Detection performance of arcing fault detectors in the Chinese market according to the Chinese Standard GB/T 31143

There are two sets of standards available in the Chinese market that specify the design requirements and operating tests for arc fault detection devices (GB/T 31143) and arcing fault detectors (GB 14287.4) respectively. While arcing fault detectors (AFDs) are claimed to have passed GB 14287.4 standard tests, it remains unclear whether these AFDs can pass GB/T 31143 standards and effectively detect arc fault signals. This study experiments to explore the operational performance of AFDs in the Chinese market based on GB/T 31143 standards, revealing that not all AFDs can pass this test and provide adequate protection for people’s lives and property. The main reason for the failure is that the arcing characteristics, such as flat shoulders and reduced amplitude, of the signal are easily masked by other branch circuit loads.


Introduction
Fires caused by arc faults have garnered significant attention in recent years.These incidents are primarily attributed to compromised insulation materials, interrupted connections, and the natural aging of electrical components.Due to the immense energy released by arcs within a short timeframe, temperatures can reach as high as 6500-12000 K [1] and equipment and surrounding combustibles can be instantaneously ignited, posing threats to both life and property safety.
AC arcing faults consist of both series arcs and parallel arcs.Parallel arcing faults often benefit from the protection provided by other circuit breakers in residential settings due to their high-amplitude current characteristics.On the other hand, the amplitude of series arc fault currents is relatively small, making it easier for the current signal characteristics to be masked.Consequently, this poses significant difficulties and challenges when it comes to identification.
To detect arc faults and prevent fires, the United States initially introduced design requirements for arc-fault circuit interrupters (AFCI) in the 1990s (UL-1699) [2].In 2013, the IEC 62606 was issued by the International Electrotechnical Commission (IEC), which applies to various countries and regions worldwide [3].Subsequently, China implemented GB/T 31143 in 2014 to regulate the design of arc fault detection devices within its market based on international standards while considering its own country's voltage level and frequency [4].Both the AFCI and AFDD standards serve to detect arcs and interrupt the circuit to prevent fires.In 2014, China proposed GB 14287.4 as a standard for arcing fault detectors (Electrical fire monitoring system-part 4: arcing fault detectors) applicable to industrial and residential buildings with power ratings up to 10kW, which function as alarms [5].
In the Chinese market, there has been a significant increase in the availability of arc fault detection products designed to identify and prevent arc faults occurring in residential properties.There have been many researchers conducting standard and additional tests on AFDDs in the Chinese market [6][7].The arc fault detection products primarily rely on algorithms that distinguish between fault current and normal current.These algorithms encompass threshold techniques [8] as well as machine learning approaches [9][10].
There is no literature on the testing and evaluation of arcing fault detectors.Although these products have been shown to pass the test requirements of standard GB 14287.4,it is not clear how well they perform in other tests.This paper focuses on evaluating AFDs in the Chinese market according to the verification requirements of operating characteristics of GB/T 31143.
The remaining sections of the paper are organized as follows.Section 2 introduces the experimental platform, followed by the methodology in Section 3. A detailed presentation of results and analysis can be found in Section 4. Lastly, conclusions are presented in Section 5.

The experimental platform
A test platform is built for detecting the performance of arcing fault detectors as shown in Figure .1.The 220 V AC-50 Hz power supply is used for powering loads and circuits.Selected AFDs are positioned at the power supply entrance to identify arc faults and raise an alarm.The current transformer is used for collecting the current signal, which is shown in the oscilloscope.The series arcs can occur in any branch of the test circuit configuration.Two types of arc fault generators are recommended in the standard.These generators consist of an arc generator and cable specimens to simulate the interruption of the arc fault connection and the deterioration of the cable, respectively [4].

Load unit
Seven loads are selected as masking loads for the arc fault experiment.Table 1 shows the rated power or current of the loads in the experiment, meeting the requirements specified in the standard.These loads include resistive load (RE), inductive load (Le), capacitive load (Ce), and switch power supply load (Sw).The lighting system tested is presented in Figure.

AFD unit
Seven representative AFD products in the Chinses market are collected for detection performance.The rated current and voltage of anonymized arcing fault detectors are listed in Table 2.

