Late phase operation
Normally, when the generator excitation system is in an overexcited state, it supplies both active and reactive power to the system, and the power factor is positive. This operating state is called delayed phase operation, also known as phase-delay operation.
Typically, a generator supplies both active and reactive power to the system, resulting in a positive power factor. This operating state is called delayed-phase operation.
Phase advance operation
Reducing the generator excitation current decreases the generator potential, causing the power factor angle to become leading. The generator load current generates an auxiliary armature reaction, and the generator delivers active power to the system but absorbs reactive power. This operating state is called leading-phase operation.
When a generator is operating normally, it provides active power to the system while also providing reactive power. The stator current lags behind the terminal voltage by an angle; this state is called delayed-phase operation. When the excitation current is gradually reduced, causing the generator to switch from providing reactive power to absorbing reactive power from the system, the stator current changes from lagging to leading the generator terminal voltage by an angle; this state is called leading-phase operation.
When a synchronous generator operates in the leading phase, the excitation current is significantly reduced compared to the lagging phase, and the generator electromotive force (Eq) also decreases accordingly. From the P-power angle relationship, with constant active power, the power angle will inevitably increase, and the ratio of total power output will decrease accordingly, leading to a decline in the generator's static stability. Its stability limit is related to the generator's short-circuit ratio, external reactance, the performance of the automatic excitation regulator, and whether it is in operation.
Phase shifting operation
Phase-shifting operation refers to the operating state in which the generator does not generate active power, but only transmits inductive reactive power to the power grid, thereby playing a role in regulating system reactive power and maintaining system voltage level.
When a generator is operating under phase-shifting conditions, it can operate in either over-excited or under-excited mode. Under-excited mode generates inductive reactive power; under-excited mode generates capacitive reactive power. Generally, operating under phase-shifting conditions refers to the generator operating in an over-excited state, i.e., generating inductive reactive power.
Leading-phase operation of generators: During power system operation, if reactive power is excessive, the system voltage will rise, affecting the normal operation of the system. In this case, it is necessary to adjust the generator to a leading-phase operation state to generate active power to absorb reactive power, thereby reducing the system voltage and bringing it into a stable operating state. However, generators operating in a leading-phase state can also have adverse effects.
The differences and connections between generator lag phase, leading phase, and phase adjustment.
I. Several grid-connected operating states of synchronous generators:
1. Delayed phase operation (normal operation) ---- The generator simultaneously delivers active power and reactive power (capacitive) to the grid.
2. Leading phase operation (advanced operation) ---- The generator sends active power to the grid and absorbs reactive power from the grid.
3. Phase-shifting operation: The generator absorbs the active power of the grid to maintain synchronous operation and sends reactive power (capacitive) to the grid.
4. Motor operation (abnormal operation) ----- The generator simultaneously absorbs active and reactive power from the power grid to maintain synchronous operation.
The first three operating states are the normal operating states of a synchronous generator. The second and fourth operating states should be avoided. The generator is prone to out-of-synchronization oscillation in the second state (leading phase operation), and the fourth operating state is wasteful and meaningless.
II. Simplify the complex:
It refers to the phase relationship between voltage and current. When the voltage leads the current, it is called a lagging phase, and when the voltage lags the current, it is called a leading phase. Phase adjustment is an operating state (synchronous motor state). In this state, the generator does not generate active power, but only reactive power, which supplements the reactive power of the power grid.
III. Using technical terms to describe my life state
The motor can operate in steady state in quadrants 1, 2, 3, and 4. Quadrant 1: Generator state, where the generator supplies active and reactive power to the grid. Quadrant 2: Phase-shifting operation state, where the motor absorbs active power from the grid while simultaneously generating reactive power. Quadrant 3: Motor state, where the motor absorbs active and reactive power from the grid to maintain its operation. Quadrant 4: Leading phase operation state, where the generator generates active power while simultaneously absorbing reactive power from the grid. In short:
Quadrant I: Active power X: Positive; Reactive power Y: Positive;
Second quadrant: Active power X: negative; Reactive power Y: positive;
Third quadrant: Active power X: negative; Reactive power Y: negative;
Fourth Quadrant: Active power X: positive; Reactive power Y: negative;
If we were to use the operating state of an electric motor as a metaphor for my life, the following would be comparable: "Having a job" means I have a job, which is what people who are usually foolish and have unrealistic dreams often call a "career." This thing is real and can drive the motor to rotate. It is the real driving force of social development and also the mate selection standard of increasingly realistic people.
The lack of reactive power represents my love affair. Love is an ethereal thing, often bringing nothing substantial and leaving only heartache. Just like reactive power not doing its proper job on the power grid, limiting generator output and increasing grid losses, but can it be absent? No, because the power grid also has so many inductive loads; even generators need to "date" during holidays. Therefore, a more complete explanation can be given for my life's current state:
Living in Quadrant One: Right now, I have a job and love;
Living in Quadrant II: Right now, I only have love, not a job;
Living in the third quadrant: At this moment, I have neither a job nor love;
Living in the four quadrants: I have a job but no love.
The motor operates normally in the first and third quadrants, but when the synchronous motor operates in the second and fourth quadrants, it is considered to be in an abnormal state. The fourth quadrant operating state (leading phase operation) reduces the excitation current and can operate for a long time. This is analogous to a person who can survive for a long time with a job but no love, but when operating in the second quadrant, the excitation current needs to be increased, and the person will have to exert a great deal of effort to maintain this phase of having only love and no work.
I currently live in Quadrant III. When I get a job, I'll jump into Quadrant IV; or when I find love, I'll jump into Quadrant II; and when I have both, I'll jump into Quadrant I—that might be my final destination. Regardless of how I jump from here into Quadrant I, one or two of Quadrants II or IV are inevitable parts of my journey, because I can't possibly find love at the same time as I find a job, or find a job at the same time as I find love.
