Stray Load Loss in Induction Motor

 

🔹 Definition

Stray load loss is the additional loss that appears in an induction motor when it operates under load, due to leakage flux, harmonics, and non-uniform current distribution, which are not included in the basic copper, iron, or mechanical losses.

It is called “stray” because it is difficult to measure and does not belong to any single loss category.

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🔹 Causes of Stray Load Loss

It occurs due to:

1️⃣ Leakage flux

• Flux leakage in slots and teeth

• Produces eddy currents in conductors and iron parts

2️⃣ Harmonics

• Slot harmonics

• Space harmonics

• Time harmonics
  → cause extra copper & iron losses

3️⃣ Skin effect

• Non-uniform current distribution in rotor bars

4️⃣ Mechanical imperfections

• Slotting

• Surface roughness

• Rotor/stator asymmetry

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🔹 Components included

Stray load loss mainly consists of:

• Extra stator copper loss

• Extra rotor copper loss

• Additional core (iron) loss

• Eddy current losses in structural parts

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🔹 Mathematical Representation

Total losses in induction motor:

$$\text{Total losses} = \text{Stator Cu loss} + \text{Rotor Cu loss} + \text{Core loss} + \text{Mechanical loss} + \text{Stray load loss}$$