Device for judging small current variables using apparent power

Abstract

The invention discloses a device for judging small current variables by apparent power, belonging to the technical field of electromagnetic measurement. The device includes a current sensor for detecting the current on a line; a current sampling circuit in the apparent power sensor collects the detected current; an arithmetic unit multiplies the collected current by a given apparent voltage to obtain the apparent power, and accumulates the apparent power in real time to obtain the apparent electric quantity; a central processing unit reads the apparent electric quantity at set time intervals, calculates the change amount of the apparent electric quantity in each time period, compares the relative change amplitude of the change amounts of the apparent electric quantity in two adjacent time periods, and makes a decision to continue detection or information reporting. This judging device judges the change trend of the destructive energy in the line according to the change amplitude of the apparent electric quantity in adjacent time periods of the same length. When the growth amplitude of the apparent electric quantity is large, a signal can be uploaded, thereby facilitating reminding the staff to take security inspection measures.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic measurement, and particularly relates to a device for judging small current variables by apparent power. Background Art

[0002] Since the late 1960s in China, in order to strengthen electrical safety, protection measures have been gradually adopted in the power system, and the leakage protector is a common technical means. The leakage protector detects abnormal current or voltage signals of monitored equipment or lines. When the detected signal reaches its set threshold, it prompts the actuator to operate and cut off the power supply, avoiding accidents such as burning electrical appliances, fires or electric shocks, so as to ensure the safety of personnel and electrical equipment and achieve the purpose of protection.

[0003] Later, some also adopted the method of small current grounding. An zero-sequence current transformer is installed at the incoming line end of high-voltage equipment (i.e., the outgoing side of the high-voltage switch), and the secondary side of the current transformer is connected to a small current grounding line selection device. When one-phase grounding or two-phase grounding occurs in the high-voltage equipment loop, an unbalanced current will be generated in this loop. The current transformer detects the unbalanced current and transmits it to the small current grounding line selection device. The small current grounding line selection device gives a tripping signal to make the high-voltage switch trip and disconnect the high-voltage equipment from the power grid, avoiding the high-voltage equipment from being burned and at the same time avoiding the expansion of the fault range through the power grid.

[0004] The above protection measures all belong to the category of post-protection. Only when the defect current develops to a certain extent and reaches the protection threshold will they operate. It is a method of starting protection by power outage, and it cannot detect the development process of the current, and cannot prevent the continuous bad development of the current by early preventive treatment without affecting safety, or even eliminate the fault in its infancy. And once the protection threshold is reached, sudden power outage will occur, bringing serious hidden dangers to production and life, especially for equipment involving people, such as elevators, transportation and entertainment equipment. With the rising construction of the ubiquitous power Internet of Things, safety, cleanliness, reduction of power outages, especially sudden power outages, have become an inevitable trend in the development of the power grid. At the same time, higher requirements are put forward for transparent power grids, fault prediction and power supply quality. This requires perceiving the working process of the entire distribution network, discovering potential hidden dangers through intelligent detection, facilitating timely disposal, achieving orderly power outages, reducing the number of power outages, shortening the power outage time or even not having power outages at critical moments.

[0005] It can be seen that technologies such as leakage protectors and small current grounding can no longer meet the development needs of the power grid. There is an urgent need to develop a new detection technology that can actively discover problems to avoid disorderly power outages and achieve the purpose of energy conservation and waste reduction in production. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a device for judging small current variables by apparent power, which can automatically judge the change trend of the current in the line according to the change amplitude of the apparent power in adjacent same-length time periods, and can report to the system when the current growth amplitude is large.

[0007] To solve the above technical problem, the technical solution of the present invention is: design a device for judging small current variables by apparent power, including a current sensor, characterized in that: it further includes a current sensor, an apparent power sensor and a central processor;

[0008] Current sensor: used to detect the current on the grounding wire, the grounding lead of the insulating part or the zero-sequence current line, and obtain the current on the corresponding line;

[0009] Apparent power sensor: a current sampling circuit and an arithmetic unit are provided,

[0010] The current sampling circuit collects the detected current of the current sensor;

[0011] The arithmetic unit multiplies the current collected by the current sampling circuit by the given apparent voltage to obtain the apparent power, and accumulates the apparent power in real time to obtain the apparent power quantity;

[0012] Central processor: reads the apparent power quantity of the apparent power sensor at a set time interval, calculates the change amount of the apparent power quantity in each time period, compares the relative change amplitude of the change amounts of the apparent power quantity in two adjacent time periods, and makes a decision to continue detection or upload information based on the relative change amplitude.

