Transformer Connections - Refresher
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Overview of MERALCO System 13.2/7.62kV
69kV 13.8kV
13.8kV
230kV
Generation
13.2/7.62kV
115kV
4.16/2.4kV
13.8kV
4.8kV
Transmission
34.5/20kV
6.24/3.6kV 13.2/7.62kV
Sub-Transmission
13.8kV Distribution
OUTLINE Transformer Nomenclature (Nameplate, Company Number)
Workshop Transformer Taps
Transformer Polarity Transformer Connections (Standards, Common Errors & Troubles)
Workshop Connection for L-G Secondary System Reminders on DT Installations
Typical MERALCO DT Primary H1 Bushing
Primary H2 Bushing
(At the Back)
Secondary
KVA Rating
Company Number
(X1, X3, X2, X4)
Bushings
Nameplate
DT Nameplate Sample KVA Rating
Secondary Voltage Rating (Dual Voltage)
Voltage Rating per tap position
Polarity (Subtractive)
Primary Voltage Rating
Schematic Diagrams
DT Nameplate Sample Primary Voltage Rating
Secondary Voltage Rating
Voltage Rating per tap position
KVA Rating
Polarity (Additive)
Schematic Diagrams
DT Nameplate Sample Company Number KVA Rating Secondary Voltage Rating
Primary Voltage Rating Voltage Rating per tap position
Schematic Diagrams
DT Nameplate Sample KVA Rating
Primary Voltage Rating
Secondary Voltage Rating
Polarity (Additive)
Symbols Used in Transformer Voltage Ratings NAME
Dash
Slant or Slash
Cross
SYMBOL
APPLICATION
-
To separate the voltage rating or ratings of separate windings.
/
To separate voltage to be applied or to be obtained from the same winding.
X
To designate separate voltages which can be obtained by reconnecting the coils of a winding in series or multiple combinations
EXAMPLES
34500 Grd.Y / 19920 V 240/120 V
-
13200 GRDY / 7620 V 120 / 240 V
34500GRDY / 19920 V 120/240 X 139/277 V
Primary Voltage Ratings of DTs Used by MERALCO VOLTAGE RATING 34500Grd.Y/19920
DESCRIPTION Single-bushing DTs for line-to-ground connection on effectively grounded systems with line-to-line voltages of 34.5kV
3600/6240Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 6.24kV
2400/4160Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 4.16kV
4800/8300Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltage of 8.3kV or for line-to-line connection on system with line-to-line voltage of 4.8kV.
Primary Voltage Ratings of DTs Used by MERALCO VOLTAGE RATING
13200
13200Grd.Y/7620
7620/13200Y
DESCRIPTION For line-to-line connection on system of 13.2kV line-to-line. Single-bushing DTs for line-to-ground connection on effectively grounded systems with line-to-line voltages of 13.2kV. Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 13.2kV
•Without slash (/) – for line-to-line connection •With slash (/) – for line-to-ground connection
DT Company Number Coding System of MERALCO I. PREFIXES (Primary Winding Rating) OLD SYSTEM
W Z Z X Y MY
NEW SYSTEM
W T Z X Y M
KV RATING
20 13.2, 13.8 7.62 3.6 4.8 2.4
DT Company Number Coding System of MERALCO II. SUFFIXES (Secondary Winding Rating) CODE LETTER
VOLTAGE RATING
A
120/240 or 240/120
B
139/277
C
240/480
D (or Y)
139/277x120/240
E
240/139*
F
480/277*
G
240
N
125/216*
* Threephase DTs
Difference Between 120/240- & 240/120-Volt Ratings 120/240
240/120
2-section secondary winding which can be connected in parallel for output voltage 120V, in series for output voltage 240V, or in series for 3-wire service for 120/240V output voltage. (Memory Aid: 120-volt winding times 2) Mid-tapped secondary suitable for 2-wire service at voltage 240V, or for 3-wire service. Cannot be connected for 2-wire service at voltage 120V . (Memory Aid: 240-volt winding divided by 2)
(Available in 4or 3-bushing transformers)
DT Company Number Sample
B-
139/277 V Secondary
W-
19.92 kV Primary
DT Company Number Sample
A-
120/240 V Secondary
M-
2.4 kV Primary
DT Company Number Sample
D-
Z-
7.62 kV Primary
Dual Voltage 120/240 X 139/277 V Secondary
External Tap-Changers Operation
1. De-energize the DT 2. Loosen lock screw 3. Rotate switch to desired position 4. Tighten lock screw 5. Energize the DT
Lock Screw
Other Types of External Tap-Changers
Internal View of a DT With an External Tap-Changer TapChanger
Internal Tap-Changers Rotary Tap-Changers
Schematic Diagram of a Dual Voltage Transformer H2
H1
DUAL VOLTAGE TAP (SET AT INNER TAP)
5 4 3 2 1
PRIMARY WINDING
139V
139V X1
X3
X2
139/277 V
X4
TAP CHANGER
Schematic Diagram of a Dual Voltage Transformer H2
H1
5 4 3 2 1
DUAL VOLTAGE TAP (SET AT OUTER TAP)
PRIMARY WINDING
120V X1
X3
120V X2
120/240 V
X4
TAP CHANGER
Samples of DTs With Dual Voltage Tap Internal Tap changer
Dual Voltage Taps Always refer to nameplate for actual ratings.
