Transformer Seminar - The Basics
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This presentation you will get basic theory, sizing & selection and general purpose information about Acme Transformers.
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Transformer Seminar - The Basics
- 1. Acme Electric Transformer Seminar Basic Theory & Selection
- 2. AGENDA • BASIC THEORY • SIZING & SELECTION • GENERAL PURPOSE TRANSFORMERS
- 5. TURNS RATIO
- 7. THREE BASIC COMPONENTS 1. Core (magnetics) 2. Coils (conductors) 3. Insulation (paper, etc.)
- 11. TRANSFORMER TAPS • Taps are “typically” located on the Primary of the transformer. • The NEMA designation for taps is: – ANFC - Above Normal Full Capacity – BNFC - Below Normal Full Capacity • Spacing of taps is usually 2 ½% or 5 % of rated voltage
- 12. DIAGRAM SHOWING TAPS 95T90T 100TStart
- 13. ACME STANDARD TAP CHART CATALOG NUMBER SUFFIX: • N0 SUFFIX = NO TAPS • -S = SHIELDED BUT NO TAPS • -1S = 2 X 5% BNFC • -2S = 1 X 5% ANFC & 1 X 5% BNFC • -3S = 2 X 2.5% ANFC & 4 X 2.5% BNFC • -4S = 2 X 2.5% ANFC & 2 X 2.5% BNFC • -5S = 2 X 5% ANFC & 2 X 5% BNFC
- 14. ACME STANDARD TAP CHART
- 16. GENERAL PURPOSE SINGLE PHASE TRANSFORMERS (Enclosure ratings) .050 - .150 kVA Totally Enclosed (3R) .250 - 25 kVA Epoxy Encapsulated (3R) 37.5 - 250 kVA Ventilated (NEMA 2*) 37.5 - 100 kVA Non-Ventilated (3R) (*NEMA 2 becomes 3R with addition of weather shield)
- 17. GENERAL PURPOSE THREE PHASE TRANSFORMERS (Enclosure ratings) 3 - 15 kVA Epoxy Encapsulated (3R) 15 - 1000 kVA Ventilated (NEMA 2/3R*) 30, 45, & 75 kVA Epoxy Encapsulated (3R) 30 - 112.5 kVA Non-Ventilated (3R) (*NEMA 3R becomes 2 by removing weather shield)
- 18. STEPS FOR SELECTING A SINGLE PHASE TRANSFORMER Determine load data: – Voltage required by load – Amperes, horsepower, or kVA required by load – Frequency – Verify load is designed for single phase Determine supply data: (Supply can be Single or Three Phase) – Voltage of supply – Frequency
- 19. SELECTING SINGLE PHASE Cont’d • If the load nameplate expresses a rating in kVA, a transformer can be selected directly from the charts in the catalog. • If motor horsepower is known, you must first select kVA from the charts in the front of Section 1 or from the KVA Card.
- 20. SIZING SINGLE PHASE TRANSFORMERS Always size based on load volts and load amps! To determine kVA with Volts and Amps known: 𝑘𝑉𝐴 = 𝑉𝑜𝑙𝑡𝑠 × 𝐴𝑚𝑝𝑠 1000 To determine Amperes with kVA and Volts known: 𝐴𝑚𝑝𝑠 = 𝑘𝑉𝐴 × 1000 𝑉𝑜𝑙𝑡𝑠
- 21. 1 - PHASE SELECTION PROBLEM #1 Load: 1-phase, 60Hz, 240 V, @ 10 A Supply: 1-phase, 60Hz, 480 V PROBLEM #2 Load: 1-phase, 60Hz, 120 V, @ 50 A Supply: 1-phase, 60Hz, 480 V
- 22. 1 - PHASE (Cont’d) PROBLEM # 3 Load: 1-phase, 60 Hz, 3HP motor, 240 V, starts 2 times/hour Supply: 1-phase, 60 Hz, 480 V PROBLEM # 4 Load: (1) 3/4 HP, 1-phase, 240v motor (2) 1/4 HP, 1-phase, 120v motors (4) 50 watt lamps, 120 v Supply: 1-phase, 60 Hz, 480 V
- 23. STEPS FOR SELECTING A THREE PHASE TRANSFORMER Determine load data – Voltage required by the load – Amperes, horsepower, or kVA required by load – Frequency – Verify load is designed for three phase Determine supply data: (Supply must be Three Phase) – Voltage of supply – Frequency
- 24. SELECTING THREE PHASE (cont’d) • If the load nameplate expresses a rating in kVA, a transformer can be selected directly from the charts in the catalog. • If motor horsepower is known, you must first select kVA from the charts in the front of Section 1 or from the kVA card.
