1B Flashcards
An ___ ___ ___ is a network of electrical components used to supply, transmit, and use electric power.
electrical power system
Oftentimes, there is a need for redundant sources of power, as there could be a drop or total loss of the primary source of energy. What offer an effective solution to these problems?
Batteries, automatic switching devices, and uninterruptible power
supplies (UPS) offer an effective solution to these problems.
____ convert chemical energy into electrical energy, specifically DC.
Batteries
Figure 1-94 shows the symbols for a battery. In both symbols, the shorter lines represent the ____ terminal, and the longer lines represent the ____ terminal.
negative
positive
A multi-cell battery consists of two or more cells in ____ (connected end-to-end). For example, a flashlight might have two (2) or three (3) “D” cell batteries connected end-to-end, where the negative terminal of one cell connects to the positive terminal of the next cell.
series
Batteries are divided in two cell categories:
Primary
Secondary
Several factors impact a battery’s life span:
the battery’s age, the temperature of the environment in which the battery is operating, the charge times, and the amount of use.
What are some examples of primary cell batteries?
Carbon zinc and alkaline are primary cells
Primary cell batteries are also called a ___ ___ because of its
moist paste electrolyte.
dry cell
___ ___ are not designed for recharging and must be discarded
following their end-of-life.
Primary cells
Carbon zinc, known as the ___ ___, was invented by Georges Leclanché in 1866.
Leclanché Cell
Despite being considered the oldest type of battery, it is still commonly used today.
Carbon Zinc
However, the carbon zinc battery has been mostly replaced by ___ ___, which will be discussed later on.
alkaline batteries
The shelf-life of carbon zinc cells degrades over time, but their shelf life can be extended by storing them at temperatures in the ___° F range.
40 degree
Carbon Zinc cells come in a variety of shapes, sizes, but all deliver a nominal voltage of 1.5V per cell. A few examples of sizes include…?
D, C, AA, AAA and 9V.
Where high current drain is required, the ___ ___ is the best choice. ___ ___ easily handle the current drain that would strain the capacity of other types of batteries.
alkaline battery
Like the carbon zinc cells discussed earlier, alkaline cells cover the entire range of all commonly used cell types like:
D, C, AA, AAA and 9V
Alkaline cells also offer a nominal output voltage of ___V per cell.
1.5V
Alkaline cells cost three times as much as carbon-zinc cells, but
despite the increase in cost, alkaline batteries account for __% of manufactured batteries in the US today.
80%
It is possible that over time the cell may ____, causing a leakage of the internal chemicals. Alkaline cells contain a very corrosive electrolyte that will destroy sensitive equipment.
rupture
A ___ ___ or ___ is one that can be recharged and reused.
secondary cell or battery
Lead-acid, nickel cadmium, and lithium are common types of ___ ___.
secondary cells
What are the two types of secondary cells?
Lead acid and lithium-ion
Recharging a cell to its original pre-discharge condition is accomplished by passing current through the circuit in the
___ ___ to the current during discharge.
opposite direction
The ___-___ ___, invented in 1859, is the oldest type of rechargeable cell.
lead-acid cell
The ___ ___ is probably the best-known application of the lead-acid cell.
car battery
Its ratio of charging power to discharge power is a big advantage.
lead-acid
The lead-acid battery cannot be sealed, as the recharge cycle generates gases that must be ___.
vented
A lead-acid cell’s nominal voltage is ___V per cell.
2.0V
nominal voltage is about ___V per cell, but it can vary from about 2.7V (discharged) to about 4.23V (fully charged).
3.0V
The lithium-ion battery is lightweight, has a high power capacity, suffers no memory effect, and has a long shelf-life. Because of its low maintenance features, the lithium-ion battery is considered
an ___ ___ when the need for a rechargeable (secondary) battery arises.
optimal choice
Generators convert ___ energy into ___ energy.
mechanical
electrical
AC generators, also known as ___, are generally capable of producing a pure sine wave output voltage of constant
frequency.
alternators
___ ___ are standalone machines that provide electricity when power from the local grid is unavailable.
electrical generators
As with batteries, the requirements of the application
will drive decisions about the ___ and ___ ___ of the
generator that is needed.
size and fuel type
Generators also provide power in two different ways: ___ ___ and ___ ___ While the type of power they provide is the same, the way that they do so varies.
single phase and three phase
Single-phase generators produce one single voltage (120V or 120/240V) that alternates ___.
