Where the MV supply varies too much, or too often, for an off-circuit tap setting: at the end of long rural feeders, on feeders where midday solar infeed lifts the voltage, and at plants where large loads pull the supply down. The tap changer moves while the transformer is energised, holding the LV close to 400 V without an outage.
10 kV Oil-Immersed OLTC Distribution Transformer
For utilities, grid contractors and E-House integrators: taps change under load to hold the 400 V bus, as a single unit or inside an E-House.
Package SubstationDistributed Node Power SupplyRenewable Grid-Connection Power Distribution
Key Metrics
200–2500kVA
Rated power
10kV
Voltage class
±10%
OLTC range
4–5%
Impedance
Product Features
Taps change on load
Tap positions change while the transformer stays energised and loaded, so the LV voltage is brought back as the feeder voltage moves, without planning an outage.
Taps change on load
Tap positions change while the transformer stays energised and loaded, so the LV voltage is brought back as the feeder voltage moves, without planning an outage.
Nine tap positions
Nine positions in 2.5 % steps cover ±10 % of rated HV, so the LV is corrected in small increments.
Losses per rating
No-load and load losses are published for each of the twelve ratings from 200 to 2500 kVA, so the energy cost of each size can be compared before ordering.
Four HV ratings
HV of 6, 6.3, 10 or 10.5 kV with a 0.4 kV LV lets one series serve both 6 kV and 10 kV distribution networks.
Dyn11 or Yyn0
Either connection is offered across all twelve ratings with the same loss figures, so the choice follows network practice alone.
Product Details
S stands for three-phase and Z for on-load tap changing; 13 is the loss-level code. After the hyphen come the rated power in kVA and the voltage class in kV. SZ13-630/10 is therefore a three-phase on-load tap-changing transformer at loss level 13, rated 630 kVA, for the 10 kV class. Without the Z, S13 designates the off-circuit version of the same loss level.
The tap changer sits on the HV winding and steps through its nine positions in service. The off-circuit version, the S13, offers ±5 % or ±2 × 2.5 % and has to be switched off before its tap is moved.
±4 × 2.5 % gives nine positions spanning ±10 % of rated HV. On a 10 kV unit the HV taps are 11.0, 10.75, 10.5, 10.25, 10.0, 9.75, 9.5, 9.25 and 9.0 kV; on a 6 kV unit they run from 6.6 to 5.4 kV in 0.15 kV steps. Each step changes the turns ratio by 2.5 %, about 10 V on the 400 V side. When a 10 kV feeder rises to 10.5 kV, the 10.5 kV tap brings the LV back to about 400 V.
Twelve ratings run from 200 to 2500 kVA. No-load loss is 304 W at 200 kVA, 768 W at 630 kVA and 2144 W at 2500 kVA; load loss at the same ratings is 2900 W, 7260 W and 21600 W. No-load current falls from 1.0 % to 0.4 % across the range. Short-circuit impedance is 4.0 % up to 500 kVA, 4.5 % from 630 to 1600 kVA and 5.0 % at 2000 and 2500 kVA. The prospective fault current on the 400 V side follows the impedance of the rating chosen.
Dyn11 has a delta HV winding and a star LV winding; Yyn0 has star windings on both sides. Both bring the LV star point out as a neutral terminal for a four-wire 400 V system. Dyn11 is the usual choice where single-phase loads are unbalanced or harmonic currents are present. Yyn0 stays the choice where the unit must run in parallel with existing Yyn0 transformers.
