CN113300363A

CN113300363A - Safe power utilization device

Info

Publication number: CN113300363A
Application number: CN202110841298.9A
Authority: CN
Inventors: 龙跃潮
Original assignee: Hunan 123 Intelligent Technology Co ltd
Current assignee: Hunan 123 Intelligent Technology Co ltd
Priority date: 2021-07-26
Filing date: 2021-07-26
Publication date: 2021-08-24

Abstract

The present application discloses a safety electrical device, comprising an isolation transformer composed of a mains side coil, a safety electrical side coil and a delta winding, a first switch is arranged on the circuit where the mains side coil is located, and a second switch is arranged on the safety electrical side On the circuit where the side coil is located, the third switch is set on the mains output circuit, and the delta winding is used to eliminate the 3k harmonics to realize the live switch. The controller detects that the current value of at least one phase of the three-phase AC current is greater than the first threshold value. When the current value of each phase is less than the second threshold (the second threshold is greater than the first threshold determined by the rated load of the isolation transformer and greater than the rated load), the state of supplying power by the first switch and the second switch is switched to the third switch. The overload emergency power supply state of direct power supply enables the safe electrical device to maintain power supply under the condition of bearing a load exceeding its own rated value without causing damage to the components of the safe electrical device, ensuring the continuity of power supply and improving the user experience. experience.

Description

Safe power utilization device

Technical Field

The application relates to the technical field of electric power, in particular to a safe power utilization device.

Background

At present, most of low-voltage power supply systems which are most widely applied are neutral point direct grounding systems, which are generally called commercial power. The commercial power forms a short circuit channel between the neutral point and the ground, when a certain phase live wire is grounded, a current path is formed between the phase live wire and the neutral wire, if the ground is metallic ground, short circuit current which is 5-10 times of rated current and above is generated, commonly called short circuit blasting, if the ground point is non-metallic short circuit, interval short circuit current which is more than 1A is generated, fire accidents such as cable burning and the like are caused, if the ground point is a human body, electric shock current which is more than 100-500 mA is generated, and if the ground point is not timely free of electric shock casualty accidents, the electric shock casualty accidents are caused.

In order to improve the safety of a low-voltage power supply system, a person in the field provides a safe power utilization device which mainly comprises an isolation transformer, a circuit breaker, a contactor, a monitoring mainboard and the like, wherein a neutral point grounding mode of the low-voltage system is changed from a neutral point direct grounding mode to a neutral point ungrounded mode through the isolation transformer. Due to the ungrounded low-voltage power supply system of the neutral point, when a certain phase live wire is grounded, the grounding current is extremely low and only a few milliamperes to ten milliamperes, so that serious safety problems such as human body electric shock, grounding arcing, short circuit tripping and the like can not be caused, and therefore, low voltage output by the safety electric device is also called safety electricity.

The maximum load that can be borne by a safety electric device mainly depends on the capacity of an isolation transformer, for example, a 20kVA three-phase isolation transformer is adopted for a 20kVA three-phase safety electric device, a 50kVA three-phase isolation transformer is adopted for a 50kVA three-phase safety electric device, and the like. If a certain phase load exceeds the allowable range of rated capacity of the isolation transformer, the phase load is called overload, short-time overload causes protection action, and long-time overload causes serious over-temperature of equipment, shortened service life of the equipment and even burnout of the equipment, so that once the overload of a certain phase of the safety electric device is detected, the overload protection action disconnects the load, which is the most effective solution. For ordinary users, overload protection is arranged on the safety electric device, so that damage to equipment caused by overload can be avoided.

However, such a safety power utilization device is easy to trip in some occasions with large load variation, and gives users a bad experience with high requirements on power supply continuity.

Disclosure of Invention

The utility model aims at providing a safe power consumption device can have certain overload capacity under the prerequisite that does not influence equipment life, guarantees power supply continuity, improves user experience.