[0013] Preferably, the processing process of the central processor for the apparent power quantity is as follows:

[0014] S1: Read the apparent power quantity once every interval time T. The reading time points divide the detection time into multiple time periods. The previous time period in two adjacent time periods is called the xth time period, and the latter time period is called the (x + 1)th time period, where x is a natural number;

[0015] S2: Read the apparent power quantity z in S3 at the starting point of the xth time period x ;

[0016] S3: Read the apparent power quantity z in S3 at the end point of the xth time period x+1 , calculate the change amount of the apparent power quantity in the xth time period as: m x = z x+1 - z x ;

[0017] S4: Read the apparent power quantity z in S3 at the end point of the (x + 1)th time period x+2 , calculate the change amount of the apparent power quantity in the (x + 1)th time period as: mx+1 = z x+2 -z x+1 ;

[0018] Calculate the change amplitude n of the change in apparent power in the (x + 1)-th time period relative to the change in the x-th time period x = m x+1 - m x , and judge n x relative to m x 's change amplitude;

[0019] S5: If n x ≤ 0.1m x , then x = x + 1, and repeat steps S4 and S5;

[0020] If 0.1m x < n x ≤ 0.3m x , then adjust the length of the time period to 1 / 5 - 1 / 10 T, reset x = 1, replace z x+2 with z x , and repeat steps S3 - 5;

[0021] If n x > 0.3m x , then upload the information of n x , m x and m x+1 to the control center.

[0022] Preferably, the central processing unit also sets a limit value K for the change in apparent power in S4. If m x+1 ≤ K, then calculate n x and then enter S5; if m x+1 > K, then upload the information of m x , m x+1 to the control center.

[0023] Preferably, the central processing unit also adds a step of detecting humidity between S4 and S5: Detect the humidity information s on the line, and the humidity set value is Q. If s > Q, then adjust the length of the time period to 1 / 5 - 1 / 10 T; if s ≤ Q, then maintain the original time period length T.

[0024] Preferably, in step S5, if n x > 0.3m x , detect the humidity information of the environment where the line is located. If s x+1 > s x , then adjust the length of the time period to 1 / 5 - 1 / 10 T, reset x = 1, replace z x+2 with z x, repeat steps S6 - 8; if s x+1 ≤s x , then upload the information of n x , m x+1 and m x+2 to the control center.

[0025] Preferably, the central processing unit also adds a step of detecting temperature rise between detecting humidity and S5: detect the temperature rise information f on the line, the temperature rise set value is P, if f > P, then adjust the length of the time period to 1 / 5 - 1 / 10 T; if f ≤ P, then maintain the original time period length T.

[0026] Preferably, the central processing unit also sets the number of stored change amplitudes n as Y, Y is a natural number, when x + 1 > Y, n, m and z each cover one digit forward, and then repeat steps S4 and S5.

[0027] Preferably, the given apparent voltage is the set numerical information or the analog signal given by the voltage supply circuit.

[0028] Preferably, the numerical range of the apparent voltage is 1 - 20V.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. Since the current sampling circuit is used to collect the grounding, insulation or leakage current and then multiply it by the given apparent voltage to form the apparent power, and the apparent power is accumulated into the form of apparent electric quantity, the change amplitude within two adjacent time periods of the same length can be calculated, reflecting the change trend of the destructive energy, taking necessary safety inspection work, controlling its development trend or eliminating the destructive energy, avoiding the sudden tripping and power-off due to the current reaching the threshold value in the prior art, thus laying a power foundation for ensuring normal production.

[0031] 2. This judging device can overcome the disadvantages of easy misjudgment due to unstable grounding, insulation or leakage current, or potential hazards due to too small current to be detected; at the same time, it realizes the accumulation effect, avoiding the untrue reflection caused by instantaneous judgment and increasing the number of unnecessary sudden power-offs; in addition, it can fully master the development trend of the destructive energy, so as to take measures such as system self-healing, online power supply without interruption, short-time power-off or planned power-off to ensure safe production, avoid waste of raw materials and reduce losses.

[0032] 3. Since the central processing unit takes into account factors such as humidity and temperature rise, it can determine whether the increase in the change amount of apparent power in two adjacent time periods is caused by the increase in humidity or temperature rise, reducing false alarm phenomena; and after the humidity or temperature rise recovers, it can judge whether the change in humidity or temperature rise has damaged the insulation performance of the line by whether the change amount drops; it can also increase the consideration of other influencing factors such as magnetic field to make a comprehensive and accurate judgment.

