Three phase Motors Parameters calculations

📊 Electrical Parameters for Motor Installation & Testing

For every motor installation, an electrical engineer must calculate certain parameters to ensure correct sizing, protection, and performance monitoring. The following formulas apply to Alternating Current (AC) motors in both single-phase and three-phase systems.

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1. Current (Amperes) when Horsepower (HP) is known

• Single-phase:

$$I = \frac{HP \times 746}{E \times \eta \times pf}$$

• Three-phase:

$$I = \frac{HP \times 746}{1.73 \times E \times \eta \times pf}$$

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2. Current (Amperes) when Kilowatts (kW) are known

• Single-phase:

$$I = \frac{kW \times 1000}{E \times pf}$$

• Three-phase:

$$I = \frac{kW \times 1000}{1.73 \times E \times pf}$$

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3. Current (Amperes) when kVA is known

• Single-phase:

$$I = \frac{kVA \times 1000}{E}$$

• Three-phase:

$$I = \frac{kVA \times 1000}{1.73 \times E}$$

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4. Kilowatts (kW)

• Single-phase:

$$kW = \frac{I \times E \times pf}{1000}$$

• Three-phase:

$$kW = \frac{1.73 \times I \times E \times pf}{1000}$$

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5. kVA

• Single-phase:

$$kVA = \frac{I \times E}{1000}$$

• Three-phase:

$$kVA = \frac{1.73 \times I \times E}{1000}$$

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6. Horsepower (HP – Output)

• Single-phase:

$$HP = \frac{I \times E \times \eta \times pf}{746}$$

• Three-phase:

$$HP = \frac{1.73 \times I \times E \times \eta \times pf}{746}$$

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🔑 Key Symbols

• $I$ = Current (Amperes)

• $E$ = Voltage (Volts)

• $pf$ = Power factor

• $\eta$ = Efficiency (decimal)

• $HP$ = Horsepower

• $kW$ = Kilowatts

• $kVA$ = Kilovolt-Amperes

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📌 Practical Tip for Engineers:
Regular monitoring of motor current (ampere) is essential to:

• Detect overloads early

• Prevent overheating & insulation damage

• Improve energy efficiency

• Avoid penalties due to poor power factor

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