If a self-excited DC generator running at rated speed fails to deliver an output voltage, which of the following conditions may be a cause of this difficulty?
• Self-excited DC generator operation and the role of residual magnetism • How the shunt-field circuit affects voltage build-up • Effects of brush pressure vs. field circuit problems on output voltage
• Think about what must happen inside the generator for voltage to "build up" starting only from residual magnetism. • Ask yourself: which of these conditions would completely PREVENT voltage from building up, rather than just reducing it or making it unstable? • Consider which choices describe a condition where current cannot properly flow in the shunt field as the generator starts to generate voltage.
• Which choice would stop shunt field current altogether so that the magnetic field cannot strengthen from its residual value? • Which conditions would more likely reduce or distort voltage rather than make it drop to zero? • Make sure you understand the difference between an open circuit and a short circuit in the shunt field and how each affects field current and voltage build-up.
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