A circuit breaker is a switch device that can close, carry and open the current under normal circuit conditions, and can also close, carry and open the current under abnormal circuit conditions within a specified time. Circuit breakers are classified into high-voltage circuit breakers and low-voltage circuit breakers based on their application scope. The boundary between high and low voltages is rather vague, and generally, anything above 3kV is considered high-voltage electrical equipment.
Circuit breakers can be used to distribute electrical energy, infrequently start asynchronous motors, and provide protection for power supply lines and motors, etc. When severe overloads, short circuits, or under-voltage faults occur, they can automatically cut off the circuit. Their functions are equivalent to the combination of fuse-type switches and over/under voltage relays, etc. Moreover, after breaking the fault current, the components generally do not need to be replaced. It has been widely applied.
In the generation, transmission and use of electricity, distribution is an extremely important link. The distribution system includes transformers and various high and low voltage electrical equipment. Low-voltage circuit breakers are a type of widely used electrical equipment. Working principle
Description
A circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a trip device, and a casing.
When a short circuit occurs, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the counterforce spring, and the trip device pulls the operating mechanism to act, causing the switch to trip instantly. When there is an overload, the current increases, and the heat generated intensifies. The bimetallic strip deforms to a certain extent, pushing the mechanism to act (the greater the current, the shorter the action time).
There are electronic types, which use transformers to collect the current of each phase and compare it with the set value. When the current is abnormal, the microprocessor sends a signal, causing the electronic trip device to drive the operating mechanism to act.
The function of a circuit breaker is to cut off and connect the load circuit, as well as to cut off the faulty circuit to prevent the accident from expanding and ensure safe operation. While a high-voltage circuit breaker needs to open 1500V of electric arcs with a current of 1500-2000A, these arcs can be stretched to 2 meters and still continue to burn without extinguishing. Therefore, arc extinguishing is a problem that high-voltage circuit breakers must solve.
The principle of arc extinguishing by blowing is mainly to cool the arc to weaken thermal ionization. On the other hand, by blowing the arc, the arc is elongated to strengthen the recombination and diffusion of charged particles, and at the same time, the charged particles in the arc gap are blown away to quickly restore the insulation strength of the medium.
Low-voltage circuit breakers are also called automatic air switches, which can be used to connect and disconnect the load circuit, and can also be used to control non-frequently started motors. Its functions are equivalent to the combined functions of knife switches, overcurrent relays, voltage loss relays, thermal relays, and leakage protection devices, etc., and is an important protective device in low-voltage distribution networks.
Low-voltage circuit breakers have multiple protection functions (overload, short circuit, under-voltage protection, etc.), adjustable action values, high breaking capacity, convenient operation, and safety. Therefore, they are widely used. The structure and working principle of low-voltage circuit breakers consist of an operating mechanism, contacts, protection devices (various trip devices), arc extinguishing system, etc.
The main contact of a low-voltage circuit breaker is operated manually or electrically to close. After the main contact is closed, the free-tripping mechanism locks the main contact in the closed position. The current trip device’s coil and the thermal trip device’s thermal element are connected in series with the main circuit, while the under-voltage trip device’s coil and the power supply are connected in parallel. When a short circuit or severe overload occurs in the circuit, the current trip device’s armature is attracted, causing the free-tripping mechanism to act, and the main contact breaks the main circuit. When the circuit is overloaded, the thermal trip device’s thermal element heats up, causing the bimetallic strip to bend, pushing the free-tripping mechanism to act. When the circuit is under-voltage, the under-voltage trip device’s armature releases. It also causes the free-tripping mechanism to act. The reed trip device is used for remote control and is in a de-energized state during normal operation. Pressing the start button will energize the coil. [1]
Main Characteristics
The characteristics of the circuit breaker mainly include: rated voltage Ue; rated current In; the setting range of overcurrent protection (Ir or Irth) and short-circuit protection (Im); rated short-circuit breaking current (for industrial circuit breakers Icu; for household circuit breakers Icn); etc.
