Pasos para seleccionar un transformador (inglés)

Selection Steps A. Find the electrical load requirements. These are: 1. Load operating voltage. 2. Load frequency (expressed in Hz). 3. Determine load size - usually expressed in kVA, amperage or horsepower. 4. Is the load designed to operate on single phase or three phase power?
This information is available from the equipment manufacturer and is typically listed on the nameplate of theequipment.

B. Know the supply voltage conditions: 1. Available source voltage. 2. Available source frequency (A transformer will not change frequency. 3. Number of phases on power source. C. Determine the transformer kVA rating: 1. If the load is expressed in kVA, select the appropriate transformer from the following
selection charts (make sure the selected transformer's kVA rating is equal to orgreater than the required load kVA). 2. If the load is expressed in amperage, use either the appropriate kVA formula listed below or the appropriate sizing chart. kVA (1Ø) = (Volts x Amps) / 1000 kVA (3Ø) = (Volts x Amps x 1.732) / 1000

The frequency of the supply voltage and the needed load voltage must be equal).

3. If the load is expressed in wattage, either utilize the formula below toconvert to kVA or refer
to the equipment nameplate to obtain amperage requirement. kVA = Wattage / (1000 x Power Factor of the load)

4. If the load is a motor and expressed in horsepower, refer to the following Full Load Current
and Motor Horsepower charts. Some sizes may require an optional weather shield for outdoor use.

Always size the transformer to the load requirements.

Full LoadCurrent Charts
Are there any special application considerations?

10°C above 40°C. B. For high altitude applications, derate the transformer nameplate KVA by 0.3% for every 330 feet over 3300 feet above sea level. This assures proper transformer convection cooling. C. Some applications may require a transformer design that limits the BTU output of the unit at full load or a design to withstand andmitigate specific electrical anomalies. For these applications, see the Special Application Transformers section (Chapter 7) or the following transformers: o o o Low Temperature Rise K-Factor Copper Wound

A. For ambient conditions over 40°C, derate the transformer nameplate KVA by 8% for each

Three things to keep in mind:

A. Motor horsepower charts are based on 1800 RPM squirrel cageinduction motors. If using

another type of motor, check running amperage against the chart and adjust as necessary.

B. Increase required transformer KVA by 20% if motors are started more than once per hour. C. If your motor service factor is greater than 1, proportionally increase full load amperage.
(i.e. – if service factor is 1.10, increase full load amperage by 10%.)

Single Phase: FullLoad Current Chart
kVA Rating .050 .075 .100 .150 .250 .500 .750 1 1.5 2 3 5 7.5 10 15 25 37.5 50 120 V .42 .63 .83 1.3 2.1 4.2 6.3 8.3 12.5 16.7 25.0 41.7 62.5 83.3 125.0 208.3 312.5 416.7 208 V .24 .36 .48 .72 1.2 2.4 3.6 4.8 7.2 9.6 14.4 24.0 36.1 48.1 72.1 120.2 180.3 240.4 240 V .21 .31 .42 .63 1.0 2.1 3.1 4.2 6.3 8.3 12.5 20.8 31.3 41.7 62.5 104.2 156.3 208.3 277 V .18 .27 .36 .54 .90 1.82.7 3.6 5.4 7.2 10.8 18.1 27.1 36.1 54.2 90.3 135.4 180.5 480 V .10 .16 .21 .31 .52 1.4 1.6 2.1 3.1 4.2 6.3 10.4 15.6 20.8 31.3 52.1 78.1 104.2 600 V .08 .13 .17 .25 .42 .83 1.3 1.7 2.5 3.3 5.0 8.3 12.5 16.7 25.0 41.7 62.5 83.3

Amperes

75 100 167 200 250

625.0 833.0 1392.0 1667.0 2083.0

361.0 481.0 803.0 962.0 1202.0

313.0 417.0 696.0 833.0 1042.0

271.0 361.0 603.0 722.0 903.0156.0 208.0 348.0 417.0 521.0

125.0 167.0 278.0 333.0 417.0

Three Phase: Full Load Current Chart
kVA Rating 3 6 9 15 30 45 75 112.5 150 225 300 500 208 V 8.3 16.7 25.0 41.6 83.3 125.0 208.2 312.0 416.0 625.0 833.0 1388.0 240 V 7.2 14.4 21.7 36.1 72.2 108.3 180.4 271.0 361.0 541.0 722.0 1203.0 480 V 3.6 7.2 10.8 18.0 36.1 54.1 90.2 135.0 180.0 271.0 361.0 601.0 600 V 2.9 5.8 8.7 14.4 28.9...