Samples of DTs With Dual Voltage Tap Tap changer
Dual Voltage Taps
Changing the DUAL VOLTAGE TAP is done by transferring the connection of the primary lead
Samples of DTs With Dual Voltage Tap Changing the DUAL VOLTAGE TAP is done by transferring the connection of the outer end of the curved copper strip
Dual Voltage Taps
Transformer Polarity Convention 200 kVA or smaller, and 8.66 kV or below
Single-phase transformers that do not meet either one or both criteria
Additive
Subtractive
Terminal Markings of DTs I. ADDITIVE POLARITY H1
X3
H2
X2
X1
H1
X3
H2
X2
X1
H1
X4
H2
X1 X2
X3
ADDITIVE - X1 IS DIAGONALLY ACROSS FROM H1
Terminal Markings of DTs II. SUBTRACTIVE POLARITY H1
X1
H2
X2
X3
H1
X1
H2
X2
X3
H1
X1
H2
X4 X3
X2
SUBTRACTIVE - X1 IS ON SAME SIDE AS H1
Polarity of DTs EXAMPLES: 1) 100 kVA, 3.6 kV-240/120 V
Additive
2) 250 kVA, 7.62 kV-240/120 V
Subtractive
3) 25 kVA, 19.92 kV-240/120 V
Subtractive
4) 167 kVA, 13.8 kV-240/120 V
Subtractive
All 20kV, 13.8kV or 13.2kV DTs are Subtractive
POLARITY TESTING OF A DT APPLY VOLTAGE HERE (240V or 120VAC ONLY) HV SIDE
Temporary Shorting Wire (Jumper)
Vm
Voltmeter
LV SIDE
If Vm reads more than the applied voltage - Additive If Vm reads less than the applied voltage - Subtractive
Polarity of DTs X1
X3
X2
X4
Subtractive Polarity:
333 kVA, 3600/6240Y V 120/240 V
Polarity of DTs
X1
X3
X2
X4 Subtractive Polarity: 250 kVA, 34500Grd.Y/ 19920 V 139/277 V
Polarity of DTs X3 X2 X1
Additive Polarity: 25 kVA, 2400/4160Y V 120/240 V
DT Connections Used By MERALCO
System
1-Phase 1-Phase Open-Wye, Ungrd. Wye- Grd. Wye- Open-DeltaL-to-N L-to-L Open-Delta Delta Grd. Wye Open-Delta
34.5 / 20 kV Wye
Yes
13.2 / 7.62 kV Wye
Yes
8.3 / 4.8 kV Wye
Yes Yes
DeltaDelta
Yes
Yes
Yes
Yes
Yes
Yes
6.24 / 3.6 kV Wye
Yes
Yes
Yes
4.16 / 2.4 kV Wye
Yes
Yes
Yes
Yes
Yes
Yes
13.8 kV Delta
Yes
Yes
Yes
4.8 kV Delta
Yes
Yes
Yes
Note: The voltage on he leftmost column refer to the system voltage of the circuit & not on the voltage rating of the DT.
Single-phase Connection Line-to-Neutral Primary (Subtractive Polarity)
A
N
H1
H2
X1
X3
X2
n a b
VOLTAGE VECTORS B
SECONDARY VOLTAGES b
n N A
a
Vab = 240V Vbn = 120V
C
PRIMARY
SECONDARY
Van = 120V
Single-phase Connection Line-to-Neutral Primary (Additive Polarity)
A
N
H1
H2
X3
X1
X2
n a b
VOLTAGE VECTORS B
SECONDARY VOLTAGES a
n N A
b
Vab = 240V Vbn = 120V
C
PRIMARY
SECONDARY
Van = 120V
Single-phase Connection Line-to-Line Primary (Subtractive Polarity)
A
B
H1
H2
X3
X1 X2
n a b
VOLTAGE VECTORS B b
A
n
SECONDARY VOLTAGES
a
C PRIMARY
SECONDARY
Vab = 240V Vbn = 120V Van = 120V
Single-phase Connection Line-to-Line Primary (Additive Polarity)
A
B
H1
H2
X1
X3 X2
n a b
VOLTAGE VECTORS B a
A
n
SECONDARY VOLTAGES
b
C PRIMARY
SECONDARY
Vab = 240V Vbn = 120V Van = 120V
Open-Wye, Open-Delta Connection 2 Subtractive Polarity DTs
A B C N
H2
H1
X3
X1
H2
X1
X3
X2
n a b
H1
X2
c
VOLTAGE VECTORS B n
A
C
PRIMARY
SECONDARY VOLTAGES b
a
N
c
SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard
Voltage
Open-Wye, Open-Delta Connection 2 Additive Polarity DTs A B C N
H2
H1
X1
X3
H2
X3
X1
X2
n a b
H1
X2
c
VOLTAGE VECTORS
SECONDARY VOLTAGES
b
B n
N A
C
PRIMARY
c
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
a
SECONDARY
Common Error in Open-Wye, Open-Delta Connections ERROR 1: X1 of Main DT was interlocked with X1 of Wing DT A B C N
H1
H2
H1
H2
X3
X1
X3
X1
n a b c
VOLTAGE VECTORS c
