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I
T
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Trying to understand how transformer banks are connected?
“Look up”...
WYE or DELTA? How can you tell? What are the similarities and differences?
Secondary? Primary? Open? Closed? What kind of language is this?
Taps? Single phase? Three phase?
What does it all mean?
Find out here, in our dynamic color-coordinated, realistic looking
DISTRIBUTION TRANSFORMER CONNECTIONS
TRAINING MANUAL and FIELD REFERENCE GUIDE
Peek underneath this cover and you will find:
Understanding Transformer Nameplates
Primary and Secondary coils and bushings
Transformer Polarity, Losses, kVa, Taps and
Turns Ratio
Primary Sources, Systems, and Lines
Three phase banks: Where & When?
Quick Reference Flow Charts
FAC Tool
Three Phase Banks:
• Primary and Secondary Connections
• DELTA and WYE
• Three Wire and Four Wire
• Open
• Closed
• Series and Parallel Connected Coils
KEEPERS
OF THE
O
N
O
R
I
TT
INTEGRITY
Closed
Open
WYE
I
T
T
Closed
Open
DELTA
Harris Institute of Technical Training
CRAFT
P
H
Distribution Transformer Connections
Training Manual and
Field Reference Guide
A
S
S
I
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It’s HIP to be a Craft Keeper
Always HONOR your craft and the craftsmen who
have gone before you.
Personal INTEGRITY is a sacred value.
Have a PASSION for all you do & share it with others.
Experience a new dynamic in visual learning with our
color-coordinated transformer connection diagrams!
Sample Pages
Transformer Taps - Thumbullets
Distribution substation voltage regulation is generally set to provide the correct primary voltage to transformer primary coils
halfway down the primary line. Correct primary voltage halfway down the line = correct secondary voltage halfway down the
line.
Transformers with taps are installed near a substation and far from a substation.
There are two types of transformers taps: “Split Taps” or “Straight Taps”.
Closed
A “Split Tap” transformer has four (4), two and a half percent (2½%) taps with two (2) taps on the plus (+) side to lower
secondary voltage and two (2) taps on the minus (–) side to raise the secondary voltage to a customer. With a “Split Tap”
transformer there are five(5) primary voltages that can be connected to the primary coil that will deliver the correct secondary
voltage.
The Closed DELTA Three Phase, Three Wire Transformer Bank Primary Connection:
n
•
•
•
•
1
Connects three single phase transformers (always).
Transformer’s are connected in a Dislike configuration (always).
Transformer’s primary coil voltage ratings match the phase to phase voltage of the primary line
e (always).
Is connected to a DELTA Primary Line.
- Alternate connection (could be) to the phase to phase voltage of a WYE Primary Line.
A “Straight Tap” transformer has 4 minus (–) side taps and each of these taps will subtract 2½% of the windings from the primary
coil to raise secondary voltage. With a “Straight Tap” transformer there are five(5) primary voltages that can be connected to the
primary coil that will deliver the correct secondary voltage.
Adding and subtracting coils in the primary winding changes the nominal turns ratio of a transformer.
With a higher than nominal primary voltage, adding windings increases the turns ratio which decreases the secondary
daar
arryy voltage.
ary
With a lower than nominal primary voltage, subtracting windings decreases the turns ratio which increases the secondary
con
nda voltage.
Ø to Ø Voltage Ø to Ø Vo
Voltage
ol
ol
Ø to Ø Voltage
H1
Ø to Ø Voltage
H2
Ø to Ø Voltage
H1
1
H2
H1
Ø to Ø Voltage
H2
3
2
• Can be matched with any of these six Closed Bank secondary connections.
(see flow chart(s) for additional information)
Closed WYE or Clo
Closed DELTA Primary Connection
H2
H1
H2
H1
Vector Representation and Phase Relationships
of the Secondary Coils in Banks 5 and 6
H2
240
X1
3
1
A
C
B
A
D
C
B
D
2
X3
X 3 X 2 X 1
X1
240 Volts
X3
C
B
D
X 3 X 2 X 1
X1
120 120
Volts Volts
240 Volts
120 Volts
120 Volts
208 Volts
A
C
B
D
X 3 X 2 X 1
A
C
B
D
X 3 X 2 X 1
P
O
L
E
G
R
O
U
N
D
2
4 Wire
120/240V
X3
X1
X3
240 Volts
il
Am
ps
90
240 Volt - 1Ø
Air Conditioner
X1
When the secondary coils are
energized by a Closed WYE or Closed
DELTA primary source they become
the Closed DELTA triangle shape. With
the secondary voltage phase
relationships established. (The phase
conductors and neutral are also shown
along with three black connection dots
representing the black banking
conductors.)
Each coil is a side of the DELTA
triangle shape and is held in its
position by the energized primary
source. The three phase conductors
attached to the corners
ers of the
condary
DELTA shape are the sec
secondary
conductors used to serve
erve
rvve
rv
e the
h
he
customer. The center tap
ta
ap conductor
ap
gives access to the phase
hasse tto neutral
voltages.
240 V
Volts
240 Volts
240 Volts
IB
120 Volt
Light bulb
X1
3
Each transformer in this bank is numbered from
1 to 3. Below each of the transformers is a coil
whose color coding matches the secondary coil
above it. With each of the lower coils is a side of
the triangle shape used to represent the four
wire Closed DELTA secondary connection. The
combination of the individual coil and side of the
triangle shape are also numbered to match the
transformer secondary coil they represent.
B Co
s
Volt
240
X3
X1
s
n
Volt
2
X3
A
X1
1
Closed
208 Volts
240
X1
X3
Connected Loads on Banks 5 and 6
X3
120 120
Volts Volts
240 Volts
240 Volts
2
2
X3
240 Volts
s
X 3 X 2 X 1
X1
D
Volt
B
X3
C
240
s
3
A
X 3 X 2 X 1
X1
Volt
240
2
X3
H1
Volt
s
5
4 Wire
120/208V
and
277/480V
240
2
Closed
X1
1
4 Wire
120/240V
and
240/480V
X3
Closed
Volt
s
Closed 3 Wire
240V
and
480V
- 3Ø
3Ø
Pump
mp
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