HP to kVA – Convert

Converting horsepower to kVA is essential in engineering when designing generators, motors, or power distribution systems.
This calculation links mechanical and electrical power, considering voltage, power factor, and overall system efficiency.

HP to kVA Conversion Formula

The general formula to convert horsepower (HP) to kilovolt-amperes (kVA) is:

Formula (Three-Phase AC)

Formula (Single-Phase AC)

Variables Explained in Detail

Extensive HP to kVA Conversion Table

For 3-phase systems, PF = 0.8, η = 0.9, V = 400V:

Note: These values assume standard industrial configurations. Adjust PF, efficiency, and voltage as needed for exact calculations.

Alternate Table: HP to kVA @ 480V, PF = 0.9, η = 0.95 (High-Efficiency Motors)

You can use these tables for quick estimation or to size transformers and generators.

Real-World Application Example #1: Sizing a Generator for a 150 HP Motor

Scenario:
A production plant uses a 3-phase 150 HP induction motor. You must size a standby generator.

Assumptions:

• Voltage: 400V
• Power factor: 0.8
• Efficiency: 0.92

Step-by-step:

Step 1: Use the formula

Step 2: Compute

Result:
A generator rated at at least 220 kVA is required. For surge loads, a 250 kVA unit is recommended.

Real-World Application Example #2: Selecting a Transformer for a 75 HP Water Pump

Scenario:
Design an electrical system for a 75 HP water pump with single-phase supply.

Assumptions:

• Voltage: 240V
• Power Factor: 0.85
• Efficiency: 0.9

Calculation:

Step 1: Use the single-phase formula

This is incorrect — let’s fix it:

Wait — this seems too low. Let’s double-check:

But clearly this is wrong — the units are not matching. Let’s recalculate:

Final Result:
A 75 HP single-phase motor requires a 74 kVA transformer minimum, ideally 80–85 kVA to handle startup inrush.

Factors Affecting HP to kVA Conversion

• Power Factor (PF): Motors often have lagging PF due to inductance. Improving PF with capacitors can reduce kVA demand.
• Voltage Variance: System voltage affects current draw. Lower voltage = higher current = higher kVA.
• Efficiency (η): Losses in motors and mechanical systems lower conversion efficiency, increasing kVA.
• Startup Load: Motors may draw 2–6 times the running kVA during startup.

HP to kVA Conversion Best Practices

1. Always size equipment above calculated value by 15–20% for safety and surge handling.
2. Use accurate nameplate values when available.
3. Consult IEEE 141 (Red Book) and IEC 60034 for electric motor standards.
4. Verify voltage and phase configuration before calculation (single/three-phase).
5. Include service factors and derating for altitude, ambient temperature, and continuous use.

Online HP to kVA Calculators

There are reliable online tools that simplify HP to kVA conversion. Some authoritative sources include:

• ABB Electrical Tools
• Schneider Electric Calculation Tools
• RapidTables Converter

These can validate or speed up your manual calculations.

Reverse Conversion: kVA to HP Formula

Sometimes you need to convert kVA back to HP—for example, when you have a generator rating and want to understand the mechanical load it can support.

Formula (Three-Phase AC)

Formula (Single-Phase AC)

Example:

You have a 100 kVA, 3-phase, 400V generator with PF = 0.85, η = 0.93.

Result: This generator can run an approximate 73 HP motor, assuming no additional load.

HP to kVA vs kW to kVA

Many confuse HP and kW in conversions. Here’s how they relate:

To convert kW to kVA, use:

To convert HP to kVA, convert HP → kW → kVA, or use the direct formula above.

Additional HP to kVA Table (PF = 0.9, η = 0.95, 230V, Single-Phase)

These are for low voltage single-phase setups, such as water pumps or agricultural motors.

Common Motor Sizes and Matching Generator Ratings (3-Phase @ 400V, PF = 0.8, η = 0.9)

Always size above calculated values to accommodate inrush currents and external loads.

Industrial Use Cases for HP to kVA Conversion

Scenario: HVAC Systems

Large HVAC units often specify their compressor or blower motors in HP. Electrical contractors need to determine if building generators or transformers can support them.

Example: A 40 HP HVAC motor at 460V, 3-phase.

• PF = 0.85
• η = 0.92

A 50 kVA transformer or generator is ideal.

Scenario: Agricultural Irrigation Pump

Pump = 60 HP, 230V single-phase

• PF = 0.88
• η = 0.9

Result: Use 60 kVA or higher rated single-phase transformer or generator.

Compliance with Standards

When doing HP to kVA conversions in real projects, always refer to:

• IEC 60034 – Rotating electrical machines
• IEEE 141 (Red Book) – Electric power distribution in industrial plants
• NFPA 70 (NEC) – National Electrical Code, for wiring sizing
• ISO 3046 – Standard for reciprocating internal combustion engines

These ensure compliance with international and regional safety and sizing guidelines.