Meaning of circuit breaker parameters detailed explanation of high voltage circuit breaker and low voltage circuit breaker parameters
Meaning of low voltage circuit breaker parameters
1 , the rated current of the circuit breaker In. It is the maximum continuous current carried under a given ambient temperature condition without abnormal heating to ensure the normal operation of the circuit breaker, also known as the rated current of the release.
2. Rated current of frame level. It represents the class of the size of the circuit breaker, which indicates the maximum rated current of the circuit breaker.
Such as: Schneider NS160N TMD80, which means Schneider NS160A frame, N means that the ultimate breaking capacity is 36KA under AC380/415V conditions, TMD80 means that the rated current of thermal magnetic release for power distribution is 80A.
3. The short-circuit breaking capacity of the circuit breaker:
The ultimate short-circuit breaking capacity Icu. Under the conditions of specified voltage, current and cosΦ, it performs two test procedures of o-co, which can completely break and extinguish the arc without exceeding the specified damage (contact damage and arcing damage). After the test product is tested, it is subjected to a certain power frequency withstand voltage test, and the overload release can trip normally under a certain set current. Satisfies the conditions specified in the specified test procedures, excluding the breaking capacity of the circuit-breaker to continuously carry its rated current capacity. It is expressed by the expected breaking current (kA) (in the case of alternating current, it is expressed by the rms value of the alternating current component).
Rated operational (working) short-circuit breaking capacity Ics. It performs three test procedures of o-co-co under the conditions of specified voltage, current and cos Φ, which can completely break and extinguish the arc without exceeding the specified damage. After the test, in addition to the verification test of the power frequency withstand voltage and overload release, the test product must also check the verification of temperature rise and operation performance (5% electrical life). meet the conditions specified in the specified test procedures, including the breaking capacity of the circuit-breaker to carry its rated current continuously. It is expressed by the expected breaking current (kA), which is equivalent to one of the specified percentages of the rated ultimate short-circuit breaking capacity and rounded to the nearest integer, which can be expressed as a percentage of Icu (for example, Ics=25[%]Icu). On the other hand, when the rated operating short-circuit breaking capacity is equal to the rated short-time withstand current, it can be specified according to the rated short-time withstand current value (kA), as long as it is not less than the corresponding minimum value. If the Icu using Category A exceeds 200kA, or the Icu using Category B exceeds 100kA, the manufacturer may declare an Ics value of 50kA.
Obviously Ics is stricter than Icu. In other words, after the Ics test, the product can continue to be used, but Icu is not the case, after the Icu test, the product can no longer be used. When we choose the circuit breaker, in order to ensure that the fault current can be disconnected reliably, without causing the fault to expand, and to ensure the continuity of the power supply after the fault. Generally, the short-circuit breaking capacity of the circuit breaker is selected according to Ics.
Rated short-time allowable (withstand) current Icw. The maximum short-circuit current that the circuit breaker can withstand in a short period of time (0.5 or 1S) without characteristic change. It reflects the short-circuit thermal stability performance of the circuit breaker in a short period of time.
Due to different usage conditions, the important circuit breaker with three-stage protection focuses on its rated operating short-circuit breaking capacity value, while the non-important circuit breaker mainly ensures that it has sufficient limit short-circuit breaking capacity value. My understanding of this is that after the fault current is removed from the important circuit, the circuit breaker needs to be able to continue to supply power, carry the rated current for a period of time, and be replaced at an appropriate time. For some important circuits, after the breaking of the limit short-circuit current and the closing and opening again, the mission has been completed, and the new one can be replaced by a power failure (the impact of a power failure is small). But whether it is frame type or molded case circuit breaker, there must be two important technical indicators of Icu and Ics. It’s just that the Ics value is slightly different on the two types of circuit breakers. The minimum allowable Ics of the molded case type can be 25[%]Icu, the minimum allowable Ics of the frame type is 50[%]Icu, and the circuit breaker with Ics=Icu is relatively rare. Molded case circuit breakers using rotary double breaking (point) technology have excellent current limiting performance and a large margin of breaking capacity, which can achieve Ics=Icu, but the price is very high.
In practice, it should be selected according to the usage conditions. When someone selects a circuit breaker according to the expected short-circuit current of the line calculated by him, he will judge a circuit breaker by the rated operation short-circuit breaking capacity of the circuit breaker (this The ultimate short-circuit capacity of the circuit breaker is greater than the expected short-circuit current of the line, and the operating short-circuit breaking capacity is lower than the calculated current) is unqualified. This is a misunderstanding.
4. The overload and short circuit protection characteristics of the circuit breaker. In the power distribution system protected by the circuit breaker, when a fault occurs, the circuit breaker closest to the fault point can correctly and selectively remove the fault according to the specified protection characteristics, while the circuit breakers at other levels do not act, so as to remove the fault. The power failure caused by the fault is limited to the minimum range, so that other fault-free power supply circuits can still maintain normal power supply, which is required for circuit breaker protection. The circuit breaker is equipped with four kinds of protection releases: ①long-time thermal overload protection with inverse time characteristics, ②short-circuit short-time delay protection with a certain time limit, ③short-circuit instantaneous protection, and ④grounding protection. In daily use, according to the intention of use and the technical and economic comparison, you can choose four types of protection, or you can choose three protections of long delay, instantaneous or short delay to form three-stage protection, and you can choose only long delay, Instantaneous two protections Two-stage protection, the short-circuit instantaneous opening time is generally within 20 ~ 30ms, and a circuit breaker with only instantaneous quick-break protection can also be selected.
