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Quick way to identify WYE or DELTA
Applies to primary side of 3-transformer installation.
Three Hot wires will drop down from overhead power lines.
If each drop wire connects to only one transformer then that
connection is WYE
If each drop wire connects to 2 different transformers, then that
connection is DELTA
Resource:
3-phase transformers .pdf
Transformer .pdf files
Difference between delta and wye
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 Power plant dispatches 3-phase WYE
Generally, at a conventional (coal, gas) power plant, the generator
produces 30,000 volt power that travels through a step up transformer
that dispatches 200,000-500,000 volt power onto groups of 3 Hot wires
that travel to local substations, where voltage is lowered, and
eventually distributed to each home and business etc.
Resources:
Read more Image showing grid
Power plant
step-up transformers are WYE-WYE, and by design, other types of generators
(solar, wind, etc) will connect to the same transmission lines and dispatch same power to match existing grid.
Therefore the grid delivers 3-phase to end users in WYE. Delta is not
used for transmission or distribution.
Resources:
Difference between Delta and WYE
Generating 3-phase AC power
Each
residential and commercial service uses transformers
A transformer is required at each end user to convert high voltage
distribution power into lower volt power that can be safely controlled
using correctly-sized circuit breaker and wire that supplies power to
moderately priced switches, outlets, bulbs, and appliances. Higher
voltages would require heavier, larger, and more expensive wire,
breaker, switchgear, appliances etc.
Residential homes receive power from a single transformer, which is
connected in only one manner, and is not part of this page since it
is neither WYE nor Delta.
Commercial transformer banks with two or three transformers are covered
on this page. |
 Transformer basics
All end user transformers have two sides, the primary and secondary
-or- the primary
coil and secondary
coil
that are located inside the transformer can. While the 3-phase
distribution circuit arriving from power plant is WYE, the end user
transformer bank
consisting of two
or three transformers can be wired in Delta or WYE on
either
the primary side or secondary side. Some transformer designs contain
the 3 primary and 3 secondary coils inside a single can, instead of 3
cans.
Generally, the difference between Delta and WYE is not the transformers, but how the transformers are
wired.
While
transformers look similar during casual observation, they vary based on
the
KW or power rating required by end user ... plus internal number
of
taps, size of wire, number of turns of wire in primary and secondary
coils, cooling fins, diameter etc. For example, residential
transformers have a 30:1 turns ratio between primary and secondary, and
they are smaller than commercial transformers since they deliver
fewer amps. Read More
Commercial transformers are larger and deliver more power. They
can have taps for 30:1 ratio, but offer other taps so higher
voltages can be achieved.
Difference
between Delta and Wye transformer wiring
WYE
transformer coils are wired in parallel.
Applies to
transformer banks with 3 transformers:
Primary
side WYE: On the 3-transformer bank for WYE, you would
observe 3 Hot wires
drop down
from the 3 overhead distribution lines. Located on top of each
transformer are two bushings that connect to the primary coil inside each transformer.
Each Hot wire connects to 1 bushing on a different transformer. The
Neutral wire connects to the second bushing on all 3
transformers.
Secondary
WYE:
Each transformer has two or three taps located on
side of transformer can. These taps connect to the secondary coil inside each transformer. The commercial building with WYE
service
receives 3 Hot wires and a Neutral from the secondary side of the
transformer. 1 Hot
wire is connected to 1 tap on each transformer. The Neutral
is connected to the other tap on all 3 transformers.
Delta
transformer coils are wired in series, like stacking batteries
end to end in a flashlight.
Applies to
transformer banks with 3 transformers:
Primary
Delta: On
the 3-can transformer bank for Delta, you would observe 3 hot wires
drop down from the 3 overhead distribution lines. Each hot wire
connects to one bushing on 2 different transformers. The Neutral wire
is not connected to any of the bushings.
Secondary
side Delta: The commercial building receives 3 Hot wires.
Each hot wire is connected to a tap on two different transformers. The
Neutral might or might not be present. If present, the Neutral will
most commonly connect to the center tap on middle transformer.
