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In high-voltage and medium-voltage power systems, circuit breakers and isolating switches (also known as disconnecting switches) are two core components that are often mentioned together but have different responsibilities. Although both are used for circuit management, there are essential differences in function positioning, working principle, and application scenarios, and confusion in use may lead to operational errors, equipment damage, and even serious safety accidents.
Professional high-voltage switchgear supplier Chuanli with deep cultivation of high-voltage switchgear field, mainly high-performance isolation switch and supporting circuit breaker products. This article will systematically sort out the core differences between the two types of equipment, clarify their respective application boundaries, and explain how to choose and use them reasonably, so as to help you establish a clear understanding of these key power components.
The differences between circuit breakers and isolating switches span multiple dimensions, including function, performance, and structure. The following is a detailed comparison from six core aspects:
The core function of circuit breaker is “active protection and current interruption”. It monitors the circuit status in real time, and when there are faults such as overcurrent, short circuit, and overvoltage, it can quickly trip and cut off the current in milliseconds, thus preventing the fault from expanding and protecting the safety of power equipment and the power grid.
Isolating switches, also known as disconnecting switches, focus on “passive isolation and safety protection”. Its main function is to form a reliable visible break gap between the equipment to be maintained and the live power grid when the power system is repaired, ensure that the maintenance section is completely de-energized, provide a safe working environment for maintenance personnel, and itself does not have the ability to actively handle faults.
Circuit breakers are specially designed for operation with load, equipped with a precise arc extinguishing system, and can reliably interrupt or connect load current in normal operation, and quickly cut off huge fault current in emergency situations. This ability to operate under load is the core feature that distinguishes it from other switches.
The isolating switch has no arc extinguishing device, so it is strictly forbidden to operate under load. It can only operate after the circuit is unloaded or the current has been cut off by the circuit breaker. For example, the GGW4-12 series circuit breaker specified in the product manual clearly states that it is prohibited from being used to connect or disconnect load current to prevent the burning of contacts or damage to equipment.
The circuit breaker has an independent and complete fault protection system, Usually, it is equipped with relay protection devices or intelligent control modules. When the system parameters exceed the set threshold, the protection system will immediately send a trip signal, and the circuit breaker will perform a disconnection action, like a “safety officer” actively responding to danger.
An isolating switch, on the other hand, does not have any fault protection capability and can only isolate circuits passively, without responding to any fault signals. Even if the connected device fails, it cannot take any protective measures, and its security value lies in “isolating danger” rather than “eliminating danger”.
The typical feature of an isolating switch is the presence of a visible contact gap. When it is in the open state, the moving and static contacts are completely separated, forming an air insulation gap that can be clearly observed by the naked eye. This gap intuitively proves that the circuit has been disconnected and is an important basis for ensuring the safety of maintenance personnel.
The circuit breaker has no visible contact gap, and its contacts are encapsulated in the arc extinguishing chamber. The status of opening and closing can only be judged by the indicator light or mechanical position indicator on the device, and cannot be directly observed. This design is to ensure the reliability of the arc extinguishing system, but it loses the intuitive safety reminder function.
The structure of circuit breaker is complex, mainly composed of contact system, arc extinguishing chamber, operating mechanism, protection system and insulating shell. Among them, the core component, the arc extinguishing chamber, needs to use special materials and precision processing technology to realize the rapid extinguishing of high-energy arcs, and the manufacturing difficulty and cost are relatively high.
The structure of the isolating switch is relatively simple, consisting of a contact system, an insulating support, an operating mechanism, and a frame. It does not require a complex arc extinguishing chamber, and its processing accuracy requirements are lower than those of circuit breakers. For example, the GGW4 series circuit breaker of Chuanli adopts modular design, is compact in size and easy to assemble, and has obvious cost advantages.
Circuit breakers are usually installed in the key parts of the power system that need fault protection, such as the entrance and exit lines of substations, the main lines of industrial and mining enterprises, the connection points of new energy power plants, and the distribution cabinets of high-rise buildings. They are the “first line of defense” for fault handling.
Isolating switches are often used in conjunction with circuit breakers, such as on both sides of circuit breakers in substations, at the front of distribution transformers, at branch points of distribution lines, and at outdoor distribution substations. Chuanli GGW4-40,5 series circuit breakers are widely used in 35kV substations to isolate transformers and circuit breaker equipment.
1.When should a circuit breaker be used?
In the following scenarios that require active fault handling and load-carrying operation capability, a circuit breaker should be selected:
Scenarios where circuits may generate fault currents such as short circuits, and the equipment needs to be protected in real time.
In situations where the load current needs to be frequently switched on or off, such as the power supply control of factory production equipment.
Places with high requirements for power supply reliability and need to quickly cut off faults to avoid large-scale power outages, such as hospitals and data centers.
High-voltage and high-current transmission and distribution links, such as substation main power supply lines.
2.When should a circuit breaker be used?