- 25. SIZING THREE PHASE TRANSFORMERS Always size based on load volts and load amps! To determine kVA with Volts and Amps known: 𝑘𝑉𝐴 = 𝑉𝑜𝑙𝑡𝑠 × 𝐴𝑚𝑝𝑠 × 1.73 1000 (1.73 due to phase shift of 120 degrees between phases) (1.73 = square root of 3)
- 26. SIZING THREE PHASE (cont’d) To determine Amperes with kVA and Volts known: 𝐴𝑚𝑝𝑠 = 𝑘𝑉𝐴 × 1000 𝑉𝑜𝑙𝑡𝑠 × 1.73 Note: A 3-phase transformer can be seen as three 1-phase transformers. Example: 30 kVA = (3)10 kVA 1-phase units.
- 27. DELTA - WYE CONNECTION
- 28. DELTA - DELTA CONNECTION
- 29. THREE PHASE SELECTION Problem # 1 Load: 3-phase, 60 Hz, 208 V @ 30 A Supply: 3-phase, 60 Hz, 480 V Problem # 2 Load: 3-phase, 60 Hz, 240 V @ 50 A Supply: 3-phase, 60 Hz, 480 V
- 30. THREE PHASE (Cont’d) Problem # 3 Load: (1) 3-phase, 240V, 30 HP motor (1) 1-phase, 240V, 5 HP motor (1) 1-phase, 120V, 2 kW heater Supply: 480Y/277, 3-phase, 60 Hz
- 31. QUESTIONS?
Editor's Notes
- Title Slide for ACME Brand. Photo/image area is defined by the photo box. The photo box can be substituted with imagery relevant to your subject.
- GENERAL INTRODUCTION AND COMMENTS ! COMMENTS ABOUT CATALOG AND LOCATION OF VALUABLE INFORMATION (QUESTIONS AND ANSWERS, NUMERICAL INDEX, PHONE NUMBERS, PRODUCT FEATURES) ALL PRODUCTS IN THE CATALOG ARE RATED 600 VOLTS OR BELOW. READ TITLE SLIDE !
- A TRANSFORMER IS AN ELECTRICAL DEVICE THAT HAS NO MOVING PARTS AND IS DESIGNED TO CONVERT ALTERNATING CURRENT (AC) FROM ONE VOLTAGE TO ANOTHER VOLTAGE. IT WORKS ON A MAGNETIC INDUCTION PRINCIPLE, AND CAN BE DESIGNED TO “STEP-UP” OR “STEP-DOWN” VOLTAGE. A TRANSFORMER CONSISTS OF TWO OR MORE COILS OF INSULATED WIRE WOUND AROUND AN IRON CORE.
- WHEN VOLTAGE IS APPLIED TO ONE COIL, USUALLY CALLED THE PRIMARY, IT MAGNETIZES THE IRON CORE, WHICH INDUCES A VOLTAGE IN THE OTHER COIL, USUALLY CALLED THE SECONDARY.
