HVAC Electricity Chapter 7 Complete Solutions

HVAC Electricity Chapter 7 Complete Solutions What are the two types of current use din the heating, cooling and refrigeration industries? AC (mostly) DC _____ current flows in only one direction. DC Brainpower Read More _____ current flows in alternating directions. AC What are the advantages of AC current over DC current? 1) cheaper 2) easier to produce 3) easier to transform from one voltage to another How is AC produced? by cutting through the magnetic field with a conductor What is a sine wave? a graphical representation of AC How many times on a sine wave is voltage at zero? three times When the conductor rotates through one complete revolution, it has generated two alternations (flow intervals, meaning changes directions twice). Two alternations equals how many cycles? one what is a cycle? when the rotor, or conductor, cuts the magnetic field of a north pole and south pole The number of complete cycles that occur in one second is known as _____. frequency In the United states, what frequency is considered "standard" frequency? 60 Hz Alternating current reaches a peak at ______ degrees. 90* What is the calculation for effective current? peak voltage x .707 = effective current (RMS) What are the four basic volt-age-current characteristics available? 240-V-single phase-60 Hz 240-V-three phase-60 Hz 208-V-three phase-60 Hz 460-V-three phase-60 Hz What is phase? Phase is the number of currents alternating at different intervals of time in the circuit How is a single phase and a three phase current produced? single phase: has one one alternator with one winding in the stator. three phase: has one alternator with three windings in the stator that are 120* apart. How is alternating current produced? by an alternator what is an alternator? a mechanical device made up of a winding or set of windings (stator) and a rotating magnet (rotor). How is the number of windings needed determined? the number of windings used depends on the desired phase characteristics of the current What determines the strength of the magnetic field? amperage of the circuit What is inductance the voltage produced by the fluctuation of the magnetic field and the conductors cutting through more than one magnetic field counteracting the original voltage. _____ is the only factor that affects the current flow in a DC circuit. Resistance _____ and _____ are the two factors that affects the current flow in an AC circuit. Resistance and Reactance What is reactance? the resistance to the changing flow of alternating current.