Methods of enhancing capacity of transformer equipment and of power flow control using phase-shifting transformers and series impedances in parallel arrangements

A method of enhancing a capacity of transformer equipment for a polyphase AC network, the transformer equipment including at least one conventional transformer branches in parallel, each including opposite ends for connection with the AC network, and a transformer having a small leakage impedance so that current in the conventional transformer branches produces at the ends thereof a small phase angle .delta..sub.sr slightly varying depending on a load level of the AC network, the method comprising the step of:

• adding a constant current transformer branch in parallel with the conventional transformer branches, the constant current transformer branch including a phase-shifting transformer to produce at ends thereof a phase angle .psi. substantially greater in absolute value than the phase angle .delta..sub.sr, and reactive elements in series with the phase-shifting transformer, for increasing an impedance of the constant current transformer branch, the reactive elements being capable to sustain at ends thereof a phase angle equal to .delta..sub.sr -.psi..

An interconnecting apparatus for power flow control between two synchronous polyphase AC network busses, comprising:

• a first branch having opposite ends for connection respectively with the two AC network busses, the first branch including an adjustable phase-shifting transformer to produce at ends thereof an adjustable phase angle .psi..sub.1 ;
• and
• a second branch in parallel with the first branch, including reactive elements to transfer conjointly with the first branch, active power between the two AC network busses depending on the phase angle .psi..sub.1.