Since Faraday discovered electromagnetic induction in 1831 and then made the first generator, electricity has been fully applied and developed to this day. In order to protect our electricity safety, various devices that can disconnect the circuit have been produced. Among them, surge devices, lightning arresters, leakage protection devices, circuit breakers, and circuit breakers are more familiar to everyone. However, everyone can't tell the difference between these types of protection devices. Today we will learn about the differences between surge devices, lightning arresters, leakage protection devices, circuit breakers, and circuit breakers. I hope it will be helpful for your future work and study.
Section 1 Overview of surge devices, lightning arresters, leakage protection devices, circuit breakers
1. Definition, working principle, classification and scope of application of surge protectors
1. Definition: Surge protector (SPD), also known as "lightning arrester" and "lightning arrester", is an electronic device that provides safety protection for various electronic equipment, instruments and meters, and communication lines. It is to limit the surges generated by strong transient overvoltages in electrical circuits and communication lines, thereby protecting equipment.
2. Working principle: When a spike current or voltage suddenly occurs in an electrical circuit or communication line due to external interference, the surge protector can conduct and shunt in a very short time, discharging the surge in the line into the ground, thereby avoiding damage to other devices in the circuit.
3. Classification:
1) According to the different protection devices, it can be divided into two categories: power surge protector and signal surge protector. Among them, the power surge protector can be divided into first-level power surge protector, second-level power surge protector, third-level power surge protector and fourth-level power surge protector according to the same capacity; signal surge protector can be divided into network signal surge protector, video surge protector, monitoring three-in-one surge protector, control signal surge protector, antenna signal surge protector, etc.
2) According to the selected surge protector and the expected environmental impact, the protection measures required for the power supply and equipment of the protection system are classified as follows:
(1) Class B surge protector: nominal discharge current In, impulse voltage 1.2/50 μs impulse voltage and maximum impulse current Iimp test, Iimp waveform is 10/350 μsUp maximum 4kv (IEC61643-1; IEC 60664-1).
(2) Class C surge protector: nominal discharge current In, impulse voltage 1.2/50 μs impulse voltage and maximum impulse current Iimp test, Iimp waveform is 8/25ms.
(3) Class D surge protector: mixed wave combination (open circuit voltage 1.2/50 μs impulse voltage, Deng circuit current 8/25 μs) test.
3) According to the working principle: According to its working principle, surge protectors can be divided into voltage switching type, voltage limiting type and combination type.
(1) Voltage switch type surge protector. It has high impedance when there is no transient overvoltage. Once it responds to lightning transient overvoltage, its impedance suddenly changes to low impedance, allowing lightning current to pass through. It is also called "short-circuit switch type SPD".
(2) Voltage limiting type surge protector. It has high impedance when there is no transient overvoltage, but its impedance will continue to decrease with the increase of surge current and voltage. Its current-voltage characteristics are strongly nonlinear, and it is sometimes called "clamp type SPD".
(3) Combined surge protector. It is composed of voltage switch type components and voltage limiting type components. It can show the characteristics of voltage switch type or voltage limiting type or both, which depends on the characteristics of the applied voltage.
4. Scope of application: It is suitable for AC 50/60HZ, rated voltage 220V/380V power supply system, to protect against indirect lightning and direct lightning effects or other transient overvoltage surges, and is suitable for surge protection requirements in residential, tertiary industry and industrial fields.
2. Definition, working principle, classification and scope of application of lightning arrester
1. Definition: Lightning arrester: An electrical appliance used to protect electrical equipment from high transient overvoltage hazards during lightning strikes, and to limit the follow-up time and often the follow-up amplitude. Lightning arresters are sometimes also called overvoltage protectors and overvoltage limiters.
