диафрагмированные волноводные фильтры / Test_of_Arc_Fault_Detection_Devices_for_Operation_from_Spark_Gaps_and_Arc_Fault_in_an_Electric_Circuit_of_0.4_kV

2023 International Ural Conference on Electrical Power Engineering (UralCon) | 979-8-3503-0339-1/23/$31.00 ©2023 IEEE | DOI: 10.1109/URALCON59258.2023.10291069

At the same time, sparking and arc breakdown are not detected by any of the listed protection devices and, accordingly, develop until critical heating occurs, leading to equipment damage and, subsequently, to fires. For example, in case of a sequential arc breakdown CB, it will not work due to the large contact resistance in the place of poor contact, where the arc burns. Therefore, the value of the current in the circuit drops, and for the circuit breaker this mode is considered nominal, therefore, no trip will occur. For the same reason, the RCD will not work, the leakage current during arc processes is less than that set by the RCD manufacturer.

II.CONNECTION DIAGRAM FOR ARC FAULT DETECTION

DEVICES

To prevent breakdowns in the form of an arc, an arc fault detection devices (AFDD) [7–10] has been developed and successfully used, which, when a breakdown is detected, turns off the damaged circuit. The probability of operation for various protection devices is given in Table 1. AFDD is a microprocessor-based modular device designed for an electrical circuit of class up to 0.4 kV [8–12].

AFDD refers to microprocessor technology. The built-in microcontroller makes a spectral analysis of the current and voltage in the load, and upon completion, if an error is detected, the circuit is turned off. The device is sensitive to interference from sparking at its output [11–15]. The AFDD consists of a power disconnector, which usually has two modules: the first contains an arc fault detection unit, the second contains the circuit breaker mechanism with thermal and electromagnetic releases. The power disconnector disconnects only the phase conductor.

At the command of the arc fault detection unit, the third release, controlled by a thyristor key, disconnects the load. Current transformers control the current in the phase conductor. The instantaneous value of the current with the mains frequency is read by the transformer of the lowfrequency channel, then the current is rectified by the diode bridge and the signal is amplified. The high-frequency channel transformer reads a signal that lies in the range from 5 to 50 MHz. The high frequency signal is rectified by an RMS detector. The built-in microcontroller digitizes and analyzes both analog signals. The power supply of the microcontroller is installed between the phase and the neutral wire.

A characteristic feature of the arc fault current is a wide frequency distribution spectrum extending up to about 1 GHz. This broadband signal is naturally modulated. The arc is

interrupted when the mains voltage passes through zero and lights up again with an increase in the instantaneous voltage value. AFDD analyze the amplitude and the rate of change of the envelope at the output of the high-frequency channel, taking into account the phase of the low-frequency signal.

If both the amplitude and the rate of change of the highfrequency signal envelope exceed the values specified by the manufacturer, then at the next mains voltage transition through zero, the program tries to recognize the signs of an emergency condition, and upon reaching the set value, the microcontroller issues a command to the thyristor switch to turn off the load. If the program does not recognize signs of emergency sparking, then the error search is reset. After the protection has been triggered, only a person can automatically reconnect the load.

It is necessary to select and adjust the algorithm so that the AFDD reliably recognizes emergency, fire hazardous sparks and excludes false alarms from harmless interference. To do this, the following conditions must be taken into account: the interference power must exceed the background level by 15 dB; the duration of the recorded interference should be at least 60% of the tripping time limit established by IEC 62606:2013 "General requirements for arc fault detection devices" [15–17], for at least 95% of this duration, modulation of the interference of twice the mains should be observed frequency; during at least 80% of this duration, the interference power must be stable; the current in the controlled circuit must be at least 1.5 A [16–18].

The connection diagram of the AFDD is shown in Fig. 1. A CB is provided in front of the AFDD for protection.

Fig. 1. The use of AFDD in the electrical installation of a residential building (a - single-phase power supply system using single-pole AFDD; b - single-phase power supply system using two-pole AFDD).

