Synchronous generator

Why is the frequency of a synchronous generator locked into its rate of shaft rotation?

The frequency is tied to the rate of shaft rotation, generating electricity at a fixed frequency based on pole number and rotor speed.

What happens to an alternator's voltage when it is loaded down with a lagging load?

The voltage drops sharply due to the inductive load causing a phase shift between current and voltage.

Why does an alternator’s voltage rise when loaded down with a leading load?

The capacitive nature of the leading load causes the current to lead the voltage, increasing terminal voltage.

What characterizes phasor diagrams for a synchronous generator at unity power factor?

Voltage and current are in phase, resulting in maximum power transfer.

What indicates a lagging power factor in phasor diagrams?

Current lags behind voltage, represented by a phase angle indicating inductive reactance.

What indicates a leading power factor in phasor diagrams?

Current leads voltage, shown by a phase angle indicating capacitive reactance.

How can synchronous impedance and armature resistance be determined in a synchronous generator?

Synchronous impedance is determined via short circuit test; armature resistance is calculated through a no-load test.

Why must a 60-Hz generator be derated if it is to be operated at 50 Hz?

To avoid overloading, typically reduced to 83.33% of rated capacity.

How does the size of a 400-Hz generator compare to a 60-Hz generator of the same power and voltage rating?

A 400-Hz generator is smaller due to reduced core and winding material requirements.

What conditions are necessary for paralleling two synchronous generators?

Generators must match in voltage, frequency, and phase sequence.

Why must the oncoming generator be paralleled at a higher frequency than the running system?

To ensure proper synchronization and avoid disturbances during connection.

What is an infinite bus?

A theoretical power system with unlimited capacity, constant voltage, and frequency.

What constraints does an infinite bus impose on a generator?

Generators must operate at the same voltage and frequency as the infinite bus.

How can real power sharing between two generators be controlled?

Through mechanical input adjustments while maintaining constant frequency.

How can reactive power sharing between two generators be controlled?

By adjusting excitation levels without affecting the system's terminal voltage.

How can the system frequency of a large power system be adjusted?

By controlling generator outputs or changing generator speeds without disrupting power sharing.

Why is overheating a serious matter for a generator?

It can lead to insulation damage, reduced efficiency, and potential mechanical failure.

What do capability curves illustrate?

They show the operational limits of a generator under various loading conditions.

What are short-time ratings and why are they important?

They reflect a generator's ability to withstand overloads briefly, crucial for managing peak demands.