In three-phase power analysis it is more common to refer to the supply and load rather than the sending end and the receiving end. The supply end is usually the sending end, but is possible for the load end to return power to the source. If someone has solar panels on their house or some other renewable energy system, they could send power to the source if they use less power than their renewable energy system supplies. In that was people often refer to their electric meter "running backwards" or their power use being negative. The source is still the considered the to be the normal "sending end," but some customers are exceptions, so their power flow is "negative" or the opposite direction of the standard.
Unless other wise stated, the voltage of a three phase system is the voltage between any two phases. Equal or balanced voltage among the phases is assumed unless otherwise specified. For a three phase, 4-wire, wye source, both the line-to-line and the line-to-neutral voltage should be specified, such as 380/220 V. If only one voltage is specified it is normally the line-to-line voltage. Just the line-to-neutral voltage would be specified only if referring a to a single-phase circuit.
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