- THE TURNS RATIO OF THE PRIMARY AND SECONDARY WINDINGS DETERMINES THE AMOUNT OF VOLTAGE TRANSFORMATION. IN THIS EXAMPLE WE SHOW 100 TURNS ON THE PRIMARY AND ONLY 50 TURNS ON THE SECONDARY. THIS IS A RATIO OF 2 TO 1. ANY TRANSFORMER IS NOTHING MORE THAN A RATIO DEVICE. NOTE: SINGLE PHASE UNITS BELOW 1 KVA SHOULD NOT BE REVERSE CONNECTED BECAUSE THE SECONDARY WINDINGS ARE COMPENSATED (ADDITIONAL TURNS) TO OVERCOME A VOLTAGE DROP WHEN THE LOAD IS APPLIED. IF REVERSE CONNECTED, THEN THE OUTPUT VOLTAGE WILL BE LESS THAN EXPECTED.
- THE VOLTAGE RATIO BETWEEN PRIMARY AND SECONDARY WILL BE THE SAME AS THE “TURNS RATIO”, EXCEPT FOR SINGLE PHASE SMALLER THAN 1 KVA WHICH HAVE COMPENSATED SECONDARIES. A PRACTICAL APPLICATION OF THIS 2 TO 1 RATIO WOULD BE A 480 TO 240 VOLTAGE CHANGE. NOTE THAT IF THE INPUT WERE ONLY 440 THEN THE OUTPUT WOULD ONLY BE 220. THE RATIO STAYS CONSTANT. TRANSFORMERS SHOULD NEVER BE OPERATED AT VOLTAGES HIGHER THAN NAMEPLATE RATING, BUT MAY BE OPERATED AT VOLTAGES LOWER THAN RATED. THIS MAKES IT POSSIBLE TO DO SOME NON-STANDARD APLLICATIONS USING STANDARD TRANSFORMERS. SINGLE PHASE UNITS 1 KVA AND LARGER MAY ALSO BE REVERSE CONNECTED TO STEP-UP VOLTAGES.
- THE TRANSFORMER’S CORE AND COIL ARE THE PRIMARY COMPONENTS FOR VOLTAGE TRANSFORMATION. THE INSULATION; TYPICALLY COMPRISED OF MYLAR, NOMEX, KRAFT PAPER, VARNISH, OR OTHER MATERIALS, IS PLACED BETWEEN THE TURNS OF WIRE TO PREVENT SHORTING TO ONE ANOTHER OR TO GROUND. SINCE A TRANSFORMER HAS NO MOVING PARTS, IT WILL TYPICALLY HAVE A LIFE EXPECTANCY OF 20 TO 25 YEARS. ACME TRANSFORMERS CARRY A TEN YEAR WARRANTY AGAINST DEFECTS IN MATERIAL AND WORKMANSHIP.
- AN ISOLATION TRANSFORMER IS ONE IN WHICH THE PRIMARY AND SECONDARY WINDINGS ARE PHYSICALLY SEPARATED FROM EACH OTHER. SOMETIMES REFERRED TO AS “INSULATED”. WINDINGS ARE INSULATED FROM EACH OTHER. IN AN ISOLATION TRANSFORMER THE OUTPUT WINDING WILL BE ISOLATED OR FLOATING FROM EARTH GROUND UNLESS BONDED AT TIME OF INSTALLATION.