To ensure reliable operation of the AFDD, it is better to install it closer to the consumers. At the same time, it should be taken into account that the AFDD will not detect dangerous sparking up to the place of installation, as well as the presence of devices that interfere with operation, which may prevent the

AFDD from correctly recognizing an arc fault. To date, clear requirements have not been formulated that regulate the number of AFDD in the switchboards, the location of the AFDD, the nature of the load protected by the AFDD.

The AFDD can be designed by the manufacturer as a single device, having a disconnecting device to disconnect the protected circuit, or incorporating a protective device. The built-in protective device is either a CB or a RCD. The AFDD must be protected against short circuits by means of CB or fuses in the absence of a built-in CB. On Fig. 2 shows the connection diagrams of the AFDD together with the CB and RCD.

a

devices" was introduced. The purpose of this standard is to establish the necessary requirements and test procedures for devices installed by qualified personnel in domestic and similar places, designed to reduce the risk of electrical ignition after the device.

An arc fault detection device in accordance with IEC 62606:2013 "General requirements for arc fault detection devices" is recommended for use in the following locations:

-in rooms with sleeping places: such as hotels and hostels, kindergartens, nurseries, boarding schools, nursing homes, hospitals, schools, houses and apartments;

-in places of increased fire danger due to the nature of the processed stored materials: such as barns, woodworking shops, warehouses of combustible materials, paper and textile industries, agricultural premises;

-in places where there are combustible materials: such as wooden houses, buildings where most building materials are combustible;

-in flame-conducting structures: such as high-rise buildings, forced ventilation systems;

-in places where endangered or non-recoverable objects are present: such as museums, national monuments, public buildings and important infrastructure, such as airports and

railway stations.

Manufacturers recommend installing an AFDD at the input of the line that it should protect.

III.COMPLEX FOR CHECKING ARC FAULT DETECTION

DEVICES

b

Fig. 2. Connection diagrams for an AFDD together with CB and RCD (a - a variant of a single-pole AFDD, a single-pole CB and a two-pole RCD; b - a variant of a two-pole AFDD, a single-pole CB and a two-pole RCD).

The arc fault protection device began to be used in the late 90s of the last century [6–8]. Due to the complex nature of the arc process, there is no ideally selected algorithm for the operation of the AFDD, which would take into account all cases in electrical networks. The complexity of designing an AFDD lies in the selection and tuning of an algorithm capable of reliably recognizing emergency, fire hazardous breakdowns and at the same time excluding false alarms from harmless interference.

Each electrical circuit has its own parameters, such as: the nature of the load, power factor, quality parameters of power networks [19–21], which means that arc processes can proceed differently and do not correspond to the templates established by the manufacturer of the AFDD [22–24]. To solve these problems, it is necessary to conduct a series of tests for specific network parameters in order to understand whether a case can really occur in the current power system when the AFDD does not work properly [14–18, 22–24].

In Russia, from July 1, 2018, a standard identical to IEC 62606:2013 "General requirements for arc fault detection

According to IEC 62606:2013 "General requirements for arc fault detection devices", the AFDD must eliminate the arc fault within a time depending on the magnitude of the actual value of the arc current shown in Fig. 3.

Fig. 3. Cut-off time limits for AFDD at Un=230 V.

IEC 62606:2013 "General requirements for arc fault detection devices" establishes the necessary list of tests (or checks) and the number of samples for manufacturers to certify devices. After the required list of tests has been carried out by the manufacturer (or a third party, for example, an independent

laboratory), certified AFDDs are mounted on site. According to clause 1.8.1 of the "Electrical Installation Rules (PUE)": "Electrical equipment up to 500 kV, newly put into operation, must be subjected to acceptance tests ...".

To conduct such tests, equipment is needed that provokes emergency situations, which ultimately leads to thermal arc breakdown and ignition in sections of a particular power system. These devices can be used to assess when the AFDD will not operate properly.

