Alencon SPOT: Installation,
Operation, and Maintenance Manual
14 |
P a g e
4.3 Repowering of Older PV Plants
Large scale PV projects installed in past decades typically used 600V rated PV modules
and 600V inverters which are in turn connected to a medium voltage distribution transformer
as shown in
Figure 7
. Typically, in these older 600V installations, an insulation transformer
was built into the inverter. This integrated transformer carried out two functions:
1.
Matched lower (208 VAC) AC voltage on the inverter output to higher 480VAC voltage
on the distribution transformer’s primary winding.
2.
Provided galvanic isolation between PV array’s ground - PV arrays are generally
negatively grounded, though in some cases are positively grounded - and the neutrally
grounded distribution transformer.
F
IGURE
7:
N
EGATIVELY GROUNDED
PV
ARRAY CONNECTED TO NEUTRALLY GROUNDED
I
NVERTER
Older 600V inverters have been largely replaced by more efficient, 1000V, transformer-less
string inverters that are connected directly to the MV distribution transformer as shown
in
Figure 8
below. This newer type of string inverter must produce 480VAC on its output
to match the primary voltage requirement of the MV distribution transformer. This requires
a DC input voltage of 680 – 1000VDC.
When replacing an older style 600V inverter with an integrated transformer for a newer, 1000V
transformer-less inverter, two issues must be considered:
a.
Matching the input voltage from the older 600V array to the higher input voltage
required by the new inverter.
b.
Assuring the inverter’s AC output matches the ground potential of the primary
winding of the MV distribution transformer.