- A SHIELDED ISOLATION TRANSFORMER HAS ALL THE FEATURES OF AN ISOLATION TRANSFORMER PLUS IT INCORPORATES A FULL METALLIC SHIELD (USUALLY COPPER OR ALUMINUM) BETWEEN THE PRIMARY AND SECONDARY WINDINGS. THIS ELECTROSTATIC SHIELD (“FARADAY” SHIELD) IS CONNECTED TO EARTH GROUND AND PERFORMS TWO FUNCTIONS: 1. ATTENUATES(FILTERS) VOLTAGE TRANSIENTS (VOLTAGE SPIKES) ATTENUATION RATIO OF 100 TO 1 2. FILTERS COMMON MODE NOISE ATTENUATION OF APPROX. 30 DECIBELS THE SHIELDED UNIT IS PREFERRED OVER A STANDARD ISOLATION UNIT BECAUSE IT PROVIDES PROTECTION FOR SENSITIVE AND CRITICAL EQUIPMENT. WHEN MORE THAN ONE “SHIELDED” UNIT IS INSTALLED BETWEEN THE SOURCE AND THE LOAD,THE EFFECT IS REFERRED TO AS “CASCADING AND GREATLY IMPROVES POWER QUALITY. ALL ACME GENERAL PURPOSE UNITS 250 VA AND LARGER ARE SHIELDED AT NO ADDED COST AS A STANDARD FEATURE. SHIELDED UNITS HAVE AN “S” AS LAST DIGIT OF CAT. #
- AN AUTO-TRANSFORMER IS ONE IN WHICH THE PRIMARY AND SECONDARY WINDINGS ARE PHYSICALLY (ELECTRICALLY) CONNECTED. THEREFORE; THERE IS NO ISOLATION BETWEEN THE LINE AND THE LOAD. AUTO- TRANSFORMERS ARE MORE ECONOMICAL THAN COMPARABLE ISOLATION UNITS. COMPARE WEIGHTS OF ISOLATION 300 KVA T-3-79526-3S (GRP M, SECTION I) TO AUTO 300 KVA T-2A-52717-1 (AUTO GRP ) AUTO’S SHOULD ONLY BE USED WHERE ISOLATION OF THE LOAD IS NOT REQUIRED. MOST COMMON APPLICATION IS FOR SINGLE PHASE AND THREE PHASE STANDARD AC MOTORS. UNITS MANUFACTURED AS AUTO TRANSFORMERS MUST HAVE THE WORD “AUTO” ON THE NAMEPLATE.
- TAPS ARE A FEATURE FOUND ON SOME TRANSFORMERS WHICH ALLOW YOU TO CORRECT FOR CONSTANTLY HIGH OR LOW VOLTAGE CONDITIONS WHILE STILL DELIVERING FULL RATED OUTPUT VOLTAGES TO THE LOAD. THE TERM “NORMAL” REFERS TO THE NOMINAL VOLTAGE. TAPS MUST BE PHYSICALLY CHANGED TO CORRECT FOR OTHER THAN NOMINAL VOLTAGE. “FULL CAPACITY” IMPLIES THAT REGARDLESS OF WHICH TAP VOLTAGE IS SELECTED THE TRANSFORMER RATING STILL REMAINS FULL NAMEPLATE KVA. REFER TO ACME STANDARD TAP CHART ON SLIDE # 12 AND IN CATALOG.
- EXAMPLE OF USING TAPS: TRANSFORMER RATED PRI: 208 V SEC: 120 V CONDITION: SUPPLY VOLTAGE IS LOW @ ONLY 187 V. IF UNIT HAS NO TAPS THEN OUTPUT WOULD BE ONLY 108 V. THIS IS DUE TO FIXED RATIO OF UNIT. IF UNIT HAS TAPS, USE TAP VOLTAGE WHICH MOST CLOSELY MATCHES THE AVAILABLE SUPPLY VOLTAGE. THIS WILL RESULT IN THE OUTPUT BEING AT OR NEAR RATED VOLTAGE. TAPS CAN NOT CORRECT A FLUCTUATING VOLTAGE PROBLEM. FLUCTUATING VOLTAGES MAY REQUIRE A CONSTANT VOLTAGE REGULATOR (CVR). SEE SECTION X IN CATALOG.
- THIS TAP CHART APPLIES TO ALL CATALOG NUMBERS IN SECTION I OF THE CATALOG. EXCEPTIONS MAY APPLY IN OTHER SECTIONS OF THE CATALOG.