[0033] 4. Since the central processing unit sets a limit value for the change amount of apparent power, it can prevent the detected current from slowly approaching the protection threshold at a small growth rate of apparent power, reducing missed alarm phenomena and making the detection more accurate.

[0034] 5. Since the given apparent voltage, whether in the form of a set value or a voltage supply circuit, is an existing technology with mature technology, stable and reliable performance, and is easy to implement.

[0035] 6. Since the apparent voltage is estimated based on on-site conditions such as ground resistance and can be adjusted according to changes in on-site conditions, and its value range is generally 1 - 20V. After adopting this apparent voltage, the detected tiny current can be converted into the form of apparent power reflecting the damage energy within a time period, truly reflecting the damage ability of the ground current, insulation level, and leakage current to the power system.

[0036] 7. The apparent power sensor in the present invention can be set on the grounding wire to detect leakage current, or on the zero-sequence current line to detect leakage current, or on the grounding lead of the equipment insulation part to detect its insulation level, and can be used in AC and DC high and low voltage lines, with flexible application scenarios.

[0037] 8. The present invention breaks through the conventional protection method and proposes a new method of active detection, monitoring the change process, and real-time appropriate handling. By monitoring the change process and trend of current through the form of apparent power, it can do a good job in pre-event safety inspection, contain the development trend of damage energy, and avoid sudden power outages, thus conforming to the construction of the ubiquitous power Internet of Things and being convenient for popularization and application in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the overall block diagram of the present invention;

[0039] Figure 2 is the schematic diagram of the time axis for the central processing unit to read apparent power;

[0040] Figure 3 is the logical control block diagram of the central processing unit (upper part);

[0041] Figure 4 is Figure 3The lower half part. Detailed implementation manners

[0042] The present invention will be further described in detail below in conjunction with the accompanying drawings and the detailed implementation manners.

[0043] The main idea of the present invention is as follows: A current detection device is used to detect the current on the grounding wire of the device, the zero-sequence current line or the grounding lead of the insulation part. The detected current is multiplied by a certain given apparent voltage to form apparent power. The apparent power is accumulated to obtain apparent electricity. Then, the apparent electricity is read once every time interval of the same length. Check the change amount of the apparent electricity in the same time period. If the change amount of the apparent electricity in each time period does not change significantly and is basically in a stable state of being flat, it indicates that the destructive energy on the line has no obvious change. Continue to maintain the above time interval to read the apparent electricity and check the change amount of the apparent electricity. If the change range of the apparent electricity reaches a certain degree, then shorten the time interval for reading the apparent electricity, increase the reading frequency, and closely monitor the change of the apparent electricity in two adjacent same time periods. If there is no obvious increase, continue to maintain the monitoring state. If the apparent electricity drops back to the state before increasing the frequency, then adjust the time interval for reading the apparent electricity back to the original length. If the change range of the apparent electricity exceeds a certain value, immediately give an on-site alarm or report to the host to notify the staff to take safety inspection measures in time, find out the reason for the change of the change amount of the apparent electricity, achieve pre-treatment, and curb the development trend of the increasing destructive energy, so as to avoid sudden tripping due to the current reaching the protection threshold in the prior art.

[0044] Of course, in the above process, a given value of the apparent power change can also be introduced. As long as the change reaches this given value, an alarm is immediately triggered or reported to the host for alarm, so as to avoid the situation where although the increase in apparent power is not large compared to the change in the adjacent time, the accumulation over multiple time periods will also cause the current in the detection circuit to approach the protection threshold. Environmental change parameters such as humidity and temperature rise can also be introduced. When the detected humidity or temperature rise reaches a certain value, the time interval for reading the apparent power is also reduced, the reading frequency is increased, and the change in apparent power between two adjacent identical time periods is closely monitored. When the change amplitude of the apparent power is relatively large, the changes in humidity and temperature rise in two adjacent time periods can also be checked. If the humidity or temperature rise increases, it indicates that the increase in the amplitude of the apparent power may be caused by the environment, and attention can be paid by increasing the reading frequency. If the humidity or temperature rise gradually decreases and the change in apparent power also decreases, it indicates that the changes in humidity and temperature rise do not damage the insulation performance of the equipment, and there is no need to alarm, reducing false alarms in the system; if the humidity or temperature rise gradually decreases and the change in apparent power does not decrease, it indicates that the changes in humidity and temperature rise have damaged the insulation performance of the equipment to a certain extent, and an alarm is required for safety inspection work, and prior treatment is carried out to nip the fault in the bud.

