How to handle emergency cases in PV system(Part II)

Author: Jonas

2022-07-04 16:12

How GoodWe solution prevents arc fault?
Arc Fault prevention for PV modules and Batteries:
Based on thousands of tests carried on-site, GoodWe arc detection and protection solution adopts the machine learning technology, which can detect the arc fault accurately and protect the system from the arcing, either from the PV module side or the battery side.

FIGURE 4 RISK OF ELECTRICAL SHOCK FROM RESIDUAL CURRENT

With an arc detection board integrated into a GoodWe inverter, an arc fault can be determined whenever there is the occurrence of abnormal arcing current detected and protective measures in consequence are triggered and taken automatically. DC current data collected through CT are transmitted to ARM. The voltage signals are processed by using FFT algorithm, which can identify the arc fault that occurs. If an arc fault or faults are identifified, the DC pathway will be automatically cut off within 0.5S seconds.

GoodWe inverters with the 2nd Generation AFCI function which trip time is less than 0.5s (much better than 2.5s industry standard) will escort the safety of PV plants.

FIG.5: PERFORMANCE OF GOODWE AFCI

1.2 Potential Fire Hazard：Residual Current

Fires caused by ground-fault currents should also be prevented at a very early stage, which is critical in an agricultural environment. In a dusty and humid environment, the insulation failure between the line conductor and the ground may cause a low-intensity arc fault according to the line conductor withstand, but high enough to cause a fire. Some tests have shown that even faults current with 300mA can induce a real risk of fire. However, this type of fault current is too low to be detected by the over-current protection.

Fig.6: cause of residual current

How GoodWe deals with residual current?

According to the requirement in IEC 62109-2:2011, the inverter shall provide residual current monitoring, i.e RCMU, which shall measure the total (both AC and DC Components) RMS current and activate an alarm. In addition, an external RCD (Residual Current Device) can also detect these currents and disconnect the circuit from the source automatically according to the preset threshold value. To prevent the fire risk RCMU or RCDs should be equipped with a maximum of 300mA rated residual operating current for inverters with a rated output power of less than 30kVA. For GoodWe GW36K-MT, GW50KN-MT ,and GW60KN-MT with over 30kVA output power, GoodWe adopts the PWM modulation method and optimizes the common-mode voltage based on SVPWM modulation to reduce the leakage current of the inverter, which is lower than that of normal inverters under the same conditions. After testing and verification, these inverter models are compatible with Type A and B RCDs with a rated residual current of 300mA or higher.

1.3 How GoodWe PVBM Products prevent fire
A roof must also be safe enough to stop the spread of fires from external sources, if the roof is located at close proximity of adjacent burning building for example. Tiles, as the outmost layer of roofs, are required to meet certain fire performance requirements set out by multiple global and national standards. Roof materials are classified into several classes, where the highest degree of fire resistance is designated Class A, and lower for B and C lower yet. The type of building will impose different safety requirements including the fire ratings for building materials used. For example, it might be mandatory for hospitals, schools and public buildings to equip their roof with Class A building materials in building codes of most countries. Thanks to the double 3.2mm tempered glasses structure, SunshineTile by GoodWe PVBM is tested and classified as Class A in fire resistance tests, making integration of clean PV energy into building without compromising fire safety a reality.

2. Surge Protection

Choosing the right material to cover your roof can offer better safety even in a direct lightning strike. A direct or close lightning strike may generate enough heat to start a fire on the roof if the roofing material does not offer a conductive path for the energy to dissipate. Grounding of metal parts and lightning rods are two of the most common techniques to construct the conductive path on the roof. Area covered by wiring loops of dc cables is also an influential factor when analyzing lightning safety of a rooftop PV array. Safety performance of roof materials during lightning conditions is also dependent on surface material type and layout of on roof conductive parts. Integrated into a conventional tile roof, GoodWe SunshineTiles offer a conductive path with easy-to-install grounding points that can be connected to the grounding system of your home. With smaller tile area and unique installation practices, wiring loops for SunshineTile roof is substantially smaller comparing to arrays that require mounting rails. Equipped with 3.2mm tempered glass, dielectric breakdown of surface material is less likely to occur on SunshineTile comparing to foil type framed PV products.

The installations of PV Plants that arise from their exposed nature and collection areas make them vulnerable to overvoltage surges from lightning. In a lightning-prone area, the lightning-induced array failures can be more detrimental to solar equipment. SPDs are particularly crucial to protect against damage from surges including direct lightning strokes and indirect lightning.

Fig.7: Lightning

SPD I can discharge the back-current from lightning spreading from the earth conductor to the network conductors. SPD II prevents the spread of overvoltage in the electrical installations and protects the loads.

SPD connected in parallel has a high impedance. Once the transient overvoltage appears in the system, the impedance of the device decreases, so surge current is driven through the SPD, bypassing the sensitive equipment.

Fig.8: SPD System Architecture

GoodWe has upgraded the surge protection devices for residential and commercial inverters. All the new residential inverters integrate Type II or III SPD on both DC and AC sides, while commercial inverters integrate Type SPD II and optional Type I SPD on both DC and AC sides. (Find the first part here)

Part III has been published, keep reading now!

O&M

Download

User feedback

Sort by:

Latest reply
Earliest reply
Official reply only

Make an Appointment