2. Working principle: Lightning arresters are devices connected between wires and the ground to prevent objects from being struck by lightning, and are generally connected in parallel with the protected equipment. Lightning arresters can effectively protect power equipment. When abnormal voltage occurs, lightning arresters can produce corresponding effects and protect the protection equipment. However, when the protected equipment is operating under normal working voltage, lightning arresters will not have any effect and will be regarded as a circuit breaker for the ground. However, when high voltage occurs unexpectedly and endangers the insulation of the protected equipment, the lightning arrester will work immediately, directing the high voltage impact current to the ground, thereby limiting the voltage amplitude and insulating the electrical equipment. When the high voltage disappears, the lightning arrester will return to its original working state and ensure the normal power supply of the system.
3. Classification:
1) According to the structure, it is divided into tube-type arresters (including general tube-type and new type), valve-type arresters (including ordinary valve-type and magnetic blow-type), and zinc oxide arresters.
2) Zinc oxide arresters are further divided into metal oxide arresters, line-type metal oxide arresters, gapless line-type metal oxide arresters, fully insulated composite jacket metal oxide arresters, and removable arresters.
4. Scope of application: AC gapless metal oxide arresters are used to protect the insulation of AC power transmission and transformation equipment from lightning overvoltage and operation overvoltage damage. It is suitable for overvoltage protection of transformers, transmission lines, distribution panels, switch cabinets, power metering boxes, vacuum switches, parallel compensation capacitors, rotating motors and semiconductor devices.
III. Definition, working principle, classification and scope of application of air switches
1. Definition: Air switch, also known as air circuit breaker, is a type of circuit breaker. It is a switch that automatically disconnects as long as the current in the circuit exceeds the rated current. Air switch is a very important electrical appliance in low-voltage power distribution network and electric traction system, which integrates control and multiple protection functions.
2. Working principle: When the line is generally overloaded, the overload current cannot cause the electromagnetic release to operate, but it can cause the thermal element to generate a certain amount of heat, causing the bimetallic strip to bend upward due to heat, pushing the lever to disengage the hook from the lock, disconnecting the main contact and cutting off the power supply. When the line is short-circuited or severely overloaded, the short-circuit current exceeds the instantaneous tripping set current value, and the electromagnetic release generates a sufficiently large suction force to attract the armature and hit the lever, causing the hook to rotate upward around the rotating shaft seat and disengage the lock. The lock disconnects the three main contacts under the action of the reaction spring, cuts off the power supply, and protects the equipment in the line from damage due to excessive current.
3. Classification:
1) According to the structural characteristics, it can be divided into push button switch, toggle switch, membrane switch, mercury switch, lever switch, micro switch, travel switch, etc.;
2) According to the structural type, it can be divided into plastic shell type, frame type, current limiting type, DC fast type, demagnetization type and leakage protection type.
3) According to the number of poles and positions of the switch, it can be divided into single-pole unit switch, double-pole double-position switch, single-pole multi-position switch, multi-pole unit switch and multi-pole multi-position switch, etc.;
4) According to the use of the switch, it can be divided into power switch, recording and playback switch, band switch, pre-selection switch, limit switch, foot switch, conversion switch, control switch, etc.;
5) According to the protection form, it can be divided into electromagnetic release type, thermal release type, compound release type (commonly used) and non-release type;
6) According to the full breaking time, it can be divided into general and fast type (before the release mechanism is activated, and the release time is within 0.02 seconds).
4. Scope of application: Lighting, pump room and other power supplies can be controlled by air switches. In addition to completing the contact and disconnection of the circuit, it can also protect the circuit or electrical equipment from short circuits, severe overloads and undervoltages, and can also be used to start the motor infrequently.
III. Definition, working principle, classification and scope of application of leakage protector
1. Definition: Leakage protector, referred to as leakage switch, also called leakage circuit breaker, is mainly used to protect the equipment from leakage faults and personal electric shock with fatal dangers. It has overload and short circuit protection functions, which can be used to protect the line or motor from overload and short circuit, and can also be used for infrequent switching and starting of the line under normal circumstances.