- ACME TRANSFORMERS ARE DESIGNED AND MANUFACTURED IN ACCORDANCE WITH APPLICABLE SAFETY STANDARDS. UL, CSA, AND CE ARE SAFETY AGENCIES. ISO 9001 IS HIGHEST QUALITY RATING. UL = UNDERWRITERS LABORATORIES CSA = CANADIAN STANDARDS ASSOCIATION CE = CONFORMITE’ EUROPEENE ANSI = AMERICAN NATIONAL STANDARDS INSTITUTE NEMA = NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION IEEE = INSTITUTE OF ELECTRICAL & ELECTRONIC ENGINEERS
- REVIEW CATALOG FOR ENCLOSURE STYLES AND PRODUCT FEATURES. ALL ENCLOSURES FALL INTO ONE OF TWO CLASSIFICATIONS: VENTILATED OR NON-VENTILATED. TOTALLY ENCLOSED AND EPOXY ENCAPSULATED FALL INTO NON-VENTILATED. SEE CATALOG FOR ENCLOSURE DEFINITIONS. THE ENVIRONMENT IN WHICH THE TRANSFORMER IS INSTALLED WILL DETERMINE THE TYPE OF ENCLOSURE REQUIRED. VENTILATED UNITS WILL REQUIRE WEATHER SHIELDS FOR OUTDOOR USE.
- SEE CATALOG FOR ENCLOSURE INFORMATION.
- READ SLIDE. REVIEW SIZING AND SELECTION INFO IN CATALOG. FREQUENCY: 60 HZ ONLY UNITS SHOULD NOT BE USED AT 50 HZ. CONTACT FACTORY AT 800-334-5214 FOR POSSIBLE EXCEPTIONS. SUPPLY AND LOAD VOLTAGE IS USED TO CHOOSE CORRECT VOLTAGE GROUP FROM SELECTION CHARTS. SINGLE PHASE CHARTS HAVE ALTERNATE WHITE LINESTO HELP DISTINGUISH THEM FRON THE THREE PHASE CHARTS WHICH HAVE ALTERNATE GRAY LINES.
- REVIEW TABLES 1 & 2 IN SECTION I. THESE TABLES ARE ALSO ON KVA CARDSWHICH WERE GIVEN OUT WITH THE CATALOGS. TABLE 2 MAKES A DIRECT CONVERSION FROM MOTOR HP TO MINIMUM TRANSFORMER KVA. EMPHASIZE NOTE STATING THAT IF MOTORS ARE STARTED MORE THAN ONCE PER HOUR, INCREASE MINIMUM KVA BY 20%. THIS IS DUE TO THE FACT THAT MOTORS START UNDER LOCKED ROTOR CONDITION AND STARTING AMPS WILL BE 6 OR 7 TIMES THE NORMAL RUNNING AMPS. AMPERE RATING ON MOTOR IS MOST ACCURATE WAY TO SIZE TRANSFORMER.
- REVIEW INFO IN SECTION I. PRACTICE USING TABLE 1 TO DETERMINE KVA FROM VOLTS AND AMPS AND ALSO AMPS FROM KVA AND VOLTS. (CAN ALSO USE KVA CARDS) REVIEW SELECTION CHARTS, DISCUSSING VOLTAGES, KVA SIZES, TAPS, SHIELDING, FREQUENCY, ETC.
- PROBLEM #1 KVA = (240V X 10A) / 1000 = 2.4 KVA NEXT LARGER STD. KVA IS 3 KVA CATALOG # IS T-2-53013-S OR T-2-53013-4S (HAS TAPS) FOUND IN GROUP I, SECTION I. PROBLEM #2 KVA= (120V X 50A) / 1000 = 6 KVA NEXT LARGER STD. KVA IS 7.5 KVA CATALOG # IS T-2-53515-3S FOUND IN GROUP I, SECTION I.
