Challenges in Terminal Arrangements of Multiple Winding Inverter Duty Transformer for Solar PV Plants by Rajesh Joshi in IEEMA Journal Mar 2022

A plant the source energy as converted to plant the source energy is converted to DC supply by using photovoltaic (PV) cells. Inverters are used to covert the generated DC to AC which onward is connected to the power grid by stepping it up popularly known, solar inverter duty transformer.

Depending on power rating and voltage level one or more inverters are connected in parallel to feed the step-up solar duty transformers. The imitation of inverter ratings required an equal number of transformers For Example, in a 10 MW solar plant using 10 inverters of 1000 KVA would require 10 Nos of transformers.

Also, the cost & space required for it & associated switchgear will also be higher, making the project economically less fensible in totality. Therefore, transformers with multiple windings are being designed these days. Five winding (with 1 number HV/MV winding & 4 numbers of LV winding) transformers are commonly being manufactured by some of the manufacturers in India in ratings such as 8.5 MVA & 125 MVA.

Basic design aspects and considerations for inverter duty transformers like measures to minimise the effects of non-synchronised output waveform of different inverter connected, harmonic distortions, voltage gradient due to pulsed output, provision of Electrostatic shield between LV & HV windings to preverit capacitive coupling etc. These factors are common for all inverter duty transformers irrespective of 2 winding or multiple winding construction is chosen. However, for suitability to unbalanced loading on individual inverters, isolation of different windings shall be proper and LV to LV Impedance required to be high enough.

Here typically, various design & construction options for physical arrangement of windings & location of terminals for higher rating such as, 12.5 MVA, with (4x 0.8 kV) LV & (1 x 33 kV) HV winding solar inverter duty transformer is considered for explanation One design option is to use 4 Nos isolated LV windings whereas the HV winding split in 4 parts ()… equal to LV), which are assembled vertically in a core However, Vertical stacking (Fig 1.a) of coils increases height of the transformer abnormally, whereas the length of transformer tank is comparatively less to accommodate 4 Nos LV Cable Boxes in a row