In order to solve the above technical problem, the present application provides a safe power consumption device, including: the isolation transformer is used for obtaining a current transformer of three-phase alternating current, a first switch, a second switch, a third switch and a controller;

the isolation transformer comprises a commercial power side coil, a safety electric side coil and a triangular winding; the first end of the first switch and the first end of the third switch are both connected with a mains supply inlet end, the second end of the first switch is connected with the mains supply side coil in series, the second end of the second switch and the second end of the third switch are both connected with a mains supply outlet end, the first end of the second switch is connected with the safety electric side coil in series, and the triangular winding is a 3 k-order harmonic wave consumption channel;

a first input end of the controller is connected with an output end of the current transformer, a first output end of the controller is connected with a control end of the first switch, a second output end of the controller is connected with a control end of the second switch, and a third output end of the controller is connected with a control end of the third switch; the controller is used for controlling the first switch and the second switch to be switched from the closed state to the open state after the third switch is switched from the open state to the closed state when at least one phase current value in the three-phase alternating current is detected to be larger than a first threshold value and each phase current value is smaller than a second threshold value, so that an overload emergency power supply state of directly supplying power by the third switch is entered;

the first threshold value is determined according to the rated load of the isolation transformer, the second threshold value is larger than the rated load of the isolation transformer, and the second threshold value is larger than the first threshold value.

Optionally, the current transformer specifically includes an incoming line side current transformer arranged at the incoming line end of the commercial power and an outgoing line side current transformer arranged at the outgoing line end of the commercial power;

the controller detects that at least one phase current value in the three-phase alternating current is greater than the first threshold value and each phase current value is less than the second threshold value, and specifically, the controller detects that at least one phase current value in the three-phase alternating current at the commercial power outlet terminal is greater than the first threshold value and each phase current value is less than the second threshold value.

Optionally, the controller is further configured to control the third switch to perform a trip operation when detecting that at least one phase current value of the three-phase alternating current is greater than or equal to the second threshold value.

Optionally, the system further comprises an alarm connected with the controller;

the controller is further used for controlling the alarm to perform overload alarm when detecting that at least one phase current value in the three-phase alternating current is larger than the first threshold value and each phase current value is smaller than the second threshold value, and controlling the alarm to perform overload alarm when detecting that at least one phase current value in the three-phase alternating current is larger than or equal to the second threshold value.

Optionally, the alarm specifically includes an alarm indicator light and an audible and visual alarm.

Optionally, after the third switch is controlled to switch from the open state to the closed state, and after the first switch and the second switch are controlled to switch from the closed state to the open state, when it is detected that the current value of each phase in the three-phase alternating current is smaller than the first threshold, the third switch is controlled to switch from the closed state to the open state, so as to recover the safe electrical state powered by the isolation transformer.

Optionally, the controller is connected with an incoming line breaker connected in series with the commercial power incoming line end, an outgoing line breaker connected with the controller connected in series with the commercial power outgoing line end, and a control power supply breaker connected with the controller and connected in series with a control loop of a control system power supply.

Optionally, the incoming line breaker is specifically a leakage protection breaker.

Optionally, the control power supply circuit breaker is specifically a miniature circuit breaker.

Optionally, the first switch, the second switch, and the third switch are ac contactors.

The application provides a safe power consumption device includes: the isolation transformer is used for obtaining a current transformer of three-phase alternating current, a first switch, a second switch, a third switch and a controller; the isolation transformer comprises a commercial power side coil, a safety electric side coil and a triangular winding; the first switch is arranged on a loop where a commercial power side coil is arranged, the second switch is arranged on a loop where a safety electric side coil is arranged, the third switch is arranged on a commercial power output circuit, 3k harmonics are eliminated by utilizing a triangular winding, so that the live switching can be realized, and then when the controller detects that at least one phase current value in the three-phase alternating current is greater than the first threshold value and each phase current value is less than the second threshold value, after controlling the third switch to switch from the open state to the closed state, controlling the first switch and the second switch to switch from the closed state to the open state, to enter an overload emergency power supply condition, in which the power is supplied directly by the third switch, so that the safety electric appliance can remain powered in the event of being subjected to a load exceeding its rating, and the device of the safety electric device cannot be damaged, so that the continuity of power supply is ensured, and the user experience is improved.