Rated working voltage (Ue): This is the voltage at which the circuit breaker operates normally (without interruption).
Rated current (In): This is the maximum current value that the circuit breaker with a dedicated overcurrent trip relay can withstand under the specified environmental temperature by the manufacturer, and will not exceed the temperature limit specified for the current-bearing components.
Short-circuit relay trip current setting value (Im): The trip current setting value of the short-circuit relay (instantaneous or short-delay) is used when a high fault current value occurs, causing the circuit breaker to trip quickly. The trip limit Im.
Rated short-circuit breaking capacity (Icu or Icn): The rated short-circuit breaking current of the circuit breaker is the highest (expected) current value that the circuit breaker can break without being damaged. The provided current value in the standard is the root mean square value of the alternating current component of the fault current, and the calculation standard value assumes that the DC transient component (always present in the worst-case short-circuit situation) is zero. The rated values for industrial circuit breakers (Icu) and household circuit breakers (Icn) are usually given in kA root mean square form.
Short-circuit breaking capacity (Ics): The rated short-circuit breaking capacity of the circuit breaker is divided into two types: rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity. The national standard “Low-voltage Switchgear and Control Equipment – Low-voltage Circuit Breakers” (GB14048.2—94) explains the rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity of the circuit breaker as follows:
1. Rated limit short-circuit breaking capacity: The breaking capacity under the specified test procedures and conditions, excluding the circuit breaker’s ability to continue carrying its rated current.
2. Rated operating short-circuit breaking capacity: The breaking capacity under the specified test procedures and conditions, including the circuit breaker’s ability to continue carrying its rated current.
3. The test procedure for rated limit short-circuit breaking capacity is O-t-CO.
The specific test is: Adjust the line current to the expected short-circuit current value (for example, 380V, 50kA), and the test button is not pressed. The tested circuit breaker is in the closed position, and press the test button. The circuit breaker breaks through 50kA short-circuit current, and the circuit breaker immediately opens (open abbreviated as O), the circuit breaker should be intact and be able to close again. t is the intermission time, generally 3 minutes. At this time, the line is still in the warm standby state, and the circuit breaker performs another connection (close abbreviated as C) and immediately opening (O) (the connection test is to assess the electrical and thermal stability of the circuit breaker under peak current). This procedure is CO. If the circuit breaker can fully break, then its limit short-circuit breaking capacity is qualified.
4. Rated operating short-circuit breaking capacity (Icn) of the circuit breaker (Icn) is tested according to the procedure O-t-CO-t-CO. It has an additional CO compared to Icn’s test procedure. After the test, if the circuit breaker can fully break, extinguish the arc, it is determined that its rated operating short-circuit breaking capacity is qualified.
Therefore, it can be seen that the rated limit short-circuit breaking capacity Icn refers to the low-voltage circuit breaker being able to operate normally and break this short-circuit current once again after breaking the maximum three-phase short-circuit current at the circuit breaker’s outgoing terminal. As for whether it can be normally connected and broken in the future, the circuit breaker does not guarantee it; while the rated operating short-circuit breaking capacity Ics refers to the circuit breaker being able to break and extinguish the arc multiple times when the maximum three-phase short-circuit current occurs at the circuit breaker’s outgoing terminal. The IEC947—2 standard for “Low-Voltage Switchgear and Controlgear – Low-Voltage Circuit Breakers” stipulates: For Class A circuit breakers (those with only overload long-delay and short-circuit instantaneous protection), the Ics can be 25%, 50%, 75%, and 100%. For Class B circuit breakers (those with three-stage protection including overload long-delay, short-circuit short-delay, and short-circuit instantaneous protection), the Ics can be 50%, 75%, and 100% of the Ics. Thus, it can be seen that the rated short-circuit breaking capacity is a lower breaking current value compared to the rated limit short-circuit breaking current. [1]
Generally speaking, circuit breakers with three protection functions – overload long delay, short circuit short delay, and short circuit instantaneous trip – can achieve selective protection. Most main lines (including the outgoing terminals of transformers) adopt them as the main protection switches. Circuit breakers without the short circuit short delay function (only having overload long delay and short circuit instantaneous trip two protection stages) cannot perform selective protection. They can only be used for branch lines. IEC92 “Marine Electrical” states: Circuit breakers with three protection stages are mainly focused on their operating short-circuit breaking capacity value, while circuit breakers used for branch lines should ensure they have sufficient limit short-circuit breaking capacity value.
