Why this transformer goes inside the building
Dry-type transformers serve local lighting, high-rise buildings, airports, docks and machinery areas - precisely the places where an oil-filled unit is unwelcome. With no oil, there is no oil-fire or oil-leak risk, so a dry-type transformer can be installed directly at the load centre, shortening low-voltage runs and cutting losses. Cooling is by natural air (AN) or forced air (AF); AF raises the usable capacity at peak.
General specification
|
Parameter |
Specification |
|---|---|
|
Type |
SC(B) cast-resin (epoxy) dry-type; SG dry-type |
|
Rated capacity |
30 – 3,150 kVA (10 kV class); larger on request |
|
HV voltage |
6 / 6.3 / 6.6 / 10 / 10.5 / 11 kV (20 kV / 35 kV options) |
|
LV voltage |
0.4 kV (others on request) |
|
Tap range |
No-load: ±5 %, ±2 × 2.5 %; on-load: ±4 × 2.5 % |
|
Vector group |
Dyn11 / Yyn0 |
|
Insulation class |
F (120 °C) / H (145 °C) |
|
Cooling method |
AN (natural air) / AF (forced air) |
|
Partial discharge |
≤ 10 pC (low-PD design) |
|
Impedance voltage |
≈ 4 – 6 % |
|
Standards |
IEC 60076, GB/T 10228, GB 6451 |
Advantages & limitations of dry-type
01
Fireproof and pollution-free
No oil, no bund, no fire wall; insulating materials such as the winding glass fibre are self-extinguishing, and a short circuit will not sustain an arc.
02
No toxic emission under heat
The cast resin does not release toxic or harmful gases.
3
Installable at the load centre
Shorter LV runs, lower losses, no separate fire compartment.
04
Low / maintenance-free No oil to test or replace.
05
Moisture-resistant
Suited to humid and severe environments.
06
High mechanical strength
The cast body has a concrete-like structure that withstands sudden short-circuit forces.
07
Low loss, low noise, low partial discharge, long life
08
Overload headroom
Forced-air (AF) cooling raises usable capacity at peak.
Limitations
Higher initial cost than an oil-immersed unit of the same rating.
Larger footprint / weight at higher ratings.
Lower maximum voltage (≈ 35 kV) and capacity than oil-immersed transformers.
Lower heat dissipation in still air - heavy duty needs AF cooling, and performance is more sensitive to ambient temperature.
Cast windings are not repairable on site - a damaged winding generally means replacement of the unit.
At very large ratings, oil-immersed is more economical.
Representative losses - SC(B) / SCB, 10 kV class
| Capacity (kVA) | No-load loss (W) | Load loss @75 °C (W) F / H | No-load current (%) | Impedance (%) |
|---|---|---|---|---|
| 100 | 290 | 1,410 / 1,520 | 1.7 | 4 |
| 250 | 515 | 2,480 / 2,660 | 1.3 | 4 |
| 400 | 705 | 3,590 / 3,850 | 1.1 | 4 |
| 630 | 965 | 5,290 / 5,660 | 0.9 | 4 |
| 1,000 | 1,275 | 7,310 / 7,830 | 0.9 | 6 |
| 1,600 | 1,765 | 10,550 / 11,300 | 0.9 | 6 |
| 2,500 | 2,195 | 15,450 / 16,540 | 0.7 | 6 |
| 3,150 | 3,110 | 18,490 / 19,800 | 0.7 | 6 |
Insulation level
| Voltage grade (kV) | Max operating voltage (kV) | Power-frequency withstand (kV/min) | Lightning impulse withstand (kV peak) |
|---|---|---|---|
| 0.4 | 0.46 | 5 | 75 |
| 10 | 12 | 35 | 75 |
| 20 | 24 | 50 | 125 |
| 35 | 42 | 70 | 170 |
Dry-type vs oil-immersed - the differences that matter
| Aspect | Dry-type (cast resin) | Oil-immersed |
|---|---|---|
| Insulating / cooling medium | Solid cast resin + air | Transformer oil |
| Fire risk | No oil - fireproof, self-extinguishing | Mineral oil is flammable (ester fluid reduces risk) |
| Where it can be installed | Indoors, basements, upper floors, tunnels - at the load centre | Outdoors or in a fire-separated room with oil bund |
| Fire protection required | None (no bund, no fire wall) | Fire wall, oil bund, extinguishing provision |
| Maintenance | Low / maintenance-free - no oil tests | Periodic oil testing and treatment |
| Leak / pollution risk | None | Oil-leak and disposal risk |
| Overload capability | Good; AF forced cooling boosts capacity | Good |
| Typical voltage / capacity | Up to ≈ 35 kV; smaller ratings | Up to 220 kV and above; large ratings |
| Footprint & weight | Larger / heavier for a given rating | More compact |
| Purchase cost | Higher for the same rating | Lower |
| Noise | Low | Low |
| Humid / harsh environment | Solid insulation resists humidity | Protected by the sealed oil system |
When should you choose a dry-type transformer?
Choose dry-type when any of these apply:
The transformer must sit indoors, at or near the load - high-rise and commercial buildings, hospitals, airports, tunnels and metro, basements.
Fire regulations restrict or prohibit oil-filled equipment in or near occupied spaces.
Oil leakage would be unacceptable - data centres, clean rooms, water treatment, public buildings.
Maintenance access is limited and a maintenance-free unit is preferred.
The environment is humid, corrosive or otherwise severe.
You need low loss, low noise and a long, maintenance-free life.
Choose oil-immersed instead when the priority is the highest voltage or capacity, an outdoor installation, lowest first cost, or the best heat dissipation at large ratings - see our oil-immersed power and distribution transformer pages.
Built for a long, quiet life
Vacuum and pressure casting. Resin mixing uses advanced agitation with a vacuum film-degassing step that removes bubbles. High- and low-voltage coils are cast under vacuum and pressure, giving both full encapsulation and turn-to-turn impregnation in a dense, cured body.
High mechanical strength. Filler in the resin minimises differential expansion and curing shrinkage, so internal stress is low and hardness is high. Pre-formed reinforcement inside the epoxy encapsulation produces a concrete-like structure that withstands sudden short-circuit forces without damage.
Low loss, low noise, maintenance-free. Losses and sound level are kept well below conventional figures, and there is no oil to test or replace.
Insulation classes, cooling & environment
Cast-resin units are offered with F-class (120 °C) and H-class (145 °C) insulation. AN covers normal duty; AF forced-air cooling adds capacity at peak. Installation limits: altitude ≤ 2000 m and ambient −50 °C to +50 °C, with a supply waveform close to a sine wave.
Intelligent temperature control
Dedicated three-phase winding temperature monitors scan and display each phase, start and stop fans automatically, and provide alarm and trip set-points - protection is designed in, not bolted on.
Product families & applications
SC(B) series - cast-resin (epoxy) dry-type, 10 kV class, Dyn11 / Yyn0. SG series - dry-type units for general duty.
Applications: high-rise and commercial buildings · airports · tunnels and metro · docks and machinery areas · local lighting · any load-centre supply where oil is not acceptable.
To quote accurately, we need:
Rated capacity (kVA) and HV/LV voltage
Insulation class (F or H) and cooling method (AN / AF)
Connection group and tap range
Altitude, ambient temperature and humidity
Indoor/outdoor placement and any fire-regulation requirement
Applicable standard (IEC 60076 and/or GB series)
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