Civil Engineering Reference
In-Depth Information
FIGURE 9-8
Power versus power angle of round rotor and salient pole synchronous machine.
The output power versus the power angle is a sine curve shown by the
solid line in
Figure 9-8
,
having the maximum value at
= 90°. The maximum
power that can be generated by the machine is therefore:
δ
VE
Xs
P
=
(9-6)
max
Some synchronous machine rotors have magnetic saliency in the pole
structure. The saliency produces a small reluctance torque superimposed on
the main torque, modifying the power angle curve as shown by the dotted
line.
The electromechanical torque required at the shaft to produce this power
is the power divided by the angular velocity of the rotor. That is as follows:
VE
Xs
T
=
ω
sin
δ
(9-7)
e
The torque also has the maximum limit corresponding to the maximum
power limit, and is given as follows:
VE
Xs
T
=
ω
(9-8)
max
9.3.4
Transient Stability Limit
The maximum power limit just described is called the steady state stability
limit. Any loading beyond this value will cause the rotor to lose synchronism,
and hence, the power generation capability. The steady state limit must not
