0
\$\begingroup\$

A 208-V Y-connected synchronous motor is drawing 40 A at unity power factor from a 208-V power system. The field current flowing under these conditions is 2.7 A. Its synchronous reactance is 0.8 Ω. Assume a linear open-circuit characteristic.

The answer is given as:

enter image description here

However, I do not understand where they got that equation for EA. I was under the impression that the equation for the phase voltage is:

enter image description here

Wouldn't this mean that the equation for the internal generated voltage is EA = VΦ + jXsIA?

EDIT: My bad. That's the equation for a synchronous generator, not a synchronous motor.

This is the equation for a synchronous motor: enter image description here

\$\endgroup\$
1
  • \$\begingroup\$ TRy again............. \$\endgroup\$ Jul 1, 2019 at 4:57

1 Answer 1

0
\$\begingroup\$

If you supply mechanical power to a synchronous machine, it becomes a synchronous generator generating electrical power.

Electrical power converts the synchronous machine into a motor providing mechanical power.

From Electric Machinery Fundamentals. As a motor:

Synchronous motor

$$V_{\phi} = E_A + j I_A X_S + I_A R_A$$ As a generator: Synchronous Generator

$$V_{\phi} = E_A - j I_A X_S - I_A R_A$$

Note direction of current. The voltage seen at the terminals \$V_{\phi}\$ will depend on whether the synchronous machine takes current or generates current, hence the change of signs. Just Kirchhoff's Voltage Law.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.