Only on the premise of less than the limit of power, the power of diesel engine and generator power can be balanced, generator can run stable and lasting.

According to the Angle of characteristic curve, shown in figure 9.6 illustrates the determination of generator stable working point.

Though the number of fixed diesel engine power P0 may have two power Angle theta a and theta b, but in fact only at theta a running is stable, and in the theta b, run is unsustainable, and is unstable.

Because when the point a is running, when there is a slight change theta a Δ theta, generator power also change accordingly Δ PE, and Δ PE and Δ theta symbols are the same.

As a result of the diesel engine power P0 is constant, the generator power increasing, the deceleration and braking, can make the rotor of the generator generator voltage vector movement towards the direction of the theta Angle decreases, until finally returned to the point a, generator and diesel engine power balance again;

When Δ theta < 0, the situation completely similar, only the rotor was accelerated after back to point a.

In theta. B, the opposite is true: if theta Angle increases Δ theta, b generator output power decreases the Δ PE, the diesel engine to further accelerate the residual power to make the rotor of the generator, thereby theta Angle increases further, until the generator out of sync;

If theta b decreases Δ theta, generator power is increasing, make the rotor further slowdown, theta Angle decreases, and further has been reduced to theta a position, power generator and diesel engine to a stable balance.

Visible, static and stable operation of the generator, it must be in Angle characteristics Δ P/Δ theta > 0, namely theta must be smaller than 90 DHS.

In theta equals 90 DHS ~ 180 DHS interval, back to the stability of the generator rotor working point (if PE > P0), or the surplus power diesel generator rotor speeds up, finally out of sync, or sliding were back to the stable working point after nearly a week.

For general diesel generator, under the condition of normal operation, the power Angle is always far less than 90 DHS, combined with the generator has automatic excitation regulator, can rapidly improve the generator voltage, so don't need to do a special check to the static stability.

But when the generator set and its control system (excitation regulation and speed adjusting) parameter mismatch, and the running state of the generator abnormal, such as load distribution is serious imbalance, and the static stability problem may come up.

For diesel engine power generator, close to power and power plant, in the case of load power is constant, a generator Angle changes, is bound to make other generator Angle change in the opposite direction, therefore, is the main factor affecting the stability of parallel unit static generator Angle difference between theta. 12.

For example, when the active load of serious imbalance between the generator, especially a generator into the motor working state, large Angle difference between generator, it is possible to lose parallel running static stability.

In addition, in under the action of periodic interference factors, such as imbalance of the diesel engine combustion, cyclical impact load, due to the generator speed control system or pressure regulating system action inconsistencies between, also can form a cyclical swing Angle, although the swing range may not beyond the limit value of power Angle, but between the generator power oscillation is considerable, because this power oscillation problems on diesel engine power station is outstanding, will be dedicated to discuss later.