8.5 : Y-Δ回路

In electrical power grids, balanced Y-to-Delta circuits feature Y-connected voltage sources and delta-connected loads, typically without a neutral line.

Assuming a positive phase sequence, the phase voltages are expressed to estimate the line voltages.

These line voltages equal the voltages across the load impedances and facilitate the calculation of phase currents, which have similar magnitudes and are out of phase by 120 degrees.

Applying Kirchhoff's Current Law at the nodes of the delta-connected loads reveals the relationship between the line and phase currents.

The magnitudes of the calculated line currents are the square root of three times the magnitudes of the corresponding phase currents, and the line currents lag the phase currents by 30 degrees.

Another way of analyzing the Y-to-Delta system is to convert the delta-connected loads to their corresponding Y-configuration.

The resulting balanced Y-to-Y system can then be analyzed by considering its single-phase equivalent circuit and determining the line currents.

The magnitudes and phase angles of the phase currents are calculated from their corresponding line currents using appropriate Delta-to-Y transformations.