3.13 - AC Theory Flashcards
What is the period of a waveform?
The time required to produce one complete cycle is called the period of the waveform.
What is the formula for the time it takes to complete 1 cycle.
I.e if a generator produces 4 cycles in 1 second, what is the period of the output sine wave?
T = 0.25 seconds
What is a cycle in terms of a sine wave?
A cycle is a complete set of positive and negative values
Frequency is measured in Hertz which is?
number of cycles / second
What is the standard frequency of aircraft electrical equipment?
How long would 1 cycle take of this value?
400 Hz
400 cycles/ second = 1/400 = 0.0025
How would you produce very high frequencies, Mechanical AC generators or electronic generators?
Mechanical AC generators cannot produce these higher frequencies. Mechanical generators cannot rotate at the very high speeds required.
Electronic generators are used to produce the required frequencies which would be necessary.
What is the maximum value of a waveform?
The maximum value of a waveform is the highest value it reaches.
What is the effective value of a sine wave?
What is the calculation for this value?
The effective value of a sine wave is usually referred to as the RMS or root mean square value.
RMS = 0.707 x Peak value
What is a rectifier?
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC) which flows in one direction only.
What is the Wattmeter?
How many terminals?
How does it measure?
The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given cirecuit.
4 terminals
Measures both voltage and current
formula: Power = I x V
A three phase generator produces a _____ ______ than a similar size ____ ___ ______
To transmit the same amount of _____ at the ___ _____ over the same distance requires less _____ _____ than a single phase generator
higher output
single phase generator
power
same voltage
conductor material
Three Phase Systems - General
Three phase motors can be used. These have high, _____ ______ and can be self-starting
Three phase generators can operate in _____ with little difficulty
_____ voltages can be made available
uniform torque
parallel
two
In what 2 ways can the ouputs of a 3 phase generator be connected?
The outputs of a 3 phase generator can be connected by either the Star or Delta method.
Describe a 3 phase generator, how it is connected?
A star connected three phase generator has the 3 phases joined at one end to form a fourth connection which is known as the ‘‘star’’ or ‘‘neutral point’’
The neutral point is normally grounded and used as the earth return in any modern aircraft. Should a fault occur in any of the phases the neutral line will carry any ‘‘out of balance’’ current
Why is a star generator used on an aircraft?
A star generator is the normal type of generator used on an aircraft distribution system because it can cope with different loads on each electrical busbar, while the delta connection cannot