Regardless of which type of circuit breaker, although they all have these two important technical indicators – Icu and Ics. However, as the circuit breaker used on branch lines, it can only meet the rated limit short-circuit breaking capacity. The more common bias is to prefer a larger one rather than a suitable one, believing that a larger one is safer. But taking too large a value will cause unnecessary waste (for the same type of circuit breakers, the H-type – high breaking capacity type, is 1.3 to 1.8 times more expensive than the S-type – ordinary type). Therefore, there is no need to blindly pursue the operating short-circuit breaking capacity index of the circuit breaker on the branch line. For circuit breakers used on the main line, not only the rated limit short-circuit breaking capacity requirements should be met, but also the rated operating short-circuit breaking capacity requirements should be met. If only the rated limit short-circuit breaking capacity Icu is used to measure whether the breaking capacity is qualified, it will bring unsafe hazards to users.
Circuit breakers are a basic low-voltage electrical appliance. Circuit breakers have overload, short circuit and undervoltage protection functions, and have the ability to protect lines and power sources.
The main technical indicators are rated voltage and rated current. Circuit breakers have different functions according to different applications, with many varieties and specifications, and many specific technical indicators.
Circuit breaker free tripping: At any moment during the closing process of the circuit breaker, if the protection action connects the trip circuit, the circuit breaker can completely and reliably open, which is called free tripping. Circuit breakers with free tripping can ensure that the circuit breaker can quickly open during short-circuit faults when closing, and can avoid expanding the scope of the accident. [1]
Main Categories
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By polarity: there are single-pole, double-pole, triple-pole and quadruple-pole types;
By installation method: there are plug-in type, fixed type and drawer type, etc.
Product Introduction A9/EC65 Miniature Circuit Breaker: for lighting distribution circuits, short circuit and overload protection.
A9LE/EPNLE Leakage Circuit Breaker: in grounding systems, short circuit, overload and leakage protection. Normal operation fault protection of the circuit breaker keeps the live wire and neutral wire disconnected when the circuit breaker is in the open position, avoiding power supply being live in case of neutral wire failure. During the operation of connecting and disconnecting, the neutral wire is connected first, and the disconnection is delayed. It has short circuit current limiting function, with high rated short circuit breaking capacity. It has overload protection, short circuit leakage and voltage protection devices, complete protection functions, and reliable wiring and connection.
Overvoltage and Undervoltage Trip Unit: The fully automatic overvoltage and undervoltage delay protector is a new generation product developed according to market needs. This protector is designed reasonably and assembled with imported components and domestic famous components. The product can quickly and reliably switch power sources under high voltage impact and undervoltage conditions, protecting household appliances. When the voltage returns to the normal value, it can automatically reconnect the circuit and restore power supply after a delay, effectively protecting appliances from power supply instantaneous connection shock. All functions are fully automated, no need for专人operation， and the dual-color light-emitting diode indicator is selected. Safe and fast.
EC100 Miniature Circuit Breaker： for industrial distribution systems， short circuit and overload protection. Rated current 63A – 125A， high rated short circuit breaking capacity， short circuit current limiting structure. Complete protection functions， overload and short circuit protection devices， safe and reliable wiring and connection， “frame type” wiring structure， simple function expansion， safe and reliable. Can be equipped with various accessories： leakage trip unit， auxiliary contact， alarm contact， de-energizing trip unit， undervoltage trip unit， bus bar.
EPD Surge Protector： EPD plug-in type adopts the same working principle and selection criteria as the fixed-type surge protector. It protects against indirect lightning and direct lightning effects or other instantaneous overvoltages.
