Transmitting electricity Flashcards
electric current
Current (electric is) the rate of flow of electric charge
Voltage/potential difference
Voltage is a measure of the change in the stored electrical energy per unit charge associated with the difference between two positions in an electric field.
Resistance (electrical)
Resistance is a measure of the opposition to the flow of electric current
Resistor
A resistor is an electrical component that resists the flow of electric current and causes a drop in voltage. Components such as light bulbs and heaters can be modeled as resistors
Series circuit
Series circuit is an electric circuit where components are connected one after the other so that there is only one path along which charge can flow
RMS (root mean square)
RMS (root-mean-square) is a measure of a time-varying (such as AC) voltage or current. A constant DC voltage or current with the same value as the RMS would deliver the same average power
Transformer
Transformer a device that uses electromagnetic induction to transfer power from one electrical circuit to another, commonly with an exchange of current for voltage, or vice versa, while (ideally) keeping the power constant
Load (electrical)
Load (electrical) is a part of an electrical circuit which consumes power.
Define Ohms Law and Formula
Ohm’s law defines the relationship between the voltage across an electrical component, the current through the component, and the resistance of the component. This given through the formula V=RI V = voltage between two points in a circuit (V) R = resistance between the two points (Ω), I = current flow between the two points (A)
Diagrams of circuit components and its circuit symbol.
Resistors in a series and its formula
The total resistance of the number o resistors connected in series is the sum of their individual resistances.
RT = R1 + R2 + …+ Rn
R = resistance (Ω)
Power in electric circuits formulas
P=VI**
P=I2R=V2/R
P = power (W), I = current (A), R = resistance (Ω), V = voltage (V)
*The equation was derived through understanding that V=ΔE/ΔQ and I=ΔQ/ΔT
What is the RMS Theory of an AC supply?
As an AC (alternating current) has a changing direction of current, voltage, and power this results in a sinusoidal graph. There are three alternatives descriptions which are the RMS, Peak to Peak, and Peak to both voltage and current.
The peak value describes the amplitude (maximum value) of the voltage or current.
The peak-to-peak value describes the difference between the maximum and the minimum values.
The RMS value is a fixed proportion of the peaked value which is the square root of the voltage squared.
Diagram of a labeled RMS, Peak, Peak to Peak AC Graph
\b
Formulas for finding VRMS and IRMS
What is the comparison between the RMS and a DC supply? Provide the formula/s relevant
What does a transformer consist of and how does it operate?
A transformer consists of two coils of wire (primary and secondary) wrapped around the same iron core.
The Transformer can operate once an AC current flows through the coils which produces a change in magnetic fields. This field is produced via the primary coil and then guided through the iron core to the secondary coil to create a changing magnetic flux.
As a transformer with an AC current which causes a changing magentic flux what is induced?
According to Faradays law a change in magnetic flux will result in an EMF and a current in the secondry coil.
What occurs when a transformer is induced with a DC current
The magnetic flux in the secondary coil would also be constant, which means that no EMF would be induced in the secondary coil.
What is an ideal transformer and what does that result with?
An Ideal transformer means that all of the power delivered to the primary coil is transferred to the secondary coil. Which gives the formula:
P1 = P2 so V1 I 1 = V2 I 2
What is the relationship with the primary and secondry coil within a transformer?
Step-up transformer
A step-up transformer is one where the voltage in the secondary side is greater than the voltage in the primary side.
Step Down transformer
A step-down transformer is one where the voltage in the secondary side is less than the voltage in the primary side.
What are the properties of a step-up transformer?
The number of turns in the secondary coil is greater than the primary coil. (N1<n>2) </n>
The voltage in the secondary coil is higher than the primary voltage V1 < V2
The current decreases from the primary coil to the secondary coil making I1>I2
What are the properties of a step-down transformer?
The number of turns in the secondary coil is less than the primary coil. (N1>N2)
The voltage in the secondary coil is lower than the primary voltage V1 >V2
The current increases from the primary coil to the secondary coil making I1<i2></i2>
What does simple power transmission system consist of?
A power system consist of a power supply/ generator, transmission lines, and a load (an electrical circuit that consumes power)
What is the formula regarding voltage drops that follows Ohms law?
Vdrop = Iline Rline
Vdrop = voltage drop across the transmission lines (V)
Iline = current in the transmission lines (A)
Rline = resistance of the transmission lines (Ω)
What is the formula/s to power loss due to the resistance in the transmission lines?
Ploss = Vdrop Iline = ILine2Rline
Ploss = power loss in the transmission lines (W)
Vdrop = voltage drop across the transmission lines (V),
I line = current in the transmission lines (A)
Rline = resistance of the transmission lines (Ω)
What is the formula for the power delivered to the load?
The power delivered to the load will be the difference between the power supply and the power loss.
Pload = Psup − Ploss
*This also applys to Transformers
What is one advantage of AC power to DC power?
AC power has an advantage over DC power for the transmission of electricity because transformers can be used.
Why does a transformer and DC power not work?
A Transformer cannot work on DC because, the primary coil will create a uniform and constant magnetic field, which will fail to induce EMF in the secondary coil.
Advantagesof AC power
The advantage of AC power as a domestic power supply is its compatibility with transformers which can reduce power loss. This is due to that transformers require changing current that only benefits from AC power.
How are transformers used to reduce power loss?
As electrical power is the product of current and voltage (P = VI) this means different levels of voltage and current can create the same amount of Power. As it is found both voltage drop and power loss is related to current by therefore reducing current it can allow for minimal power loss.
Therefore using a low current but high voltage results in less power loss which is shown through the formula: (Ploss = Iline2 Rline )
Voltage drop is also dependant on current as shown through: Vdrop = IlineRline
How can a step-up transformer affect the power supply to the transmission lines?
A step-up transformer between the power supply and the transmission lines allows power to be generated at a high current/low voltage and be transmitted at a low current/ high voltage.
How can a step-up transformer affect the power to the transmission lines and the load?
A step-down transformer between the transmission lines and the load allows power to be transmitted at a low current/high voltage and be consumed at a high current/low voltage
