CN112630519A

CN112630519A - Residual current detection device and method

Info

Publication number: CN112630519A
Application number: CN202011518596.6A
Authority: CN
Inventors: 智建立; 徐强; 杨阳; 李春林; 郑燕飞
Original assignee: Anhui Zhongxin Jiyuan Information Technology Co ltd
Current assignee: Anhui Zhongxin Jiyuan Information Technology Co ltd
Priority date: 2020-12-21
Filing date: 2020-12-21
Publication date: 2021-04-09

Abstract

The invention relates to a residual current detection device, which comprises a peridium coil, a controller and a control circuit, wherein the peridium coil is used for collecting residual current of a primary circuit and providing a detection signal for the controller; the intermediate connection cable is used for connecting the secondary side of the wrapped coil and the primary side of the secondary CT so as to realize signal transmission; secondary CT, wherein a miniature current transformer is adopted to realize signal conversion from 5A or 1A current to 0-3.53V; and the controller is used for converting the acquired analog signals into digital signals and carrying out signal calculation processing. The invention also discloses a detection method of the residual current detection device. According to the invention, one peril coil simultaneously penetrates A, B, C, N four wires, only 2 wires are led out to detect residual current, and the field construction wiring is simplified; the discrimination of fault signals and normal signals is increased, the switching locking fixed value can be set to be very small, the discrimination of the system is increased, and the primary side grounding current can be detected by 100% when reaching more than 10mA through field application verification.

Description

Residual current detection device and method

Technical Field

The invention relates to the technical field of residual current detection, in particular to a residual current detection device and a residual current detection method.

Background

With the rapid development of national economy and the improvement of the living standard of people, the demand of society on electric power is increasing day by day, and higher requirements on the reliability and the quality of power supply are provided. Due to the increasing load, the reactive power demand of the power grid also increases. And the flow of reactive power in the power grid can increase the power grid loss, reduce the utilization rate of power grid equipment and reduce the power supply quality of a power system. Therefore, the solution of the reactive compensation problem has great significance for reducing loss and saving energy. Among them, 380V distribution side centralized packet switching capacitor compensation application is the most common.

The electric equipment in the power supply area has the characteristics of multiple points and wide range, and the electric equipment of different types can generate the problems of three-phase imbalance, harmonic interference, interphase short circuit, ground fault and the like. Therefore, the low-voltage reactive compensation must increase the locking conditions such as fault locking, three-phase unbalanced locking, harmonic content exceeding locking and the like so as to ensure the personal safety and the equipment safety. However, the fault characteristics of the fault are different in different development stages, the indexes are different, and particularly, the single-phase ground fault with different ground impedances is more difficult to accurately detect and identify in the early stage of the fault development, so that a large accident potential exists with a fault switching capacitor. Therefore, a high-precision method for detecting a single-phase earth fault signal is urgently needed to lock the capacitor switching at the early stage of the fault and send an alarm signal.

The conventional residual current detection comprises 4 links, namely a primary CT 5, a connecting cable 6, a secondary CT 7 and a controller. The primary CT 5 converts a large primary current into a current signal of a rated output 5A or 1A. The converted current signal is connected to a secondary CT 7 of the controller through a connection cable 6, the length of which is generally about 3 to 5 meters. The secondary CT 7 is responsible for converting the current of 5A or 1A into a weak current signal which can be directly sampled and calculated by the controller AD chip, such as +/-5V. The schematic block diagram of the whole system is shown in fig. 1.

Detection errors may be introduced in 4 links of conventional residual current detection:

error of primary CT 5: the accurate grades of the current transformers are generally 0.2, 0.5, 1.0, 0.2S, 0.5S, 5P, 10P and the like. The special current transformer with S requires high enough precision within the load range of 1% -120%; the precision within the range of 20% -120% of the load is generally required to be high enough within 0.2, 0.5 and the like, the error of measuring 4 load points is generally smaller than a specified range, the error comprises a specific difference and an angular difference, so that the accuracy in vector calculation is ensured, and the current transformers such as 5P, 10P and the like are generally used for protecting relay appliances, namely the composite error under the short-circuit current is required to be smaller than a certain value, the 5P is smaller than 5%, and the 10P is smaller than 10%. The current transformer specifies different accuracies, i.e. error accuracies in different current ranges, depending on the application. In short, there is an accuracy error in a specified measurement range, and the accuracy cannot be guaranteed if the signal is small.

The connection cable 6: the connecting cable 6 can be essentially equivalent to a certain impedance (R + jX), and the equivalent impedances of cables with different lengths are different at different frequencies, so that the influence on the error is mainly to increase the angular difference of each phase.

Secondary CT 7: secondary CT 7 is similar to primary CT 5, except that it introduces both specific and angular differences outside the measurement range.

A controller: in the acquisition and calculation process of the controller, due to the limitation of AD digit, the problem of theoretical minimum resolution exists, the size and the phase of an analog signal are difficult to restore by 100%, and errors are also generated in the process of calculating the residual current by vector synthesis.

