A ZGS pad-mounted transformer houses its load-break switch and HV fuses in the transformer oil tank, keeping the assembly to the size of a single transformer. A compartmented compact substation has separate HV, transformer and LV compartments for switchgear, metering and protection equipment. The compartmented form suits additional switchgear bays, metering or secondary equipment; the common-tank form saves space where step-up transformation and HV switching and protection are sufficient.
Pad-Mounted Transformer for Solar and Wind
For solar and wind contractors and integrators: step-up, switching and protection in one unit, with LV matched to the inverter or turbine output.
PV Inverter Step-Up StationWind Converter Support FacilityRenewable Grid-Connection Power DistributionPackage Substation
Key Metrics
10 / 35kV
High voltage
315–1140V
Low voltage
800–3150kVA
Rated power
3700–9200kg
Total mass
Product Features
No separate HV panel
Step-up transformation, HV switching and fuse protection share one sealed tank, saving space by removing the need for a separate HV switchgear panel beside each unit.
No separate HV panel
Step-up transformation, HV switching and fuse protection share one sealed tank, saving space by removing the need for a separate HV switchgear panel beside each unit.
Inverter-matched LV
LV connects directly to the inverter or turbine AC output at selectable voltages from 0.315 kV to 1.14 kV, with HV connected to the 10 kV or 35 kV collector circuit.
Dual LV windings
Two separate LV windings (dual secondary) let two inverters share one step-up transformer, reducing the number of transformers and HV cable joints in the plant.
Loop-feed connection
Loop-feed units connect in sequence along one collector circuit, so each transformer does not need its own HV cable back to the collector substation.
Cold-start oil grade
Oil grades I-10 °C, I-20 °C and I-30 °C give the lowest cold-start energising temperature (LCSET) and are chosen for the minimum site temperature.
Product Details
Z stands for the integrated (combined) design, G for the common tank shared by the active part, load-break switch and fuses, and S for three-phase; the next position is the loss-level code. After the first hyphen, H identifies loop feed and Z radial feed. The final part is -rating/voltage, in kVA and kV. ZGS□-H-2500/35 therefore identifies a three-phase common-tank loop-feed unit rated 2500 kVA at 35 kV; □ is the selected loss-level code.
The transformer active part, load-break switch and HV fuses occupy one fully sealed oil tank. The switch handles HV switching and the fuses provide protection; both are immersed in the same oil that insulates and cools the active part. Cooling is ONAN (oil natural, air natural). Insulation is Class A, with a winding temperature rise of 65 K and a top-oil temperature rise of 60 K.
The 10 kV class has a highest voltage for equipment (Um) of 12 kV, a short-duration power-frequency withstand of 35 kV, and a lightning impulse withstand (BIL) of 75 kV full wave and 85 kV chopped wave. For the 35 kV class, these values are 40.5 kV, 85 kV, 200 kV and 220 kV respectively. Loop feed (H) has one incoming and one outgoing HV connection, linking the preceding and following units along the collector circuit. Radial feed (Z) has a single incoming connection, for the end of the circuit or a stand-alone radial connection. Tap changing is off-circuit (de-energised tap changer), with the tap range agreed for the project.
LV options include 0.315 kV, 0.48 kV, 0.69 kV, 0.8 kV, 0.95 kV and 1.14 kV, selected to match the connected equipment’s rated AC output voltage. Rated frequency is 50 Hz. The vector group is specified with the order. A single LV winding uses Dy11 or Yd11, with a delta or star HV winding respectively. Dy11-y11 and Yd11-d11 have two LV windings (dual secondary) under one HV winding; the two LV circuits are not interconnected inside the transformer and can each connect to a separate inverter.
Delivery Scope Options
Scope 1
Single Unit or Complete Package Supply
Scope 1Single Unit or Complete Package Supply
Transformers are supplied as single units against the order schedule, or as a complete package together with the protective enclosure, the temperature controller and the cooling fans. The active part is wound, assembled and routine-tested at the works and shipped as a complete unit; the assembly interface for the accessories follows the transport conditions. Where the transformer is to arrive together with a prefabricated power module, the E-House line takes on the enclosure, the internal arrangement and the foundation fixing, and the transformer is delivered as equipment housed within it.