B
b n
N A
C
PRIMARY
X2
X2
SECONDARY VOLTAGES Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
a
SECONDARY
Vca = 416V Vcn = 317V
Common Error in Open-Wye, Open-Delta Connections ERROR 2: H2 instead of H1 of one DT was connected to the primary
A B C N
H1
H2
H1
H2
X3
X1
X3
X1
X2
n a b c
VOLTAGE VECTORS B
A
C
PRIMARY
SECONDARY VOLTAGES b
N
X2
n a
Vab = 240 V Van = 120V Vbc = 416 V Vbn = 120V
c
SECONDARY
Vca = 240 V Vcn = 317V
Common Trouble in Open-Wye, Open-Delta Connections TROUBLE: H1 of both DTs energized from the same primary
To Source
Detached jumper
A B C N
H1
H2
H1
H2
X3
X1
X3
X1
X2
n a b c
VOLTAGE VECTORS b
B
n
SECONDARY VOLTAGES Vab = 240 V Van = 120V Vbc = 480 V Vbn = 120V
C
PRIMARY
a
N A
X2
c
SECONDARY
Vca = 240 V Vcn = 360V
Wye-Delta Connection 3 Additive Polarity DTs A B C N
Floating Neutral
H1
X3
H2
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
n
a b
X2
c
VOLTAGE VECTORS b B n
N A
C PRIMARY
X2
SECONDARY VOLTAGES
c
a SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard Voltage
Common Error in Wye-Delta Connections (Ex. 1 Subtractive & 2 additive DTs) ERROR: X1 of Wing 1 was connected to X1 of Main while X3 of Main was connected to X3 of Wing 2 A B C Floating Neutral Wing 1
H1
X3
C’
C
n a b
H2
H1
X1
X1
X2
H2
H1
X3 X2
c
C PRIMARY
SECONDARY VOLTAGES Vab = 240V
Vc’a = 416V
Van = 120V
Vbc = 416V
Vbc’ = 240V
Vbn = 120V
Vca = 240V
Vcc’ = 480V Vcn/Vc’n = 317V
n
N A
X2
a
B
H2
X1
X3
VOLTAGE VECTORS
Wing 2
c
Main
b
c’
SECONDARY
Corrected Error in Wye-Delta Connection (Subtractive & 2 additive DTs) CORRECTION: H2 instead H1 of Main DT was tapped to the phase conductor. This results in the imaginary swapping of the X1 & X3 leads.
A B C
Floating Neutral
Wing 1
H1
H2
H1 H2
X1
X1 X3
X3
X2
n a b
X2
VOLTAGE VECTORS b B n
A
C PRIMARY
a SECONDARY
H1
X3 X1
X3
Wing 2
H2
X1 X2
N
H2 H1
c
Main
SECONDARY VOLTAGES
c
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard Voltage
Wye-Wye Connection for 240-volt Service 3 Subtractive Polarity DTs
A B C N
H1
H2
X1
X4
n
X3
X2
139V
X1
a b
H1
X3
c
A PRIMARY
a
H1
H2
X4
X1
X4
X3
X2
SECONDARY VOLTAGES
n C
X2
H2
VOLTAGE VECTORS b B N
139V
c
SECONDARY
Vab = 240V
Van = 139V
Vbc = 240V
Vbn = 139V
Vca = 240V
Vcn = 139V
Wye-Wye Connection for 480-volt Service 3 Subtractive Polarity DTs
A B C N
H1
H2
X1
X4 X3
H1
139V
X1
X2
X3
139V
H2
H1
H2
X4
X1
X4 X3
X2
n
a b
c
A PRIMARY
SECONDARY VOLTAGES
n C
a
VOLTAGE VECTORS b B N
X2
c
SECONDARY
Vab = 480V
Van = 277V
Vbc = 480V
Vbn = 277V
Vca = 480V
Vcn = 277V
Wye-Wye Connection for 240-volt Service 3 Additive Polarity DTs
A B C N
H1
H2
X4
X1
X2
X3
n a b
H1
H2
H1
H2
X4
X1
X4
X1
X2
VOLTAGE VECTORS b B
PRIMARY
X2
a
X3
SECONDARY VOLTAGES
n
N C
X3
c
A
c
SECONDARY
Vab = 240V
Van = 139V
Vbc = 240V
Vbn = 139V
Vca = 240V
Vcn = 139V
Wye-Wye Connection for 480-volt Service 3 Additive Polarity DTs
A B C N
H1
H2
X4
X1 X2
n a b
H1
H2
H1
H2
X4
X1
X4
X1
X3
X2
X2
X3
X3
c
VOLTAGE VECTORS b B
A
C PRIMARY
SECONDARY VOLTAGES
n
N a
c
SECONDARY
Vab = 480V
Van = 277V
Vbc = 480V
Vbn = 277V
Vca = 480V
Vcn = 277V
Open-Delta, Open-Delta Connection 2 Subtractive Polarity DTs A B C
H1
X1
H2
H1
H2
X3
X1
X3
X2
n a b
c
VOLTAGE VECTORS B A
n
C PRIMARY
SECONDARY VOLTAGES
b 0º angular displacement
a
X2
c SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Open-Delta, Open-Delta Connection 2 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
c
VOLTAGE VECTORS c B A