2. Working principle:
1) When electrical equipment leaks electricity, two abnormal phenomena occur: one is that the balance of the three-phase current is destroyed and zero-sequence current appears; the other is that the metal shell that is not charged normally has a voltage to the ground (normally, the metal shell and the earth are both at zero potential).
2) The role of zero-sequence current transformer The leakage protector obtains abnormal signals through current transformer detection, and converts and transmits them through the intermediate mechanism to activate the actuator and disconnect the power supply through the switch device. The structure of the current transformer is similar to that of the transformer. It consists of two coils that are insulated from each other and wound on the same core. When there is residual current in the primary coil, the secondary coil will induce current.
3) Working principle of leakage protector The leakage protector is installed in the line, the primary coil is connected to the line of the power grid, and the secondary coil is connected to the tripper in the leakage protector. When the electrical equipment is operating normally, the current in the line is in a balanced state, and the sum of the current vectors in the transformer is zero (the current is a directional vector, such as the outflow direction is "+" and the return direction is "-". The currents in the transformer are equal in magnitude and opposite in direction, and the positive and negative currents cancel each other out). Since there is no residual current in the primary coil, the secondary coil will not be induced, and the switch device of the leakage protector is in a closed state. When the equipment casing leaks and someone touches it, a shunt is generated at the fault point. This leakage current passes through the human body? The earth? Working grounding returns to the neutral point of the transformer (without passing through the current transformer), causing the current flowing in and out of the transformer to be unbalanced (the sum of the current vectors is not zero), and the primary coil generates residual current. Therefore, it will induce the secondary coil. When this current value reaches the action current value specified by the leakage protector, the automatic switch will trip and cut off the power supply.
3. Classification:
1) Classification by protection function and structural characteristics: It can be divided into leakage protection relay, leakage protection switch, and leakage protection socket;
(1) Leakage protection relay refers to a leakage protection device that has the function of detecting and judging leakage current but does not have the function of cutting off and connecting the main circuit. The leakage protection relay consists of a zero-sequence transformer, a tripper, and an auxiliary contact for output signals. It can be used in conjunction with a large current automatic switch as the total protection of the low-voltage power grid or the leakage, grounding or insulation monitoring protection of the main road.
When there is leakage current in the main circuit, since the auxiliary contact and the disconnector of the main circuit switch are connected in series to form a circuit, the auxiliary contact connects the disconnector and disconnects the air switch, AC contactor, etc., causing them to trip and cut off the main circuit. The auxiliary contact can also connect the sound and light signal device to send out a leakage alarm signal to reflect the insulation condition of the line.
(2) A leakage protection switch refers to a switch element that can connect or disconnect the main circuit like other circuit breakers, and has the function of detecting and judging leakage current. When leakage or insulation damage occurs in the main circuit, the leakage protection switch can connect or disconnect the main circuit according to the judgment result. It can be combined with a fuse and a thermal relay to form a fully functional low-voltage switch element.
(3) A leakage protection socket refers to a power socket that can detect and judge leakage current and cut off the circuit. Its rated current is generally below 20A, the leakage action current is 6 to 30mA, and the sensitivity is relatively high. It is often used to protect handheld power tools and mobile electrical equipment and in civil places such as homes and schools.
2) Classification by working principle: voltage-operated leakage protector, current-operated leakage protector;
3) Classification by structural characteristics of intermediate links: electromagnetic leakage protector, electronic leakage protector;
4) Classification by rated leakage action current value: high-sensitivity leakage protector, medium-sensitivity leakage protector, low-sensitivity leakage protector.
5) Classification by action time: instantaneous leakage protector, delayed leakage protector, inverse time leakage protector;
6) Classification by the circuit of the main switch and the number of poles of the current: single-click two-wire leakage protector, secondary leakage protector, secondary three-wire leakage protector, tertiary leakage protector, tertiary four-wire leakage protector, tertiary leakage protector.
