GB/T 37408-2019Technical requirements for photovoltaic gird-connected inverter (English PDF)

3.1 Decisive voltage classification

The highest continuous voltage level that can occur between any live parts under the most severe operating conditions.

3.2 Protective extra-low voltage (PELV) system

An electrical system for which the rms voltage of 50 V AC or 120 V DC is not greater in normal operation or single fault conditions (excluding earth faults in other circuits). Also called a PELV system.

3.3 Safety extra-low voltage (SELV) system

An electrical system in which the rms voltage of ac does not exceed 50 V or the dc voltage does not exceed 120 V under normal operation or single fault conditions (including earth faults in other circuits). Also called a SELV system.

3.4 Protective bonding

An electrical connection that provides electrical continuity between accessible conductive parts or protective shielding and the protective conductor terminal.

3.5 Protective separation

Structures and measures that separate circuits of different protection levels from each other through basic insulation and supplementary insulation or other equivalent protection measures (such as reinforced insulation or protective impedance).

3.6 Functional insulation; FI

Insulation measures to ensure the normal operation of equipment. They cannot protect against electric shock hazards, but can reduce the possibility of ignition or fire.

3.7 Basic insulation

Under normal operating conditions, the insulation that can only provide basic protection against electric shock.

3.8 Supplementary insulation

Independent insulation in addition to basic insulation. It can provide protection against electric shock when the basic insulation fails.

3.9 Double insulation

Insulation consisting of basic insulation and supplementary insulation.

3.10 Reinforced insulation

Under specified conditions, the degree of protection against electric shock provided by a single insulation system is equivalent to double insulation.

NOTE: A single insulation system is composed of one or more insulation layers, but each insulation layer cannot be separated into basic insulation or supplementary insulation layer by layer.

3.11 Protective class I

Electric shock is prevented by basic insulation and protective earthing of accessible conductive parts. When basic insulation fails, accessible conductive parts are not energized.

3.19 Islanding

The state in which a portion of the power grid, including loads and power sources, continues to operate in isolation after being disconnected from the main grid.

NOTE: Islanding can be divided into unplanned islanding and planned islanding. Unplanned islanding refers to the unplanned and uncontrolled occurrence of islanding. Planned islanding refers to the planned occurrence of islanding according to pre-configured control strategies.

3.20 Anti-islanding

Prevent the occurrence of unplanned islanding.

4.1 Classification by the number of communication output phases

Inverters can be classified according to the number of AC output phases into.

- Single-phase inverter;

- Three-phase inverter.

4.2 Classification by use environment

Inverters can be classified according to the use environment.

- Outdoor inverter refers to an inverter that is fully or partially exposed outdoors;

- Indoor type I inverter refers to an inverter installed in a building or protective cover with an air conditioning device;

- Indoor type II inverter refers to an inverter installed in a building or protective cover without an air conditioning device.

4.3 Classification by access voltage level

Inverters can be classified according to the access voltage level.

- Class A inverters, which refer to inverters used in photovoltaic power stations with grid-connected voltage levels that meet the requirements of GB/T 19964;

- Class B inverters, which refer to inverters used in photovoltaic power generation systems with grid-connected voltage levels that meet the requirements of GB/T 29319.

4.4 Classification by electrical structure

Inverters can be classified according to electrical structure into.

- Isolated inverter;

- Non-isolated inverter.

NOTE 1: An isolated inverter refers to an inverter with basic insulation isolation between the AC output circuit and the DC input circuit.

NOTE 2: A non-isolated inverter refers to an inverter that does not have basic insulation isolation between the AC output circuit and the DC input circuit.

5.1 Pollution level

5.1.1 Pollution level classification

The pollution level of the inverter's external environment can be divided into.

- Pollution level 1.No pollution or only dry non-conductive pollution;

- Pollution level 2.Generally, there is only non-conductive pollution, but occasional short-term conductive pollution caused by condensation shall be considered;

- Pollution level 3.There is conductive pollution, or dry non-conductive pollution becomes conductive pollution due to condensation;

- Pollution level 4.Persistent conductive pollution, such as pollution caused by conductive dust or rain and snow.

5.1.2 Pollution level tolerance

The inverter shall be able to withstand pollution levels that meet the following requirements.

a) Outdoor inverters and indoor type II inverters shall meet the requirements for normal use under pollution level 3 conditions;

b) Indoor type I inverters shall meet the requirements for normal use under pollution level 2 conditions.

5.1.3 Change of pollution level

When relevant protective measures are adopted in specific areas inside the inverter, the changes in pollution levels in specific areas inside the inverter are shown in Table 1.

5.2 Protection level

The protection level of the inverter shall not be lower than the following requirements.

- Indoor type I inverter. IP20;

- Indoor type II inverter. IP20;

- Outdoor type inverter. IP54.

5.3 Temperature

The inverter shall be able to operate normally within the following ambient temperature range.

- Indoor type I inverter. 0°C~40°C;

- Indoor type II inverter. -20°C~50°C;

- Outdoor type inverter. -20°C~50°C.

5.4 Humidity

The inverter shall be able to operate normally within the following ambient humidity range.

- Indoor type I inverter. <=85%, without condensation;

- Indoor type II inverter. <=95%, without condensation;

- Outdoor inverter. <=100%, with condensation.

5.5 Ultraviolet radiation

Plastic and polymer materials on outdoor enclosures shall not show visible signs of degradation, including cracks or breaks, under normal use. Their protective performance shall not be reduced.

6.1 Electric shock protection requirements

6.1.1 Basic requirements

The minimum protection level of each circuit in the inverter shall be determined according to the decisive voltage classification of each circuit in the inverter. The electric shock protection requirements include direct contact protection and indirect contact protection. The overall requirements for electric shock protection are shown in Figure 1.