180º angular displacement
a PRIMARY
SECONDARY VOLTAGES
n
C
X2
b SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Open-Delta, Open-Delta Connection of 2 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
X2
c
VOLTAGE VECTORS B A
n
b 0º angular displacement
a C PRIMARY
SECONDARY VOLTAGES
c SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Common Error in Open-Delta, Open-Delta Connections ERROR: Secondary Interlock was Connected X3 to X3 A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
c
VOLTAGE VECTORS c B A
b C PRIMARY
a
X2
SECONDARY VOLTAGES Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
n
SECONDARY
Vca = 416V Vcn = 317V
Delta-Delta Connection 3 Subtractive Polarity DTs A B C
H1
X1
n
a b
X2
H2
H1
H2
H1
H2
X3
X1
X3
X1
X3
X2
c
n
SECONDARY VOLTAGES b
a
A C PRIMARY
X2
VOLTAGE VECTORS B
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
c SECONDARY
Delta-Delta Connection 3 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
n
a b
X2
c
VOLTAGE VECTORS b B n
A C PRIMARY
X2
SECONDARY VOLTAGES
c
a SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
SINGLE-PHASE 240V, LINE-TO-GROUND SECONDARY SYSTEM
A B C N
H1
H2
X3
X1 X2
a b
INSULATED PHASE CONDUCTOR
BARE GROUNDED PHASE CONDUCTOR
OPEN-WYE, OPEN-DELTA CONNECTION FOR 3-PHASE, CORNER-GROUNDED DELTA SECONDARY A B C N
H2
H1
X1
X3
X2
a b
c
H1
H2
X3
X1
X2
INSULATED PHASE CONDUCTORS
BARE GROUNDED PHASE CONDUCTOR b
B
SECONDARY VOLTAGES N A
c a C
PRIMARY VECTORS
SECONDARY VECTORS
Vab = 240V Vbc = 240V Vca = 240V
WYE-DELTA CONNECTION FOR 3-PHASE, CORNER-GROUNDED DELTA SECONDARY
A B C N
H1
X3
c
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
a b
H2
X2
INSULATED PHASE CONDUCTORS
X2
BARE GROUNDED PHASE CONDUCTOR
b
B
SECONDARY VOLTAGES
c
N A
C
PRIMARY VECTORS
a SECONDARY VECTORS
Vab = 240V Vbc = 240V Vca = 240V
Reminders on DT Installation A. New Installation Inspect DT for any physical defects Check specifications of withdrawn DT Install as per safety & construction standards Check for compliance to W.O. or F.O.
Before energizing: Check for shorted/grounded service entrance conductors Ensure customer main switch (CMS) is open & check for possible voltage presence Energize DT Check voltage at CMS
Accomplish Transformer Report (TR)
Reminders on DT Installation B. Replacement Inspect DT for any physical defects Check specifications of withdrawn DT Eliminate all possible sources of power Ground or short-circuit the secondary line or leads Establish secondary phase markings/sketch existing connection Install as per safety & construction standards Before re-energizing: Remove all temporary grounding wires Check DT connection against sketch/drawing/phase markings
Release pressure by operating the pressure relief device Energize DT Check voltage & phase sequence at CMS (verify with customer) Accomplish Transformer Report (TR)
A Transformer Rated 13200 V
A Transformer Rated 13200 Grd.Y/7620 V
A Transformer Rated 7620/13200Y V
Available DT Banks at the Training Grounds 1) 3 – 15 kVA, 3600/6240Y – 120/240 Volts 2) 2 – 25 kVA, 34500Grd.Y/19920 – 240/120 Volts 3) 3 – 100 kVA, 34500Grd.Y/19920 – 120/240 x 139/277 Volts
4) 2 – 15 kVA, 34500Grd.Y/19920 – 240/120 Volts 5) 3- 10 kVA, 7620/13200Y – 120/240 Volts 6) 3- 15 kVA, 13200 – 120/240 Volts 7) 1-15 kVA, 13200Grd.Y/7620 - 240/120 Volts (Sub.) 1-10 kVA, 13200Grd.Y/7620 – 120/240 Volts (Add.)
