SPEED GOVERNORS TIME RESPONSE OF SYNCHRONOUS GENERATORS

We introduced models that are typical for steam reheat or nonreheat turbines (Figure 3.9 and Figure 3.10) and hydraulic turbines (Figure 3.40 and Equation 3.42). Here we add them to the speeddroop primitive governor with load reference, as discussed in the previous paragraph (Figure 6.10a and Figure 6.10b)

• TCH is the inlet and steam chest delay (typically: 0.3 sec)

• TRH is the reheater delay (typically: 6 sec)

• FHP is the high pressure (HP) flow fraction (typically: FHP = 0.3)

With nonreheater steam turbines: TRH = 0.

For hydraulic turbines, the speed governor has to contain transient droop compensation. This is so because a change in the position of the gate, at the foot of the penstock, first produces a short-term turbine power change opposite to the expected one.

For stable frequency response, long resetting times are required in stand-alone operation. A typical such system is shown in Figure 6.10b:

• TW is the water starting constant (typically: TW = 1 sec)

• Rp is the steady-state speed droop (typically: 0.05)

• TGV is the main gate servomotor time constant (typically: 0.2 sec)

• TR is the reset time (typically: 5 sec)

• RT is the transient speed droop (typically: 0.4)

• D is the load damping coefficient (typically: D = 2)

Typical responses of the systems in Figure 6.10a and Figure 6.10b to a step load (ΔPL) increase are shown in Figure 6.11 for speed deviation Δωr (in P.U.). As expected, the speed deviation response is rather slow for hydraulic turbines, average with reheat steam turbine generators, and rather fast (but oscillatory) for nonreheat steam turbine generators.

The speed governor turbine models in Figure 6.10 are standard. More complete (nonlinear) models are closer to reality. Also, nonlinear, more robust speed governor controllers are to be used to improve speed (or power angle) deviation response to various load perturbations (ΔPL).