Power factor, reactive power, active power, apparent power

This is a mind map about power factor, reactive power, active power, and apparent power. The main contents include: 4. Power factor PF: (in an AC power supply environment) the ratio of active power to apparent power, 3 , reactive power Q: (pass In current power supply environment), 1. Apparent power S: (in AC power supply environment) the product of voltage effective value and current effective value, 2. Active power P: (in AC power supply environment), 0. Instantaneous power p: certain The power of a device at a certain moment.

Edited at 2024-11-15 15:37:06

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Power factor, reactive power, active power, apparent power

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Outline

Power factor, reactive power, active power, apparent power

0. Instantaneous power p: the power of a certain device at a certain moment

1. (When positive, the device absorbs electrical energy in the circuit; when negative, the device releases electrical energy into the circuit)

2. For inductance circuits (voltage u is higher than current i, leading π/2 phases) and capacitive circuits (voltage u is higher than current i, lagging π/2 phases), so in an AC power environment, the instantaneous power at the load end often Alternate positive and negative

Note: Under normal circumstances, for inductive and capacitive loads, the phase difference of current and voltage may also be other values due to the complex organization of the system.

1. Apparent power S: (in an AC power supply environment) the product of the effective value of voltage and the effective value of current,

1. From the perspective of the power supply: when the voltage and current of the power supply are maintained relatively stable, the maximum power that can be output to the outside world is

2. The current and voltage used here are the effective values of 0.707 times the peak current and voltage.

3. Unit of apparent power: 1w=1AV

2. Active power P: (in AC power supply environment)

3. Reactive power Q: (in AC power supply environment)

1. For resistive load, S=P, there is no reactive power at both the power supply and load ends.

2. For inductive or capacitive circuits: P<S, there is reactive power; within a cycle, the electric energy corresponding to the reactive power circulates back and forth between the power supply, capacitor, and inductor (one decreases and the other increases), but will not be consumed

3. In the case of an inductive load (motor), connect an appropriate capacitor in series: the reactive power can be trapped between the capacitor and the load as it circulates between the power supply and the load.

1. Benefit 1: The power supply side will no longer participate in the cycle of undertaking reactive power ---> avoid the problem of phase voltage instability on the power supply side.

2. Benefit 2: Limit the periodic circulation of reactive power to the local network between the capacitor and the motor to avoid any impact on the overall circuit system.

3. Benefit 3: Reactive power itself does not cause energy loss, but when it is circulated between different ends (capacitors, inductors, power supplies), it will be lost due to the resistance on the circuit line, so use series capacitors to reduce the reactive power. Power circulation routing is reduced to a small area, helping to reduce line losses

Another way of understanding: At this time, the series connected capacitor can be regarded as a reverse voltage source, which is used to balance and neutralize the rise and fall of the power supply side phase voltage caused by the motor.

4. Power factor PF: (in an AC power supply environment) the ratio of active power to apparent power,

1. The power factor value is between 0 and 1

1. Pure resistance circuit RF=1, the phase difference φ between u and i is 0, and there is no reactive power in the system

2. Pure inductance or capacitance circuit RF=0, u, i phase difference is 0.5π, there is only reactive power in the system; the system as a whole does not work externally.

Note 1: The higher the power factor, the higher the efficiency of the electrical equipment in converting electrical energy into useful work.

Note 2: Low power factor means that a large amount of electrical energy is transferred back and forth between the source and the load as reactive power.

1. This will lead to increased losses in transmission lines and reduced utilization of power supply equipment (such as generators, transformers, etc.)

2. The phase voltage fluctuation of power supply equipment (such as generators, transformers, etc.) becomes larger and the stability is insufficient.

2. Cases of power factor changes

1. Inductive load (three-phase motor): When idling, the power factor will be low (around 0.2-0.3); as the load increases, the power factor will rise, but generally it will not rise to 1

2. In a factory's power supply system, if a large number of inductive loads (such as various motors) run at the same time without taking reactive power compensation measures, the power factor of the entire system will be very low.

1. At this time, the redundant capacity of power grid voltage stabilization will be occupied - resulting in a waste of power grid facility resource allocation.

2. The transformers entering the factory need to be configured beyond specifications to cope with the pressure of phase voltage rise and fall instability caused by the low power factor of the system.

3. Power factor improvement methods

1. Connect the capacitor in parallel: Let the capacitor be called a voltage balancing device

For example: In the factory distribution box, according to the size of the load and the power factor, a capacitor bank of a certain capacity is reasonably installed, and the power factor is maintained at a high level by controlling the input and withdrawal of the capacitors.

Note: It is also possible to connect capacitors in series, but this method only protects the power supply side and cannot solve the problem of voltage rise and fall on the load side.

2. Use synchronous generators (power supply and grid end): the power supply has higher reactive power absorption and stabilization capabilities