Electricity Basics Flashcards
Use this deck to learn about all of the basics of electricity.
A 2500-W inverter is used to supply a 120-V AC load of 1500 watts. The ampacity of the wire at the inverter output must be at least how much?
26 A
What determines the voltage drop (not voltage drop percentage)?
Resistance and current
The duration, path, and path amount of current are all factors that depend on what?
The severity of electrical shock
What is a common use for linear current boosters?
Direct pumping applications and drop voltage
How does a battery charger work?
A battery charger sends an electric current through the battery in an efficient manner
Wire width determines what?
Ampacity
What are sealed batteries?
Valve-regulated lead-acid batteries
Four 6-volt, 240-Ah batteries are connected in 2 series groups, and there are 120-Ah batteries by another manufacturer available. Under what circumstance is it acceptable to incorporate all of these batteries into a 12-volt PV battery storage bank?
There is no acceptable connection of the batteries into a single battery bank
Can the same inverter used for a grid-tied system be used for off-grid with a charge controller?
No
A 26 ampacity of the wire at the inverter output with a 2500-W inverter is used to supply what?
A 120-V AC load of 1500 watts
If the maximum AC output of an inverter with 120-V AC output is 1500 W, what should be the rating of the circuit breaker at the point-of-utility connection?
20A
What is measured in watts per square meter?
Irradiance
What is the first step in system checkout?
Visually checking the entire system
All else being equal, what happens to temperatue when PV system voltage increases?
Since voltage and temperature have an inverse relationship, temperatue will decrease as PV system voltage increases.
What can a bimodal do?
It can work as grid-tied or stand-alone
What does low cell temperature do?
Increases voltage
What does irradiance proportionally affect?
Amperage
If the open circuit voltage (Voc) of a crystalline silicon PV array is 315V at 25 degree Celcius (STC), then according to the NEC (National Electric Code) chart, if the array is operated at -20 degrees Fahrenheit, maximum system voltage must be corrected to?
369 V
What is between the inverter and the array?
DC disconnect and/or sometimes a charge controller
A crystalline silicon PV array that has bipolar outputs of + 252V and - 252V with a common grounded conductor under Standard Test Condition is selected for a large single-family residence. The lowest expected temperature at the installation site is -25 degrees C. For this system, the maximum system voltage is closest to what?
605V
Valve-regulated lead-acid is a type of battery that is between what?
Sealed batteries
What can coincide with a loss of power in a 2 phase system?
Loss of power in a 3 phase system
What is an advantage of larger wire size?
Lower wire temperature, which decreases overall risk of electrical hazards.
What type of measurement do amperes express?
Rate of electric charge in circuit (current)
Besides increased ampacity potential, what should wires be oversized in battery interconnections?
To keep all battery currents as equal as possible
What factors affect ampacity?
Temperature, conductor type, and insulation type
Which of the following exhibits the most distortion: square wave, modified sine wave, and sine wave?
Square wave
What is sometimes in a grid-tied system?
Charge controllers
If an inverter is at maximum current, 2500W, full rating closest to 129A, and 88% efficiency, what is the input-voltage range at full output?
____V to ____V.
22V to 32V
When is a wire better than a conductor?
If the gauge is a number below 8
A 12 watt light is working on 12 volts. Approximately how many kilowatt hours does it use in a year if it is on 8 hours a day?
12w x 8hrs x 365 days/100 = 35.04 kwh/yr
On an I-V curve, what causes the curve to rise vertically?
More sunlight, more panels in series, and/or more amperage
What type of weather causes a voltage drop?
Because voltage and temperature have an inverse relationship, hot weather causes voltage to drop.
How do you find the wattage at the maximum power point?
Multiply the voltage at maximum power by the current at maximum power
An over-current protection, fuse, and switch all have the same function as what?
Circuit breaker
How do you find the value of the current at the maximum power point on the I-V curve?
Extend a horizontal line from the curve in order to read the value on the vertical current scale, which represents the Imp
If the rating of the circuit breaker at the point-of-utility connections is 20A, then what is the maximum AC output rating of an inverter with 12-V AC?
1500 W
Ohm’s Law states that an increase in resistance is proportional to what?
An increase in voltage
On a cloudy day, what effect does Ohm’s law have on PV watts?