Drawings

For a clearer explanation of the embodiments or technical solutions of the prior art of the present application, the drawings needed for the description of the embodiments or prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a circuit diagram of a safety electric device according to an embodiment of the present application;

fig. 2 is a control flowchart of a safety electric device controller according to an embodiment of the present application.

Detailed Description

The core of this application is to provide a safe power consumption device, can have certain overload capacity under the prerequisite that does not influence equipment life, guarantee power supply safety, guarantee power supply continuity, improve user experience.

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Fig. 1 is a circuit diagram of a safety electric device according to an embodiment of the present application; fig. 2 is a control flowchart of a safety electric device controller according to an embodiment of the present application.

Once the rated load of a power supply product, such as a transformer, a generator, a UPS or a safety power utilization device is exceeded, in order to protect power supply equipment from being damaged, generally, only two processing modes, load reduction and trip protection are provided, and a mode of automatically reducing the load is generally only used for a system of 10kV or more, namely, the load is divided into several types according to importance, when the load is overweight, the load is stopped firstly, the influence of power failure is not large, at the moment, if the load is not reduced, the load is stopped again, namely, the two-type load and the three-type load are important, and the first type of load is ensured to be not powered off. Other situations, particularly low voltage power supply devices, are almost always the way in which overload protection trips.

However, the safety electric device belongs to a low-voltage power supply product, and the phenomenon that the rated load is exceeded frequently occurs due to the use of a large amount of air conditioners, fans or electric heaters in winter and summer. In this case, if the conventional overload trip mode is adopted, the power supply of the important load is influenced, and the power supply reliability is greatly reduced. To this problem, the embodiment of the present application provides a safety power consumption device, realizes not tripping operation when the safety power consumption device overloads even heavily transships under the prerequisite that does not damage safety power consumption device components and parts, ensures the power supply high reliability of important load.

As shown in fig. 1, the safety power utilization device provided in the embodiment of the present application includes: an isolation transformer T1, a current transformer for obtaining three-phase ac current, a first switch KMK11, a second switch KMK12, a third switch KMK13 and a controller;

the isolation transformer T1 comprises a commercial power side coil, a safety electric side coil and a triangular winding; the first end of the first switch KMK11 and the first end of the third switch KMK13 are both connected with a mains supply inlet end, the second end of the first switch KMK11 is connected with a mains supply side coil in series, the second end of the second switch KMK12 and the second end of the third switch KMK13 are both connected with a mains supply outlet end, the first end of the second switch KMK12 is connected with a safety electric side coil in series, and the triangular winding is a 3 k-order harmonic consumption channel;

a first input end of the controller is connected with an output end of the current transformer, a first output end of the controller is connected with a control end of the first switch KMK11, a second output end of the controller is connected with a control end of the second switch KMK12, and a third output end of the controller is connected with a control end of the third switch KMK 13; the controller is used for controlling the first switch KMK11 and the second switch KMK12 to be switched to the open state from the closed state after controlling the third switch KMK13 to be switched to the closed state from the open state when detecting that at least one phase current value in the three-phase alternating current is larger than a first threshold value and each phase current value is smaller than a second threshold value, so as to enter an overload emergency power supply state in which power is directly supplied by the third switch KMK 13;

the first threshold is determined according to the rated load of the isolation transformer T1, the second threshold is greater than the rated load of the isolation transformer T1 and the second threshold is greater than the first threshold.

