QF1 are Class A circuit breaker, short-circuit occurred F point, short-circuit current value of a certain value, QF1, QF2 action at the same time, QF1 circuit breaker and all power under the slip, it would not be selective protection.
To achieve selective protection of the reason is that for the Class B QF1 breaker, it is short-circuit short latency performance, when F points short circuit, short-circuit current flowing QF2 slip, QF1 flow loop QF2 instantaneous action Release action (usually its wholly-off time less than 0.02s ), because QF1 short delay, QF1 will not move in the 0.02s (≥ its short delay 0.1s or 0.2,0.3,0.4 s). Moves to cut off the QF2 fault line, the whole system was restored to normal.
Thus, selective protection if it is to meet the requirements of the circuit breaker on a three paragraph should use a B-breaker protection. Motor protection for the direct protection of the motor circuit breaker, as long as it had set lapse and short-circuit protection instantaneous second member of the obvious, which means it can choose to Class A circuit breaker (including Molded Case and Universal), DZ5, DZ15, TO, TG, GM1, TM30, Molded and DW15 series except for the distribution of protection, and their Tech the following specifications are protected motor function.
Household and similar establishments protection (also called it the past Traverse protection or lighting protection), is a small Class A circuit breaker, its typical products C45N, PX200C, HSM8 and so on.
Distribution (Wiring), and household and motor overcurrent protection circuit breakers for the protection of objects (such as transformers, wire and cable, electrical and household appliances, etc.) under the load current capability (including motor starting current and the starting time) difference, therefore, the choice circuit breaker protection features are different.
1) Table 1-breaker protection for the distribution of anti-off time of Note: can return characteristics: Taking into account the distribution lines within Motor Group, because motor load is only part of a motor and not starting at the same time, it identified as 3In (In the breaker rated current , In ≥ IL, IL lines for the current ratings), the circuit breaker test, test, maintain current of 3In 5s (In ≤ 40A), 4-8 (40A 250A), and then return to current In, circuit breakers should not move, which is the return characteristics.
(2) Table 2 for motor protection circuit breaker - type of time off Note: Supported by the motor can choose nature 2,4,8 and 12 minutes of action, the general election 2 ~ 4 min. 7.2In is to be a characteristic, it must avoid the starter motor current (5 to 7 times In), Tp for the delay, according to the optional nature of the load motor movements for the time Tp 2s (3) protection of the instantaneous distribution of the current setting 10In (error of ± 20%), and 400A In the above specifications, and the alloy can alternatively 10In (by the user, factory setting); Motor protection of the instantaneous dynamic setting for the current 12In generally located In time can mean motor rated current.
(4) Table 3 for the home and similar places with a breaker of the Release Notes: B, C, D type is the type of instantaneous Release: B-Release Current> 3 ~ alloy, C-Trip current> 5 ~ 10In, D-Release Current> 10 ~ 50In. Users may need the protection of the objects, hold them in kind.
，3～6In(Inm为2500A、4000A时)，。 (5) Category B short-circuit breaker short delay of DW15-breaker: 3 ~ 10In (Inm for 1600A, Inm shell for the current rating), 3 ~ 6In (Inm for the 2500A, 4000A), short latency time of 0.2 or 0.5s.3～12In ME-breaker: 3 ~ 12In short time delay 0 ~ adjustable 0.3s.0.4～15In， Conventional - breaker: 0.4 ~ 15In short time delay adjustable TEM and 0.4s. In engineering design, according to the load of different objects to choose a different protection characteristics (as noted above) the circuit breaker to avoid the improper selection of serious consequences. In practice most likely to confuse the motor load is chosen as the protection of misuse of power distribution protection or protection of home. Miniature Circuit Breaker (MCB) are motor-protection, such as Tianjin, Lan Mei-the C45AD, they should be consistent with the protection of Table 2.
2, choose different types of short-circuit breaking capacity of the circuit breaker to adapt to different lines expected short-circuit current (when I in the same situation) needs Breaker selection principle is:
Short circuit breaker circuit breaking capacity than the expected short-circuit current.
