Three Phase Transformers - Dan Dudley

Three Phase Transformers Theory and Calculations Copyright 1999-2019 Dan Dudley

DELTA Transformer Copyright 1999-2019 Dan Dudley

WYE Transformer Copyright 1999-2019 Dan Dudley

Voltage and Current in a Delta Transformer Copyright 1999-2019 Dan Dudley

Voltage and Current in a WYE Transformer Copyright 1999-2019 Dan Dudley

Delta – Volts are Equal ü Delta Configuration Transformer Voltage is EQUAL Phase and Line Ø The Phase Voltage Line Voltage Current is NOT EQUAL Ø Phase Ø Line Current Line Current / 1.732 Current Phase Current X 1.732 D V W I , Phase Divide, Line Multiply, by 1.732 Copyright 1999-2019 Dan Dudley

Wye – Current is Equal ü Wye Configuration Transformer Current is EQUAL Phase and Line Ø The Phase Voltage Line Voltage Voltage is NOT EQUAL Ø Phase Voltage Line Voltage / 1.732 Ø Line Voltage Phase Voltage X 1.732 n D V W I , Phase Divide, Line Multiply, by 1.732 Copyright 1999-2019 Dan Dudley

DELTA Configuration WYE (“Y”) Configuration Copyright 1999-2019 Dan Dudley

Ratio of Transformation Copyright 1999-2019 Dan Dudley

(4) (1) (2) (3) 1. Primary Line 2. Primary Phase 3. Secondary Phase 4. Secondary Line Core Copyright 1999-2019 Dan Dudley

230 V 6.25 amps 6.25 amps X 25 amps What is the Primary Line voltage of a Delta-Wye connected transformer with a secondary line voltage of 230 volts, secondary line current of 25 amps, and primary line current of 6.25 amps Answer 1. Ratio Primary amps / Secondary amps 25/6.25 4 2. Secondary Line to Secondary Phase 230 / 1.732 132.8v 3. Primary Phase volts using ratio 132.8 X 4 531.2 volts 4. Delta Phase Volts Line Volts 531.2 volts Primary Line Copyright 1999-2019 Dan Dudley

1920 V 125 amps 15.6 amps What is the Secondary Line voltage of a Delta-Wye connected transformer with a Primary line voltage of 1920 volts, secondary line current of 125 amps, and primary line current of 15.6 amps Answer 1. Ratio Primary amps / Secondary amps 125/15.6 8 2. Primary Line to Primary Phase 1920v 1920v Primary Phase 3. Secondary phase using ratio 1920 / 8 240 volts 4. Wye Line Volts Phase Volts X 1.732 415.68 volts Sec Line Copyright 1999-2019 Dan Dudley

7200v 480v 26 a X What is the Secondary Line Current of a Delta-Wye connected transformer with a Primary line voltage of 7200 volts, secondary line voltage of 480, and primary line current of 26 amps Answer 1. Ratio Primary volts / Secondary volts 7200/480 15 2. Pri Line amps to Pri Phase amps 26 / 1.732 15.01 amps 3. Sec phase amps using ratio 15 X 15.01 225.17 amps 4. Wye Line amps Phase amps 225 amps Sec Line Current Copyright 1999-2019 Dan Dudley

120 V 1440 V 140 amps What is the Primary Line current of a Delta-Wye connected transformer with a secondary line voltage of 120 volts, secondary line current of 140 amps, and primary line voltage of 1440 volts. Answer §1. Ratio Primary volts / Secondary volts 1440/120 12 §2. Secondary Line to Secondary Phase 140 140a (Wye ) §3. Primary Phase current using ratio 140 / 12 11.66 amps §4. Delta Line Current 11.66a X 1.732 20.20 amps Pri Line Delta Copyright 1999-2019 Dan Dudley

Three Phase example #2 Phase volts for a 3 phase transformer are 208 v, what is the line voltage connected Wye ? Line Volts Phase Volts X 1.732 208 X 1.732 360.256 Volts Copyright 1999-2019 Dan Dudley

Three Phase example #3 Phase Current for a Delta connected transformer, 480 v, 45 kva, with 20 amps on the line are ? Phase Amps Line amps / 1.732 20 / 1.732 11.547 amps Copyright 1999-2019 Dan Dudley

Three Phase Fault Current Calculation Transformer: 3phase, 265 kva, 208/120 volt with 2.5% impedance I W / E (no Power Factor W VA 3 Phase use 1.732 I - 3 phase VA / E X 1.732 Whatever your Impedance simply Divide it into 100 Convert K (Kilo) by dividing by 1000 265,000 / 208 X 1.732 Do this calc first 265,000 / 360.256 735.58802 Multiplier 100 / 2.5 40 736 amps X 40 29,440 amps fault current Copyright 1999-2019 Dan Dudley

Service Entrance Raceway & Conductors NESC HIGH LEG PHASE “C” Meter Base NEC 230.56 & 215.8 HIGH LEG – PHASE “B” Service Equipment Feeder CB HIGH LEG Phase “B” 408.3(E) 215.8 Feeder Circuit The HIGH LEG IS ALWAYS Grounding Electrode Conductor Electrical Equipment ORANGE Copyright 1999-2019 Dan Dudley

NEC – Phase Arrangement 408.3(E) A–B–C Front to Back Top to Bottom Left to Right Higher Voltage to Ground B Phase – Center Phase Copyright 1999-2019 Dan Dudley

Open Delta System 1. Requires 3 transformers 2. Advantage: 3 phase power 3. Disadvantage: Reduced capacity Approx: 58% of total Copyright 1999-2019 Dan Dudley

You can derive two (2) Different voltages from this Transformer 120 volts and 208 volts Copyright 1999-2019 Dan Dudley

You can derive three (3) Different voltages from this Transformer 120, 208 and 240 volts This transformer configuration Is also called a “Center Tapped Delta” Copyright 1999-2019 Dan Dudley

Copyright 1999-2019 Dan Dudley

Copyright 1999-2019 Dan Dudley

Transformer Connection Identification Copyright 1999-2019 Dan Dudley

Transformer Connection Identification Copyright 1999-2019 Dan Dudley

Transformer Connection Identification Copyright 1999-2019 Dan Dudley

Three Phase Transformer Questions 30 Minutes Copyright 1999-2019 Dan Dudley

What is the Primary Line voltage of a Delta-Wye connected transformer with a secondary line voltage of 230 volts, secondary line current of 25 amps, and primary line current of 6.25 amps Answer 1. Ratio Primary amps / Secondary amps 25/6.25 4 2. Secondary Line to Secondary Phase 230 / 1.732 132.8v 3. Primary Phase volts using .