It should be noted that most low-voltage power supply devices generally need to analyze harmonic components generated by electric equipment and their influence on the system, and take corresponding measures to eliminate or reduce the harm of the harmonic. For a 380V/220V power frequency low-voltage power grid, the content and the generated harm of 3k harmonics are the most important of all higher harmonics. The major electric loads for 3k harmonic power sources include fluorescent lamps, energy saving lamps and their ballasts, arc welding equipment, and the like. In order to eliminate the 3k harmonic, one conventional approach is to use the power input side of the safety power device as a 3k harmonic elimination channel, which results in a phase angle leading or lagging by 30 degrees between the utility power at the input side and the safety power at the output side of the safety power device. The phase angle difference exists between the safety power supply and the commercial power supply, the switching operation is carried out after power failure, otherwise, the switching operation without power failure generates huge short-circuit current when the same phase is connected to the grid, and electrical accidents are caused. Compared with the technical scheme that the input side of the power supply is used as a 3 k-order harmonic elimination channel, an independent 3 k-order harmonic elimination channel is arranged in the embodiment of the application, and 3 k-order harmonics are eliminated through the 3 k-order harmonic elimination channel. Meanwhile, the phase angle between the commercial power at the input side of the safety electric device and the safety electricity at the output side is consistent, and no voltage exists between the input side and the output side in phase, so that the stable switching operation between the commercial power and the safety electricity can be realized under the conditions of electrification and load, and the short-time grid connection is realized without impulse voltage and current. Based on this, the controller has the basis of controlling switching in a charged state, namely, uninterrupted switching of loads can be realized between 'safe power' (power converted by an isolation transformer T1) and 'commercial power', and when the loads are lower than the rated load of the isolation transformer T1, a safe power operation mode is adopted, namely, the controller is operated with loads through an isolation transformer T1. When the load is greater than the rated load of the isolation transformer T1, the automatic conversion is carried out to the commercial power working condition, at the moment, the maximum long-term working load is allowed to be only related to the rated current of the circuit breaker, the contactor, the main lead and the current transformer, and at the moment, the overload capacity of the isolation transformer T1 can be improved on the premise of extremely low cost increase or even no cost increase.

In specific implementation, the current transformer specifically comprises an incoming line side current transformer arranged at an incoming line end of the mains supply and an outgoing line side current transformer arranged at an outgoing line end of the mains supply; the controller detects that at least one phase current value in the three-phase alternating current is greater than the first threshold and each phase current value is less than the second threshold, and may detect that at least one phase current value in the three-phase alternating current at the commercial power outlet terminal is greater than the first threshold and each phase current value is less than the second threshold. Typically each device will be allowed to withstand a load slightly exceeding its rated load, the first threshold may be 1.05 times the rated load of the isolation transformer T1.

The first switch KMK11, the second switch KMK12 and the third switch KMK13 can be ac contactors, and the overall cost of the device can be reduced. For safety reasons, the first switch KMK11, the second switch KMK12, and the third switch KMK13 may be dc contactors, i.e., the contacts are controlled by the rectifier output and the battery is used for power supply.

On the basis, if the three-phase alternating current value continuously rises, in order to ensure the safety of the low-voltage power supply system, the controller is further configured to control the third switch KMK13 to perform a trip operation when detecting that at least one phase current value in the three-phase alternating current is greater than or equal to the second threshold value. The second threshold may be K times (K > 1) the first threshold, and the value of K may be determined experimentally, and an appropriate value is selected from the group consisting of ensuring the safety and the power supply continuity of the low-voltage power supply system. Under the working condition of a mains supply, the load allowed to operate continuously for a long time is usually more than 1.2-2 times of the rated load of the isolation transformer T1, namely the heavy load coefficient K can be set to be 1.2-2, and the load can operate for a long time under the condition that the load is less than 1.05 x K times of the rated current. When its heavy load bearing capacity is exceeded, the heavy load protection trips.

Preferably, the safety electric device provided by the embodiment of the application further comprises an alarm connected with the controller; the controller is also used for controlling the alarm to carry out overload alarm when detecting that at least one phase current value in the three-phase alternating current is greater than a first threshold value and each phase current value is less than a second threshold value, and controlling the alarm to carry out overload alarm when detecting that at least one phase current value in the three-phase alternating current is greater than or equal to the second threshold value.