4. Scope of application:
1) Various low-voltage electrical equipment and sockets are used in places with high requirements for electric shock and fire prevention and in new, modified and expanded projects.
2) Hand-held power tools (except Class III), other mobile electromechanical equipment, and electrical equipment with high risk of electric shock.
3) Leakage protectors must be installed in places with humidity, high temperature, high metal occupancy coefficient, and other places with good conductivity.
4) Leakage protectors should not be used as substitutes for places where safe voltage should be used. If it is really difficult to use safe voltage, leakage protectors must be approved by the enterprise safety management department before they can be used as supplementary protection.
5) Leakage protectors with a rated leakage current not exceeding 30mA can be used as supplementary protection for direct contact when other protection measures fail, but they cannot be used as the only direct contact protection.
6) The selection of leakage protectors should be determined according to the protection range, personal equipment safety and environmental requirements. Generally, current type leakage protectors should be selected.
7) When the leakage protector is used for hierarchical protection, the selectivity of the upper and lower switch actions should be met. Generally, the rated leakage current of the upper leakage protector is not less than the rated leakage current of the lower leakage protector or twice the normal leakage current of the protected line equipment.
8) Under the condition that it does not affect the normal operation of the line and equipment (i.e., no misoperation), a leakage protector with a smaller leakage current and action time should be selected.
9) When overload protection or fire protection requirements are required, a leakage protector with overcurrent protection function should be selected.
10) In places with explosion hazards, explosion-proof leakage protectors should be selected; in places with high humidity and water vapor, closed leakage protectors should be selected; in places with high dust concentration, dustproof or closed leakage protectors should be selected.
IV. Definition, working principle, classification and scope of application of circuit breakers
1. Definition: Circuit breaker refers to a switch device that can close, carry and disconnect the current under normal circuit conditions and can close, carry and disconnect the current under abnormal circuit conditions within a specified time.
2. Classification:
1) According to the scope of use, it is divided into high-voltage circuit breakers and low-voltage circuit breakers. The boundary between high and low voltage is relatively vague. Generally, those above 3kV are called high-voltage electrical appliances.
Low-voltage circuit breakers are also called automatic switches, commonly known as "air switches", which also refer to low-voltage circuit breakers. It is an electrical appliance that has both manual switching functions and can automatically perform loss of pressure, undervoltage, overload, and short-circuit protection.
High-voltage circuit breakers are the main power control equipment of power plants and substations. They have arc extinguishing characteristics. When the system is operating normally, they can cut off and connect the no-load and load current of the line and various electrical equipment; when the system fails, it cooperates with the relay protection to quickly cut off the fault current to prevent the expansion of the accident scope.
2) Classification by number of poles: single pole, two poles, three poles and four poles, etc.
3) Classification by installation method: plug-in type, fixed type and drawer type, etc.
4) Classification by use category: selective type and non-selective type;
5) Classification by structural type: universal type and plastic shell type;
6) Classification by operation method: manpower operation, non-manpower operation, power operation, non-power operation and energy storage operation;
7) Classification by arc extinguishing medium used: air type and vacuum type;
3. Working principle:
1) Circuit breakers are generally composed of contact system, arc extinguishing system, operating mechanism, release, shell, etc.
2) When short-circuited, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the reaction spring, the release pulls the operating mechanism to operate, and the switch trips instantly. When overloaded, the current becomes larger, the heat generation increases, and the bimetallic strip deforms to a certain extent to drive the mechanism to operate (the larger the current, the shorter the operation time).
3) There are electronic types, which use mutual inductors to collect the current of each phase and compare it with the set value. When the current is abnormal, the microprocessor sends a signal to drive the electronic release to drive the operating mechanism.
4) The function of the circuit breaker is to cut off and connect the load circuit, as well as to cut off the fault circuit, prevent the accident from expanding, and ensure safe operation. The high-voltage circuit breaker needs to break the arc of 1500V and the current of 1500-2000A. These arcs can be stretched to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that high-voltage circuit breakers must solve.
