transformer nameplate provides information
necessary to complete connections. The voltages
should be measured when the transformer is energized
to ensure that the connections are correct before the
load is connected to the transformer.
Single-phase distribution transformers can be
connected to obtain three-phase secondary service
(fig. 4-20). There are four normal connections: the
delta-delta (D/D). the wye-wye (Y/Y). the delta-wye (
D/Y), and the wye-delta (Y/D). Figure 4-21 shows the
proper connections for three single-phase
distribution transformers connected to a three-phase
three-wire ungrounded delta primary-voltage system
to obtain three-phase three-wire delta secondary
service. The illustration is for a 2,400-volt primary
system and voltages would be connected the same.
Single-phase transformers with secondary windings
constructed for voltage of 240/480 should be used to
obtain 480-volt three-phase secondary service.
Figure 4-22 shows the proper connections for three
single-phase distribution transformers connected to a
three-phase four-wire grounded neutral wye primary-
voltage system to obtain 208Y/l20- or 480Y/277-volt
Figure 4-20.Cluster-mounted bank of transformers.
Figure 4-21.Three single-phase distribution transformers
Figure 4-22.Three single-phase distribution transformers
secondary service. Figure 4-23 shows the proper
connections for three single-phase distribution
transformers connected to a three-phase three-wire
ungrounded neutral delta primary-voltage system to
obtain 208Y/l20-or 480Y/277-volt secondary service.
Transformers must be constructed with the proper
windings for the primary-voltage system and the
desired secondary voltage. Properly manufactured
distribution transformers can be connected wye-delta
if it is desired to obtain three-wire three-phase
secondary voltages from a three-phase four-wire
ground neutral wye primary-voltage system. The