The alarm may specifically comprise an alarm indicator light and an audible and visual alarm. For overload alarm and heavy overload alarm, the controller can control the alarm to send out signals of different degrees to prompt users of different warning degrees, for example, the overload alarm can be sound and light alarm, when the controller controls the neutral point of the low-voltage power supply system to be converted from grounding through the safety power utilization device to commercial power grounding, the alarm sound is stopped, only the alarm indicator lamp is reserved, the heavy overload alarm can be sound and light alarm with larger sound and larger light intensity compared with the overload alarm, and the alarm is stopped after the third switch KMK13 is tripped.

Further, the controller is further configured to control the third switch KMK13 to switch from the closed state to the open state after controlling the third switch KMK13 to switch from the open state to the closed state and after controlling the first switch KMK11 and the second switch KMK12 to switch from the closed state to the open state when it is detected that the current value of each phase in the three-phase alternating current is smaller than the first threshold value and after controlling the first switch KMK11 and the second switch KMK12 to switch to the closed state, so as to restore the safe electrical state powered by the isolation transformer. When the current values of all phases in the three-phase alternating current are smaller than the first threshold value, the controller controls all the switches to switch back to the output state of the safety electric device, and the safety of the low-voltage power supply system is guaranteed. In the case of heavy-load operation, if the load drops below 1.05 times the rated current, the power supply from the isolation transformer T1 is automatically returned, i.e. the so-called "safe-electricity" operating state.

In addition, the safety power utilization device provided by the embodiment of the application can further comprise an input/output interface, a wireless communicator, a temperature sensor, a humidity sensor, a fan control loop, a human-computer interaction device, a voltmeter and the like, wherein the input/output interface is connected with the controller. The input and output interface can be connected with the upper computer in a wired connection mode to carry out information interaction and parameter debugging. The communicator may employ a remote 4G communicator, a Wi-Fi communicator, or the like. Temperature and humidity parameters in the transformer and the box can be detected through the temperature sensor and the humidity sensor, and the fan is controlled by the fan control loop to cool. The human-computer interaction device can comprise a manual control panel and a liquid crystal touch screen, a user can input a control signal through the manual control panel, and can check real-time monitoring parameters such as voltage and current and debug configuration parameters of the controller through the liquid crystal touch screen.

Based on the above structure of the safety electric device, the control logic of the controller may be as shown in fig. 2:

s201: KMK11, KMK12 are in closed position and in safe electric operation state;

s202: judging that the output current { Ia, Ib, Ic } max is more than 1.05 In; if yes, go to step S203; if not, repeating the step S202;

s203: overload alarm is carried out; closing KMK13, and inputting commercial power;

s204: judging KMK13 whether the switch is in place; if yes, go to step S205; if not, returning to the step S203;

s205: KMK11 and KMK12 are disconnected, after the first preset time is delayed, the overload alarm indicator lamp is reserved, and the alarm prompt tone is stopped;

s206: judging the output current { Ia, Ib, Ic } max > 1.05 xK In; if yes, go to step S211; if not, go to step S207;

s207: judging that the output current { Ia, Ib, Ic } max is more than 1.05 In; if yes, go to step S208; if not, returning to the step S206;

s208: closing KMK11 and KMK12, and stopping overload alarm;

s209: judging whether KMK11, KMK12 are in place; if yes, go to step S210; if not, returning to the step S208;

s210: disconnection KMK13, and putting into safe electric operation state; returning to step S201;

s211: heavy overload alarm; after delaying for a second preset time, the overload control KMK13 is protected from tripping according to an inverse time curve.

Wherein, the first preset time period may be 15 s. The second preset time is used for preventing the overload misjudgment.

Based on the description of the embodiment, it can be seen that the safety power utilization device provided by the embodiment of the application is different from a conventional safety power utilization device, namely, an alarm trip is performed when any one phase actual load exceeds a rated load of the safety power utilization device, when any one phase actual load exceeds the rated load of the safety power utilization device, an alarm is given, the load is converted into a commercial power running state while the load is ensured not to be powered off, at the moment, the load can work for a long time with the load more than 1.2-2 times or even more than the rated load, and when the load is reduced to be within the rated load, the load is converted into the safety power running state while the load is ensured not to be powered off, and meanwhile, an overload alarm signal is eliminated. The damage of heavy load to power supply equipment is avoided in the commercial power running state, and the safe power running state is automatically returned when the load returns to the rated load, so that the safe power utilization device can keep power supply under the condition of bearing the load exceeding the rated value of the safe power utilization device, the device of the safe power utilization device cannot be damaged, the power supply continuity is ensured, and the user experience is improved.

