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Electric Service -
Gas Service
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Safety / Damage Prevention
Transformer Impedances
The tables below list the current transformer impedances for Detroit Edison's power distribution transformers. This information is necessary for calculating available fault current.
| Single Phase Overhead Distribution Transformers | |
| Dual Voltage 7.6kV X 4.8kV Primary Single Phase - 120/240 | |
| Size in kVA | % Impedance |
| 15 | 1.6 - 3.0 |
| 25 | 1.6 - 3.0 |
| 50 | 1.6 - 3.0 |
| 100 | 1.6 - 3.0 |
| 167 | 1.8 - 3.0 |
| Dual Voltage 7.6kV X 4.8kV Primary Single Phase - 277 VOLT | |
| Size in kVA | % Impedance |
| 50 | 1.6 - 3.0 |
| 100 | 1.6 - 3.0 |
| 167 | 1.8 - 3.0 |
| Dual Voltage 7.6kV X 4.8kV Primary Single Phase - 120 VOLT | |
| Size in kVA | % Impedance |
| 15 | 1.6 - 3.0 |
| 25 | 1.6 - 3.0 |
| 50 | 1.6 - 3.0 |
| 100 | 1.6 - 3.0 |
| 167 | 1.8 - 3.0 |
| 7.6 kV Primary Single Phase - 7620/13,200Y - 120/240 VOLTS | |
| Size in kVA | % Impedance |
| 100 | 1.6 - 3.0 |
| 250 | 3.0 - 3.5 |
| Isolation transformers 7620/13,200 - 4800/8320 VOLTS | |
| Size in kVA | % Impedance |
| 75 | 1.6 - 3.0 |
| 250 | 1.6 - 3.5 |
| 333 | 1.6 - 3.7 |
| 500 | 1.6 - 3.7 |
| Pad Mounted, Dead Front, Single Phase, Distribution Transformers | |
| 13,200 Grd Y/7620 - 240/120 VOLTS | |
| Size in kVA | % Impedance |
| 25 | 1.5 - 2.75 |
| 50 | 1.5 - 2.5 |
| 100 | 1.5 - 2.5 |
| 167 | 1.8 - 3.0 |
| 250 | 3.0 - 3.4 |
| Pad Mounted, Dead Front, Single Phase, Distribution Transformers | |
| Dual Voltage 4800/8320Y X 13,200 GrdY/7620 - 240/120 VOLTS | |
| Size in kVA | % Impedance |
| 50 | 1.5 - 2.5 |
| 100 | 1.5 - 2.5 |
| 167 | 1.8 - 3.0 |
| Pad Mounted, Dead Front, Three Phase, Distribution Transformers | |
| 13,200 GRD Y/7620 - 208/120 VOLTS | |
| Size in kVA | % Impedance |
| 150 | 1.6 - 2.5 |
| 300 | 1.6 - 2.5 |
| 500 | 1.8 - 3.5 |
| 750 | 5.75 |
| 13,200 GRD Y/7620 - 480/277 VOLTS | |
| Size in kVA | % Impedance |
| 150 | 1.6 - 2.5 |
| 300 | 1.6 - 2.5 |
| 500 | 1.8 - 3.5 |
| 750 | 5.75 |
| 4800 X 13,200 GRD Y/7620 - 208/120 VOLTS* | |
| Size in kVA | % Impedance |
| 75 | 1.6 - 2.5 |
| 150 | 1.6 - 2.5 |
| 300 | 1.6 - 2.5 |
| 500 | 1.8 - 3.5 |
| 4800 X 13,200 GRD Y/7620 - 240/120 VOLTS* | |
| Size in kVA | % Impedance |
| 300 | 1.6 - 2.5 |
| 500 | 1.8 - 3.5 |
| 4800 X 13,200 GRD Y/7620 - 480/277 VOLTS* | |
| Size in kVA | % Impedance |
| 75 | 1.6 - 2.5 |
| 150 | 1.6 - 2.5 |
| 300 | 1.6 - 2.5 |
| 500 | 1.8 - 3.5 |
| Pad Mounted, Live Front, Three Phase, Distribution Transformers | |
| 4800 X 13,200 - 208/120 VOLTS | |
| Size in kVA | % Impedance |
| 750 | 5.75 |
| 1000 | 5.75 |
| 50 | 1.6 - 3.0 |
| 4800 X 13,200 - 480/277 VOLTS | |
| Size in kVA | % Impedance |
| 750 | 5.75 |
| 1000 | 5.75 |
| 1500 | 5.75 |
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