5. Rated working voltage Ue. Generally, it represents the voltage between phases. For the three-phase four-wire neutral grounding system, it refers to the phase-to-ground voltage, including the phase-to-ground voltage (eg 277/480V), and for the three-phase three-wire ungrounded or impedance grounded system, it means the phase-to-ground voltage (eg 480V).
rated frequency of circuit breaker. If it is stipulated that the circuit breaker is only used for one frequency, the rated frequency should be marked (
6. Others include: use category, structure, number of poles, installation method, installation size, rated duty, protection Class (if not IP20), reference ambient air temperature (if not 30°C); isolation.
Isolation means: For safety reasons, cut off by separating it from all power sources The power supply of the whole device or one of its independent parts.
High voltage circuit breakerParameter meaning
1. Rated voltage (Nominal voltage): It is a parameter that characterizes the insulation strength of the circuit breaker, and it is the standard voltage for the long-term operation of the circuit breaker. In order to meet the requirements of the power system, the circuit breaker also specifies the highest working voltage corresponding to the rated voltage at all levels. For 3-220KV levels, the maximum working voltage is about 15% higher than the rated voltage; for 330KV and above, the maximum working voltage is about 10% higher than the rated voltage. The circuit breaker should be able to work reliably for a long time under the highest working voltage
2. Rated current: It is a parameter that characterizes the long-term current capability of the circuit breaker, that is, the maximum current that the circuit breaker allows to pass continuously for a long time.
3. Rated breaking current: It is a parameter that characterizes the breaking capacity of the circuit breaker. Under the rated voltage, the maximum current that the circuit breaker can ensure reliable breaking is called the rated breaking current, and its unit is the effective value of the cycle component of the instantaneous short-circuit current separated by the circuit breaker contacts. It is expressed in kiloamperes. When the circuit breaker works in a power grid with a voltage lower than its rated voltage, its breaking current can be increased. However, limited by the mechanical strength of the arc extinguishing chamber, the breaking current has a maximum value, which is called limit breaking Current.
4. Dynamic stable current: It is a parameter that characterizes the ability of the circuit breaker to pass short-term current, and reflects the ability of the circuit breaker to withstand the electrodynamic effect of short-circuit current. The circuit breaker is in the closed state or closed Instantaneously, the maximum peak value of the current allowed to pass through is called electrodynamic stability 5. Closing current: It is a parameter that characterizes the closing current capability of the circuit breaker. Because when the circuit breaker is connected to the circuit, there may be a short-circuit fault in the circuit. The circuit breaker will close a large short-circuit current. In this way, on the one hand, the electromotive force of the short-circuit current weakens the closing operation force, and on the other hand, because the contacts break down before they come into contact, an arc is generated, which may cause the contacts to melt. Welding, thereby causing damage to the circuit breaker. The maximum peak value of the current that the circuit breaker can reliably close is called the rated closing current. The rated closing current and dynamic stable current are equal in value, and both are equal to the rated breaking current. 2.55 times of .
6. Thermally stable current and duration of thermally stable current: The stable current is also a parameter that characterizes the ability of the circuit breaker to pass short-term current, but it reflects the ability of the circuit breaker to withstand the thermal effect of short-circuit current .Thermal stable current means that the circuit breaker is in the closed state, within a certain duration, the allowable The maximum effective value of the periodic component of the passing current, at which time the circuit breaker should not be damaged due to short-term heating. The national standard stipulates that the rated thermal stable current of the circuit breaker is equal to the rated breaking current. The duration of the rated thermal stable current is 2S, and 4S is recommended when more than 2S is required.
7. Closing time and opening time: These are the parameters that characterize the operating performance of the circuit breaker. Different types of circuit breakers have different opening and closing times, but they all require quick action. The closing time refers to the time from the closing coil of the circuit breaker operating mechanism to the contact of the main contact. The opening time of the circuit breaker includes two parts: the inherent opening time and the arc extinguishing time. The inherent opening time refers to the time from the opening coil of the operating mechanism to the separation of the contacts. The arc extinguishing time refers to the time from the separation of the contacts to the arc extinguishing of each phase. Therefore, the opening time is also called the full opening time.
8. Operation cycle: This is also an indicator to characterize the operation performance of the circuit breaker. Most of the short-circuit faults of overhead lines are temporary. After the short-circuit current is cut off, the fault disappears quickly. Therefore, in order to improve the reliability of power supply and the stability of system operation, the circuit breaker should be able to withstand one or more times of closing, opening, or immediate opening after closing. This operation of dividing and closing multiple times at a certain time interval is called an operation cycle.
The rated operating cycle of circuit breakers stipulated in my country is as follows:
Automatic reclosing operating cycle: minute——t’——close——t——close
Non-automatic reclosing operation cycle: open-t-close-open-t-close-open
Among them, open-indicates opening action;
close Minutes – indicates the action of opening immediately after closing; t’ – no-current interval time, that is, the time from the breaker to disconnect the fault circuit, from the arc extinguishing to the automatic reconnection of the circuit, the standard time is 0.3S or 0.5 S, that is, the reclosing action time.
t——For the operator to force the power transmission time, the standard time is 180S