Assumptions a power supply (transformer SL710/0.4kV) while the capacity of secondary current of 2312A, 5m at the end against short circuit current of 42.96kA. A slip of the rated current of 125A, as the slip road from the transformer close, as in the 10m, while the slip road circuit breakers need to consider using HSM1_125H - Molded Case Circuit Breaker (the limit short-circuit breaking capacity of 400V, J). But 50m from the transformer, such as bus resistance and reactance of value, the short-circuit current 50m Department has declined to 34.5kA and 100m, demoted to 28.8kA.This can choose HSM1_125M - Molded Case Circuit Now many domestic circuit breaker manufacturers, the same shell the current level of short-circuit breaking capacity into E, S, M, H, L (Hangzhou Jiang Switch Factory Molded series), or C, L, M, H (Changshu Switch plant nitrogen series) or S, H, R, U (Tianjin low-voltage electrical company TM30 series) level. Among them, E-economy, the standard S, M for breaking-in short, to score off of H, L-limited flow, C for economic, L for low scores broken; M-off score, for the high H-breaking; S for standard, off-H for the high score, the current limit of R, U of ultrahigh-breaking. To HSM1_125 - MCCB example, the E-type limit short-circuit breaking capacity of 400V, Output, S-400V for, beam, the M-400V, 35kA, the 400V H, J. Their prices also vary greatly, such as E-1, S-120, M-140, H-2, H-purchase of a circuit breaker money can buy two Taiwan-E. Users in the design selection, not artificially add the so-called coefficient of insurance to avoid wastage.
3, the circuit breaker on the short circuit breaking capacity limit, running short circuit breaking capacity and the current short-term tolerance
Limit short circuit breaking capacity (Icu), refers to a certain test parameters (voltage, short-circuit current, power factor) conditions, as a pilot program to get through, breaking the short-circuit current, fractured by this - not to renew its rated load current of breaking capacity. Its testing procedures for the 0-t (online) C0 ( "0" for breaking, t intermittent time, usually 3 minutes, "C0" said immediately after breaking connected).Test after test Release seized and the frequency of pressure.
Running short circuit breaking capacity (Ics), refers to a certain test parameters (voltage, short-circuit current, and power factor) conditions, as a pilot program to get through, breaking the short-circuit current, as this fractured Qualcomm, will continue to carry its rated current capacity of breaking it testing procedures for the 0-t (online) C0-t (online) C0.
0.05Short-term tolerance current (Icw), refers to a certain voltage, short-circuit current, power factor, or endure 0.05,0.1,0.25,0.5 1s and not allowed to release the circuit breaker, Icw short delay in the release, Stability of electric circuit breakers and thermal stability assessment targets, it is against the Class B circuit breaker, the minimum is usually Icw: When In ≤ 2500A, or it 12In 5kA, In> 2500A, it is 30kA (DW45_2000 the Icw to 400V, J, DW45 _3200 the Icw to 400V, 65kA).
Running short circuit breaking capacity of the extremely harsh conditions (first breaking, second-off), because it will continue to test the rated load current (for the life of their number to 5%), it not only validate Release characteristics, the frequency pressure, but also validated temperature.IEC947_2 (and the new IEC60947_2 1997) and China's national standards GB140482, Ics can limit short-circuit breaking capacity Icu Numerical 25%, 50%, 75% and 100% (B circuit breaker of 50%, 75% and 100% category B with 25% for the majority of its protection is the main trunk line).
The above-mentioned option circuit breaker is an important principle of a short circuit breaker circuit breaking capacity than the expected short-circuit current, the circuit breakers are usually short-circuit breaking capacity refers to its limit short-circuit breaking capacity.
Both Class A or Class B circuit breakers, and their running short circuit breaking capacity is less than the vast majority of its limit short-circuit breaking capacity of Icu. A类：DZ20系列Ics＝50%～77%Icu，CM1系列Ics＝58%～72%Icu，TM30系列Ics＝50%～75%Icu，(个别产品Ics＝Icu)。 A: DZ20 series Ics = 50% to 77% Icu, wholly series Ics = 58% to 72% Icu, TM30 series Ics = 50% to 75% Icu (individual products Ics = Icu).
DW45系列Ics＝62.5%～80%Icu。 Category B: DW15 series Ics = 60% Icu, (such as individual 630AIcs Icu =, but only short-circuit breaking capacity of 30kA at 400V), Series Conventional Ics = 62.5% to 80% Icu.
Both Class A or Class B breaker, as long as it Ics with IEC947_2 (or GB14048) standards for Icu percentage value of a qualified product.