The isolating switch (also known as a disconnecting switch) is the optimal choice in the following scenarios, where the core requirement is safety isolation and there is no requirement for load operation:
When power equipment (such as transformers and capacitors) need to be repaired, it is necessary to form a visible break gap to ensure safety.
Fault lines need to be isolated to prevent the fault from spreading to other parts of the power grid.
Power supply mode conversion scenarios, such as switching between main and backup power sources in substations.
For outdoor distribution lines with stable load and simple isolation requirements, such as rural network and suburban road lighting power supply, the GGW4-12 series outdoor isolation switch from Chuanli is highly suitable for such scenarios.
In practical power systems, circuit breakers and isolating switches are not mutually exclusive, but rather complement each other to form a complete control and protection system. Their coordinated operations follow strict procedures, taking the inspection of substation equipment as an example:
Cut off the load current: First, operate the circuit breaker connected to the equipment to be repaired, cut off the load current in the circuit, and at this time, the circuit breaker completes the active protection and current interruption work.
Form the isolation gap: After confirming that the circuit breaker has been opened, operate the isolating switch on both sides of the circuit breaker to open it, forming a visible gap between the equipment to be repaired and the live power grid.
Grounding protection (optional): For high-voltage equipment, the grounding switch can be closed (usually integrated with the isolation switch) to transfer the residual charge of the equipment to the earth, further improving the safety of maintenance.
Recovery operation: After the inspection is completed, first close the isolating switch (isolating switch) to restore the circuit connection, and then close the circuit breaker (circuit breaker) to restore the power supply. The operation sequence cannot be reversed, and the isolating switch should not be operated under load.
The operation sequence of “the circuit breaker acts first and the isolation switch acts later” ensures the safe and reliable operation and maintenance of the power system. Keli isolation switch products can be equipped with mechanical interlocking devices with circuit breakers to prevent misoperation and ensure the correctness of operation sequence.
When setting up the power system, it is equally important to choose a reliable switch equipment supplier and to clarify the differences between circuit breakers and isolating switches. With its professional strength and high-quality products, Chuanli has won the trust of many customers, and its advantages are mainly reflected in the following aspects:
Complete product series: Chuanli provides a complete series of switchgear, including high-voltage circuit breakers, isolation switches (such as the GGW4 series), load switches, and ground switches, with voltage levels ranging from 12 kV to 126 kV. Customers can purchase all products in one place to avoid the trouble of matching different brand products.
Excellent product performance: Chuanli isolation switches use high-quality copper alloy contacts and epoxy resin insulating materials. The contact resistance is small and the corrosion resistance is strong. The outdoor series protection level reaches IP65, and can operate stably in harsh environments such as -40 ℃ to 60 ℃, heavy rain, strong sand and wind.The interrupting performance of the circuit breaker product is excellent, and it can reliably interrupt fault currents of up to 50kA.
Customized solutions: According to the specific needs of the customer’s power system (such as voltage level, installation environment, operation mode), Chuanli can provide personalized product customization services. For example, the GGW4 series isolation switches can be equipped with manual or electric operation mechanisms, and can also match interlocking devices to meet different application scenarios.
Strict quality control: All products of Chuanli have passed the national type test and obtained relevant qualification certificates. The production process implements strict quality control. From the purchase of raw materials to the product factory, multiple inspection links ensure that each product meets the standard requirements.
Perfect after-sales service: Provide pre-sales technical consulting, in-process installation guidance, and after-sales maintenance and maintenance services throughout the process. The professional technical team will respond quickly and solve customer problems in a timely manner. Field services can be provided for key projects to ensure the smooth operation of the equipment.
Circuit breakers and isolating switches are both indispensable components of power systems. However, there is a clear division of labor: the circuit breaker is the “active guardian” that handles faults and controls the load current, while the isolation switch is the “passive defender” that ensures the safety of maintenance and realizes circuit isolation. Clarifying the differences between the two is the basis for the safe and efficient operation of the power system.
In practical application, the two need to work together according to the operation process to form a complete control and protection system.
Whether it is substations, industrial enterprises or new energy power plants, choosing the switch equipment solution of Chuanli is to choose a solid guarantee for the safe and stable operation of the power system.
Q1: Why do substations require both isolators and circuit breakers?
A1: The two have complementary functions: the circuit breaker handles faults and load current, while the isolation switch provides visible isolation to ensure safety during maintenance.
Q2: Is a disconnecting switch the same as an isolating switch?
A2: Yes. The two are different names for the same device, and the core function is circuit isolation with a visible gap.
Q3: How do I choose the right isolator specifications?
A3: Refer to the reference system voltage/current, installation environment (outdoor optional, Chuanli GGW4 series) and operation mode, details can be consulted with Chuanli.
Q4: Can a circuit breaker act as an isolator?
A4: No. The circuit breaker has no visible gap and cannot replace the isolation and safety warning function of the circuit breaker.
Q5: Where are isolating switches commonly installed?
A5: Substation (next to circuit breaker), front end of transformer, outdoor distribution line, and power supply branch, etc.