6.1.2 Decisive voltage classification and its protection requirements

The decisive voltage classification limits are shown in Table 2. The circuit protection requirements are shown in Table 3. The electric shock protection measures shall be determined according to the decisive voltage classification and the circuit protection measures. Meet the following requirements.

a) When each circuit in the inverter meets the decisive voltage classification limit requirements but cannot meet the circuit protection measures requirements, the decisive voltage classification of the circuit shall be increased by one level;

b) Two circuits directly connected or separated only by functional insulation shall be considered as one circuit;

c) The electric shock protection measures shall meet the requirement that a voltage higher than the decisive voltage classification A limit shall not appear in the accessible circuit or accessible conductive parts due to a single fault;

e) Protective earth conductor and touch current The contact current of a plug-connected single-phase inverter shall not exceed 3.5 mA AC or 10 mA DC. When the contact current of other inverters exceeds 3.5 mA AC or 10 mA DC, one or more of the following protection measures shall be adopted and the 15th symbol of Annex A shall be marked.

- Use fixed connection and the cross-sectional area of the protective earthing conductor is at least 10 mm² (copper) or 16 mm² (aluminum);

- Use fixed connection and automatically disconnect the power supply in the event of interruption of the protective earthing conductor;

- Provide an additional protective earthing conductor with the same cross-sectional area and indicate it in the installation instructions;

- Use industrial connectors and the minimum cross-sectional area of the protective earthing conductor in the multi-conductor cable is 2.5 mm² and has strain relief measures.

6.1.6.2 Protective class II - double or reinforced insulation

For equipment or equipment parts designed for protective class II, the insulation of live parts and accessible surfaces shall meet the following requirements.

a) Protective class II devices shall not be connected to an external protective earth conductor;

b) When the protective class II device uses a metal casing, the casing can be used for equipotential connection;

c) Protective class II devices can be functionally grounded;

d) Protective class II devices shall use the 12th symbol in Annex A.

6.1.7 Electrical clearance and creepage distance

6.1.7.1 Basic requirements

When the voltage fundamental frequency across the insulation is higher than 30 kHz, the insulation shall also meet the requirements of GB/T 16935.1. The electrical clearance and creepage distance under high-frequency working voltage shall meet the requirements of GB/T 16935.4.

6.1.7.2 Insulation voltage

The impulse withstand voltage and temporary overvoltage shall meet the requirements of Table 7.

Operating the inverter under normal use and single fault conditions shall not cause mechanical hazards. Edges, protrusions, corners, holes, shields, handles and other parts that operators can touch shall be smooth.

6.4.2 Moving parts

The inverter's cooling fan and other moving parts shall meet the following requirements.

a) Moving parts can only be accessed with the aid of tools;

b) Covers or parts that can only be accessed by disassembly shall have warning signs;

c) Automatically reset thermal circuit breakers, overcurrent protection devices or automatic timed start devices shall not be installed.

6.4.3 Stability

Inverters that are not fixed to building components shall be stable. When the inverter is turned on, a device that maintains stability shall be automatically turned on or a warning sign shall be provided.

6.4.4 Transportation measures

The handle of the inverter shall be able to withstand a force four times the weight of the inverter. Inverters with a mass of 18 kg or more shall have transportation guidance documents.

6.4.5 Wall mounting

The inverter mounting bracket shall be able to withstand a force four times the weight of the inverter.

6.4.6 Projectile components

In case of inverter failure, no parts that may cause harm to people shall be ejected. When the inverter inevitably has ejected parts, their ejection energy shall be limited. The protective measures for the equipment against ejected parts shall be removed with tools.

6.5 Protection against fire hazards

6.5.1 Requirements for the flammability of equipment materials

The flammability of the inside and outside of the equipment shall comply with the requirements of Table 14.

a) When an isolated inverter or non-isolated inverter is connected to the grid through a transformer and meets the requirements of 30 mA contact leakage current and ignition leakage current, a fault shall be indicated and the inverter can be operated during the fault. The alarm can be stopped when the impedance meets the above requirements.

b) When a non-isolated inverter is directly connected to the grid or a non-isolated inverter is connected to the grid through a transformer but does not meet the requirements of 30 mA contact leakage current and fire leakage current, a fault shall be indicated and the inverter shall not be connected to the grid. When the impedance meets the above requirements, the alarm can be stopped and the inverter can be connected to the grid.

6.7.1.2 Inverters for functionally grounded PV arrays

The inverter used for functionally grounded photovoltaic arrays shall meet the following requirements.

a) Including the preset resistor for functional grounding, the total grounding impedance shall not be less than Vmaxpv/30 mA. The expected impedance value can be calculated based on 40 M ohm per square meter of insulation array when the area of the connected array is known, or it can be calculated based on the rated power of the inverter and the efficiency of the worst solar panel connected to the inverter.

b) When the total grounding resistance does not meet the requirements of a), the inverter shall be able to provide a current detection device to detect the current through the total grounding resistance during operation. When the residual current response time does not meet the requirements of Table 15, the resistor shall be disconnected or other methods shall be used to achieve current limiting.

c) When a non-isolated inverter is directly connected to the grid or a non-isolated inverter is connected to the grid through a transformer but it does not meet the requirements of 30 mA contact leakage current and ignition leakage current, it shall be disconnected from the grid.

6.7.2 Photovoltaic array residual current

6.7.2.1 Basic requirements

The basic requirements are as follows.

a) When the inverter is connected to an ungrounded PV array of decisive voltage classification B and decisive voltage classification C, a non-isolated inverter is directly connected to the grid or a non-isolated inverter is connected to the grid through a transformer but does not meet the requirements of 30 mA contact leakage current and ignition leakage current. Protection against electric shock […]