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What Happens To The Phase Advancement Of The Hydro-generator

July 25, 2020

What happens to the phase advancement of the hydro-generator

When the generator is running normally, it provides active power to the system while also providing reactive power. The stator current lags behind the terminal voltage by an angle, which is a late phase operation. When the excitation current is gradually reduced, the generator changes from providing reactive power to the system. In order to absorb reactive power from the system, the stator current changes from lagging to leading the generator terminal voltage by one angle.This state is the phase advance operation.
When the synchronous generator is running in phase, the excitation current of the later phase is greatly reduced, and the generator potential Eq is also reduced accordingly. From the perspective of the P-power angle relationship, under the condition of constant active power, the power angle will increase accordingly. The ratio of the full-step power is also reduced correspondingly, and the static stability of the generator is reduced. Its stability limit is related to the generator's short-circuit ratio, external reactance, automatic excitation regulator performance and whether it is put into operation.
The magnetic flux leakage at the end of the generator stator increases during the advanced phase operation compared to the later phase operation. Especially for large generators, the line load is high, and the end magnetic flux leakage is relatively large during normal operation, and the temperature of the end iron core pressing finger connecting piece increases. When the phase is running, the magnetic leakage increases, and the temperature rise is aggravated. When the phase is running, the voltage at the generator terminal is reduced, and the voltage of the auxiliary power is also reduced accordingly. If it exceeds 10%, it will affect the operation of the power.
Therefore, the phase advance operation of the synchronous generator must be tested to determine the phase advance operation depth. That is, under a certain active power state, how much reactive power can be absorbed to maintain the static and transient stability of the system, and the temperature rise of each component does not exceed the limit, and can meet Voltage requirements.

What factors are restricted by the generator's advanced operation?


When the system provides more inductive reactive power than needed, it will cause the system voltage to rise, requiring the generator to generate less reactive power or even absorb reactive power.At this time, the generator can change from late phase operation to advance phase operation.
The main factors that restrict the generator's advanced operation are:
(1) Limitations of system stability
(2) Limitation of the temperature of the stator end parts of the generator
(3) Limitation of stator current
(4) Limitation of auxiliary power voltage
Phenomenon, the excitation current and excitation voltage are greatly reduced, the power factor is greater than 1 or above 0.97, the reactive power indicator is negative, the stator current increases, the temperature of the stator end rises, and the factory power voltage decreases. The factory power voltage is generally Leaded from the generator outlet or generator bus voltage, when the phase is running, the generator terminal voltage is reduced due to the reduction of the generator excitation current and the reactive power reverse transmission, and the auxiliary power voltage is also reduced