2.3 Related Standards

Currently, the major international standards for AFCI in PV systems include:

UL 1699B standard: The UL Outline standard issued by UL for the first time in 2011 and updated many times. The latest version is UL 1699B-2018. This standard specifies the test requirements and performance indicators of arc fault protection devices (AFCI) in PV systems.

IEC 63027 standard: An international standard developed by the International Electrotechnical Commission (IEC) for the first time in 2017, specifying the end performance requirements for AFCI in PV power generation systems.

AS/NZS 5033 standard: The AFCI standard issued by Australia and New Zealand for the first time in 2019 AS/NZS 5033:2019, specifying the functional requirements and test methods for AFCI in PV systems.

NEC 2017 Section 690.11: The National Electrical Code (NEC) 2017 edition first introduced the requirements for AFCI, stipulating that AFCI devices complying with UL 1699B standard shall be installed in DC circuits of photovoltaic systems.

CSA C22.2 No. 293 standard: A safety standard for photovoltaic systems issued by CSA Group of Canada. Since the 2019 edition, it has incorporated the functional requirements and test provisions of AFCI and requires reference to the UL 1699B standard.

In addition, the PV installation specifications in several European countries have gradually increased the requirements for the introduction of AFCI with reference to IEC 63027.

In summary, UL 1699B and IEC 63027 standards are currently two major international standards for AFCI detection and protection. They have high consistency in the definition of AFCI functions, technical requirements, test methods, etc. Standards in other countries and regions mostly refer to or reference these two major standards. This helps to facilitate the interoperability and internationalization of AFCI technology and products.

The specific requirements for key parameters vary in different AFCI standards. In comparison, UL 1699 standard has the most stringent and detailed requirements for AFCI performance and technology. IEC 63027 basically adopts the UL 1699 regulations but slightly relaxes some specific numerical requirements. The AS/NZS 5033 standard mainly refers to UL 1699 for some technical requirements but does not require high-end product levels and focuses more on basic AFCI products. Some key parameters in UL1699B are as follow:

In general, all these requirements do propose higher benchmarks for key functions of AFCI, such as response speed, detection sensitivity, and protection range, which help to improve AFCI technology and optimize product performance in the industry. 

3. Solution

When damage (to module frame, cables, connectors etc.) and arcing occurs at any position of the DC-side, according to Joule's law, the thermal effect of a short-circuit point is in direct proportion to the square of the current, greater current thus increases the fire risk. Therefore, one of the methods in which the risk of fire can be effectively reduced is to disconnect the DC current, by disconnecting the inverter AC side and stopping the DC to AC current conversion and thus the current injection on the DC side.

DC Arcing Protection Function of Inverter

3.1 How to Identify an Arc Fault?

Consequently, the key for the DC arcing test protection function is to identify the arcing current and timely switch off the current injection at the DC side.

Essentially, arcing occurs when gas suffers from electrical breakdown due to the strong electric field between conductors to form continuous plasma and generate very bright ultraviolet radiation and strong heat. The arcing generation mechanism and positions are different in the photovoltaic system, so the arcing current is generally identified by measuring the current at the DC side and using the spectral analysis method.

The plasma is in a disorderly state due to the ionization of the air during the arcing, and the current flowing through the arc will have strong fluctuations. This highly volatile current on the spectrogram shows a very wide noise band, which is the so-called "white noise" in the spectrum analysis, while the normal DC current without interference shows a relatively stable state. As shown in the figure below, the DC spectrum only shows the switching frequency of the inverter when there is no arcing. However, a certain "noise frequency" will appear when arcing begins, and the more disorderly noise frequency will be generated during the continuous arcing.

Arc Spectrogram

After the DC arcing protection function of the inverter is enabled, the inverter will test the input current of each string in real time. After the characteristic current phenomenon of the arc (as shown in the figure above) is tested, the inverter will immediately switch off the AC side and report an error. The current circuit at the DC side will be switched off and the arc will be eliminated when the AC current is switched off.

3.2 Technical Characteristics

GoodWe focuses on the safety issues of the power plant and continuously improves AFCI technology, including algorithms and test accuracy, etc. After several technological changes, a breakthrough progress has been made in DC arcing test technology, and the new AFCI technology has now been launched.

AI Integrated Deep Learning:

Different from the traditional solution where the arc testing algorithms and threshold settings are mainly based on personal experience, GoodWe AFCI calculates and iterates the massive data, continuously learns the arc characteristics, and forms a unique arc characteristics library to eliminate false and omitted reports caused by environmental noise. The AI integrates the deep learning to enable the test model to continuously learn the unknown spectra and adapt to various application scenarios thereby.

Powerful Data Acquisition Capability:

With a special arcing sensor, the GoodWe AFCI has the powerful data acquisition capability to continuously search for the arc characteristics. Once the arc is found, it will timely report to the chip.

Strong Adaptability and Flexibility:

It meets the requirements for the cable length and input current of high-current modules for larger photovoltaic installations, quickly switches off the power supply within milliseconds, which is far better compared to the UL 1699B.