On the basis of the above embodiments, as shown in fig. 1, the safety electric device provided in the embodiment of the present application further includes an incoming line breaker QF1 connected to the controller in series with the incoming line terminal of the utility power, an outgoing line breaker QF2 connected to the controller in series with the outgoing line terminal of the utility power, and a control power breaker QF3 connected to the controller in series with the control loop of the control system power.

In a specific implementation, the control power circuit breaker QF3 may be a miniature circuit breaker.

In order to ensure that the safety electric device still has two main safety functions of a safety electric device which can not cause electric shock of human bodies and fire caused by grounding arcing in the commercial power running state, the power supply side circuit breaker QF1 is designed into a leakage protection circuit breaker with the action time of 30mA and less than or equal to 0.1S. In the safety electric operating state, the earth leakage protection circuit breaker does not work on the load side due to the isolation transformer T1; when the electric supply enters a working state, once the load side is grounded, the leakage protection circuit breaker is rapidly tripped, and the safety of personnel and equipment is ensured.

The safety electric device provided by the embodiment of the application needs to check and adjust technical parameters of a mains supply loop except an isolation transformer T1 for ensuring that the safety electric device does not need to trip when exceeding a rated load by a certain multiplying power, and properly improves the current bearing capacity of partial raw materials on the premise of ensuring economy.

As can be seen from the above embodiment and fig. 1, the main raw materials determining the cost of the safety electric device are the main components of the main conductor of the circuit in which the isolation transformer T1 and the third switch KMK13 are located, the main conductor of the circuit in which the safety electric side coil is located, the circuit conductor in which the micro circuit breaker is located, the leakage protection circuit breaker, the micro circuit breaker, the current transformer, the ac contactor, and the like, and the relations between the control system conductor and the components and the capacity are not substantially consistent.

The heavy overload operation mode is realized on the premise that the capacity of the isolation transformer T1 is not changed and the size of other main raw materials is not increased as much as possible.

The following list of main raw material specifications and technical parameters of a 20kVA, 50kVA three-phase safety electric device is shown in the following table 1:

table list of main raw material specifications and technical parameters of 120 kVA, 50kVA three-phase safety electric device

Note: and (4) searching a table according to a BVR copper wire, an exposed coating and the ambient temperature of 40 ℃ to obtain the rated current-carrying capacity.

As can be seen from table 1, even if any main material technical parameter is not changed, when the safety electric device operates under the condition of outputting the commercial power (at this time, the isolation transformer T1 has no load and does not affect the rated capacity under this condition), the 20kVA three-phase safety electric device will have an energy band of 33kVA, which is 1.65 times of the rated capacity of 20 kVA; the 50kVA three-phase safety electric device has the energy band of 63kVA which is 1.26 times of the rated capacity of 50 kVA. And, because the isolation transformer T1 accounts for more than 60% of the total cost, if the main conductor gauge and the contactor current are artificially increased by one specification, the overload capacity is increased by 1 time or more under the condition of the utility power, and there is no great difficulty, for example, if 20kVA adopts a main conductor of 10mm2 (exposed, the current-carrying capacity at 40 ℃) and the rated current of the contactor is selected to be 60A, the cost is increased by less than 5%, and when the device works under the condition of outputting the utility power, the 20kVA three-phase safety power utilization device can carry 41.6kVA (2.1 times of the rated capacity of 20 kVA).

Based on this, the safe power consumption device that this application embodiment provided can be at rated load more than 1.2~2 times still continuous work of continuous not cutting off power supply, can expand the application field of safe power consumption device, especially to not allowing to have bigger meaning to promoting the application of safe power consumption device in 1 type and 2 types of load of cutting off power supply easily.