- PROBLEM # 3 FROM TABLE 2 IN SECTION I, A 3 HP MOTOR REQUIRES 4.1 KVA OF TRANSFORMER SINCE MOTOR STARTS 2 TIMES/HOUR WE MUST INCREASE KVA BY 20%. 4.1 X 1.2 = 4.92 KVA OR USE A 5 KVA UNIT CATALOG # T-2-53014-4S (GRP I, SECTION I) PROBLEM # 4 3/4 HP = 1.66 KVA 1/4 HP =0.7 KVA 4 X 50W = 200W OR 0.2 KVA TOTAL KVA = (1.66 + 0.7 + 0.7 + 0.2) = 3.26 KVA USE A 5 KVA UNIT CATALOG # T-2-53014-4S WHEN DEALING WITH INCANDESCENT LIGHTING AND RESISTIVE HEATING, WATTAGE WILL EQUAL VA.
- READ SLIDE. REVIEW INFO IN SECTION I OF CATALOG. FREQUENCY: 60 HZ ONLY UNITS SHOULD NOT BE USED AT 50 HZ. CONTACT FACTORY AT 800-334-5214 FOR POSSIBLE EXCEPTIONS. SUPPLY AND LOAD VOLTAGE IS USED TO CHOOSE CORRECT VOLTAGE GROUP FROM SELECTION CHARTS. THREE PHASE CHARTS HAVE ALTERNATE GRAY LINES.
- REVIEW TABLES 3 & 4 IN SECTION I. THESE TABLES ARE ALSO ON KVA CARDS. (REVIEW CARDS) TABLE 4 IN THE CATALOG MAKES A DIRECT CONVERSION FROM THREE PHASE MOTOR HP TO MINIMUM TRANSFORMER KVA. EMPHASIZE NOTE ABOUT MOTORS WHICH START MORE THAN ONCE PER HOUR REQUIRING AN EXTRA 20% OF TRANSFORMER KVA.
- PRACTICE USING TABLE 3 IN SECTION I TO DETERMINE KVA FROM VOLTS AND AMPS. THREE PHASE FORMULA DIFFERS FROM SINGLE PHASE FORMULA BY THE MULTIPLIER OF 1.73 CONSIDER 3-PHASE VOLTAGE OF 208Y/120. PHASE TO PHASE VOLTS 208 208 = 1.73 MULTIPLIER NEUTRAL TO PHASE VOLTS 120 120 IN A 208Y/120 CIRCUIT, THE VOLTAGE BETWEEN THE PHASE CONDUCTORSWILL BE 208V AND THE VOLTAGE BETWEEN THE NEUTRAL AND ANY PHASE CONDUCTOR WILL BE 120V. SAME RELATIONSHIP APPLIES TO 480Y/277 , 230Y/133 , 460Y/266 , 380Y/220 , ETC.
- PRACTICE USING TABLE 3 IN SECTION I TO DETERMINE AMPS WHEN KVA AND VOLTS ARE KNOWN. RECOMMEND USING TABLE RATHER THAN CALCULATOR TO REDUCE ERRORS. WHEN PUTTING 1-PHASE LOADS ON 3-PHASE UNITS IT IS BETTER TO WORK WITH KVA VALUES THAN TO WORK WITH AMPS, BECAUSE IN DELTA SYSTEMS MAXIMUM COIL CURRENT DIFFERS FROM MAXIMUM PHASE CURRENT BY THE FACTOR OF 1.73. REVIEW THREE PHASE SELECTION CHARTS, DISCUSSING VOLTAGES, KVA SIZES, TAPS, SHIELDING, ETC.