Reasons
for choosing WYE or Delta
Delta can deliver same power with lower amps/ meaning
less heat.
For example, transformer banks are often wired Delta on the Power
company or Primary coils, and Wye on the customer or secondary
coils. According to one manufacturer's manual, the reason for Delta
primary is to save money since the
delta configuration means lower amps for the same power output, which
means the transformer manufacturer can
use smaller
wires on the primary side coils. It also reduces heat
and need for transformer cooling.
Using WYE on the secondary, or
customer side, supplies a Neutral connection, and gives more
voltage combinations and higher-amp service, with equal voltage on all
3
legs. WYE offers Line voltage, single-phase Hot-to-Hot or 3-phase
Hot-to-Hot-to-Hot, and offers Phase voltage measured Hot to Neutral
which is single-phase line voltage divided by square root 3. What is 3-phase 208 volt WYEContrast
Delta without a Neutral and the service supplies fewer voltage options:
single-phase Hot-to-Hot or 3-phase Hot-to-Hot-to-Hot. Delta with a center tap Neutral offers the widest range of voltages, but also can create additional load balance problems. What is High Leg DeltaUsing
small customer-installed Buck Boost or Industrial transformers can
supply additional voltages at any commercial location. Buck-boost transformers
WYE is frequently called Star, for example Star-Delta motor starter or
timer. Motors consume large amounts of amperage when
starting, so the Star or WYE configuration (more amps) is used for
starting, and
after the motor gets going, the circuit is switched to Delta (low amps)
for higher
efficiency. This basic strategy meets electrical regulations intended
to reduce voltage surges on the grid.
Resources:
Name part on electric poles
Pulling overhear power wire
Electricity from power plant to end user
How to wire 3-phase
3-phase timer
3-phase surge protectors/
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Delta primary/ WYE secondary
1 supply wire connects to TWO transformers
Each hot wire from the power pole connects to two transformers
Ground wire to each transformer NOT shown |
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WYE WYE
1 supply wire connects to ONE transformer
Each hot wire from the power pole connects to one transformer
Ground wire to each transformer shown |
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Delta Delta
Ground wire to each transformer NOT shown |
Larger image
Original image
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Delta WYE
Transformer wiring/ how to identify transformer wiring
Image shows Delta Primary and 4-wire WYE Secondary
Primary is Delta: How do we know? Each hot wire connects to two
transformers.... so they are wired in series
Secondary
is WYE. One wire connects to all three transformers, and to Neutral.
One wire from each transformer is Hot... so they are wired in parallel
System neutral connects to Neutral and ground
There are many different transformer configurations
This
is 'most common type of wiring' because Delta has lower amps/ meaning
less heat, so insulation on primary coil is less expensive.
Transformers can be wired different ways depending on the incoming
electric supply and end user need.
Two key factors for the grid are economic performance and reliability.
Reliability
is necessary because electricity must run clean without big-voltage
spikes and low-voltage brownouts. Otherwise motors and HVAC equipment
will have shorter lifespan.
Resources:
Transformer configurations
Transformer manuals
What is 3-phase electricity/ power plant to
end user
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Larger image
Larger image of grid from power plant |
Delta-WYE
Delta
primary/ WYE secondary ... because Delta carries less amperage, so
primary coils can use smaller wire ... saves cost of transformer
Normally, the Neutral service wire is located on top of other three How
wires
Primary wires are not insulated/ Secondary wires to service are
insulated.
Neutral on pole connects to Neutral going to service, and to ground
wire that bonds each transformer to the earth |
Larger image
Larger image of grid from power plant
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WYE-WYE
Normally, the Neutral service wire is located on top of other three Hot
wires
Primary wires are not insulated/ Secondary wires to service are
insulated.
Neutral
on pole connects to Neutral going to service, and to ground wire that
bonds each transformer to the earth, illustration does not clearly show
this. Installations might use bare solid copper, or use the stranded
aluminum per more recent practice.