The device for checking the AFDD refers to the field of measuring and fire fighting equipment, in particular, to test equipment, which is designed to test devices for protecting against arcing and spark gaps. A device for testing protective devices is known, based on the principle of loading them with current [13–15]. The disadvantage of this equipment is that it does not have the ability to test arc fault protection devices and arc gaps.

The proposed device should provide a safe test for the

declared characteristics (tprocessing = f (Iarc)) of all types of arc fault and arc gap protection devices of domestic and foreign

manufacturers.

The technical result is the device for checking the AFDD, which eliminated the disadvantages of the analogue [15]. The technical result is achieved by the fact that the device for checking the AFDD contains a CB, a stopwatch, an arc generator, a starter, a limit switch, an adjustable load and an ammeter. The scheme of the proposed device is shown in Fig. 4.

Fig. 4. The device for checking the AFDD (1 - a circuit breaker; 2 - stopwatch; 3 – arc generator; 4 - starter; 5 - limit switch; 6 - adjustable load; 7 - ammeter; 8 - protection apparatus).

The device for checking the AFDD works as follows (Fig. 4). When the circuit breaker 1 is turned on, mains voltage is supplied to input 8 of the protection device. When the protection device 8 is turned on, the starter 4 is activated, preparing the stopwatch circuit 2 (by closing the contacts), and the current measured by the ammeter 7 flows through the closed arc generator 3 and the connected load 6. The arc generator adjusting screw (the adjusting screw is conditionally not shown in the drawing) open the electrodes, creating a spark gap with the subsequent occurrence of a stable electric arc. At the same time, the limit switch 5 is closed and the stopwatch 2 is started. Under the influence of the arc on a working protection device, it is triggered, the stopwatch is turned off

and the arc stops burning. In this case, the stopwatch records the time of operation of the AFDD protection device. Thus, the advantage of the proposed device for checking the AFDD is that it contains:

•protection against short circuit currents and overload when checking the AFDD;

•the ability to regulate the values of the arc current and change the nature of the load to ensure safe and highprecision verification of the declared characteristics for all types of AFDD.

The heart of the entire test setup is the arc generator. Tests can be carried out in the presence of an arc discharge in air (like a bad contact) or a thermal arc discharge (damaged cable). In this case, air arc breakdown is simulated using an arc generator [15, 17, 18]. The generator is designed in accordance with the international standard IEC 62606:2013 "General requirements for arc fault detection devices", which allows you to simulate a process that is close to a real electric arc or sparking in a domestic environment. The electric arc generator is connected to an alternating voltage source and a load.

The electric arc generator works as follows. In the initial position, the adjusting drive is in a position in which the carbon-graphite electrode 7 adjoins directly to the nozzle of the fixed electrode 4. When the electrodes are separated using the adjusting drive, a stable electric arc occurs between the moving and fixed electrodes (successive arc breakdown), under the influence of which verification of the arc fault protection device and spark gaps. The design of the arc generator ensures the smooth approach of the electrodes, it is implemented by translational movement without their scrolling. All elements except electrodes are insulated. The carbon-graphite electrode has the best conductivity, does not melt, and at the same time retains its properties and criteria, unlike metal counterparts.

IV. CONCLUSIONS

To obtain more data, it is necessary to test loads of different nature at different currents. An electronic oscilloscope can be added to the test setup to examine current fluctuations during arcing, which could give a more complete understanding of why the device in each case works or not. According to the oscillograms of the connected various loads, one can see the changes inherent in the arc, register the response time of the AFDD, compare it with the standards IEC 62606:2013 "General requirements for arc fault detection devices".

The proposed device for testing devices for protection against arcing and spark gaps allows you to control the fact of the mandatory operation of the AFDD for a certain time and formulate the requirements necessary for the design, namely: the location of the AFDD in the boards; the number of AFDD in the shields; the nature of the load protected by the AFDD; maximum power of the protected load AFDD; the greatest remoteness of the protected load from the AFDD.

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