CONSTRUCTION & ENERGY

What does transformer power (kVA) represent?
The transformer label is kVA; this is apparent power. The actual power of the loads is kW, and the reactive part is kvar, and the relationship between them is established with cosφ (power factor). If cosφ is low (e.g., 0.80), a larger kVA is required for the same kW. Therefore, using the "total kW" calculation alone gives incorrect results.

Label:
kVA (apparent power)
Relationship:
kW • kvar • cosφ
Simple relationship
kVA ≈ kW / cosφ
Selection logic: first demand power, then kVA
The backbone of transformer selection is this: You find the demand power, not the installed power. Because not all loads operate at full capacity at the same time. Demand power is determined by simultaneity (diversity) and usage profile. Then you convert it to kVA using the power factor and leave a margin for operational safety.

Generally followed process:

• Remove loads
  Lighting, sockets, HVAC, pumps, elevator, charging station, process, etc.
  Find demand kW simultaneously
  Descend from installed power to demand with diversity and usage profile.
  Convert to kVA with cosφ
  Demand kW → demand kVA conversion.
  Add 15–25% reserve
  For growth margin and operational safety.
  Round to standard range
  250 / 400 / 630 / 800 / 1000 / 1250 kVA…
  Quick rule: operating the transformer at 60–80% load is ideal
  Continuous 90–100% load is not good in terms of heating and lifespan. Very low load (20–30%) reduces efficiency due to no-load losses. Therefore, the practical target is: 60–80% range in normal operation. This target both maintains the temperature class and leaves room for growth.

Critical Points to Consider
There are several main issues that disrupt transformer selection before considering "kVA":

Motor/Start-up Effects
Motors/pumps/compressors/elevators put short-term strain on the transformer due to starting currents. In motor-heavy profiles, a one-step increase may be necessary.

Harmonic Loads
VFDs/inverters, UPSs, LED drivers, chargers increase heating and losses. K-factor/derating should be evaluated if necessary.

Voltage Drop & Line Length
Even if a large transformer is selected, voltage problems at the end will occur if cable cross-sections and distances are incorrect. Cable length/cross-section should be considered together.

Redundancy (N+1)
In critical installations, 2x transformers (N+1) may be more appropriate than a single large transformer; maintenance and outage management are facilitated.

A very practical calculation example (general)
Example calculation
Power demand: 320 kW, cosφ: 0.90 kVA ≈ 320 / 0.90 = 355 kVA 20% share: 355 × 1.20 ≈ 426 kVA Standard stage: 400 kVA or 630 kVA?
At this point, the characteristics of the load are considered. If there is no motor/harmonic and growth is limited, 400 kVA may be sufficient. However, if there is growth, EV charging or motor weight, 630 kVA is a safer choice.

Practical Approach for Housing (Very Roughly)
The "per apartment" approach is frequently used in housing projects, but this must be verified with project and local standards. Apartment types, electric heating/air conditioning density, number of elevators, common areas, and commercial units significantly alter the result. Therefore, instead of stating "this many kVA" with a single number, proceeding with the load list + simultaneity method is the most accurate approach.

2G CONSTRUCTION & ENERGY APPROACH
2G Construction & Energy determines the transformer level by considering not only the current need but also operational safety, growth margin, and acceptance/operation criteria. A correctly selected transformer reduces outages and maintains the return on investment in the long term.