DC Generator Power Calculations and Winding Definitions
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Shunt Excitation Generator Analysis
A shunt excitation generator develops an EMF of 130 V. When a load is connected, the terminal voltage is 120 V. Find the current supplied to the network if the excitation resistance is 10 ohms and the armature resistance is 0.05 ohms.
Calculations
- Exciting current: Iexc = V / Rexc = 120 / 10 = 12 A
- Armature current: V = E - (Ri · Ii) => 120 = 130 - (0.05 · Ii) => Ii = 10 / 0.05 = 200 A
- Load current: I = Ii - Iexc = 200 - 12 = 188 A
DC Generator Mechanical Power Calculation
A DC generator has a 4-pole armature with 564 conductors turning at 800 rpm, with a 20 mWb flux. The current through the conductors is 60 A. Calculate the internal mechanical power.
Parameters
- Poles (p) = 4
- Conductors (z) = 564
- Speed (n) = 800 rpm
- Flux (φ) = 20 × 10-3 Wb
- Current (I) = 60 A
Results
E = (z · p / 60) · (n · φ) = (564 · 4 / 60) · (800 · 20 × 10-3) = 150.4 V
Ii = 60 · 4 = 240 A
Pmi = E · Ii = 150.4 · 240 = 36,096 W (36.096 kW)
Power Balance in a Shunt DC Generator
The power balance of a DC generator in parallel consists of:
- Input Power: Pi = Ii · E
- Mechanical Losses: Pmec
- Induced Power: Pmi = E · Ii
- Excitation Losses: Pexc
- Armature Losses: Parm = I2 · Ri
- Output Power: Pout = V · I
Definitions
Conductor
Each section of the winding housed in an armature groove. Active conductors are located in the top layer (near the air gap) and the bottom layer of the slot.
Front and Rear Connections
Segments of conductors connecting two active drivers to form coil heads. Front connections are on the collector side, while rear connections are at the opposite end.
Loop
The part of the winding consisting of active conductors, including one front and one back connection.
Section or Elementary Coil
A set of coils connected between two commutator segments.
Composite Coil
A set of sections housed in the same slot sharing external insulation. If u is the number of sections per composite coil, then u = S / R, where S is the total number of sections and R is the number of rotor slots.
Total Conductors
The total number of active armature conductors is Nc = 2 · S · Ne.