PV watts decrease because of the relationship of volts to watts
Which component of a PV system does NOT require UL or equivalent listing?
The concrete anchors
Visually inspecting the entire system is the first step to what?
System checkout
What is the term for what happens when you add small amounts of impurity elements to semiconductors to alter their electrical properties?
Doping
How is irradiance measured?
Watts per square meter
A 100 watt light bulb is working on .91 amps. How many volts are there?
110 volts
V = P/I = (100/.91) = 110
What is the maximum number of series connected Kyocera KC200GT (Vmp = 26.3) modules that would be in the operating range of the SMA 2500 U inverter? Assume STC conditions.
22
The ___ converts DC at one voltage to AC at the same or another voltage.
Inverter
How does wire size relate to temperature?
Increased wire size prevents wires from over-heating
When are charge controllers required?
For systems with PV amps that are more than 3% of the battery capacity
An AC connect is between what?
The panel and the inverter
If the gauge is a number below 8, then the wire is what?
A better conductor
Vmp is horizontal to Imp on what?
On an I-V curve
What type of inverter can work as grid-tied or stand-alone?
Bimodal
In terms of voltage, Amps determine what?
Voltage drop (not voltage drop percentage)
In the event that the utility voltage is lost in a utility-interactive system that has battery backup and an optional standby system AC distribution panel, what happens if the inverter is programmed in the sell mode?
The inverter should not supply power to the terminals connected to utility point-of-connection.
A crystalline silicon PV array that has bipolar outputs of + 252V and - 252V with a common ground conductor under STC is selected for a large single-family residence. The lowest allowable ambient temperature in which the system can be installed at a single-family dwelling is what?
-25 degrees Fahrenheit
If the current in one source circuit is significantly lower than the currents in the remaining source circuits of a PV array, and all modules are in full sun, then without disconnecting any conductors, what is an appropriate follow-up test?
To measure the individual module voltages in this source circuit
A 2500-W inverter with an input-voltage range of 22V to 32V has an efficiency of 88% at full output. What will the maximum inverter input current at full rating be closest to?
129 A
What converts a high input voltage to a lower output voltage and a low input current to a higher output current?
A linear current booster
What is the order of wave types from most distorted to least distorted?
Square wave, modified sine wave, sine wave
What does the order of PV charge controller, battery inverter, and grid accomplish?
Utility interconnection
Why are sine wave inverters required for connection to utility lines?
They are the only inverters that have low enough harmonic distortion
What does irradiance NOT affect proportionally?
Nominal operating cell temperature (NOCT), air mass, and voltage
A 200 watt clothes dryer is working on 220 volts. How many kilowatt hours does it take to dry clothes for 45 minutes with a duty cycle of 50%?
200 w = 2kw x .75hr x .5 duty = .75 kwh
What is irradiance?
Power
What is commonly used in direct pumping applications and drop voltage?
Linear current boosters
Imp is on the vertical y-axis of what?
An I-V curve
What does the severity of electrical shock depend on?
The duration, path, and amount of current
If I = V/P then what do V and P equal?
V = IR and P = VI
The purpose of a linear current booster is to…
Convert a high input voltage and low input current to a lower output voltage and a higher output current.
The purpose of an inverter is to…
Convert DC at one voltage to AC at the same or another voltage.
A 100 watt light bulb is working on 110 volts. How many amps are there?
0.91
(100/110)
What is the order of devices by which utility interconnection is accomplished?
PV charger controller, battery inverter, grid
What is between the panel and the inverter?
An AC disconnect
The possibility of using junction boxes (terminal blocks) or switch boxes that are too small to house the large wire is a concern associated with what?
A concern with 12-V PV systems that use large wire sizes to minimize voltage drop
Keeping all battery currents as equal as possible is a good reason for doing what?
A good reason for large wire sizes in battery interconnections even if they are oversized for ampacity
Is STC an I-V curve parameter?
No
Where are functions of linear current boosters commonly used?
In grid-tied systems
Does an electrolyte freeze if a battery is fully charged?
No. Unless the temperature drops to -92 fahrenheit
Concrete anchors do NOT require what?
UL or equivalent listing
What is doping?
Adding small amounts of impurity elements to semiconductors to alter their electrical properties
