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
In these transients, the transition occurs cyclically towards states, which when reached, become unstable themselves.
Relaxation Transients
A smooth output from a generator is obtained by?
design of the armature winding
In a DC machine, stray loss is the sum of?
Iron loss and Mechanical loss
A DC generator works on the principle of?
Faraday’s Law of Electromagnetic Inductuon
These are produced in a circuit, which is originally dead, is energized.
Initiation Transients
These are produced in a circuit which is simultaneously subjected to two transients due to two independent disturbance or when the disturbing force producing the transients is itself variable.
Complex Transients
Transient current in an RLC circuit is oscillatory when
R<2sqrt(L/C)
The transient current in a loss-free LC circuit when excited from an AC source is a/an _______ sine wave.
undamped
Double energy transients are produced in circuits consisting of… (3)
- resistance
- inductance
- capacitance