69kV 13.8kV
13.8kV
230kV
Generation
13.2/7.62kV
115kV
4.16/2.4kV
13.8kV
4.8kV
Transmission
34.5/20kV
6.24/3.6kV 13.2/7.62kV
Sub-Transmission
13.8kV Distribution
OUTLINE Transformer Nomenclature (Nameplate, Company Number)
Workshop Transformer Taps
Transformer Polarity Transformer Connections (Standards, Common Errors & Troubles)
Workshop Connection for L-G Secondary System Reminders on DT Installations
Typical MERALCO DT Primary H1 Bushing
Primary H2 Bushing
(At the Back)
Secondary
KVA Rating
Company Number
(X1, X3, X2, X4)
Bushings
Nameplate
DT Nameplate Sample KVA Rating
Secondary Voltage Rating (Dual Voltage)
Voltage Rating per tap position
Polarity (Subtractive)
Primary Voltage Rating
Schematic Diagrams
DT Nameplate Sample Primary Voltage Rating
Secondary Voltage Rating
Voltage Rating per tap position
KVA Rating
Polarity (Additive)
Schematic Diagrams
DT Nameplate Sample Company Number KVA Rating Secondary Voltage Rating
Primary Voltage Rating Voltage Rating per tap position
Schematic Diagrams
DT Nameplate Sample KVA Rating
Primary Voltage Rating
Secondary Voltage Rating
Polarity (Additive)
Symbols Used in Transformer Voltage Ratings NAME
Dash
Slant or Slash
Cross
SYMBOL
APPLICATION
-
To separate the voltage rating or ratings of separate windings.
/
To separate voltage to be applied or to be obtained from the same winding.
X
To designate separate voltages which can be obtained by reconnecting the coils of a winding in series or multiple combinations
EXAMPLES
34500 Grd.Y / 19920 V 240/120 V
-
13200 GRDY / 7620 V 120 / 240 V
34500GRDY / 19920 V 120/240 X 139/277 V
Primary Voltage Ratings of DTs Used by MERALCO VOLTAGE RATING 34500Grd.Y/19920
DESCRIPTION Single-bushing DTs for line-to-ground connection on effectively grounded systems with line-to-line voltages of 34.5kV
3600/6240Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 6.24kV
2400/4160Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 4.16kV
4800/8300Y
Two-bushing DTs for line-to-ground connection on system with line-to-line voltage of 8.3kV or for line-to-line connection on system with line-to-line voltage of 4.8kV.
Primary Voltage Ratings of DTs Used by MERALCO VOLTAGE RATING
13200
13200Grd.Y/7620
7620/13200Y
DESCRIPTION For line-to-line connection on system of 13.2kV line-to-line. Single-bushing DTs for line-to-ground connection on effectively grounded systems with line-to-line voltages of 13.2kV. Two-bushing DTs for line-to-ground connection on system with line-to-line voltages of 13.2kV
•Without slash (/) – for line-to-line connection •With slash (/) – for line-to-ground connection
DT Company Number Coding System of MERALCO I. PREFIXES (Primary Winding Rating) OLD SYSTEM
W Z Z X Y MY
NEW SYSTEM
W T Z X Y M
KV RATING
20 13.2, 13.8 7.62 3.6 4.8 2.4
DT Company Number Coding System of MERALCO II. SUFFIXES (Secondary Winding Rating) CODE LETTER
VOLTAGE RATING
A
120/240 or 240/120
B
139/277
C
240/480
D (or Y)
139/277x120/240
E
240/139*
F
480/277*
G
240
N
125/216*
* Threephase DTs
Difference Between 120/240- & 240/120-Volt Ratings 120/240
240/120
2-section secondary winding which can be connected in parallel for output voltage 120V, in series for output voltage 240V, or in series for 3-wire service for 120/240V output voltage. (Memory Aid: 120-volt winding times 2) Mid-tapped secondary suitable for 2-wire service at voltage 240V, or for 3-wire service. Cannot be connected for 2-wire service at voltage 120V . (Memory Aid: 240-volt winding divided by 2)
(Available in 4or 3-bushing transformers)
DT Company Number Sample
B-
139/277 V Secondary
W-
19.92 kV Primary
DT Company Number Sample
A-
120/240 V Secondary
M-
2.4 kV Primary
DT Company Number Sample
D-
Z-
7.62 kV Primary
Dual Voltage 120/240 X 139/277 V Secondary
External Tap-Changers Operation
1. De-energize the DT 2. Loosen lock screw 3. Rotate switch to desired position 4. Tighten lock screw 5. Energize the DT
Lock Screw
Other Types of External Tap-Changers
Internal View of a DT With an External Tap-Changer TapChanger
Internal Tap-Changers Rotary Tap-Changers
Schematic Diagram of a Dual Voltage Transformer H2
H1
DUAL VOLTAGE TAP (SET AT INNER TAP)
5 4 3 2 1
PRIMARY WINDING
139V
139V X1
X3
X2
139/277 V
X4
TAP CHANGER
Schematic Diagram of a Dual Voltage Transformer H2
H1
5 4 3 2 1
DUAL VOLTAGE TAP (SET AT OUTER TAP)
PRIMARY WINDING
120V X1
X3
120V X2
120/240 V
X4
TAP CHANGER
Samples of DTs With Dual Voltage Tap Internal Tap changer
Dual Voltage Taps Always refer to nameplate for actual ratings.