[0045] To implement the above idea, as Figure 1 shown, in the specific early warning management platform adopted, a current sensor, an apparent power sensor, and a central processor are set. Among them

[0046] Current sensor: used to detect the current on the grounding wire, the grounding lead of the insulating part, or the zero-sequence current circuit, and serve as the current sampling device for the line;

[0047] The apparent power sensor is provided with a current sampling circuit and an arithmetic unit. The current sampling circuit collects the detected current of the current sensor, and then the arithmetic unit multiplies the collected detected current by the given apparent voltage to obtain the apparent power, and accumulates the apparent power in real time to obtain the apparent power as the cumulative value;

[0048] The central processor reads the apparent power of the apparent power sensor at the set time interval, calculates the change in apparent power in each time period, compares the relative change amplitude of the apparent power change between two adjacent time periods, and makes a decision to continue detection or upload information based on the relative change amplitude. As Figure 3 and Figure 4 shown, its processing process for the apparent power is as follows:

[0049] S1: Read the apparent power once every time interval T. The reading time points divide the detection time into multiple time periods. The previous time period in two adjacent time periods is called the xth time period, and the latter time period is called the (x + 1)th time period, where x is a natural number;

[0050] S2: Read the apparent power in S3 at the start point of the x-th time period as z x ;

[0051] S3: Read the apparent power in S3 at the end point of the x-th time period as z x+1 , and calculate the change in apparent power during the x-th time period as: m x = z x+1 - z x ;

[0052] S4: Read the apparent power in S3 at the end point of the (x + 1)-th time period as z x+2 , and calculate the change in apparent power during the (x + 1)-th time period as: m x+1 = z x+2 - z x+1 ;

[0053] Calculate the change amplitude n of the change in apparent power during the (x + 1)-th time period relative to the change during the x-th time period x = m x+1 - m x , and judge n x relative to m x 's change amplitude;

[0054] S5: If n x ≤0.1m x , then x = x + 1, and repeat steps S4 and S5;

[0055] If 0.1m x <n x ≤0.3 m x , then adjust the length of the time period to 1 / 5 - 1 / 10 T, replace z x+2 with z 1 , restore x = 1, and repeat steps S3 - 5;

[0056] If n x >0.3 m x , then report the information of n x , m x and m x+1 to the host to remind the staff to take security inspection measures.

[0057] To avoid the detection current slowly approaching the protection threshold due to the small growth rate of the apparent power, a limit value K of the change in apparent power is introduced, that is, m x+1 must be less than K for the above comparison. Once m x+1In the case of being greater than K, it is also necessary to immediately report to the host. At the same time, considering reducing the change of the environment, as long as the detected humidity exceeds the given value Q or the temperature rise exceeds the given value P, the time interval for reading the apparent power is adjusted to increase the reading frequency. When it is judged that n x >0.3m x When, the consideration of humidity change is also introduced. If the average humidity in the latter time period is greater than the average humidity in the previous time period, it is considered that the change amplitude of the apparent power may increase due to the change of humidity. Therefore, instead of directly sending a host alarm, the reading frequency is increased and continuous close attention is paid; if the average humidity in the latter time period is not significantly greater than the average humidity in the previous time period, the host will be reported.

[0058] In order to avoid storing data that is far from the reading time as the detection time extends, resulting in the accumulation of a lot of data with little reference value, the number of the change amplitude n can be set to Y. Y is a natural number and can be set to 5, 10 or 15 according to specific situations. It can be flexibly set, that is, only n 1 、n 2 、n 3 ……n Y and the related m values are retained. When x + 1>Y, m 2 is used to replace m 1 , m 3 is used to replace m 2 , until m x+1 is used to replace m x , z 2 is used to replace z 1 , z 3 is used to replace z 2 , until z x+2 is used to replace z x+1 , n 2 is used to replace n 1 , n 3 is used to replace n 2 , until n x is used to replace n x-1 , which is equivalent to n, m and z each covering one digit forward, and then calculating the new n x , and then calculating the new n x , and continuing to compare with m x ; if not satisfied, continue to detect until Y n values are saved.

