Technical description of Siemens leakage circuit breaker 5SM6AFD detection device

Overview of Siemens Leakage Circuit Breaker 5SM6AFD

Earlier leakage protection devices such as fuses, miniature circuit breakers and residual current operated protectors are not suitable for detecting arc faults, especially arc faults that are limited by impedance. Therefore, a new type of protection device for detecting arc faults eliminates this potential safety hazard. The Siemens residual current circuit breaker 5SM6AFD (with arc fault detection) function can also detect the type of arc fault, including the loose contact at the first level of the series fault point. The arc fault that occurs at the location, or the arc fault caused by the insulation fault between an effective wire and another or between an effective wire and the protection wire, is very effective in preventing fire caused by electrical appliances. .

This article will not only explain the physical properties of the arc, but also explain the structure and working principle of the Siemens circuit breaker 5SM6ADF device, as well as various types and many application examples, so that you can use it more correctly when choosing.

Ignition and combustion conditions of the arc

The so-called "contact arc" (see the figure below) can be generated by direct or indirect contact between metal parts at the point of failure, which are in operation or have low conductivity. The movement (vibration, thermal expansion) of these metal parts that are in direct contact with each other at the beginning generates an arc and eventually blows the fuse. Through further heating and continuous breakage of the fuse, a temporary unstable arc is formed. The result is that the metal parts (electrodes) generate high temperature, the air is ionized, and after the current crosses zero and the arc is extinguished, the arc reignites, so nearby combustible materials (such as cable insulation) will be carbonized.

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If the insulation between the two wires is damaged, even if there is no direct metal contact, a parallel arc fault will occur on the conductive insulation gap (see the figure below).

If there are other substances between the wires, the insulation performance may be damaged due to aging, chemical, thermal or mechanical load. Leakage current is formed on surfaces contaminated by dust or condensation. These leakage currents and short-term discharges will heat and carbonize the plastic. The high temperature at the fault point will cause a part of the carbonized material to ignite a stable arc by heating the surrounding materials significantly. After the current crosses zero, the carbonization path between the wires causes the arc to be reignited, further heating until a fire occurs.

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Use an example of a cable shrinkage to illustrate a fire caused by a series arc fault. The flow of current makes the temperature of the shrinkage higher. This temperature increase causes the hot copper to oxidize, which in turn causes the resistance to increase, so the temperature becomes higher. , In some cases melted copper. The production gas, especially the peak current point, produces the arc air gap at least temporarily. The insulation at the fault point is carbonized, the stable arc in this gap will burn, and the flame will cause a fire (the specific situation is shown in the figure below).

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Basic Design of Siemens Leakage Circuit Breaker 5SM6AFD

According to the design diagram below, when the leakage circuit breaker is tested, all active conductors-in this case, the line conductor and the neutral conductor-pass through the device and switch. The line conductor passes through two separate sensors: one is a current sensor for detecting low-frequency (line frequency) signals, and the other is a high-frequency sensor for detecting high-frequency signals. The analog electronics enable the signal to be processed in the controller, which scans the current high frequency power in the range of 22 to 24 MHz. Hereinafter, it is called RSSI (Received Signal Strength Indication), which represents the arc power at a specified frequency and bandwidth.

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When the microcontroller observes that it meets the arc fault specification, it will generate a trip signal, which is transmitted to the switching mechanism through the parallel trip device. When using Siemens circuit breaker 5SM6AFD leakage protection device, the mechanical shaft link connecting rod is used to drive the working mechanism of the installed miniature circuit breaker or the residual current operated circuit breaker with overcurrent protection. The installed protection device trips together with its contacts, and the network is disconnected from the faulty part.

Siemens leakage circuit breaker 5SM6AFD series arc fault detection The detection of circuit breaker series arc faults accounts for about 80% of the total calculation work done by the microcontroller analysis algorithm, and the remaining 20% ​​is parallel arc detection. The specific situation is shown in the figure below. The Siemens Leakage Circuit Breaker 5SM6AFD is based on testing the RSSI on the steep edge. The derivative dRSSI/dt is used to calculate the reference signal "uploaded" from |dRSSI/dt| when the edge is in the zero-crossing zone of the current I. Two conditions must be met to interpret the system signal as an arc, and then the fault integrator rises:

1. Reference signal> limit G4 and

2. The RSSI reaches at least the threshold G2.

Once the fault integrator rises above the limit G2, the microcontroller of the Siemens residual current circuit breaker will switch the device to send a trip command.

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In order to prevent unexpected shutdowns, it is necessary to draw a clear line between the arc fault on the one hand and the signal from loads that generate high-intensity high-frequency noise during normal operation (such as commutator motors and electronic transformers). This is achieved by immediately resetting the leakage circuit breaker fault integrator to zero when an "atypical arc" event occurs. The characteristics of this type of event, such as the RSSI display interruption in the signal curve.

Siemens leakage circuit breaker 5SM6AFD parallel arc fault detection

Series and parallel arc faults have different characteristics, so they are analyzed by different methods. The specific situation is shown in the figure below and an overview of Siemens circuit breaker signal processing is given.

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Compared with the overall algorithm, the micro-controller needs less computational effort to detect parallel arc faults, but this is not because the detection of parallel arc faults requires less work than the detection of series arc faults. The reason is that it is used to detect series arcs. Some signal variables of the leakage circuit breaker can also be used for parallel arc faults.

Siemens Leakage Circuit Breaker 5SM6AFD Model Description

Generally speaking, the 5SM6AFD detection device has two models to choose from, and it is also suitable for two installation widths, with a rated voltage of 230V and a rated current of 16A.

The 5SM6AFD Siemens leakage circuit breaker must be used together with another protection device (small circuit breaker or residual current operated circuit breaker with overcurrent protection). This combination forms an AFDD (that is, an arc fault detection device).

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The 5SM6 011-1 AFD model is designed to be equipped with a compact 5SY60 miniature circuit breaker (1+N in 1 modular width) with a maximum rated current of 16A.

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The 5SM6 021-1 AFD model is designed to be equipped with a 5SY series miniature circuit breaker (1+N in 2 modular widths), with a maximum rated current of 16A.

Siemens leakage circuit breaker 5SM6AFD internal self-test function

This type of circuit breaker has an internal self-test function. The specific working principle can be shown in the figure below.

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This self-test is automatically activated every 13 hours to test analog electronic devices and detection algorithms. The software in the microcontroller generates a synthetic high frequency and current signal, similar to an arc fault signal. These signals are input into the system detection path behind the sensor, and then evaluated by the Siemens leakage circuit breaker analog circuit and microcontroller.

The above is the technical description of Siemens leakage circuit breaker 5SM6AFD detection device, I hope it can help everyone.