Samples of DTs With Dual Voltage Tap Tap changer
Dual Voltage Taps
Changing the DUAL VOLTAGE TAP is done by transferring the connection of the primary lead
Samples of DTs With Dual Voltage Tap Changing the DUAL VOLTAGE TAP is done by transferring the connection of the outer end of the curved copper strip
Dual Voltage Taps
Transformer Polarity Convention 200 kVA or smaller, and 8.66 kV or below
Single-phase transformers that do not meet either one or both criteria
Additive
Subtractive
Terminal Markings of DTs I. ADDITIVE POLARITY H1
X3
H2
X2
X1
H1
X3
H2
X2
X1
H1
X4
H2
X1 X2
X3
ADDITIVE - X1 IS DIAGONALLY ACROSS FROM H1
Terminal Markings of DTs II. SUBTRACTIVE POLARITY H1
X1
H2
X2
X3
H1
X1
H2
X2
X3
H1
X1
H2
X4 X3
X2
SUBTRACTIVE - X1 IS ON SAME SIDE AS H1
Polarity of DTs EXAMPLES: 1) 100 kVA, 3.6 kV-240/120 V
Additive
2) 250 kVA, 7.62 kV-240/120 V
Subtractive
3) 25 kVA, 19.92 kV-240/120 V
Subtractive
4) 167 kVA, 13.8 kV-240/120 V
Subtractive
All 20kV, 13.8kV or 13.2kV DTs are Subtractive
POLARITY TESTING OF A DT APPLY VOLTAGE HERE (240V or 120VAC ONLY) HV SIDE
Temporary Shorting Wire (Jumper)
Vm
Voltmeter
LV SIDE
If Vm reads more than the applied voltage - Additive If Vm reads less than the applied voltage - Subtractive
Polarity of DTs X1
X3
X2
X4
Subtractive Polarity:
333 kVA, 3600/6240Y V 120/240 V
Polarity of DTs
X1
X3
X2
X4 Subtractive Polarity: 250 kVA, 34500Grd.Y/ 19920 V 139/277 V
Polarity of DTs X3 X2 X1
Additive Polarity: 25 kVA, 2400/4160Y V 120/240 V
DT Connections Used By MERALCO
System
1-Phase 1-Phase Open-Wye, Ungrd. Wye- Grd. Wye- Open-DeltaL-to-N L-to-L Open-Delta Delta Grd. Wye Open-Delta
34.5 / 20 kV Wye
Yes
13.2 / 7.62 kV Wye
Yes
8.3 / 4.8 kV Wye
Yes Yes
DeltaDelta
Yes
Yes
Yes
Yes
Yes
Yes
6.24 / 3.6 kV Wye
Yes
Yes
Yes
4.16 / 2.4 kV Wye
Yes
Yes
Yes
Yes
Yes
Yes
13.8 kV Delta
Yes
Yes
Yes
4.8 kV Delta
Yes
Yes
Yes
Note: The voltage on he leftmost column refer to the system voltage of the circuit & not on the voltage rating of the DT.
Single-phase Connection Line-to-Neutral Primary (Subtractive Polarity)
A
N
H1
H2
X1
X3
X2
n a b
VOLTAGE VECTORS B
SECONDARY VOLTAGES b
n N A
a
Vab = 240V Vbn = 120V
C
PRIMARY
SECONDARY
Van = 120V
Single-phase Connection Line-to-Neutral Primary (Additive Polarity)
A
N
H1
H2
X3
X1
X2
n a b
VOLTAGE VECTORS B
SECONDARY VOLTAGES a
n N A
b
Vab = 240V Vbn = 120V
C
PRIMARY
SECONDARY
Van = 120V
Single-phase Connection Line-to-Line Primary (Subtractive Polarity)
A
B
H1
H2
X3
X1 X2
n a b
VOLTAGE VECTORS B b
A
n
SECONDARY VOLTAGES
a
C PRIMARY
SECONDARY
Vab = 240V Vbn = 120V Van = 120V
Single-phase Connection Line-to-Line Primary (Additive Polarity)
A
B
H1
H2
X1
X3 X2
n a b
VOLTAGE VECTORS B a
A
n
SECONDARY VOLTAGES
b
C PRIMARY
SECONDARY
Vab = 240V Vbn = 120V Van = 120V
Open-Wye, Open-Delta Connection 2 Subtractive Polarity DTs
A B C N
H2
H1
X3
X1
H2
X1
X3
X2
n a b
H1
X2
c
VOLTAGE VECTORS B n
A
C
PRIMARY
SECONDARY VOLTAGES b
a
N
c
SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard
Voltage
Open-Wye, Open-Delta Connection 2 Additive Polarity DTs A B C N
H2
H1
X1
X3
H2
X3
X1
X2
n a b
H1
X2
c
VOLTAGE VECTORS
SECONDARY VOLTAGES
b
B n
N A
C
PRIMARY
c
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
a
SECONDARY
Common Error in Open-Wye, Open-Delta Connections ERROR 1: X1 of Main DT was interlocked with X1 of Wing DT A B C N
H1
H2
H1
H2
X3
X1
X3
X1
n a b c
VOLTAGE VECTORS c
B
b n
N A
C
PRIMARY
X2