[0059] To avoid the influence of the environment on the read data and be able to truly reflect the insulation performance of the equipment, the consideration of humidity and temperature rise is also introduced. The humidity set value is set to Q, and the temperature rise set value is set to P. Each time the apparent power is read, the humidity value s and the temperature rise value f are checked. If s>Q or f>P, the same as 0.1m x <n x ≤0.3 mx In the same situation, adjust the length of the time period to 1 / 5 - 1 / 10 T, and set z x+2 to replace z 1 , restore x = 1, and repeat steps S3 - 5. Also, when n x > 0.3 m x , check the value s of the humidity information in the next time period x+1 whether it is greater than s x . If s x+1 > s x , then temporarily do not report to the host, and still take measures to adjust the length of the time period. Adjust the length of the time period to 1 / 5 - 1 / 10 T, and set z x+2 to replace z 1 , restore x = 1, and repeat steps S3 - 5 to closely monitor and determine that the change in the change amplitude has nothing to do with humidity and temperature rise. The humidity information used can be obtained by the maximum value analysis method, the average value analysis method, the cumulative amount analysis method, the humidity influence amount analysis method, and the seasonal variable analysis method.

[0060] The working process of the present invention is as follows:

[0061] The current sensor detects the current on the grounding wire, the grounding lead of the insulating part, or the zero-sequence current line to obtain the current on the corresponding line. The current sampling circuit in the apparent power sensor collects the detected current, and then the arithmetic unit multiplies the collected current by the given apparent voltage to obtain the apparent power; the obtained apparent power is accumulated in real time to obtain the apparent electricity consumption.

[0062] The central processing unit first detects the humidity value s and the temperature rise value f. If the humidity value s does not exceed its set value Q and the temperature rise value f does not exceed its set value P, then read the above-mentioned apparent electricity consumption once every time period length T; if either the humidity value s or the temperature rise value f exceeds its set value or both exceed their set values, then adjust the reading interval time to 1 / 5 - 1 / 10 T, and the apparent electricity consumption read for the first time is z 1 , take the first time period as the 1st time period, and read the apparent electricity consumption at the end point of the 1st time period as z 2 , calculate the change amount m of the apparent electricity consumption within the 1st time period 1 = z 2 - z 1 . The apparent electricity consumption read at the end point of the 2nd time period is z 3 , calculate the change amount m of the apparent electricity consumption within the 2nd time period 2 = z 3 - z 2 , and the change amplitude of m 2 relative to m 1 is n 1 = m 2 - m1 If n 1 ≤0.1 m 1 then, at the end point of the 3rd time period, read the apparent power as z 4 Calculate the change in apparent power m within the 3rd time period 3 = z 4 - z 3 m 3 The change amplitude of m relative to m 2 is n 2 =m 3 -m 2 n 2 ≤0.1 m 2 then, at the end point of the 4th time period, read the apparent power as z 5 Read successively downwards until the Y + 2 time period is read, and calculate n Y Then, replace the value of the previous point with the value of the next point, and replace the value of the previous time period with the value of the next time period. If the time axis extends to the right, it is equivalent to that every time the time T passes, the time axis moves one unit T to the left, while the coordinates on the time axis remain unchanged, and keep detecting. As Figure 2 shown, it is equivalent to that n, m, and z each cover one digit forward respectively.

[0063] During the above process, once 0.1m x <n x ≤0.3 m x , and the value range of x is 1 to Y, then adjust the length of the time period to 1 / 5 to 1 / 10 T, restore x = 1, and use z x+2 to replace z x , and restart the detection with the adjusted time period. Once n x >0.3 m x , and when the humidity does not rise, then report the information of n x , m x and m x+1 to the host.

[0064] In the above embodiments, the given value of the apparent voltage can be predicted by multiplying the known grounding resistance by the measured current value, and adjusted according to the on-site situation. Its value range is generally 1 to 20V, and it can be any value within this range specifically. The apparent voltage can be selected in the form of a digital signal with a set value, or in the form of an analog signal of a voltage given circuit. After adopting this apparent voltage, the detected tiny current can be converted into the form of apparent power reflecting the damage energy within a time period, truly reflecting the damage ability of the grounding current, insulation level, and leakage current to the power system.

[0065] This device can be used to detect leakage current on the grounding wire, detect leakage current on the zero-sequence current line, and also detect the insulation level on the grounding lead of the equipment insulation part. It can be used in AC and DC high-voltage and low-voltage lines, as well as AC and DC high-voltage and low-voltage lines, with flexible application scenarios. It can comprehensively refer to detection conditions, on-site temperature, humidity, magnetic field and other influencing factors to truly reflect the damage energy on the line, which is conducive to making accurate disposal measures.

[0066] The time interval for reading the apparent power can be flexibly set manually, and the specific length of the time period can be 1, 2, 3,..., up to 24 hours, and multiples of 10 of the above times.