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 with the protection, temperature-monitoring and cooling accessories in the order, matched to the insulation and cooling type. 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, two-winding oil-immersed distribution transformer with on-load tap changing (OLTC)
Type designation
SZ13-□/□ (rated power in kVA / voltage class in kV), for example SZ13-630/10
Rated power
200 / 250 / 315 / 400 / 500 / 630 / 800 / 1000 / 1250 / 1600 / 2000 / 2500
kVA
High voltage (HV)
6, 6.3, 10 or 10.5
kV
Low voltage (LV)
0.4
kV
On-load tap range
±4 × 2.5 % on the HV winding: nine positions spanning ±10 %
Vector group
Dyn11 or Yyn0
Short-circuit impedance
4.0 (200–500 kVA); 4.5 (630–1600 kVA); 5.0 (2000–2500 kVA)
%
No-load loss
200 kVA: 304; 250 kVA: 352; 315 kVA: 424; 400 kVA: 512; 500 kVA: 608; 630 kVA: 768; 800 kVA: 896; 1000 kVA: 1088; 1250 kVA: 1248; 1600 kVA: 1536; 2000 kVA: 1816; 2500 kVA: 2144
W
Load loss
200 kVA: 2900; 250 kVA: 3420; 315 kVA: 4100; 400 kVA: 4950; 500 kVA: 5890; 630 kVA: 7260; 800 kVA: 8890; 1000 kVA: 10400; 1250 kVA: 12300; 1600 kVA: 14700; 2000 kVA: 18600; 2500 kVA: 21600
W
No-load current
1.0 (200 kVA); 0.9 (250–315 kVA); 0.8 (400–500 kVA); 0.6 (630–1000 kVA); 0.5 (1250–1600 kVA); 0.4 (2000–2500 kVA)
%
Total mass, typical
200 kVA: 1085; 250 kVA: 1200; 315 kVA: 1400; 400 kVA: 1870; 500 kVA: 1980; 630 kVA: 2305; 800 kVA: 2740; 1000 kVA: 3160; 1250 kVA: 3595; 1600 kVA: 4220; 2000 kVA: 4730; 2500 kVA: confirmed for the project
kg
Dimensions, tank form, tap-changer make and control
Agreed for the selected rating on the approval drawing
| Parameter | Specification |
|---|---|
| Product form | Three-phase, two-winding oil-immersed distribution transformer with on-load tap changing (OLTC) |
| Type designation | SZ13-□/□ (rated power in kVA / voltage class in kV), for example SZ13-630/10 |
| Rated power | 200 / 250 / 315 / 400 / 500 / 630 / 800 / 1000 / 1250 / 1600 / 2000 / 2500 kVA |
| High voltage (HV) | 6, 6.3, 10 or 10.5 kV |
| Low voltage (LV) | 0.4 kV |
| On-load tap range | ±4 × 2.5 % on the HV winding: nine positions spanning ±10 % |
| Vector group | Dyn11 or Yyn0 |
| Short-circuit impedance | 4.0 (200–500 kVA); 4.5 (630–1600 kVA); 5.0 (2000–2500 kVA) % |
| No-load loss | 200 kVA: 304; 250 kVA: 352; 315 kVA: 424; 400 kVA: 512; 500 kVA: 608; 630 kVA: 768; 800 kVA: 896; 1000 kVA: 1088; 1250 kVA: 1248; 1600 kVA: 1536; 2000 kVA: 1816; 2500 kVA: 2144 W |
| Load loss | 200 kVA: 2900; 250 kVA: 3420; 315 kVA: 4100; 400 kVA: 4950; 500 kVA: 5890; 630 kVA: 7260; 800 kVA: 8890; 1000 kVA: 10400; 1250 kVA: 12300; 1600 kVA: 14700; 2000 kVA: 18600; 2500 kVA: 21600 W |
| No-load current | 1.0 (200 kVA); 0.9 (250–315 kVA); 0.8 (400–500 kVA); 0.6 (630–1000 kVA); 0.5 (1250–1600 kVA); 0.4 (2000–2500 kVA) % |
| Total mass, typical | 200 kVA: 1085; 250 kVA: 1200; 315 kVA: 1400; 400 kVA: 1870; 500 kVA: 1980; 630 kVA: 2305; 800 kVA: 2740; 1000 kVA: 3160; 1250 kVA: 3595; 1600 kVA: 4220; 2000 kVA: 4730; 2500 kVA: confirmed for the project kg |
| Dimensions, tank form, tap-changer make and control | Agreed for the selected rating on the approval drawing |
Product FAQs
An on-load tap changer (OLTC) changes position while the transformer is energised and carrying load; an off-circuit tap changer (OCTC, also called a de-energised tap changer) is moved only with the transformer switched off. This series has an OLTC with nine positions (±4 × 2.5 %). Where the feeder voltage is steady and a seasonal setting is enough, the off-circuit Oil-Immersed Distribution Transformer, with ±5 % or ±2 × 2.5 %, is the simpler choice.
At 10 kV the HV current is one twenty-fifth of the LV current, about 36 A against 909 A at 630 kVA, so the tap changer switches far less current. The HV winding also has enough turns for 2.5 % steps. All nine positions of this series are on the HV winding.
The difference comes from the on-load tap changer itself, its operating mechanism and control, and the tank arrangement that carries them; it varies with the rating and the tap-changer make chosen. Both versions of the same rating can be quoted side by side, so the difference is exact for the project.
The HV supply voltage and how far it varies, the rating, the LV voltage and earthing system, the vector group, the preferred tap-changer make and control arrangement, site altitude and ambient temperature, the grid frequency, any loss-evaluation figures, and the documents the destination market requires.
Yes. The ETENZ E-House line supplies the enclosure, the internal layout and the HVAC and fire-protection systems, with the transformer installed as housed equipment; options include the Integrated E-House and the Containerized MV Switchgear E-House. For an oil-immersed unit, oil containment, ventilation openings and access to the tap-changer mechanism are laid out on the enclosure drawings before dispatch.
This series covers HV of 6, 6.3, 10 and 10.5 kV with a 0.4 kV LV. For 35 kV networks, the 35 kV Oil-Immersed Power Transformer includes on-load tap-changing ratings from 2000 to 20000 kVA. Other HV or LV values and 60 Hz service are confirmed against the specific design at enquiry.
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