EE Mid Flashcards
The zero sequence component of the unbalanced 3-phase system of vectors VA, VB, and VC is ______ of their vector sum.
one third
In most generators, the output voltage is induced by?
relative motion between the field and the armature coils
Wave winding is employed in a dc machine of?
low current and high voltage rating
The function of an equalizer ring is? (2)
- To avoid unequal distribution of current at brushes.
- To help get sparkless commutations
The teeth in the armature of a DC machine are sometimes skewed. This is done to reduce?
Vibrations
A quantity that contains all the power information in a given load is the?
Complex Power
Transient disturbance is produced in a circuit whenever… (3)
- It is suddenly connected or disconnected from the supply.
- It is shorted.
- Its applied voltage is changed suddenly.
There are no transients in pure resistive circuit because they…
have no stored energy
Transient currents in electrical circuit are associated with… (2)
- inductors
- capacitors
It is the name given to that property of a material which opposes the creation of magnetic flux in it. It, in fact, measures the opposition offered to the passage if magnetic flux through a material.
Reluctance
It is a property that implies the case or readiness with which magnetic flux is developed.
Permeance
Kirchhoff’s current law is applicable to only…
junctions in a network
Maxwell’s loop current method of solving electrical networks…
utilizes kirchhoff’s voltage law
One kWh of electric energy equals?
860 kcal
The unit of absolute permittivity of a medium is?
farad/meter
In parallel resonance, what will happen to the current?
Minimum
Between no-load and full-load, ________ motor develops the least torque.
series
The shaft torque of a DC motor is less than its armature torque because of ___________ losses.
rotational
What DC motor would be suitable for drives requiring high starting torques but inly fairly constant speed such as crushers?
compound
A 200V, 10A motor could be rewound for 100V, 20A by using _____ as many turns per coil of wire, having _____ the cross-sectional area.
half, twice
Unlike a shunt motor, it is difficult for a series motor to stall under heavy loading because? (2)
- it develops high overload torque
- it slows down considerably
The quantity which maintains the same direction whether a DC machine runs as a generator or as a motor.
Field Current
In a DC motor, the mechanical output power actually comes from?
electrical input power
These are produced when the energized circuit is rapidly de-energized and reaches an eventual steady-state of zero current or voltage, as in this case of short-circuiting an RL or RC circuit suddenly.
Subsidence Transients