continuously
Because the power for single-phase generators is generated in ___ ___ ___, the level varies throughout its cycle. These varying waves cause the power level to drop throughout the process. These drops generally go undetected to the eye and ear in normal, residential, and smaller operations. However, sensitive electronic equipment, such as heavy-duty electric motors and large data centers, can be negatively impacted by the power drops of single-phase power.
one single wave
___ ___ ___ work by producing three separate waves of AC power that operate in a sequence.
Three-phase generators
Three-phase generators has continuous flow of energy. The power level ___ ___ as it does with single-phase generators. Because of this uninterrupted reliability, three- phase generators are much more powerful.
never dips
___ ___ are often used to supply backup power to facilities, businesses, or homes during power outages. These are typically three-phase generators, producing 120/208V or 277/480V of usable power.
Industrial generators
Traditionally, ___ ___ (CE) is responsible for installing and maintaining equipment such as generators.
Civil Engineering
Alternators have three major assemblies:
the stator, the rotor, and the brush.
A sometimes-confusing issue when discussing alternators is the term “armature.” In all motors and DC generators, the terms “___” and “___” are synonymous.
rotor
armature
With alternators, “armature” always refers to the ___ supplying the output voltage.
coils
Since an alternator’s output may be taken from either the rotor or stator coils, the term armature may…?
apply to either
The stator assembly has three component items:
the frame, the pole pieces, and the coils.
What does the frame in the stator assembly do?
The frame supports the pole pieces and the coils.
What do the pole pieces do in the stator assembly?
The pole pieces are made of laminated, soft steel segments around which the coils are wound.
What do the coils do in the stator assembly?
The coils are made of several turns of insulated wire wrapped
around each of the pole pieces which forms the stator.
The rotor assembly consists of four component items:
the shaft, the core, the coils, and the slip rings.
The rotating axle on which the rotor core and coils are mounted is called the ___.
shaft
The brush assembly consists of:
a brush, a spring, and a holder for each slip ring
____ are small blocks of carbon-graphite which provide a
current path to the rotating slip ring.
Brushes
___ push the brushes firmly against the slip rings to maintain good electrical contact.
Springs
Basic alternator theory consists of three main factors:
They are all required to mechanically generate electricity.
a conductor, a magnetic field, and relative motion.
A ___ ___ must supply the relative motion by turning the rotor inside the stationary stator.
prime mover
A ___ ___ must supply the relative motion by turning the rotor inside the stationary stator. The armature coils provide the conductor. Permanent magnets or electromagnets provide the magnetic field. Most alternators use a battery or rectified AC to provide current to the field windings to create the magnetic field.
prime mover
The field windings will be either the ___ or ___ coils, depending on where the output voltage is taken.
stator or rotor
There are two types of alternators:
rotating armature and rotating field
The term armature refers to an alternator’s ___ ___.
output coils
With alternators “Armature,” always refers to the coils supplying the output voltage. Since an alternator’s output may be taken from either the rotor or stator coils, the term armature may ___ ___ ___.
apply to either
The main disadvantage of the rotating armature design is that heavy load current flows from the slip rings to the brushes, which are then subject to ___. Because of this, it is only used for low voltage applications.
arcing
The three-phase alternator is widely used because of its greater ___; it can develop more useable power for a given physical size.
efficiency
A three-phase alternator has ___ single-phase windings spaced so that the voltage induced in each armature winding is ___° out of phase with the voltages in the other two armature windings.
three
120 degrees
Three-phase alternators produce most ___ power.
commericial
The output frequency of the alternating current is determined by the rotational speed of the ___ ___ and the number of pairs of ___ ___.
prime mover
armature coils
Output voltage for an alternator is determined by the rotational ____ of the prime mover, the total ____ of armature coils, and the ____ of the magnetic field. Voltage is directly proportional to each of the factors.
speed
number
strength
___ ___ is rated in kilowatts (kW) or kilovolt-amperes (kVA), voltage, amperes, and power factor (pf).
alternator output
In review, generators turn mechanical energy into ___.
electricity
____ operates on the principle of electromagnetic induction.
Generators
A revolving ___ inside a stationary magnetic field produces voltage
and current.
coil
Current in the armature changes direction every ___° of rotation.
