112.5 kva transformer
The 112.5 kVA transformer is a medium-capacity power transformer, mainly used for converting voltage levels and transmitting
electrical energy in the power distribution system. The following explanations are carried out from aspects such as **technical
parameters, calculation methods, application scenarios, and model selection suggestions**:
I. Core Parameters and Definitions
- **Apparent Power**: 112.5 kVA (kilovolt-ampere), which represents the **total capacity** of the transformer, including active
power (kW) and reactive power (kVar).
- **Formula Relationships**:
**Active Power (kW) = 112.5 kVA × Power Factor (cosφ)**
**Reactive Power (kVar) = 112.5 kVA × Reactive Factor (sinφ)**
II. Calculation of Rated Current (Single-phase vs. Three-phase)
1. Single-phase Transformer
- **Rated Voltage**: Commonly 230V/115V (low voltage side) or 10kV/230V (high voltage side).
- **Current Formula**:
**I (A) = 112,500 VA ÷ Voltage (V)**
- **Example**: For a 230V single-phase transformer
**I = 112,500 ÷ 230 ≈ 489A** (current on the low voltage side).
2. Three-phase Transformer
- **Rated Voltage**: Commonly 400V/230V (low voltage side) or 10kV/400V (high voltage side).
- **Current Formula**:
**I (A) = 112,500 VA ÷ (√3 × Line Voltage)**
- **Example**: For a 400V three-phase transformer
**I = 112,500 ÷ (1.732 × 400) ≈ 162A** (line current on the low voltage side).
# III. Typical Application Scenarios
| Field Field | Application Scenario | Load Example |
| Commercial Buildings | Power distribution for shopping malls and office buildings | Lighting, air conditioning, elevators (total power < 90kW) |
| Industrial Equipment | Power supply for small factories and production lines | Motors, welding machines (power factor compensation needs to be considered) |
| Distributed Energy | Grid connection of photovoltaic/wind power, energy storage systems | New energy power generation systems below 100kW |
| Special Purposes | Dedicated for welding machines, power supplies for test equipment | Low voltage and high current scenarios (such as 20V/5,625A) |
IV. Key Technical Parameters
| Parameter | Common Value | Explanation |
| Rated Capacity | 112.5 kVA | Standard specification (can be customized) |
| Voltage Ratio | 10kV/400V, 20kV/480V, etc. | Needs to match the grid voltage level |
| Impedance Voltage (Uk%) | 4% - 6% (three-phase) | Affects the short-circuit current and voltage stability |
| Efficiency | 98% - 99% (full load) | No-load loss < 200W, load loss < 1.5kW |
| Cooling Method | Oil cooling (ONAN), air cooling (OFAF) | Oil cooling is suitable for indoor use, and air cooling is suitable for outdoor use |
| Connection Group | Dyn11 (three-phase), Single-phase | Dyn11 allows unbalanced three-phase loads |
V. Model Selection and Configuration Suggestions
1. Load Calculation
- **Active Power Demand**:
If the total load power is 90kW (cosφ = 0.8), then a transformer of 90kW ÷ 0.8 = 112.5 kVA is required.
- **Impact Load**:
When welding machines and motors start, the current can reach 5-7 times the rated current. A transformer with an
overload capacity of 1.2-1.5 times is required.
2. Voltage Level Matching
- **High Voltage Side**: Select 10kV, 20kV or 35kV according to the power grid.
- **Low Voltage Side**:
- If the load is mainly single-phase: Select 230V single-phase or 400V/230V three-phase (three-phase four-wire system).
- If the load is mainly three-phase motors: Select 400V three-phase.
3. Brands and Standards
- **International Brands**: ABB (SCB14 series), Schneider (SM6 series).
- **Domestic Brands**: TBEA (S13-M series), CHINT (NB series).
- **Standards**: Comply with IEC 60076 (international) or GB 1094 (China).
VI. Precautions
1. **Power Factor Compensation**:
If the load power factor < 0.8, parallel capacitors need to be used for compensation, otherwise the actual load-carrying
capacity of the transformer will decrease.
**Example**: When cosφ = 0.6, a 112.5 kVA transformer can only carry 67.5 kW of active load.
2. **Short-circuit Protection**:
The circuit breaker on the high voltage side needs to be selected according to the **short-circuit current** (for example,
the short-circuit current on the 10kV side can reach 15kA).
3. **Installation Environment**:
Oil-cooled transformers need to be equipped with an **oil storage tank**, and air-cooled transformers need to ensure
good ventilation (ambient temperature < 40℃).
**Conclusion**: The 112.5 kVA transformer is suitable for small and medium-sized power distribution scenarios. When
selecting the model, key attention should be paid to **voltage levels, load types, and power factors**, and a 20% overload
margin should be reserved to deal with impact loads. In practical applications, it is recommended that professional electrical
engineers design the scheme according to on-site requirements.
