Choice of transformer rating: Difference between revisions
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When an installation is to be supplied directly from a MV/LV transformer and the maximum apparent-power loading of the installation has been determined, a suitable rating for the transformer can be decided, taking into account the following considerations | When an installation is to be supplied directly from a MV/LV transformer and the maximum apparent-power loading of the installation has been determined, a suitable rating for the transformer can be decided, taking into account the following considerations (see {{FigRef|A15}}): | ||
*The possibility of improving the power factor of the installation (see | *The possibility of improving the power factor of the installation (see [[Power Factor Correction}}) | ||
*Anticipated extensions to the installation | *Anticipated extensions to the installation | ||
*Installation constraints (e.g. temperature) | *Installation constraints (e.g. temperature) | ||
*Standard transformer ratings | *Standard transformer ratings | ||
{| class="wikitable" | {| class="wikitable" | ||
| Line 16: | Line 12: | ||
! rowspan="2" | | ! rowspan="2" | | ||
'''Apparent power kVA''' | '''Apparent power kVA''' | ||
! colspan="2" | In (A) | ! colspan="2" | In (A) | ||
|- | |- | ||
| Line 87: | Line 82: | ||
where | where | ||
*Pa = kVA rating of the transformer | *Pa = kVA rating of the transformer | ||
*U = phase-to-phase voltage at no-load in volts (237 | *U = phase-to-phase voltage at no-load in volts (237 V or 410 V) | ||
*In is in amperes. | *In is in amperes. | ||
For a single-phase transformer: | |||
<math>\mbox{In}=\frac{\mbox{Pa}\times10^3}{\mbox{V} }</math> | |||
where | |||
*V = voltage between LV terminals at no-load (in volts) | *V = voltage between LV terminals at no-load (in volts) | ||
| Line 100: | Line 96: | ||
*In = kVA x 1.4 | *In = kVA x 1.4 | ||
*The IEC standard for power transformers is IEC | *The IEC standard for power transformers is IEC 60076. | ||
[[ru:Выбор номинальной мощности трансформатора]] | [[ru:Выбор номинальной мощности трансформатора]] | ||
[[zh:变压器额定容量的选择]] | [[zh:变压器额定容量的选择]] | ||
Revision as of 01:50, 16 November 2016
When an installation is to be supplied directly from a MV/LV transformer and the maximum apparent-power loading of the installation has been determined, a suitable rating for the transformer can be decided, taking into account the following considerations (see Fig. A15):
- The possibility of improving the power factor of the installation (see [[Power Factor Correction}})
- Anticipated extensions to the installation
- Installation constraints (e.g. temperature)
- Standard transformer ratings
|
Apparent power kVA |
In (A) | |
|---|---|---|
| 237 V | 410 V | |
| 100 | 244 | 141 |
| 160 | 390 | 225 |
| 250 | 609 | 352 |
| 315 | 767 | 444 |
| 400 | 974 | 563 |
| 500 | 1218 | 704 |
| 630 | 1535 | 887 |
| 800 | 1939 | 1127 |
| 1000 | 2436 | 1408 |
| 1250 | 3045 | 1760 |
| 1600 | 3898 | 2253 |
| 2000 | 4872 | 2816 |
| 2500 | 6090 | 3520 |
| 3150 | 7673 | 4436 |
Fig. A15 – Standard apparent powers for MV/LV transformers and related nominal output currents
The nominal full-load current In on the LV side of a 3-phase transformer is given by:
[math]\displaystyle{ \mbox{In}=\frac{\mbox{Pa}\times10^3}{\mbox{U}\sqrt3} }[/math]
where
- Pa = kVA rating of the transformer
- U = phase-to-phase voltage at no-load in volts (237 V or 410 V)
- In is in amperes.
For a single-phase transformer:
[math]\displaystyle{ \mbox{In}=\frac{\mbox{Pa}\times10^3}{\mbox{V} } }[/math]
where
- V = voltage between LV terminals at no-load (in volts)
Simplified equation for 400 V (3-phase load)
- In = kVA x 1.4
- The IEC standard for power transformers is IEC 60076.