180 degrees
Two types of AC generators are the:
rotating-armature and the rotating-field
Single, two, and three-phase generators are available, with ___-___ being the most common due to its efficiency.
three-phase
Generator output is regulated to ensure a stable voltage and current under…?
varying load conditions
Generators are rated according to their available output power, usually given in ____.
kilovolt-amperes (kVA)
For critical sites to continue their mission when the primary electrical source has been disconnected, they must use what is known as an…?
Automatic Transfer Switch (ATS)
An ATS (Figure 104) is an integral part of the power generation process. It allows for smooth and immediate transfer of electrical current between multiple sources and the load (e.g., end-user equipment), while maintaining ____ between the sources (e.g., utility power and generator power).
isolation
When the generator is operating, the transfer switch prevents dangerous feedback of current to the utility’s system. It also ensures
that different power sources are fully ____ before their power is combined or loads are transferred, which is imperative for safe operation.
synchronized
The ATS senses when utility power is interrupted and starts up the emergency generator if the utility power remains absent. In ____ seconds, when the generator is producing full power, the transfer switch disconnects the load from the utility and connects it to the generator, restoring electricity to the load. The transfer switch continues to monitor utility power, and when it is restored, the ATS switches the load from the generator back to the utility power. Once the generator is disconnected, it goes through a cool-down routine and is automatically shut down.
5-10 seconds
The primary purpose of an ____ ____ ____ system is to provide an alternate source of clean AC power in an emergency.
Uninterruptible Power Supply (UPS)
When power is interrupted, or fluctuates outside safe levels, a UPS will ___ provide backup power and surge protection for
plugged-in, sensitive equipment (e.g., computers, servers,
routers, some radios, etc.).
instantly
UPSs come in a variety of topologies, depending on the
level of protection needed. In general, and as seen in
Figure 105, the basic UPS is a combination of a…?
battery, a charger and an inverter
The UPS itself uses utility ___ power to keep the internal battery charged.
AC
In the event the main utility power drops, the UPS takes control; the battery outputs to the inverter, which converts DC back into AC, thereby supplying the loads with an ____ source of power, resulting in zero downtime for connected equipment.
uninterrupted
In short-term outages (__-__ minutes), the UPS system provides backup power to mask the outage.
5-15 minutes
During ___-___ outages, the UPS ensures systems can be shut down properly to prevent loss of data or equipment damage.
long-term outages
An ___ is an electrical device that converts DC to AC.
Inverter
In the previous section on the UPS, we learned that a UPS has batteries that store power for use when utility power fails. The batteries in the UPS provide DC just like another other battery does. However, home appliances, small electronics, computers, servers, etc. typically require AC power. Therefore, an inverter must be
used to convert the UPS’ battery __ power into __ power the load devices can use.
DC
AC
A rectifier is an electrical device, specifically a diode or collection of diodes, that converts __, which periodically reverses direction, to ___, which flows in only one direction.
AC
DC
One of the most common uses for rectifiers is ___ ___. Many
electronic devices run on DC, but the vast majority of buildings have AC power.
power supplies
To allow these electronic devices to operate, inverters are built into power supplies so that the building’s AC power can be converted to DC, providing an alternative to ____, particularly in non-portable
electronics.
batteries
There are a couple of phases (___ or ___) that rectifiers can be configured; it depends on the application.
single or multi
In general, ___-wave and ___-wave rectifiers are used for similar low-power applications such as, appliances, transformers, soldering, AM radio, pulse generating circuits, and signal demodulation.
half-wave
full-wave
However, in terms of efficiency, ___-wave rectifiers are preferred, thus they are more widely used in power supply circuitry compared to other rectifiers (e.g., half-wave).
full-wave
The process of converting AC into DC and vice versa doesn’t happen without the need for quality control. During the conversion process, the signal has to pass through different components (e.g.
inverters, rectifiers, etc.) in order to complete the changeover. By doing so, the signal tends to acquire additional, undesirable frequencies called, “____”.
ripple
The following are a list of disturbances that are caused by what?
- ___ ___and harmonics that are within the audio band, therefore they able to be heard on equipment such as radio receivers.
- ___ ___ that are within television video bandwidth will cause analogue TV receivers to display a pattern of moving, wavy lines.
- ___ ____ can reduce the resolution of electronic test and measurement instruments and is viewable on an oscilloscope as a pattern on the screen.
