Dual-voltage and delta-wye switch
Transformers equipped for dual-voltage or delta-wye
(reconnectable winding) operations usually have an
externally-operable switch mounted on the faceplate in the
high-voltage terminal compartment. Units combining dual-
voltage and delta-wye may have two separate switches.
The transformer must be de-energized and grounded
before dual-voltage or delta-wye switches are operated.
Attempting to change dual-voltage or delta-wye switches
on an energized transformer may result in damage to the
equipment and severe personal injury.
Dual-voltage windings are either connected in series (for the
higher voltage) or in parallel (for the lower voltage). Dual-
voltage and delta-wye switches have two positions. Switch
positions are identified on the transformer nameplate and
marked by corresponding numerals on the switch mounting
plate.
When dual-voltage or delta-wye switches are set to connect
transformer windings in parallel, tap-changers must be
in the position shown on the transformer nameplate.
Tap-changers cannot be used to adjust voltage when
transformer windings are connected in parallel. Improper
tap-changer settings will cause circulating currents in the
windings, which will damage the windings and cause failure
of the transformer.
To change dual winding switch settings:
The standard type of dual-voltage or delta-wye switch will
have a hotstick-operable handle (see Figure 22).
This type of dual-voltage or delta-wye switch can be
switched to a new position as follows:
1. Verify that tank is grounded. De-energize transformer
from a remote upstream source. Ground all bushings
and terminals before operating dual-voltage or delta-
wye switch.
2. Back out lock screw to clear index plate.
3. Pull handle out to clear index plate and rotate handle
90°. Drop handle into new position.
4. Secure handle in its new position by tightening lock
screw through index plate until it bottoms.
5. Padlocking may be accomplished through hole
provided.
On some transformers, dual-voltage or delta-wye switches
have a lever handle (see Figure 23).
This type of dual-voltage or delta-wye switch can be
switched to a new position as follows:
1. Verify that tank is grounded. De-energize transformer
from a remote upstream source. Ground all bushings
and terminals before operating dual-voltage or delta-
wye switch.
2. Back out lock screw to clear index plate.
3. Rotate handle 90° to new position.
4. Secure handle in its new position by tightening lock
screw through index plate until it bottoms.
Figure 22. Dual-voltage/delta-wye switch (hotstick-
operable).
Figure 23. Dual-voltage/delta-wye switch (lever handle).
WARNING
Hazardous voltage. Can cause severe injury, death,
or damage to equipment. De-energize transformer
from a remote upstream source before operating non-
loadbreak tap-changers, dual-voltage switches, or
delta-wye switches.
CAUTION
Excessive current. Can cause damage to transformer
winding. When dual-voltage or delta-wye switches
are set to connect transformer windings in parallel,
tap-changers must be in the position shown on the
transformer nameplate.
14 Three-phase pad-mounted compartmental type installation and maintenance instructions MN202001EN August 2015
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