Therefore, as the links of detecting and calculating residual current are more, and error factors with different sizes exist in each link, small fault signals are difficult to accurately detect in the early stage of the single-phase earth fault, and effective fault characteristics cannot be extracted.

Disclosure of Invention

The invention aims to provide a residual current detection device which reduces detection links and reduces errors.

In order to achieve the purpose, the invention adopts the following technical scheme: a residual current detection device comprising:

the included coil is used for collecting residual current of a primary circuit and providing a detection signal for the controller;

the intermediate connection cable is used for connecting the secondary side of the wrapped coil and the primary side of the secondary CT so as to realize signal transmission;

secondary CT, wherein a miniature current transformer is adopted to realize the signal conversion from 5A or 1A current to 0-3.53V, and the requirement of an AD sampling range is met;

and the controller is used for converting the acquired analog signals into digital signals and carrying out signal calculation processing, thereby realizing line state monitoring, normal switching of the capacitor and locking protection during faults.

The peripheric coils are square with the side length of 800mm, and are sleeved on A, B, C, N four wires.

Another object of the present invention is to provide a method for detecting a residual current detection device, wherein an externally input three-phase primary current signal is collected by a peridium coil, the current signal collected by the peridium coil is transmitted to a secondary CT through an intermediate connection cable, a controller collects and calculates an output signal of the secondary CT, determines a current operating state of a line, performs capacitor switching according to a line condition, and prevents a line fault from being enlarged when a line fault is locked and input.

According to the technical scheme, the beneficial effects of the invention are as follows: firstly, one covering coil simultaneously penetrates through A, B, C, N four wires, only 2 wires are led out to detect residual current, the number of cables is changed from 6 to 2, and the field construction wiring is simplified; secondly, the discrimination of fault signals and normal signals is increased, as the residual current is infinitely close to 0 and the switching locking fixed value can be set to be very small regardless of the load current and the load balance condition in a normal state, the discrimination of the system is increased, and the primary side grounding current can be detected by 100% when reaching more than 10mA through field application verification; and thirdly, the residual current detection is applied to capacitor switching locking for the first time, so that the safety of capacitor switching is improved.

Drawings

Fig. 1 is a schematic view of a conventional residual current detection device;

FIG. 2 is a schematic view of the apparatus of the present invention;

fig. 3 is a schematic diagram of the structure of the wrap coil in fig. 2.

Detailed Description

As shown in fig. 2, a residual current detection device includes:

the included coil 1 is used for collecting residual current of a primary circuit and providing a detection signal for the controller;

the intermediate connection cable 2 is used for connecting the secondary side of the peripherical coil 1 and the primary side of the secondary CT 3 so as to realize signal transmission;

secondary CT 3, a miniature current transformer is adopted to realize the signal conversion from 5A or 1A current to 0-3.53V, and the requirement of an AD sampling range is met;

The peripheric coil 1 is a square with the side length of 800mm, and the peripheric coil 1 is sleeved on A, B, C, N four wires.

When the circuit works, an externally input three-phase primary current signal is collected through the enveloping coil 1, the current signal collected by the enveloping coil 1 is transmitted to the secondary CT 3 through the middle connecting cable, the controller collects and calculates an output signal of the secondary CT 3, judges the current running state of the circuit, performs capacitor switching according to the circuit condition, and prevents the circuit fault from being expanded when the circuit fault locking control input occurs.

As shown in figure 3, the peripherical coil 1 is square (800 × 800mm), A, B, C three phases are arranged horizontally in the middle, the horizontal distances between the phases and the side phases from the peripherical coil 1 are both 200mm, and I is realized_a+I_b+I_c+I_NAnd (4) obtaining the residual current by vector synthesis.

In conclusion, one included coil 1 simultaneously penetrates A, B, C, N four wires, only 2 wires are led out to detect residual current, the number of cables is changed from 6 to 2, and the field construction wiring is simplified; the discrimination of fault signals and normal signals is increased, as the load current and the load balance condition are irrelevant under the normal state, the residual current is infinitely close to 0, the switching locking fixed value can be set to be very small, the discrimination of the system is increased, and the primary side grounding current can be detected by 100 percent when reaching more than 10mA through field application verification.

Claims

1. A residual current detection device, its characterized in that: the method comprises the following steps:

2. The residual current detection device according to claim 1, characterized in that: the peripheric coils are square with the side length of 800mm, and are sleeved on A, B, C, N four wires.

3. The method for detecting a residual current detection device according to any one of claims 1 to 2, characterized in that: an externally input three-phase primary current signal is acquired through the peridium coil, the current signal acquired by the peridium coil is transmitted to the secondary CT through the intermediate connecting cable, the controller acquires and calculates an output signal of the secondary CT, judges the running state of the current line, performs capacitor switching according to the line condition, and prevents the line fault from being expanded when the line fault is locked and controlled to be input.