Increasing the Input Current of GoodWe MT series

Author: Jonas

2022-12-26 11:22

GoodWe MT series are configured with fuse protectors inside the inverter that limits the input current. This document will describe how to increase the input current of GW50KN-MT, GW60KN-MT and GW80K-MT by replacing the fuses.

 

Background

With the rapid development of the PV modules, high-power modules have become more common, followed by a larger working current (I_mp) and short-circuit current (I_sc). The I_mp of 182 modules can reach up to 15A. The GW50K-MT, 60K-MT, and GW80K-MT model have a maximum working current (input current), which is distributed over several string inputs, leaving the maximum working current per string at 11A. Some modules have a higher I_mp current and will thus be limited from the inverter side. This causes no damage to the equipment of either the inverter or modules but could lead to a loss of power generation. However, if the connected modules work with very high currents and the total I_sc per MPPT is higher than the maximum allowed short-circuit current of the inverter, the devices will be damaged.

 

For some use cases where the installers want to use higher current modules to connect the MT series, there is one more important point needs to be considered in addition to the current limit of each MPPT. The fuse protectors will impact the input current as well.

 

Problem and Product Design

 

For connection of modules with high current, it’s possible to connect fewer string to ensure the total input current per MPPT is less than the maximum current per MPPT. However, the above mentioned inverter models are designed with more than 2 string inputs for each MPPT.

 

 

If one MPPT is connected to N (N≥3) strings, when a grounding short circuit occurs somewhere in one string, the (N-1) times short- circuit current will appear in this string, which will cause a fire risk. Therefore, the mentioned MT series is equipped with a 15A fuse protectors on each string input. If the I_sc of some modules exceeds 15A, the 15 A fuses will be blown. Hence the replacement of the internal fuse with a higher fuse is necessary, if PV modules with higher currents are used.

 

Use Case

 

To make the inverter compatible with higher current PV-modules, less PV inputs can be used to distribute the current limit of the MPPT on fewer inputs. For example, the installers want to use the 15A I_sc module in for the GW80K-MT. Then we can only use 3 strings and replace the fuses with 20A fuses to support the 15A modules. Then the total I_sc of each MPPT is 45 A, which is lower than the max. I_sc of 55A.

 

Limitations and Options

When there are three or more stings in parallel, a fault in one string will be subjected to the maximum circuit currents of all other connected strings, with each string delivering 1.25 x Isc under worst-case conditions. Therefore, the nominal fuse ampere rating should be greater than 1.25 x Isc. Besides, the hardware of the inverter can only withstand a maximum current of 20A per input. Therefore, the integrated fuses should only be replaced with maximum 20A fuses and the I_sc of the connected modules should be less than 16A (20A/1.25). Besides, we only recommend the installers to replace the fuses on the inputs they want to use.

Please also refer to the following limitation:

Its only allowed to remove maximum 1 input from each MPPT to not exceed 20A per input.

The GW80K-MT comes with 4 MPPT and 4 input each. This model can only be limited to 3 inputs per MPPT.

The GW60KN-MT comes with 4 MPPT and 3 input each. This model and can only be limited to 2 inputs per MPPT.

The GW50KN-MT comes with 4 MPPT with different number of inputs. MPPT 1 and MPPT 2 can only be limited to 2 inputs each, and MPPT 3 and MPPT 4 can only be limited to 1 input per MPPT.

 

How to replace the fuse

The integrated fuses use plug-and play design, so the installers can replace them quickly and easily.

Please follow this guide step by step to exchange the fuses and follow all safety instructions in the inverters installation manual when working with the product.

1.  Make sure the inverter is disconnected from any power sources before working with it.

2.  Wait at least 10 minutes.

3.  Open the lower front cover of the inverter.

4.  Remove the fuses vertically as shown in the figures below. (figure 3 for GW50KN-MT, figure 4 for GW60KN-MT, figure 5 for GW80K-MT)

5.  Install the new 20A fuse into the corresponding fuse holders. (leaving the 3rd string input of each MPPT for GW50/60KN-MT and 4th input of each MPPT for GW80K-MT without any fuse)

For more details, pls download the file below. 

 

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