Scope Includes:
Single unit or complete package
Complete-unit shipment and assembly interface
Foundation and fixing interface
In-cabin delivery handled by the E-House line
Technical Specifications
Product form
Three-phase oil-immersed transformer with active part, load-break switch and HV fuses in one fully sealed common tank
Type designation
ZGS□-□-□/□ (loss-level code-HV arrangement-rated power/voltage class)
High-voltage class
10 or 35
kV
Highest voltage for equipment (Um)
12 or 40.5
kV
Rated power, 10 kV class
800 / 1000 / 1250 / 1600
kVA
Rated power, 35 kV class
800 / 1000 / 1600 / 2000 / 2500 / 3150
kVA
Low voltage
0.315 / 0.48 / 0.69 / 0.8 / 0.95 / 1.14 kV and other values matched to the connected equipment’s output
HV arrangement
Loop feed (H) or radial feed (Z)
Vector group
Dy11, Yd11; two LV windings: Dy11-y11, Yd11-d11, as ordered
Tap changing
Off-circuit (de-energised); tap range agreed for the project
Insulation level (power frequency / lightning impulse full wave / chopped wave)
10 kV class: 35 / 75 / 85; 35 kV class: 85 / 200 / 220
kV
Rated frequency
50
Hz
Cooling
ONAN (oil natural, air natural)
Insulation class and temperature rise
Class A; windings 65 K, top oil 60 K
Insulating oil
I-10 °C, I-20 °C or I-30 °C grade (LCSET), selected for the minimum site temperature
Total mass, 10 kV class
800 kVA: 3700; 1000 kVA: 4220; 1250 kVA: 4500; 1600 kVA: 4950
kg
Total mass, 35 kV class
800 kVA: 4300; 1000 kVA: 4940; 1600 kVA: 6150; 2000 kVA: 7200; 2500 kVA: 8400; 3150 kVA: 9200
kg
Losses, impedance, dimensions, degree of protection
Agreed for the selected rating, loss level and service conditions
| Parameter | Specification |
|---|---|
| Product form | Three-phase oil-immersed transformer with active part, load-break switch and HV fuses in one fully sealed common tank |
| Type designation | ZGS□-□-□/□ (loss-level code-HV arrangement-rated power/voltage class) |
| High-voltage class | 10 or 35 kV |
| Highest voltage for equipment (Um) | 12 or 40.5 kV |
| Rated power, 10 kV class | 800 / 1000 / 1250 / 1600 kVA |
| Rated power, 35 kV class | 800 / 1000 / 1600 / 2000 / 2500 / 3150 kVA |
| Low voltage | 0.315 / 0.48 / 0.69 / 0.8 / 0.95 / 1.14 kV and other values matched to the connected equipment’s output |
| HV arrangement | Loop feed (H) or radial feed (Z) |
| Vector group | Dy11, Yd11; two LV windings: Dy11-y11, Yd11-d11, as ordered |
| Tap changing | Off-circuit (de-energised); tap range agreed for the project |
| Insulation level (power frequency / lightning impulse full wave / chopped wave) | 10 kV class: 35 / 75 / 85; 35 kV class: 85 / 200 / 220 kV |
| Rated frequency | 50 Hz |
| Cooling | ONAN (oil natural, air natural) |
| Insulation class and temperature rise | Class A; windings 65 K, top oil 60 K |
| Insulating oil | I-10 °C, I-20 °C or I-30 °C grade (LCSET), selected for the minimum site temperature |
| Total mass, 10 kV class | 800 kVA: 3700; 1000 kVA: 4220; 1250 kVA: 4500; 1600 kVA: 4950 kg |
| Total mass, 35 kV class | 800 kVA: 4300; 1000 kVA: 4940; 1600 kVA: 6150; 2000 kVA: 7200; 2500 kVA: 8400; 3150 kVA: 9200 kg |
| Losses, impedance, dimensions, degree of protection | Agreed for the selected rating, loss level and service conditions |
Product FAQs
For a solar plant, add up the rated AC output of the inverters connected to the transformer; for wind, use the rated power of the connected turbine. Then select the next standard rating at or above that total. The 35 kV class has no 1250 kVA rating. For more than 3150 kVA per unit, see the 35 kV Oil-Immersed Power Transformer.
The price mainly depends on the voltage class, kVA rating, LV voltage and number of LV windings, loss level and accessories. For a quotation, provide the collector-circuit voltage, the inverter model and quantity per transformer (or the turbine model), the required rating and vector group, loop feed or radial feed, the minimum site temperature and altitude, and the document requirements.
The pad-mounted transformer normally stands beside an inverter or turbine. When the step-up transformer, MV switchgear and LV switchboard share one enclosure, the ETENZ E-House line supplies the enclosure, the internal layout and the HVAC and fire-protection systems. Options include the BESS Step-Up Substation Enclosure (20 ft) and the Containerized MV Switchgear E-House. Transformer and enclosure layouts are confirmed together before dispatch.
Yes. Specify the grid frequency, HV and LV voltages, vector group and document language with the order. The rated frequency is 50 Hz; 60 Hz operation is agreed for the project. The document package follows the destination country’s requirements and includes drawings, test records, a packing list and installation and maintenance instructions.
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