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Unformatted text preview: Problem 11-9:
Prated := 10⋅ hp Vt := 125⋅ volt Irated := 75⋅ amp Rfldckt := 125⋅ Ω Ra := 0.1⋅ Ω n rated := 1750⋅ rev
min At no load, the armature current is zero so Ea = Vt
At full load, the armature current is the line current minus the field current
If := Vt If = 1 A Rfldckt Ia := Irated − If Ia = 74 A
Ea := Vt − Ia⋅ Ra so the CEMF is Ea = 117.6 V The flux is virtually constant for the shunt DC motor, so the CEMF is
proportional to speed
n fl := 1750⋅ n nl := SR := Vt
min ⋅ n rated n nl − n fl
n fl Pout := 10⋅ hp 100% 3 rev n nl = 1.86 × 10 min SR = 6.293 % Pin := Vt ⋅ Irated Pout = 7.457 kW
η := Pout
Pin 100% η = 79.541 % Pin = 9.375 kW ...
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- Spring '12