INSTALLATION, USE AND
MAINTENANCE
SUNWAY STRING BOX
LT 1500V 24 INPUTS
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Figure 15: String voltage measurement points
Danger
Avoid opening and closing the fuse-holders when the string is live. Check
string polarity before inserting a fuse. Make sure that no current flows in the
string box before removing a fuse. The presence of a short-circuit on the string
connected to the fuse to be removed may lead to current flowing in case the
safety fuse is not open.
Do the following to remove and insert a fuse:
•
Open the front cover of the SUNWAY STRING BOX LT 1500V
•
Open the disconnector in the SUNWAY STRING BOX LT 1500V.
•
Make sure that no current is flowing.
•
Remove or insert the fuse from the fuse-holder
•
Upon completion, restore all operating conditions.
•
Close the front cover in the SUNWAY STRING BOX LT 1500V.
Danger
Wear PPE when removing or inserting a fuse. In particular, dielectric gloves are
required (see section 2.6), as opening the fuse-holder does not ensure that
both fuse contacts are properly cut off (dual voltage power supply).
7.5. Commissioning
Once all the string boxes have been connected, do the following to carry out the equipment commissioning:
•
Close the disconnector in the SUNWAY STRING BOX LT 1500V.
•
Close the front cover of the SUNWAY STRING BOX LT 1500V.
•
Close the inverter DC-side switch disconnector.
7.6. Notes on Output Short-Circuit
The SUNWAY STRING BOX LT 1500V are equipped with a suitable under-load disconnect device in output
but are not fitted with protection against short circuits, such as fuses, in output.
Fault caused by a short circuit on the output cables must be envisaged during the design phase and
appropriate protective measures must be adopted.
Some design examples:
1. If the PV field is composed of multiple SUNWAY STRING BOX LT 1500V, the Sunway DC-Parallel or
input fuses inside the inverter effectively solves this problem.
2. If the PV plant is made up of a very small number of SUNWAY STRING BOX LT 1500V, a connection
directly to the inverter can be envisaged, without inserting fuses, as long as the cables are sized for the
maximum fault current.
3. If the PV plant is made up of just one SUNWAY STRING BOX LT 1500V, the problem does not exist.
In the first case, the Sunway DC-Parallel input fuses protect the equipment against short-circuits. In the
second case, oversized cables are adopted, that are capable of withstanding the short-circuit fault. In the
third case, cable oversizing shall make it possible to withstand the short-circuit current of each individual
string.
Being as the PV field is a current-limited generator, even in the event of a short circuit the current delivered
by this kind of generator cannot exceed the maximum sizing value.
If the PV plant is made up of more than one SUNWAY STRING BOX LT, consider the example of a short-
circuit occurring downstream from a SUNWAY STRING BOX LT, but upstream from the connection to the
Sunway DC-Parallel, as shown in Figure 16.
When this happens, the current from all the strings but one is localized in the section of cable between the
point where the short circuit has occurred and the connection to the Sunway DC-Parallel.
