Connections Distribution transformer

phase-to-phase transformer in britain



primary line on right toward front , secondary lines in of single-phase transformer



three phase distribution transformer in syria

both pole-mount , pad-mount transformers convert high primary voltage of overhead or underground distribution lines lower secondary voltage of distribution wires inside building. primaries use three-phase system. main distribution lines have 3 wires, while smaller laterals (close customer) may include 1 or 2 phases, used serve customers single-phase power. if three-phase service desired, 1 must have three-phase supply. primaries provide power @ standard distribution voltages used in area; these range low 2300 volts 35,000 volts depending on local distribution practice , standards; 11,000 v (50 hz systems )and 13,800 v (60 hz) systems used many other voltages standard.

primary

the high voltage primary windings brought out bushings on top of case.

single phase transformers, used in usa system, attached overhead wires 2 different types of connections:

wye – on wye distribution circuit, wye or phase neutral transformer used. single phase wye transformer has 1 bushing on top, connected 1 of 3 primary phases. other end of primary winding connected transformer s case, connected neutral wire of wye system, , grounded. wye distribution system preferred because transformers present unbalanced loads on line cause currents in neutral wire , grounded. delta distribution system unbalanced loads can cause variations in voltages on 3 phase wires.
delta – on delta distribution circuit, delta or phase phase transformer used. single phase delta transformer has 2 bushings on top connected 2 of 3 primary wires, voltage across primary winding phase-to-phase voltage. disadvantage of delta transformer if 1 of 2 primary phases deenergized, remaining phase backfeed through transformer winding deenergized phase, hazard line workers.


transformers providing three-phase secondary power, used residential service in european system, have 3 primary windings , attached 3 primary phase wires. windings connected in wye configuration, ends of 3 windings connected , grounded.

the transformer connected primary distribution lines through protective fuses , disconnect switches. pole-mounted transformers takes form of fused cutout . electrical fault causes fuse melt, , device drops open give visual indication of trouble. can manually opened while line energized lineworkers using insulated hot sticks. in cases self protected transformers used, have circuit breaker built in, fused cutout isn t needed.

secondary

the low voltage secondary windings attached 3 or 4 terminals on transformer s side.

in usa , countries using system, secondary split-phase 120/240 volt system. 240 v secondary winding center-tapped , center neutral wire grounded, making 2 end conductors hot respect center tap. these 3 wires run down service drop electric meter , service panel inside building. connecting load between either hot wire , neutral gives 120 volts. connecting between both hot wires gives 240 volts.
in europe , countries using system, secondary 3 phase 400y/230 system. there 3 230 v secondary windings, each receiving power primary winding attached 1 of primary phases. 1 end of each secondary winding connected neutral wire, grounded. other end of 3 secondary windings, along neutral, brought down service drop service panel. 230 v loads connected between of 3 phase wires , neutral.

higher secondary voltages, such 480 volts, required commercial , industrial uses. industrial customers require three-phase power @ secondary voltages. provide this, three-phase transformers can used. in us, uses single phase transformers, 3 identical single phase transformers wired in transformer bank in either wye or delta connection, create 3 phase transformer.