EIC1 AC Contactor： mainly used for industrial power distribution systems， short circuit and overload protection. Rated voltage 50Hz or 60Hz up to 660V， high rated short circuit breaking capacity， short circuit current limiting structure. Complete protection functions， overload and short circuit protection devices， safe and reliable wiring and connection， “frame type” wiring structure， simple function expansion， safe and reliable. Can be equipped with various accessories： leakage trip unit， auxiliary contact， alarm contact， de-energizing trip unit， undervoltage trip unit， bus bar.
ENS Molded Case Circuit Breaker： Molded case circuit breaker is one of the new types of circuit breakers developed by integrating international advanced technologies. It is used in distribution network circuits with rated insulation voltage of 800V， suitable for 50Hz and 60Hz AC， rated working voltage up to 690V， rated working current from 6A to 1250A， to distribute electric energy and protect lines and power equipment from damage caused by overload， short circuit， undervoltage and other faults. It can also be used as a non-frequent motor starting and overload short circuit undervoltage protection. This circuit breaker has the characteristics of small size， high breaking capacity， short arcing (or no arcing)， and is an ideal product for users. The circuit breaker can be installed vertically (i.e.， upright) or horizontally (i.e.， horizontal).
ENSLE Molded Case Leakage Circuit Breaker： used for indirect contact protection of people， can also prevent fire hazards caused by insulation damage of equipment， generating grounding fault current， and can be used to distribute electric energy and protect lines and power equipment from overload and short circuit， and can also be used for non-frequent switching of lines and non-frequent starting of motors. The leakage protection module of the conventional residual current protection circuit breaker takes the power sampling of two phases. This series of circuit breakers is three-phase. If any one phase is missing， the leakage protection module of the circuit breaker can still work normally. The rated residual action current and maximum opening time can be adjusted according to actual conditions.
EGL-125 Isolating Switch： Isolating switch is the most commonly used electrical appliance in high-voltage switchgear， serving to isolate circuits. Its working principle and structure are relatively simple. However, due to its large usage volume and high reliability requirements, it has a significant impact on the design, establishment, and safe operation of substations and power plants. The main feature of the circuit breaker is that it has no arc extinguishing capability and can only open or close the circuit without load current. EGL-125-4000A is suitable for switching two low-voltage circuits or converting and safely isolating two load devices.
EATS3 Dual Power Conversion Switch: It uses two power sources to ensure the reliability of power supply. This product performs reliable switching between the two power sources. This product has two switching functions: automatic transfer and automatic transfer without automatic re-energization. This is a manual conversion switch. It is designed innovatively, safe and reliable, has a high degree of automation, and has a wide range of applications.
EW45 Universal Intelligent Circuit Breaker: It is mainly used to distribute electrical energy and protect lines and power equipment from damage caused by overload, short circuit, under-voltage, single-phase grounding, etc. This circuit breaker has multiple intelligent protection functions and can be used for selective protection, with precise operation and avoiding unnecessary power outages, improving power supply reliability and safety. [1]
Components
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Internal attachments
Auxiliary contacts: Contacts that mechanically link with the main circuit opening and closing mechanism of the circuit breaker. They are mainly used for displaying the opening and closing status of the circuit breaker, and are connected to the control circuit of the circuit breaker to control or interlock related electrical appliances through the opening and closing of the circuit breaker. For example, they output signals to signal lights, relays, etc. The rated current of the plastic housing circuit breaker frame is 100A for single-point conversion contacts, 225A and above for bridge contact structure, and the agreed heating current is 3A; for frame rated current 400A and above, two normally open and two normally closed can be installed, and the agreed heating current is 6A. The number of operation performances is the same as the total number of operation performances of the circuit breaker.
Alarm contacts: Alarm contacts used for circuit breaker accidents, and this contact only operates when the circuit breaker trips and opens. They are mainly used for free tripping when the load of the circuit breaker has overcurrent short circuit or under-voltage faults. The alarm contact converts from the original normally open position to the closed position, and connects the indicator lights or bells, buzzers, etc. in the auxiliary circuit to display or alert the fault of the circuit breaker.