Delta M125HV - Medium Voltage Transformer

3.4.1 Medium Voltage Transformer
*1 When the neutral of the utility side is grounded, additional device (e.g., a recloser) needs to be
installed to detect an open phase on the utility side."
*2 The winding configuration of the transformer on the inverter side must be wye for all Delta 3-phase
string inverters to detect an open phase on utility side.
The MV transformer installed along with the inverter should meet the following
requirements:
1. The MV transformer can be oil-type or dry-type.
2. It is suggested to have tap changer on the high voltage side to align the voltage
level to medium voltage.
3. MV transformer should be capable of withstanding max 5% of total harmonic
current at nominal power.
4. Transformer with a short-circuit impedance 6% (permissible tolerance: ±10%)
is recommended.
5. For the thermal rating, the load curve of the transformer and environment
conditions should be taken into account.
6. The transformer must be protected against overloading and short circuit.
7. The winding configuration of the transformer on the low voltage side must be
wye for the inverter to detect an open phase on utility side.
8. The following list shows the compatibility of different transformer winding
configuration:
Delta
Delta
Y
Y
Yn
Yn
Any type
Primary Winding
(Utility side)
Secondary Winding
(Inverter side)
Compatibility
Yn
Y
Yn
Y
Yn
Y
Delta
Compatible
Compatible
Compatible
Compatible
Conditionally Compatible*
1
Not Recommended*
2
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Installation