Choice of transformer rating: Difference between revisions
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{{Menu_General_rules_of_electrical_installation_design}} | {{Menu_General_rules_of_electrical_installation_design}} | ||
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|A16}}): | |||
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| | |||
*The possibility of improving the power factor of the installation (see [[Power Factor Correction]]) | *The possibility of improving the power factor of the installation (see [[Power Factor Correction]]) | ||
| Line 8: | Line 7: | ||
*Standard transformer ratings | *Standard transformer ratings | ||
{{ | {{tb-start|id=Tab1016|num=A16|title=Standard apparent powers for MV/LV transformers and related nominal output currents|cols=2}} | ||
{| class="wikitable" | |||
|- | |- | ||
! rowspan="2" | | ! rowspan="2" | | ||
| Line 14: | Line 14: | ||
! colspan="2" | In (A) | ! colspan="2" | In (A) | ||
|- | |- | ||
! 237 V | ! 237 V{{tn|A}} | ||
! 410 V | ! 410 V{{tn|A}} | ||
|- | |- | ||
| 100 | | 100 | ||
| Line 72: | Line 72: | ||
| 7673 | | 7673 | ||
| 4436 | | 4436 | ||
| | |} | ||
{{ | {{tb-notes | ||
|A= transformer '''no-load''' voltage | |||
}} | }} | ||
| Line 81: | Line 82: | ||
where | where | ||
For a single-phase transformer: | {{def | ||
|Pa|kVA rating of the transformer | |||
|U|phase-to-phase voltage at no-load in volts (237 V or 410 V)}} | |||
<br>'''In''' is in amperes. | |||
For a single-phase transformer: | |||
<math>\mbox{In}=\frac{\mbox{Pa}\times10^3}{\mbox{V} }</math> | <math>\mbox{In}=\frac{\mbox{Pa}\times10^3}{\mbox{V} }</math> | ||
| Line 91: | Line 94: | ||
where | where | ||
{{def|V|voltage between LV terminals at no-load (in volts)}} | |||
*In = kVA x 1.4 | Simplified equation for 400 V (3-phase load): | ||
*In = kVA x 1.4 | |||
The IEC standard for power transformers is IEC 60076. | |||
Latest revision as of 09:49, 22 June 2022
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. A16):
- 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[a] | 410 V[a] | |
| 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 |
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.
