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55 lines
4.9 KiB
Markdown
55 lines
4.9 KiB
Markdown
## Power types in motor
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| Type | Description | Equivalent terms |
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| ------------------ | ---------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------- |
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| Input power | Power into machine. $V_T=V_{3\phi}$, $I_L=I_{3\phi}$ | $P_\text{in}$, $\sqrt{3}V_TI_L\cos(\theta)$ |
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| Output power | Mechanical output power of the machine, excludes losses | $P_\text{out}$, $P_\text{load}$ |
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| Converted power | Total electrical power converted to mechanical power, includes useful power and mechanical losses inside machine | $P_\text{conv}$, $P_\text{converted}$, $P_\text{mech}$, $P_\text{developed}$, $\tau_\text{mech}\times\omega_m$ |
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| Airgap power | Power transmitted over airgap. | $P_\text{AG}$, $\tau_\text{mech}\times\omega_s$ |
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| Mechanical loss | Power lost to friction and windage | $P_\text{mechanical loss}$, $P_\text{F\\\&W}$, $P_\text{friction and windage}$ |
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| Core loss | Power lost in machine magnetic material due to hysteresis loss and eddy currents | $P_\text{core}$ |
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| Rotor copper loss | Due to resistance of rotor windings | $P_r$, $P_\text{RCL}$ |
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| Stator copper loss | Due to resistance of stator windings | $P_s$, $P_\text{SCL}$ |
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| Miscellaneous loss | Add 1% to losses to account for other unmeasured losses | $P_\text{misc}$, $P_\text{stray}$ |
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$$
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\begin{align}
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P_\text{in}&=P_\text{SCL}+P_\text{RCL}+P_\text{core}+P_\text{F\\\&W}+P_\text{misc}+P_\text{out}\\
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P_\text{AG}&=P_\text{RCL}+P_\text{F\\\&W}+P_\text{misc}+P_\text{out}\\
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P_\text{mech}&=P_\text{F\\\&W}+P_\text{misc}+P_\text{out}
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\end{align}
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$$
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## No-load test
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| Assumption | Eqn | Reason |
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| ------------------------------ | ----------------- | ------------------------------ |
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| rotor current is insignificant | $I_r \approx 0$ | high rotor resistance |
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| no output mechanical power | $P_\text{out}=0$ | no load |
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| high rotor resistance | $R_r/s\to \infty$ | $s\to 0$, high slip at no load |
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Using assumptions, remove rotor part of circuit and only consider stator and magnetizing path.
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## Blocked rotor test
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| Assumption | Eqn | Reason |
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| ----------------------- | ---------------------------------- | ------------------------------------------------------------------------------- |
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| ignore magnetizing path | $I_r\ggg I_m$ | magnetizing current is low compared to rotor current as rotor resistance is low |
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| low rotor resistance | $R_r/s\approx R_r$ | $s\approx 1$, slip is $1$ when blocked |
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| | $X_r\approx f_0/f_{BL}\times X_r'$ | $X_r'\approx X_{BL}/2$ |
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| | $X_r'\approx X_{BL}/2$ | $X_s\approx X_r'$ |
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| | $X_s\approx X_r'$ |
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## Equivalent model
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| Assumption | Eqn | Reason |
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| ---------- | ------------------------ | ------------------------------------ |
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| | $x_m\approx X_m$ | $R_c\ggg X_m\Rightarrow r_c\lll x_m$ |
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| | $r_c\approx {X_m}^2/R_c$ | $R_c\ggg X_m\Rightarrow r_c\lll x_m$ |
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