Distribution transformers
630 kVA transformer
A 630 kVA transformer delivers 909 A at 400 V and 840 A at 433 V. At this rating the impedance on the order, 4 or 6 percent, moves the fault level at the low voltage board by about a third.
- Rated current at 400 V
- 909 Acalculated
- Rated current at 433 V
- 840 Acalculated
- Fault level at 400 V, at 4 or 6 %
- about 22.7 or 15.2 kAupper bound, infinite source
- EU load loss ceiling, liquid
- ≤ 4,600 WTier 2, Table I.1
- EU no load loss ceiling, liquid
- ≤ 540 WTier 2, Table I.1
What 630 kVA supplies
630 kVA is the R10 step that many compact and walk in substations are built around. In service it carries a school, a supermarket, a workshop with a few large machines or a charging hub of moderate size.
A 500 kW load at a power factor of 0.9 needs 556 kVA, and 630 kVA carries it with margin. At 0.8 the same load needs 625 kVA. The unit is then full on day one.
Kahramaa's low voltage network in Qatar runs at 240/415 V within 6 %, with a design fault level of 31 MVA at 415 V.
Rated currents at 630 kVA
| Primary | Secondary | Primary current | Secondary current |
|---|---|---|---|
| 10 kV | 400 V | 36 A | 909 A |
| 11 kV | 400 V | 33 A | 909 A |
| 11 kV | 433 V | 33 A | 840 A |
| 20 kV | 400 V | 18 A | 909 A |
4 or 6 percent impedance
Manufacturers offer both values at 630 kVA, and the order fixes one. At 4 percent the voltage at the board holds steadier when motors start, and more fault current flows. At 6 percent the fault current falls and the voltage drop at full load grows a little.
Moving from 4 to 6 percent takes the upper bound of the fault current at 400 V from about 22.7 kA to about 15.2 kA. That step can decide the breaking capacity of every breaker on the board. A unit that will run in parallel with an existing transformer has to match its impedance.
Low voltage fault current, upper bound
| Secondary | Rated current | At uk 4 % | At uk 6 % |
|---|---|---|---|
| 400 V | 909 A | 22.7 kA | 15.2 kA |
| 433 V | 840 A | 21.0 kA | 14.0 kA |
Rated current divided by uk, the short circuit impedance, with an infinite source upstream. The fault study, run with the impedance of the unit offered, gives the real value, which is lower.
Incomer and cables at 630 kVA
909 A sits just under the common 1000 A frame. A moulded case incomer is still usual at this current, and an air circuit breaker appears where the design calls for withdrawable units or finer selectivity.
Cable still works between transformer and board, usually in parallel runs. Busbar trunking therefore shapes the room less at 630 kVA than at the ratings above it.
Transformer alone or a complete station
At 630 kVA the first choice is often between the transformer alone and a complete station. A station brings the lifting, the earthing points and the cable entries into one type tested product, and its quotation covers the enclosure and switchgear too.
For the transformer alone, the price turns on the construction, the losses below the ceiling, the impedance, the tapping range and the delivery terms. The drawing and mass of the unit offered come with the quotation. They set the vehicle, the crane and the foundation.
630 kVA under the GB loss rules
Regulation (EU) No 548/2014 still applies in Great Britain as assimilated law. For a liquid immersed 630 kVA unit, Tier 2 cut the ceilings on 1 July 2021 from 6,500 W load and 600 W no load losses to 4,600 W and 540 W. The GB text keeps the EU's Tier 1 allowance for a one to one replacement where meeting Tier 2 would cost disproportionately, which can matter when a 630 kVA unit goes into an existing station.
What a 630 kVA transformer request needs
- 630 kVA, or the connected load if the rating is still open
- The impedance on the order, 4 or 6 percent, and the breaking capacity of the board it feeds
- The transformer alone, or a complete compact or walk in station
- The nameplate of any unit it will run beside in parallel
Specification template
Fill it in on screen or by hand, then upload it with your request.
Questions buyers ask
What is the full load current of a 630 kVA transformer?
909 A at 400 V and 840 A at 433 V on the low voltage side. On the primary it is about 36 A at 10 kV, 33 A at 11 kV and 18 A at 20 kV.
Is 630 kVA enough for a 500 kW load?
Yes, at a power factor of 0.9: the load needs 556 kVA and 630 kVA leaves some margin. At 0.8 it needs 625 kVA and the unit is full. Planned growth or a large motor start usually points to 800 kVA.
Why does the impedance matter more at 630 kVA than at smaller ratings?
Both values are offered at this rating, and they give different fault levels at the board: up to about 22.7 kA at 4 percent and 15.2 kA at 6 percent, at 400 V. The breakers on the board are rated for the one on the order.