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WYE-High Leg Delta
Identify High Leg transformer
bank: 3 wires come off one transformer and 1 wire (the high leg) comes
off another transformer
-Typical buildings, businesses and factories have 3
transformers that
provide three-phase service.
Some services that require less power have 3-phase from 2 transformers.
The 3-transformer 3-phase service is the source for High Leg Delta, but
not every
commercial installation has High Leg, unless specified for the service.
How it happens: If High Leg Delta service is specified by the
architect, builder, end user or electrical engineer, then the power
company
brings the correct transformers, and connects three-phase 4500-7200
volt distribution line to the three
transformers on the primary side in a WYE configuration as shown.
Primary side can also be wired in Delta.
To achieve high leg, the transformers on the secondary, or the
service side, are wired in Delta configuration. |
 Open Delta
2
transformer 3-phase open delta for smaller loads
Identify High Leg
open delta. There
are 2 transformer, one is larger than other, 3 wires come off large
transformer and 1 wire (the high leg) comes
off another transformer
Open Delta is a
lower-power 3-phase Delta option that uses 2 transformers instead of 3.
One of the transformers is larger than other.
On the primary side, you
would observe 2 hot wires drop down from the overhead distribution
lines. Each hot wire
connects to one bushing on 2 different transformers. The Neutral wire
is not connected to any of the bushings.
On the secondary side, the
commercial building receives 3 Hot wires and a Neutral. The smaller
transformer has 2 taps. The larger transformer has 3 taps: The Neutral
comes from center tap. One Hot wire comes from another taps. Another
hot wire comes from the third tap on the large transformer plus one tap
from smaller transformer. The third hot wire comes from the second tap
on small transformer. See image
High
Leg Delta (or open delta) can be achieved using 2 transformers that
pull 2 Hots and a Neutral off the distribution line, instead of 3 Hots
and Neutral.
Open Delta can also be identified by 3 drop wires
(two Hots and a Neutral) connecting to 1 transformer, and 1 drop (Hot
wire) connected to the smaller transformer. The secondary
side still supplies 4-wire high leg to the business, with 3
wires
coming off 1 transformer and 1 wire (the high leg) coming off the
smaller transformer.
This configuration is common for businesses
that consume less power, but still want 3-phase, and/or want the
selection of voltages found with high leg ... that is 240 volt, 120
volt, and 208 volt.
For example, this service provides power to a windshield repair
company, with an office and garage for dispatching trucks.
This configuration is also used in case of emergency to restore power
if one transformer goes bad in a 3-transformer bank.
If
the business needs more power, then a third transformer can be added at
any time ... and this would change the high leg open delta into
ordinary high leg delta.
A 3-transformer service is more efficient at delivering high power than
2-transformer service.
Two
transformers can also be configured to deliver Open WYE, and can supply
4 wires, with 2
sets of single-phase, but not 3 phase. This would generally be found in
a repair condition when 1 transformer in a 3-transformer bank fails. |
Larger image
Larger image of whole grid |
Delta-Delta
Neutral on pole connects to Neutral going to service, and to ground
wire that bonds each transformer to the earth. |
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Delta Primary / WYE secondary/ same as above
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Larger image
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WYE Primary / DELTA secondary/
distribution transformers at substation handle high
voltage
Shows 3 transformers, with 3 primary coils and 3 secondary coils
Primary WYE 69,000 volts ... because 1 69,000 volt wire connects to 1
transformer
Secondary Delta 4,400 volts ... because 1 4400 volt wire connects to 2
transformers
Generally 4,400 volts is lowest voltage for distribution without heat
loss from high amperage
The lower the voltage, the higher the amperage.
High amperage causes heat loss.
The transmission of electric power requires high voltage and low
amperage.
When amperage is high, the distribution distance is reduced.
However high voltage switchgear is expensive
It is impractical for end user to install high voltage appliances and
motors because of the expense
As a result, the end user must receive low volts with higher amperage
To meet demands on the grid, transformers are used to raise and lower
volts and amps in inverse proportion
When volts are reduced, amps are increased.
Resources:
What is 3-phase electricity/ power plant to
end user
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