- THE TERM “DELTA” GENERALLY REFERS TO A THREE PHASE, THREE WIRE SYSTEM. IT MAY BE EITHER GROUNDED OR UNGROUNDED AND IS GRAPHICALLY DRAWN AS A TRIANGLE. EACH SIDE OF THE TRIANGLE WOULD REPRESENT ONE WINDING OF EACH COIL OF THE THREE PHASE TRANSFORMER. REFER TO PHOTO IN SECTION I. MOST 600 V CLASS THREE PHASE UNITS WILL HAVE A “DELTA” PRIMARY. THE TERM “WYE” REFERS TO A THREE PHASE, FOUR WIRE SYSTEM WHERE THE FOURTH WIRE (NEUTRAL) HAS THE SAME VOLTAGE RELATIONSHIP TO EACH OF THE PHASES. IT IS GRAPHICALLY DRAWN AS THE LETTER “Y”, WITH THE NEUTRAL BEING THE CENTER. EACH SEGMENT FROM NEUTRAL TO PHASE WOULD REPRESENT ONE WINDING OF EACH COIL OF THE THREE PHASE TRANSFORMER. SEE PHOTO IN SECTION I. IF LOADS ARE BALANCED ON ALL THREE PHASES, THEN CURRENT IN THE NEUTRAL WILL APPROACH ZERO AMPS. THE NEUTRAL WILL ONLY CARRY THE UNBALANCED CURRENT OF THE PHASES. NOTE: NEUTRAL TO PHASE VOLTS = PHASE TO PHASE VOLTS DIVIDED BY 1.732 (SQUARE ROOT OF 3), BECAUSE VOLTAGES IN EACH PHASE OF 3-PHASE SYSTEM ARE 120 DEGREES OUT OF PHASE WITH EACH OTHER.
- THE “DELTA” PRIMARY SHOWN HERE IS THE SAME AS ON THE PREVIOUS SLIDE. NOTE THAT THE SECONDARY HERE IS ALSO A “DELTA” CONFIGURATION BUT THAT IT HAS A CENTER TAP ON ONE WINDING (MIDDLE COIL). THIS TAP CAN BE USED FOR SINGLE PHASE POWER, BUT IS LIMITED TO 5% OF NAMEPLATE KVA. A DELTA HAVING THIS CENTER TAP IS KNOWN AS A “HI-LEG” DELTA (ALSO REFERRED TO AS A WILD-LEG OR STINGER-LEG). THE TERM “HI-LEG” REFERS TO THE VOLTAGES FROM THIS CENTER TAP TO THE THREE PHASES. VOLTAGE FROM TAP TO ADJACENT PHASES WOULD BE EQUAL, WHILE VOLTAGE FROM TAP TO OPPOSITE PHASE WOULD BE “HIGHER” THAN THE OTHER TWO.
- PROBLEM # 1 KVA = (208V X 30A X 1.73) / 1000 = 10.8 KVA NEXT LARGER STD KVA IS 15 KVA. CATALOG # T-3-53311-1S (GROUP D, SECTION I) PROBLEM # 2 KVA = (240V X 50A X 1.73) / 1000 = 20.76 KVA NEXT LARGER STD KVA IS 30 KVA. CATALOG # T-3-53342-3S (GROUP G, SECTION I) WHAT WOULD PRIMARY FULL LOAD AMPS BE FOR THIS UNIT? AMPS = (30KVA X 1000) / (480V X 1.73) = 36.1A ALSO SEE TABLE 3 OR KVA CARD.
- PROBLEM # 3 USE TABLE 4 OR KVA CARD (3-PHASE) 30 HP = 32.4 KVA USE TABLE 2 OR KVA CARD (1-PHASE) 5 HP = 6.72 KVA TRANSFORMER KVA = (32.4 + 6.72 + 6.72 + 6.72) = 52.56 KVA 1-PHASE LOAD WAS ADDED 3 TIMES TO GIVE EQUIVALENT 3-PHASE RATING. NEXT LARGER STD KVA IS 75 KVA CATALOG # T-3-53344-3S (GROUP G, SECTION I) SEE NOTE # 2 AT BOTTOM OF PAGE ABOUT 120 V TAP RATING. 75 KVA X 5% = 3.75 KVA TAP RATING THIS IS SUFFICIENT TO POWER 2 KW HEATER.
- Closing Slide.