5) The principle of arc blowing and arc extinguishing is mainly to cool the arc and weaken the thermal ionization. On the other hand, the arc is stretched by blowing 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 dielectric strength.
6) Low-voltage circuit breakers are also called automatic air switches, which can be used to connect and disconnect load circuits, and can also be used to control motors that are not frequently started. Its function is equivalent to the sum of some or all functions of electrical appliances such as knife switches, overcurrent relays, undervoltage relays, thermal relays and leakage protectors. It is an important protective electrical appliance in low-voltage distribution networks.
7) Low-voltage circuit breakers have multiple protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action values, high breaking capacity, convenient operation, and safety, so they are widely used. Structure and working principle Low-voltage circuit breakers are composed of operating mechanisms, contacts, protection devices (various releases), arc extinguishing systems, etc.
8) The main contacts of low-voltage circuit breakers are closed manually or electrically. After the main contacts are closed, the free tripping mechanism locks the main contacts in the closed position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the power supply. When a short circuit or severe overload occurs in the circuit, the armature of the overcurrent release is attracted, causing the free tripping mechanism to operate and the main contacts to disconnect the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats up and bends the bimetallic strip, pushing the free tripping mechanism to operate. When the circuit is undervoltage, the armature of the undervoltage release is released. It also causes the free tripping mechanism to operate. The shunt release is used for remote control. During normal operation, its coil is de-energized. When distance control is required, press the start button to energize the coil. 4. Scope of application:
1) High-voltage circuit breakers (or high-voltage switches) are the main power control equipment in power plants and substations. They have arc extinguishing characteristics. When the system operates normally, they can cut off and connect the line and the no-load and load current of various electrical equipment; when the system fails, it cooperates with the relay protection to quickly cut off the fault current to prevent the scope of the accident from expanding.
2) Low-voltage circuit breakers are widely used in feeder lines at all levels of low-voltage distribution systems, power supply control of various mechanical equipment, and control and protection of power terminals. They are used in various places such as industry, commerce, high-rise buildings and residential buildings.
Section 2 Differences between surge devices, lightning arresters, leakage protection devices, circuit breakers, and circuit breakers
1. Differences between surge devices and circuit breakers
1. Different working principles: When the transient overvoltage in the line increases, the surge protector will be turned on in time to discharge the overvoltage on the line to the ground; while the air switch will automatically disconnect when the current on the line exceeds the rated current to protect the electrical equipment.
2. Different protection functions:
Surge protectors are devices that protect electrical equipment, communication equipment, etc. in the line from damage caused by surges in the line, while air switches protect short circuits, overloads, etc. in the line.
3. Different protection ranges:
Surge protectors can not only protect power supplies, but also protect equipment on communication lines; air switches protect electrical equipment.
2. Differences between surge protectors and lightning arresters
Surge protectors and lightning arresters both have the function of preventing overvoltage, especially lightning overvoltage, but in terms of application, there are still obvious differences between the two.
1. Lightning arresters have multiple voltage levels, ranging from 0.38KV low voltage to 500KV ultra-high voltage, while surge protectors generally only have low-voltage products.
2. Lightning arresters are mostly installed on the primary system to prevent direct intrusion of lightning waves, while surge protectors are mostly installed on the secondary system. They are supplementary measures after the lightning arrester eliminates the direct intrusion of lightning waves, or when the lightning arrester does not eliminate the lightning waves completely.
3. Lightning arresters are used to protect electrical equipment, while surge protectors are mostly used to protect electronic instruments or meters.
4. Since lightning arresters are connected to the primary electrical system, they must have sufficient external insulation performance and a relatively large appearance size, while surge protectors can be made very small in size because they are connected to low voltage.
3. The difference between air switches and leakage protectors
1. Different control forms: air switches will be disconnected when a short circuit occurs in the circuit, while leakage protectors will be disconnected when they accidentally touch the circuit and cause electric shock.
