 | Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.) |
 |  | 11. Basic symbols and formulas of electrical engineering |
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11.1. General direct current engineering
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Ohm’s Law |
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power |
P = U2 · I |
[W] |
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P = I2 · R |
[W] |
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[W] |
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work |
W = U · I · t |
[V · A · s = Ws] |
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W = P · t |
[W · s = Ws] |
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diameter of a conductor |
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[mm2] |
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resistance of a conductor |
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[W] |
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[W] |
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influence of temperature on the resistance of the conductor |
RW = RK |
[1 + µ(J2 - J1)] |
Connection of resistances and power sources
· series connection
Figure
Figure
RG = R1 + R2 + R3 (total resistance)
U = U1 + U2 + U3.....
EG = E1 + E2 + E3
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condition: Ri1 = Ri2 = Ri3 |
U = I · Ra
2. Kirchhoff’s Law
The sum of all voltages around a closed path in an electrical system is zero.
The sum of the impressed voltage is equal to the sum of the voltage drops.
· parallel connection
Figure
Figure
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RE = equivalent resistance | |
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IG = total current intensity | |
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Condition: |
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Equal power sources are connected in parallel. |
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E = E1 = E2 = E3 |
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for 2 resistances connected |
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for n equal resistances |
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IG = I1 + I2 + I3 |
1. Kirchhoff’s Law
At each junction the sum of the currents flowing toward the junction is equal to the sum of the currents flowing away from the junction.
IG - I1 - I2 - I3 = 0
Figure
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