Are infinite power sources real? What features?

Infinite high-power power supply exists in theory, not in reality. It refers to a power supply that can maintain constant terminal voltage and frequency even if disturbances occur outside the power supply.

When studying the heuristic process of a power system, it is assumed that the capacity of some power sources is infinite, which is usually called an infinite power source to simplify analysis and calculation. Infinite high-power power supply is a power supply model in circuit theory. There are two types: 1. Ideal voltage source: It requires series resistance and zero resistance, which can provide high wireless current. 2. Ideal current source: the parallel conductance is zero, which can provide infinite voltage.

When the power supply capacity is infinite, the power variation caused by the short circuit (disturbance) of the external circuit is negligible compared with the power supply capacity, and the effective power and reactive power in the system are always balanced, so it is conceivable that the voltage and The frequency remains constant.

Obviously, infinite power is a relative concept, and real infinite power does not exist in a real power system. However, when multiple generators with limited capacity are operated in parallel or the power source is far away from the short-circuit point, the equivalent power source can be approximated as an infinite power source. In the former case, whether the power supply can be regarded as an infinite power supply is usually judged according to the relative magnitude of the internal impedance of the equivalent power supply and the total impedance of the short circuit. If the internal impedance of the power supply is less than 10% of the total impedance of the short circuit, the power supply can be regarded as an infinite power supply. In the latter case, the reactance is judged by the reference value of the reactance between the power supply and the short circuit point. If Taking the rated capacity of the power supply as the reference capacity, the reactance is greater than 3, then the power supply is an infinite power supply.

The processing method of infinite high-power power supply in engineering: if it is a constant voltage source, any large load current must be applied, and the output voltage of the power supply will not drop. A constant current source will not drop the current through any large load resistors.

Infinite high-power power supply has two characteristics: 1. The frequency and voltage of the power supply remain constant; 2. The internal resistance of the power supply is zero.

If a three-phase short circuit occurs in an infinite power supply system, what is the relationship between the initial subtransient current and the steady state short circuit current?

When a three-phase short circuit occurs suddenly, in addition to the short-circuit current and excitation current of the steady-state component of the stator remaining constant, the sudden change of the magnetic field induces aperiodic component currents in the corresponding circuit and generates these currents. The periodic component current of the induced magnetic field on the other side is attenuated by the circuit resistance energy consumption due to no energy support. The decay of the non-periodic component current is effective. The periodic component current induced by the magnetic flux generated by each aperiodic component current decays as the aperiodic component current decays, and drives the decay of the periodic component current.

After introducing the concept of infinite high-power power supply, when analyzing the temporary process of sudden three-phase short circuit in the network, the temporary process inside the power supply can be ignored and the analysis is simplified, which is suitable for construction. By deriving the short-circuit current calculation formula, the infinite power supply is calculated, rather than the actual equivalent power supply, and the short-circuit current is safely biased.