Users choose the design of the circuit breaker when they meet short-circuit breaking capacity limit ≥ line short-circuit current can be expected to meet the requirements of the line itself, for example, the above example is the transformer capacity while the lines may arise about 43kA short-circuit current, it is only calculated from the distance between the transformer 5m , and the knife switch, transformer and circuit breaker resistance are calculated as zero (thus short-circuit current than the actual situation beingSuch short-circuit the very small probability.In selecting devices, as long as it limits short-circuit breaking capacity> 43kA, such as J was sufficient. A "0" first, "C0" Once completed its mission, we must replace the circuit breaker, short-circuit breaking capacity running, for example, 50% Icu , also reached beam, both can be achieved first breaking, second-off (in the short-circuit current beam) then fault current to carry its rated current task is very arduous. According to some users that run short circuit breaker breaking capacity (Ics) ≥ line short-circuit current is expected to design, in fact, is a misunderstanding, but also unnecessary.
Some factories in the sample publicity, its products Ics = Icu, if it indicated its Icu indicators margin, if not indeed, that it is water, not the whole letter, but Ics = Icu breaker, much higher price, uneconomical.
Popular abroad for decades a cascade (cascade) protection (also known as backup protection), in figure 2 QF2 selected short circuit breaker breaking the limit of its capacity is less than the expected short circuit breaking capacity (for example, the rated current of 250A circuit, short-circuit current and expected to spark), QF2 choice the HSM1_250S Breaker (Icu to 400V, 35kA), when a short circuit at F (short-circuit currents up to J), by QF1 (at the rated current QF1 for 400A, QF1 election HSM1_400H, Icu for 400V, 65kA), and with breaking QF2 , QF2 bear only part of the breaking of short-circuit current, the rest of the commitment by QF1), and right QF2 most of the line is less than 35kA the fault current, borne by the QF2. This cascade protection have certain conditions, such as the slip road adjacent load is not important (because once QF1 tripping circuit also QF3 power), while the blink of QF1 setting value and QF2 blink fixed value to the coordination, this cascade main purpose is to protect savings investment.
Reference should be made that all the short-circuit breaker breaking capacity (whether or Icu Ics) are periodic components RMS. 在短路试验中的“C0”的C( In short circuit test of "CO" C (close access) is the current peak current Ich. In short circuit test station for the breaking tests, voltage, short-circuit current (RMS), and power factor (cos) has adjusted well, it will be connected to current defined. Connect current test ( "C" test), the peak current is to contact and the assessment of other affordable electrical conductivity and thermal stability of repulsion, what kind of RMS current (breaking current), in the corresponding power factor, what will be the peak current, the use of the need to consider this peak current parameters. 表4 Table 4
The peak current (Impulse Current) = ich evaluated (radical sign) 2Ic, Ic cycle component RMS, evaluated the impact of a coefficient 4, the selection of four pole circuit breaker
The following cases, it is necessary to use a circuit breaker 4: 1) a two-switching power supply requirements of the system must choose four pole circuit breaker, the entire system to meet the maintenance, repair, testing and isolation; 2) single-phase residential household should use the switch with a two N pole switch (available four pole circuit breaker); 3) Residual Current Protection (switch leakage), we must guarantee the protection circuit of all live wires disconnect, therefore, the residual current operated circuit protection requirements should be selected with great N (quadrupole) leakage circuit breakers. At present, domestic market supply of four very MCCB six types: a) N breaker with the most current Release, N Poles and the other three lines of a circuit with a points; 2) N breaker with the most current Release, N is always connected, and the other three phase lines with a disconnect; 3) N breaker with the most current Release, N Poles and the other three lines of a circuit with a points; 4) N breaker with the most current Release, N is always connected, and the other three lines of a very disconnected; 5) Broken Road-N is installed for the protection of neutral line broken, N most of the other three lines with a very sub-circuit; 6) N breaker is installed for the protection of neutral line broken, N is always connected, and the other three lines of a very disconnected. 11) and 2) applies to type neutral line current phase of not more than 25% of the current normal state (Transformer group linked to Yyno label), 2) type applies to TN_C System (PEN line allowed disconnected); 3) and 4) apply to Type 3 phase load imbalance, and a large load of electronic equipment (great harmonic components), resulting in line N equal to or greater than the current line of current, and N lines are not using a three-phase overcurrent Release action to cut off the fault; 4) type system for TN_C ; 5) and 6) for the type of line break in neutral, and cut off the center line to protect the three-phase single-phase equipment to avoid damage and indirect electrocution incidents, 6) type suitable for TN_C system. |
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