X2
SECONDARY VOLTAGES Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
a
SECONDARY
Vca = 416V Vcn = 317V
Common Error in Open-Wye, Open-Delta Connections ERROR 2: H2 instead of H1 of one DT was connected to the primary
A B C N
H1
H2
H1
H2
X3
X1
X3
X1
X2
n a b c
VOLTAGE VECTORS B
A
C
PRIMARY
SECONDARY VOLTAGES b
N
X2
n a
Vab = 240 V Van = 120V Vbc = 416 V Vbn = 120V
c
SECONDARY
Vca = 240 V Vcn = 317V
Common Trouble in Open-Wye, Open-Delta Connections TROUBLE: H1 of both DTs energized from the same primary
To Source
Detached jumper
A B C N
H1
H2
H1
H2
X3
X1
X3
X1
X2
n a b c
VOLTAGE VECTORS b
B
n
SECONDARY VOLTAGES Vab = 240 V Van = 120V Vbc = 480 V Vbn = 120V
C
PRIMARY
a
N A
X2
c
SECONDARY
Vca = 240 V Vcn = 360V
Wye-Delta Connection 3 Additive Polarity DTs A B C N
Floating Neutral
H1
X3
H2
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
n
a b
X2
c
VOLTAGE VECTORS b B n
N A
C PRIMARY
X2
SECONDARY VOLTAGES
c
a SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard Voltage
Common Error in Wye-Delta Connections (Ex. 1 Subtractive & 2 additive DTs) ERROR: X1 of Wing 1 was connected to X1 of Main while X3 of Main was connected to X3 of Wing 2 A B C Floating Neutral Wing 1
H1
X3
C’
C
n a b
H2
H1
X1
X1
X2
H2
H1
X3 X2
c
C PRIMARY
SECONDARY VOLTAGES Vab = 240V
Vc’a = 416V
Van = 120V
Vbc = 416V
Vbc’ = 240V
Vbn = 120V
Vca = 240V
Vcc’ = 480V Vcn/Vc’n = 317V
n
N A
X2
a
B
H2
X1
X3
VOLTAGE VECTORS
Wing 2
c
Main
b
c’
SECONDARY
Corrected Error in Wye-Delta Connection (Subtractive & 2 additive DTs) CORRECTION: H2 instead H1 of Main DT was tapped to the phase conductor. This results in the imaginary swapping of the X1 & X3 leads.
A B C
Floating Neutral
Wing 1
H1
H2
H1 H2
X1
X1 X3
X3
X2
n a b
X2
VOLTAGE VECTORS b B n
A
C PRIMARY
a SECONDARY
H1
X3 X1
X3
Wing 2
H2
X1 X2
N
H2 H1
c
Main
SECONDARY VOLTAGES
c
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V - Bastard Voltage
Wye-Wye Connection for 240-volt Service 3 Subtractive Polarity DTs
A B C N
H1
H2
X1
X4
n
X3
X2
139V
X1
a b
H1
X3
c
A PRIMARY
a
H1
H2
X4
X1
X4
X3
X2
SECONDARY VOLTAGES
n C
X2
H2
VOLTAGE VECTORS b B N
139V
c
SECONDARY
Vab = 240V
Van = 139V
Vbc = 240V
Vbn = 139V
Vca = 240V
Vcn = 139V
Wye-Wye Connection for 480-volt Service 3 Subtractive Polarity DTs
A B C N
H1
H2
X1
X4 X3
H1
139V
X1
X2
X3
139V
H2
H1
H2
X4
X1
X4 X3
X2
n
a b
c
A PRIMARY
SECONDARY VOLTAGES
n C
a
VOLTAGE VECTORS b B N
X2
c
SECONDARY
Vab = 480V
Van = 277V
Vbc = 480V
Vbn = 277V
Vca = 480V
Vcn = 277V
Wye-Wye Connection for 240-volt Service 3 Additive Polarity DTs
A B C N
H1
H2
X4
X1
X2
X3
n a b
H1
H2
H1
H2
X4
X1
X4
X1
X2
VOLTAGE VECTORS b B
PRIMARY
X2
a
X3
SECONDARY VOLTAGES
n
N C
X3
c
A
c
SECONDARY
Vab = 240V
Van = 139V
Vbc = 240V
Vbn = 139V
Vca = 240V
Vcn = 139V
Wye-Wye Connection for 480-volt Service 3 Additive Polarity DTs
A B C N
H1
H2
X4
X1 X2
n a b
H1
H2
H1
H2
X4
X1
X4
X1
X3
X2
X2
X3
X3
c
VOLTAGE VECTORS b B
A
C PRIMARY
SECONDARY VOLTAGES
n
N a
c
SECONDARY
Vab = 480V
Van = 277V
Vbc = 480V
Vbn = 277V
Vca = 480V
Vcn = 277V
Open-Delta, Open-Delta Connection 2 Subtractive Polarity DTs A B C
H1
X1
H2
H1
H2
X3
X1
X3
X2
n a b
c
VOLTAGE VECTORS B A
n
C PRIMARY
SECONDARY VOLTAGES
b 0º angular displacement
a
X2
c SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Open-Delta, Open-Delta Connection 2 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
c
VOLTAGE VECTORS c B A
180º angular displacement
a PRIMARY