2. Different power-off principles: The circuit breaker disconnects after inferring whether the circuit current is overloaded, while the leakage protector disconnects the switch when the human body touches the live wire. At this time, only the live wire has current and the switch is disconnected.
3. Different protection levels: The circuit breaker is overcurrent protection, while the leakage protector belongs to the milliampere level, so the power supply must be disconnected immediately.
4. Different protection functions: Generally speaking, the air switch is suitable for preventing the circuit from being overloaded and preventing the human body from being electrocuted, so it plays the role of a fuse. The leakage protector also prevents human body from being electrocuted and leaking, but this kind of circuit will not play a big role when the circuit is overloaded. For some small circuits, it can play a protective role.
5. Different action detection methods: When the circuit is too heavy and the conductor trips, it can be used to protect the safety of electricity use. The leakage protector can detect the remaining current, the purpose is to protect the circuit current, can avoid the leakage value, cut off the leakage protector, and prevent contact with the leakage current.
6. Different reasons for tripping: The air switch mainly passes through the live wire and the neutral wire. If the current between the two wires is relatively large, it will trip. The main reason for the leakage protector is the live wire. When it contacts the live wire and the ground, there will be a loop, and the device inside will automatically sense it, so that the purpose of tripping can be achieved and it plays a protective role.
4. The difference between air switches and circuit breakers
1. The difference in voltage level: There is a certain difference in voltage level between circuit breakers and air switches. For air switches, its voltage level is generally below 500V, while circuit breakers are above 220V, and the load capacity will be stronger.
2. The difference in arc extinguishing methods: For air switches, it mainly uses air as a medium to achieve the arc extinguishing effect. It is not only easy to operate, but also very safe, so it is widely used in the market. For circuit breakers, there are many ways to extinguish arcs, and the ability will be relatively strong. If used in high-voltage electrical appliances, it basically uses vacuum and sulfur hexafluoride as a medium to achieve the effect of arc extinguishing.
3. Difference in function: There is a certain difference between air switches and circuit breakers in terms of function. For air switches, it mainly plays a protective role in the circuit. Circuit breakers can disconnect the load when the voltage is high or the current is large.
Section 3 Summary and layout principles
I. Summary
1. Air switches are load switches that can cut off the power supply when there is an overcurrent. The so-called "switch" refers to a switch that can be reused and manually operated (connecting or disconnecting the power supply).
2. "Circuit breaker protector" is a passive type of protection switch device that is generally not used frequently (such as large high-voltage circuit breakers in transformers and distribution stations; or small household fuses, etc.).
3. "Leakage protector" is a protective switch. In addition to the properties of air switches, it also has the function of leakage protection. When the load has a leakage current that endangers personal safety (≤30mA), it can quickly (<0.1 seconds) open the gate and cut off the power supply.
4. Air switches, in a broad sense, refer to all switches that use air as an arc isolation and arc extinguishing medium. Including air circuit breakers, air load switches, air disconnectors, etc. In this sense, low-voltage frame circuit breakers, molded case circuit breakers, small circuit breakers, knife switches, disconnectors, high-voltage compressed air load switches, high-voltage disconnectors, etc. In a narrow sense, it refers specifically to low-voltage circuit breakers, and in a narrower sense, it refers specifically to molded case circuit breakers and small (micro) circuit breakers.
So it can be said that: air switches include some circuit breakers, and circuit breakers are not necessarily all air switches (such as SF circuit breakers). It should be noted that: the leakage protector is an independent category of electrical appliances, different from the circuit breaker, it is an outdated product that is currently recommended to be discontinued, and it is different from the leakage circuit breaker that is often used in the distribution cabinet. But some of our electricians often confuse the two. The leakage protector only plays a role in leakage protection, and needs to cooperate with the circuit breaker to achieve comprehensive protection against overload, short circuit, and leakage. The leakage circuit breaker itself includes all the above functions.