The actual active power (kW) a 250 KVA transformer can handle depends directly on the power factor (PF) of your connected electrical load—this is a critical factor in matching the transformer to your system’s needs.
- When the load power factor reaches 1.0 (a purely resistive load, e.g., heating equipment), the transformer can deliver a maximum active power of 250 kW, as the apparent power (KVA) equals active power at PF=1.
- For most real-world applications (where PF typically ranges from 0.8 to 0.9, such as motors, pumps, or commercial lighting), the usable active power is calculated as: 250 KVA × Load Power Factor. At PF=0.9, this translates to 225 kW of reliable output.
Additionally, 250 KVA pole mounted transformers are engineered with short-term overload capability to accommodate temporary peak demands (e.g., sudden equipment startups). In such cases, the overload capacity can reach several times the rated output for brief intervals, ensuring system stability without compromising long-term performance.
The standard rated current for a 250 KVA three-phase pole mounted transformer is 360 A (low-voltage side, typically 0.4 kV). This value represents the safe, continuous current the transformer can supply under normal operating conditions.
Transformer rated current is derived from the following industry-standard formulas, applicable to both high-voltage (HV) and low-voltage (LV) sides:
- Input Rated Current (HV Side) = Transformer Capacity (KVA) ÷ (√3 × Input Voltage Rating (kV))
- Output Rated Current (LV Side) = Transformer Capacity (KVA) ÷ (√3 × Output Voltage Rating (kV))
For a common 10 kV (HV) / 0.4 kV (LV) 250 KVA oil-cooled pole mounted transformer (efficiency ≥ 0.95):
- High-Voltage Side Rated Current = 250 ÷ (1.732 × 10) ≈ 14.4 A
- Low-Voltage Side Rated Current = 250 ÷ (1.732 × 0.4) ≈ 360 A
This example aligns with typical grid configurations, helping you verify current requirements for cable sizing, circuit protection, and system integration.