Ripple frequencies
Electronic ___ are electrical circuits which perform signal processing functions. Specifically, they are used to remove unwanted frequency components from the signal, enhance wanted frequency components, or both.
filters
Filters help to eliminate the unwanted frequencies by setting
____ for the circuit and the signal that passes through.
limitations
___ ___ (Figure 1-107) are comprised of many of the components previously mentioned in this objective. For example, generators provide a source of current and voltage (power) to the power supply. The transformer contains inductors. The rectifier has diodes and resistors. The filter has capacitors and inductors. The voltage regulators contain resistors, diodes, and other components.
Power Supplies
The purpose of a power supply is to convert AC voltage to DC voltage for use in circuits where AC voltage is not acceptable. The AC source can be 120V AC/ 60 Hz, available at most wall outlets. The input voltage from the AC source is applied to the transformer, which ___ ___ or ___ ___ the voltage as needed.
steps up or steps down
The transformer in a power supply provides the necessary voltage
needed for the load circuit, but it must be routed through the ___ and ___ first.
rectifier and filters
As learned earlier, the ___ is a diode (or collection of diodes).
rectifier
The rectifier converts AC voltage into ___ DC voltage.
pulsating
The pulsating DC, as seen in Figure 1-108, is either positive or negative and is constantly changing in amplitude. The pulsating DC is applied to the ____ section and is converted into a smoother DC.
filter
The task of converting AC into DC is called ___.
rectification
The pulsating DC has current increasing or decreasing but always in the same direction. The voltage level has a distinct ripple to it, rising and falling in synchronization with the rising and falling of the positive or negative alternations of the incoming AC signal. There are three distinct types of rectifier circuits:
half-wave, full-wave, and full-wave bridge
The simplest type of rectifier is made from a single diode. This type of rectifier is called a ___-___ ____ because it passes just half of each AC cycle (either the positive alternation or the negative alternation, depending on the direction of the diode) while still producing the full input peak voltage from the transformer secondary.
half-wave rectifier
A half-wave rectifier passes just ___ of each AC cycle while still producing the full input peak voltage from the transformer secondary.
half
Half-wave rectifiers aren’t very efficient. This is because one half of the cycle of the AC input is ___ by the diode. As a result, output voltage is zero half of the time. This causes inconsistency in the voltage level and can be detrimental to electronic equipment. This also causes the output frequency to be the same as the input frequency. For every one Hertz (or cycle per second), there
will be only one output pulse per second. Even though the half-wave only passes one alternation of the AC sine wave, it still produces an output voltage that is equal to the input voltage (peak) from the transformer’s secondary (Vs).
blocked
The solution to overcome the issues of the half-wave rectifier is the ___ ___ ___ rectifier.
full-wave bridge rectifier
A full-wave bridge rectifier utilizes ___ the input AC voltage rather than just half.
all
As seen in Figure 1-110, a full-wave bridge rectifier uses ___ diodes
instead of one. The diodes are arranged in a diamond pattern on the diagram for illustration purposes only.
four
The polarity of the DC voltage is determined by the orientation of the ___.
diodes
The output frequency of a half-wave rectifier is the same as the frequency of the input AC. The output frequency is measured in pulses per second (pps). If the input frequency is 60 Hz then the output frequency is ___.
60pps
Which type of rectifier is made from a single diode?
Half-wave rectifier
The output frequency of a full-wave rectifier is twice the frequency of the input AC. If the input frequency is 60 Hz then the output frequency is ___.
120pps
which type of rectifier is the following describing?
Two diodes, and a center-tapped secondary
Two output pulses
Full wave
which type of rectifier is the following describing?
Four diodes
Two output pulses
Easiest to filter
Full wave bridge
The easiest way to understand this is by determining which side of the diode is closest to the ___ ___ ___. Figure 1-111A shows a half-wave rectifier where the anode of the diode is closest to the transformer’s secondary. The anode is the positive material of the diode, so current will flow during the positive alternation, and the rectifier will generate a positive DC output signal. In Figure 1-111B, the diode is reversed. Now, the cathode is closest to the transformer’s secondary. Current will flow during the negative alteration, and the rectifier will generate a negative DC output signal. On the full-wave bridge rectifier, all diodes must be reversed to change the output of the DC signal’s polarity.
transformer’s secondary coil
The purpose of a ___ is to change pulsating DC into a smoother DC voltage.
filter
Although the output from an electronic rectifier circuit is technically DC, that is, all the current flows in the same direction, the voltage still rises and fall in rhythm with the AC input signal. This is true for both
the half-wave and full-wave rectifiers. The pulsating DC isn’t ___ ___ for most electronic applications. This is why filtering is required.