Methodology
There are three experiments conducted to evaluate the ability of AFDs to detect arc faults.The series arc fault tests evaluate the ability of AFDs to recognize arc faults in a circuit connected in series to a resistive load.The masking tests evaluate the ability of AFDs to detect an arc fault when a masking load is present in the circuit.Unwanted tripping tests examine the performance of AFDs to resist interference when there is an interfering load in the line.According to the test regulations, each type of test is performed three times and the alarm time issued by AFDs shall not exceed the maximum break time [4].
It is indicated that the experiment is considered successful when all three times meet the time requirements.
Based on the standard requirement, the main purpose of conducting series arc fault tests is to test the performance of AFDs when a sudden arc fault occurs in the circuit, inserting an arc-fault load, and closing the series arc fault.A selected AFD shall detect the arcing fault within the specified time.All AFDs shall be tested up to the rated current.
The AFDs shall detect the arcing fault within a specified time in different inhibition configurations: inhibition loads, EMI filter, and line impedance.A first series of tests with no inhibition load and a second series of tests with masking loads shown in Table 1 are performed.Four configurations are applied by the tests because the arc fault can occur in every branch as presented in Figure .1.The arcing fault detectors shall clear the arcing fault with the EMI filter and line impedance.When the AFDs perform the unwanted tripping tests, the device will not trip.Unwanted tripping tests consist of crosstalk tests and tests with various disturbing loads.When the loads in Table 1 are energized for at least 5 s, the AFDs shall not trip.

Results and analysis
From the overall results in Table 3, two AFDs passed the tests according to GB/T 31143.Two detectors do not serve as a good warning with the failed items exceeding 30.The remaining three AFDs failed with 6,14 and 14 items respectively, which can recognize the arc fault to a certain extent.In the series arc fault tests, three AFDs passed all the items.The three arcing fault detectors experienced a delay in detecting the arc fault current, which was supposed to be detected at a threshold of 3A.It indicates that the signal feature of a small current is not obvious, which causes trouble in the detection of the AFDs.In the masking test, two detectors passed all the tests.Two AFDs failed items over 25 and had little ability to recognize arcing faults in masked loads.AFD5 showed unstable alarms in several tests, i.e., some of the three repetitive tests were able to alarm in time and some were not able to detect the arc faults.The stability of the detectors is also an issue that needs to be improved.Four detectors passed the test and the failed items of the rest are no more than in the unwanted tripping test.The failed items of the unwanted tripping test are mainly concentrated in the switching power supplies, an electronic lamp dimmer with a tungsten load, and fluorescent lamps.These three loads themselves have current waveforms like the arc fault, which can easily cause misjudgment.From the comparison of the front and back periods, the current signal exhibits a slight decrease in amplitude and distinct flat shoulder characteristics during the occurrence of a series arc fault.When 3 A resistive load is shielded by switching power supplies, it can be seen from Figure .6 that these characteristics are weakened, which brings great trouble to arc fault signal detection.On the other hand, the normal current waveform of some appliances has current features like arc signals.Figure .7 shows the normal signal waveform of an electronic lamp dimmer with tungsten loads (conduction angles of 60°), which makes identification very difficult.

Conclusion
The performance of seven arcing fault detectors available in the Chinese market was assessed in this study based on the series arc fault tests, masking test, and unwanted tripping test in the standard GB/T 31143.It was found that only two AFDs passed all the tests and protected residents from fire.The arc faults with small current levels are difficult to detect in the series of arc fault tests.Masking tests are a huge challenge for these products, while the immunity to various loads is generally better because the current features are easy to be masked and mistaken by other normal signals.
These manufacturers claim these arcing fault detectors passed the tests in the GB/T 14.287.4.Unfortunately, only a small percentage of products pass the tests of the GB 31143 and prevent residents from fires.These products need to be trained and tested with more loads and line configurations to improve accuracy and stability.
The detection of current and voltage signals is achieved by employing a current transformer (CP8050A) with a frequency range from DC to 50 MHz, along with a voltage probe capable of capturing signals up to 250 MHz.Figure.3 shows the arcing fault detector being tested with the current transformer.These signals are collected and recorded in a Rigol Oscilloscope MSO5000 as shown in Figure.4.

Figure. 6
Figure.6 Arc-fault current waveforms of 3 A resistive load (arc-fault load) and switching power supplies.

Figure. 7
Figure.7Normal current waveforms of an electronic lamp dimmer with tungsten loads (conduction angles of 60).

Figure. 5
Figure.5 shows the current waveform collected by a 3 A resistive load under a series arc fault test.From the comparison of the front and back periods, the current signal exhibits a slight decrease in amplitude and distinct flat shoulder characteristics during the occurrence of a series arc fault.When 3 A resistive load is shielded by switching power supplies, it can be seen from Figure.6 that these characteristics are weakened, which brings great trouble to arc fault signal detection.On the other hand, the normal current waveform of some appliances has current features like arc signals.Figure.7 shows the normal signal waveform of an electronic lamp dimmer with tungsten loads (conduction angles of 60°), which makes identification very difficult.

Table 1
Specific parameters of loads.

Table 2
Detailed parameters of AFDs.

Table 3
Test results.