Heat Losses from Electrical Equipment

Heat loss to the ambient air from some typical electrical equipment are indicated below: 

Transformers

Transformers are in general highly efficient and large power transformers - 100 MVA and larger - can be more than 99% efficient. Smaller transformers - like used in consumer electronics - may be less than 85% efficient.

Heat loss for

• 150 kVA and smaller : 50 Watts/kVA  (aprox. 5%)
• 150 - 500 kVA : 30 Watts/kVA (aprox. 3%)
• 500 - 1000 kVA : 25 Watts/kVA (aprox. 2.5%)
• 1000 - 2500 kVA : 20 Watts/kVA (aprox. 2%)
• larger than 2500 kVA : 15 Watts/kVA (aprox. 1.5%)

Switch Gear - Circuit Switch Breakers

• Low voltage breaker 0-40 Amps : 10 Watts
• Low voltage breaker 50-100 Amps : 20 Watts
• Low voltage breaker 225 Amps : 60 Watts
• Low voltage breaker 400 Amps : 100 Watts
• Low voltage breaker 600 Amps : 130 Watts
• Low voltage breaker 800 Amps : 170 Watts
• Low voltage breaker 1600 Amps : 460 Watts
• Low voltage breaker 2000 Amps : 600 Watts
• Low voltage breaker 3000 Amps : 1100 Watts
• Low voltage breaker 4000 Amps : 1500 Watts
• Medium voltage breaker/switch 600 Amps : 1000 Watts
• Medium voltage breaker/switch 1200 Amps : 1500 Watts
• Medium voltage breaker/switch 2000 Amps : 2000 Watts
• Medium voltage breaker/switch 2500 Amps : 2500 Watts

Motor Control Centers

• Section : 500 Watts per section
• Low voltage starters size 00 : 50 Watts
• Low voltage starters size 0 : 50 Watts
• Low voltage starters size 1 : 50 Watts
• Low voltage starters size 2 : 100 Watts
• Low voltage starters size 3 : 130 Watts
• Low voltage starters size 4 : 200 Watts
• Low voltage starters size 5 : 300 Watts
• Low voltage starters size 6 : 650 Watts
• Medium voltage starters size 200 Amp : 400 Watts
• Medium voltage starters size 400 Amp : 1300 Watts
• Medium voltage starters size 700 Amp : 1700 Watts

Variable Frequency Drive

• Variable frequency drive : 2 - 6% of kVA rating
• Bus duct : 0.015 Watts /ft Amp
• Capacitors : 2 Watts / KVAR