stable enough
In previous lessons, we learned that filters allow certain frequencies to pass and block others. In this application, we are using filters to “___” the wave to obtain a flat-line DC level.
shape
Filtering is usually accomplished by introducing a ___ into the power supply circuit. However additional components can be added to improve the filter’s quality.
capacitor
Notice in Figure 1-112 the capacitor is placed directly on the output of the ___ ___r. A capacitor has the useful characteristic of resisting changes in voltage. It accomplishes this by building up a charge across its plates when the input voltage increases. Then, when the input voltage starts to decrease, the voltage across the capacitor will not decrease as fast. The capacitor will start discharging its energy down through the grounds that are connected, up through RL to the top half of the capacitor. In other words, instead of the voltage going up and down in rhythm with the AC signal, like it does in the rectifier, the capacitor makes up the difference, keeping the voltage more constant across RL, as shown at the bottom of the figure.
bridge rectifier
The difference between the minimum DC voltage and the maximum DC voltage in the filtering stage is called the ___ ___ (Figure 1-113).
ripple amplitude
The bigger the capacitor, the more energy it stores, and the lower the resulting ripple amplitude. The lower the ripple amplitude, the smoother the filtered waveform, and the closer the output will be to a ___ ___ ___.
flat DC voltage
Capacitor resists changes in ___.
voltage
Ripple voltage, or just ripple, is the difference between the ___ DC voltage and the ____ DC voltage in the filtering stage.
minimum
maximum
The filter circuit can be improved by using two ____ in combination with a ___.
capacitors
resistor
Inductors can also be used in a filter circuit. Unlike a resistor-capacitor filter, an inductor-capacitor filter doesn’t significantly reduce the DC output voltage. Inductor-capacitor
filter circuits create the…?
smallest ripple on the output
Because consistent DC voltage is critical in electronic equipment, ___ ___ are necessary to maintain a constant voltage level.
voltage regulators
Voltage regulator circuits maintain power supply output at a ____ voltage level, even with changes in load resistance or changes in input voltage.
predetermined
A shunt voltage regulator is also called a ___ ___.
Zener Diode
The output voltage of a power source can change for two reasons:
a) there is a change in input voltage, or (b) current being drawn from the load changes.
Many electronic circuits operate satisfactorily with a moderate amount of variation in the power supply voltage output. However,
some circuits are very sensitive and even a slight deviation from the normal supply voltage will cause unsatisfactory operation of the load circuit/device. These load circuits require a ___ ___ ___ be inserted between the filter and the load. The purpose of voltage regulator circuits is to maintain a constant DC voltage output despite variations in the AC source voltage or changes in the resistance of the load device.
voltage regulating circuit
The Shunt voltage regulator, also called a Zener diode voltage regulator, has the Zener diode in ___, or shunt, to the load device.
parallel
The Shunt voltage regulator, also called a Zener diode voltage regulator, has the Zener diode in parallel, or shunt, to the load device. Figure 1-116 shows the Zener diode (D1) is in parallel with
the load device and in series with the current-limiting resistor (R1). Note also that the normal current flow through a Zener diode is with the ___. The reverse bias voltage of D1 regulates the output voltage on the load. The entire operation of the shunt regulator is in response to changes in voltage or current.
arrow
If the input’s supply voltage from the filter increases, current also increases. This increase in current is ___ from the load because of the Zener diode.
diverted
The shunt voltage regulator will also correct for ___ ___ that may occur due to changes in current in the load device(s).
voltage changes
Remember from prior lessons that current changes are caused by
either a change in ___ or ___ (Ohm’s Law).
voltage or resistance
Resistance changes are more common. An example of this would be if additional ___ ___ are added or subtracted.
load devices
Remember that if you add or subtract parallel branches the total circuit resistance changes. When that happens, it changes the voltage on the ____ of the regulator.
input
Even though a shunt voltage regulator regulates output voltage, it is limited to a predetermined input voltage range (set by the manufacturer), therefore it cannot handle ___ ___.
large fluctuations
Load device is the actual device(s) which draw current from the ___ ___.
power supply
Load is the ____ drawn by the load device
current
A ___ ___ ___ resistance means there is a large load or demand for high current is required
low load device
Change in input voltage or change in current drawn from the source (called “____” the circuit) can cause the output voltage of a power source to change.
loading the circuit
Voltage regulators are necessary to maintain…?
constant output voltage level