SECONDARY VOLTAGES
n
C
X2
b SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Open-Delta, Open-Delta Connection of 2 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
X2
c
VOLTAGE VECTORS B A
n
b 0º angular displacement
a C PRIMARY
SECONDARY VOLTAGES
c SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
Common Error in Open-Delta, Open-Delta Connections ERROR: Secondary Interlock was Connected X3 to X3 A B C
H1
X3
H2
H1
H2
X1
X3
X1
X2
n a b
c
VOLTAGE VECTORS c B A
b C PRIMARY
a
X2
SECONDARY VOLTAGES Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
n
SECONDARY
Vca = 416V Vcn = 317V
Delta-Delta Connection 3 Subtractive Polarity DTs A B C
H1
X1
n
a b
X2
H2
H1
H2
H1
H2
X3
X1
X3
X1
X3
X2
c
n
SECONDARY VOLTAGES b
a
A C PRIMARY
X2
VOLTAGE VECTORS B
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
c SECONDARY
Delta-Delta Connection 3 Additive Polarity DTs A B C
H1
X3
H2
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
n
a b
X2
c
VOLTAGE VECTORS b B n
A C PRIMARY
X2
SECONDARY VOLTAGES
c
a SECONDARY
Vab = 240V
Van = 120V
Vbc = 240V
Vbn = 120V
Vca = 240V
Vcn = 208V
SINGLE-PHASE 240V, LINE-TO-GROUND SECONDARY SYSTEM
A B C N
H1
H2
X3
X1 X2
a b
INSULATED PHASE CONDUCTOR
BARE GROUNDED PHASE CONDUCTOR
OPEN-WYE, OPEN-DELTA CONNECTION FOR 3-PHASE, CORNER-GROUNDED DELTA SECONDARY A B C N
H2
H1
X1
X3
X2
a b
c
H1
H2
X3
X1
X2
INSULATED PHASE CONDUCTORS
BARE GROUNDED PHASE CONDUCTOR b
B
SECONDARY VOLTAGES N A
c a C
PRIMARY VECTORS
SECONDARY VECTORS
Vab = 240V Vbc = 240V Vca = 240V
WYE-DELTA CONNECTION FOR 3-PHASE, CORNER-GROUNDED DELTA SECONDARY
A B C N
H1
X3
c
H1
H2
H1
H2
X1
X3
X1
X3
X1
X2
a b
H2
X2
INSULATED PHASE CONDUCTORS
X2
BARE GROUNDED PHASE CONDUCTOR
b
B
SECONDARY VOLTAGES
c
N A
C
PRIMARY VECTORS
a SECONDARY VECTORS
Vab = 240V Vbc = 240V Vca = 240V
Reminders on DT Installation A. New Installation Inspect DT for any physical defects Check specifications of withdrawn DT Install as per safety & construction standards Check for compliance to W.O. or F.O.
Before energizing: Check for shorted/grounded service entrance conductors Ensure customer main switch (CMS) is open & check for possible voltage presence Energize DT Check voltage at CMS
Accomplish Transformer Report (TR)
Reminders on DT Installation B. Replacement Inspect DT for any physical defects Check specifications of withdrawn DT Eliminate all possible sources of power Ground or short-circuit the secondary line or leads Establish secondary phase markings/sketch existing connection Install as per safety & construction standards Before re-energizing: Remove all temporary grounding wires Check DT connection against sketch/drawing/phase markings
Release pressure by operating the pressure relief device Energize DT Check voltage & phase sequence at CMS (verify with customer) Accomplish Transformer Report (TR)
A Transformer Rated 13200 V
A Transformer Rated 13200 Grd.Y/7620 V
A Transformer Rated 7620/13200Y V
Available DT Banks at the Training Grounds 1) 3 – 15 kVA, 3600/6240Y – 120/240 Volts 2) 2 – 25 kVA, 34500Grd.Y/19920 – 240/120 Volts 3) 3 – 100 kVA, 34500Grd.Y/19920 – 120/240 x 139/277 Volts
4) 2 – 15 kVA, 34500Grd.Y/19920 – 240/120 Volts 5) 3- 10 kVA, 7620/13200Y – 120/240 Volts 6) 3- 15 kVA, 13200 – 120/240 Volts 7) 1-15 kVA, 13200Grd.Y/7620 - 240/120 Volts (Sub.) 1-10 kVA, 13200Grd.Y/7620 – 120/240 Volts (Add.)
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