[0067] The above is only a preferred embodiment of the present invention, and it is not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A device for evaluating small current variables using apparent power, including a current sensor, Characterized in that: It further includes a current sensor, an apparent power sensor, and a central processing unit; Current sensor: used to detect the current on the grounding wire, the grounding lead of the insulating part, or the zero-sequence current line, and obtain the current on the corresponding line; Apparent power sensor: A current sampling circuit and an arithmetic unit are provided. The current sampling circuit collects the detected current of the current sensor. The arithmetic unit multiplies the current collected by the current sampling circuit by a given apparent voltage to obtain the apparent power, and accumulates the apparent power in real time to obtain the apparent electricity quantity; the apparent voltage is a set numerical information or an analog signal given by a voltage supply circuit; Central processing unit: reads the apparent electricity quantity of the apparent power sensor at a set time interval, calculates the change amount of the apparent electricity quantity in each time period, compares the relative change amplitude of the apparent electricity quantity change amounts in two adjacent time periods, and makes a decision to continue detection or upload information based on the relative change amplitude.

2. The device for evaluating small current variables using apparent power according to claim 1, Characterized in that: The processing process of the central processing unit for the apparent electricity quantity is as follows: S1: Read the apparent electricity quantity once every time interval T. The reading time points divide the detection time into multiple time periods. The previous time period in two adjacent time periods is called the x-th time period, and the latter time period is called the (x + 1)-th time period, where x is a natural number; S2: Read the apparent power in S3 as z at the start point of the x-th time period x ; S3: Read the apparent power in S3 as z at the end point of the x-th time period x+1 , and calculate the change in apparent power during the x-th time period as: m x = z x+1 -z x ; S4: Read the apparent power as z in S3 at the end point of the (x + 1)-th time period x+2 , and calculate the change in apparent power in the (x + 1)-th time period as: m x+1 = z x+2 - z x+1 ; Calculate the change amplitude n of the change in apparent power in the (x + 1)-th time period relative to the change in the x-th time period x = m x+1 - m x , and judge n x relative to m x for its change amplitude; S5: If n x ≤ 0.1 m x , then x = x + 1, and repeat steps S4 and S5; If 0.1 m x <n x ≤0.3 m x , then the length of the adjustment time period is 1 / 5 to 1 / 10 T, restore x = 1, and use z x+2 to replace z x , and repeat steps S3 to S5; If n x > 0.3 m x , then upload the information of n x , m x and m x+1 to the control center.

3. The device for evaluating small current variables using apparent power according to claim 2, Characterized in that: The central processing unit also sets a limit value K for the apparent power change amount in S4. If m x+1 ≤K, then calculate n x and enter S5; if m x+1 >K, then upload the information of m x , m x+1 to the control center.

4. The device for evaluating small current variables using apparent power according to claim 3, Characterized in that: The central processing unit also adds a step of detecting humidity between S4 and S5: detect the humidity information s on the line, the humidity set value is Q. If s > Q, then adjust the length of the time period to 1 / 5 - 1 / 10 T; If s ≤ Q, then maintain the original time period length T.

5. The device for evaluating small current variables using apparent power according to claim 4, Characterized in that: In step S5, if n x > 0.3 m x when, detect the humidity information of the environment where the circuit is located. If s x+1 > s x , then adjust the length of the time period to 1 / 5 - 1 / 10 T, resume x = 1, and use z x+2 to replace z x , and repeat steps S6 - 8; if s x+1 ≤ s x , then upload the information of n x , m x+1 and m x+2 to the control center. s x+1 is the humidity information of the next time period, and s x is the humidity information of the previous time period.

6. The device for evaluating small current variables using apparent power according to claim 4, Characterized in that: When s ≤ Q in the step of detecting humidity, the central processing unit also adds a step of detecting temperature rise between detecting humidity and S5: detect the temperature rise information f on the line, the temperature rise set value is P. If f > P, then adjust the length of the time period to 1 / 5 - 1 / 10 T; if f ≤ P, then maintain the original time period length T.

7. The device for evaluating small current variables using apparent power according to any one of claims 1 to 6, Characterized in that: The central processing unit also sets the number of stored change amplitudes n to Y, where Y is a natural number. When x + 1 > Y, n, m, and z each cover one digit forward, and then repeat steps S4 and S5.

8. The device for evaluating small current variables using apparent power according to claim 7, Characterized in that: The numerical range of the apparent voltage is 1 - 20V.

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