Lesson 11: Transformer Name Plate Data and Connections
Lesson 11_et332b.pptx
3/2/2018
ET 332b Ac Motors, Generators and Power Systems
LESSON 11: TRANSFORMER NAME PLATE DATA AND CONNECTIONS
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Lesson 11_et332b.pptx
LEARNING OBJECTIVES
After this presentation you will be able to: Identify transformer polarity using dot and conventional labeling. Explain and interpret information found on transformer name
plates. Compare and contrast the performance of three phase transformer
connections. Indentify the schematic symbols of potential and current
transformer. List characteristics on these devices and explain how they relate to performance.
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3/2/2018
Lesson 11_et332b.pptx
TRANSFORMER MARKINGS AND POLARITY
Dot Notation - Terminals marked with a dot are considered instantaneously positive
A I1 +
EAB
B
-
+
I2
C
0 degree
shift
-
D
N1
N2
Above Terminals A and C are positive at the same time
Phasor Diagram
EAB
ECD
0 degrees
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Lesson 11_et332b.pptx
TRANSFORMER MARKINGS AND POLARITY
A + +
EAB
B
- I2
C
180 degree
+
shift
+ D
Above Terminals A and D are positive at the same time
Phasor Diagram
EAB
ECD
180 degrees
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3/2/2018
Lesson 11_et332b.pptx
TRANSFORMER MARKINGS AND POLARITY
Conventional Labeling H = high voltage side X = low voltage side
H1
+
+
X1
H2
-
0 phase shift X2
-
Terminal H1 more positive than H2. On secondary side X1 more positive than X2
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Lesson 11_et332b.pptx
TRANSFORMER MARKINGS AND POLARITY
Conventional Labeling H = high voltage side X = low voltage side
H1
+
H2
-
-
X2
180 phase shift
X1
+
+
Note: Polarity of secondary is reversed creating 180 degree phase shift across transformer
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Lesson 11_et332b.pptx
TRANSFORMER NAMEPLATE DATA
Voltage ratings
high side and low side values (no-load values)
Additional Voltage Markings
Dash (-) = Indicates voltages from different windings
Slant (/) = voltages from same winding Cross(x) = voltages obtained by series
or parallel connection of two part windings Wye (Y) = wye-connected windings
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Lesson 11_et332b.pptx
TRANSFORMER VOLTAGE RATINGS
Single Phase Examples
240/120 240x120 240-120
Three Phase Example
240 V winding with a center tap
Two part winding that can be connected in series for 240 V and parallel for 120 V
A 240 V and separate 120 V winding
12470-480Y-277 V
Two winding transformer. Wye connected secondary with 277V and 480 V available
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Lesson 11_et332b.pptx
OTHER NAME PLATE DATA
Frequency kVA
Rated frequency of transformer
Rated Apparent power of transformer
Apparent power rating determined by construction and cooling- oil cooled. Oil also provides insulation
Power ratings AO rating - natural convection air and
oil. FA rating - natural convection of oil and
forced air FOA rating - forced air and oil circulation
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Lesson 11_et332b.pptx
TRANSFORMER POWER RATINGS
Typical ratings 30/40/50 MVA AO/FA/FOA
Dry Type Insulated transformers (no oil) Typical at voltages of 15 kV and below
Classes AA - dry type, self-cooled, natural convection of air AFA - Dry type, forced-air cooling AA/FA Dry type self-cooled/forced air cooled
Dual rating that requires fans
Forced oil by circulating
pumps
Forced air by radiators and
fans
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