- #1

mikehsiao789

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## Homework Statement

A locked rotor test is performed on a permanent magnet DC machine with the following results:

Terminal Voltage 5 V DC

Input Current 10 A DC

Locked rotor torque. 20 Nm

a) Making suitable approximations deduce the effective rotor resistance in ohms?

b) Making suitable approximations deduce the torque constant kφ in Nm/A?

c) If a light running test was now performed with a terminal voltage of 50V DC what approximate shaft speed in rpm would you expect?

I did some calculations, however I am not sure if what I am doing is correct.

## Homework Equations

[/B]

**Short circuit current at normal voltage**

**Short circuit power factor**

[PLAIN]http://upload.wikimedia.org/math/8/4/3/843762fe06455b51d90ae61f2ee1c042.png[URL='http://en.wikipedia.org/wiki/Blocked_rotor_test#cite_note-12'][12][/URL]

**Leakage reactance**

## The Attempt at a Solution

[/B]

a) V/I= R => 0.5 ohms

b)Torque = k*Ia => Torque/Ia = k = 20 N*m/10 = k = 2

c) w= k*v => 50v*2= 100 rpm

I am not too sure if these are correct, it would be great if someone can help! Thank you :)

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