The safety electric device provided by the application is described in detail above. The embodiments are described in a progressive manner in the specification, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications also fall within the scope of the claims of the present application.

It is further noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Claims

1. A safe electrical device, comprising: an isolation transformer, a current transformer for obtaining three-phase alternating current, a first switch, a second switch, a third switch and a controller;

Wherein, the isolation transformer includes a mains side coil, a safety power side coil and a delta winding; the first end of the first switch and the first end of the third switch are both connected to the mains incoming line end, and the The second end of the first switch is connected in series with the mains side coil, the second end of the second switch and the second end of the third switch are both connected to the mains outlet, and the second end of the second switch is connected to the mains outlet. One end is connected in series with the safe electric side coil, and the delta winding is a 3k harmonic consumption channel;

The first input terminal of the controller is connected to the output terminal of the current transformer, the first output terminal of the controller is connected to the control terminal of the first switch, and the second output terminal of the controller is connected to the control terminal of the first switch. The control terminal of the second switch is connected, and the third output terminal of the controller is connected to the control terminal of the third switch; the controller is used for detecting the current value of at least one phase of the three-phase alternating current. When the current value of each phase is greater than the first threshold value and the current value of each phase is less than the second threshold value, after controlling the third switch to switch from the open state to the closed state, control the first switch and the second switch to switch from the closed state to the open state. open state to enter the overload emergency power supply state directly powered by the third switch;

The first threshold is determined according to the rated load of the isolation transformer, the second threshold is greater than the rated load of the isolation transformer, and the second threshold is greater than the first threshold.

2 . The safe electrical device according to claim 1 , wherein the current transformer specifically comprises an incoming-line-side current transformer disposed at the mains incoming end and an outgoing wire disposed at the mains outgoing end. 3 . side current transformer;

The controller detects that the current value of at least one phase of the three-phase AC current is greater than the first threshold value and the current value of each phase is less than the second threshold value. Specifically, the controller detects three phases of the mains outlet. In the phase alternating current, the current value of at least one phase is greater than the first threshold value, and the current value of each phase is less than the second threshold value.

3 . The electrical safety device according to claim 1 , wherein the controller is further configured to control the current value of at least one phase of the three-phase alternating current when it is detected that the current value of at least one phase is greater than or equal to the second threshold value. 4 . The third switch performs a tripping operation.

4. The electrical safety device according to claim 3, further comprising an alarm connected to the controller;

The controller is further configured to control the alarm to perform an overload alarm when it is detected that the current value of at least one phase of the three-phase alternating current is greater than the first threshold value and the current values of each phase are less than the second threshold value, When it is detected that the current value of at least one phase of the three-phase alternating current is greater than or equal to the second threshold value, the alarm is controlled to perform a heavy overload alarm.

5 . The safe electrical device according to claim 4 , wherein the alarm device specifically comprises an alarm indicator light and an acousto-optic alarm device. 6 .

6 . The electrical safety device according to claim 1 , wherein the controller is further configured to control the first switch and the third switch after controlling the third switch to switch from an open state to a closed state. 7 . After the second switch is switched from the closed state to the open state, when it is detected that the current value of each phase in the three-phase alternating current is less than the first threshold, the first switch and the second switch are controlled to switch After reaching the closed state, the third switch is controlled to switch from the closed state to the open state, so as to restore the safe electrical state powered by the isolation transformer.

7 . The safe electrical device according to claim 1 , further comprising an incoming circuit breaker connected to the controller in series with the mains incoming end, and an incoming circuit breaker connected in series with the controller. 8 . The outlet circuit breaker at the mains outlet end, and the control power circuit breaker connected to the controller in series with the control loop of the control system power supply.

8 . The safe electrical device according to claim 7 , wherein the incoming circuit breaker is a leakage protection circuit breaker. 9 .

9 . The safe electrical device according to claim 7 , wherein the control power circuit breaker is a miniature circuit breaker. 10 .

10 . The safety electrical device according to claim 1 , wherein the first switch, the second switch and the third switch are all AC contactors. 11 .