Year 1 Power and Energy: AC Circuits Flashcards by Falu Mutshipay

What does T&D stand for in “The conventional electrical T&D system”?

Transmission and Distribution

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What are the four parts of the conventional electrical T&D system?

Bulk generation
Transmission system
Distribution system
The consumers

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What happens during the bulk generation part of the conventional electrical T&D system?

Energy is provided to the system

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What happens during the transmission system part of the conventional electrical T&D system?

Bulk energy is transferred using high voltage alternating currents which are very efficient

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What happens during the distribution system part of the conventional electrical T&D system?

Energy is delivered to individual users from high voltage to low voltage for convenience and safety

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What happens during the consumers part of the conventional electrical T&D system?

The energy supply is absorbed

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What is the SI unit and symbol of length?

Meter, m

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What is the SI unit and symbol of time?

Seconds, s

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What is the SI unit and symbol of mass?

Kilogram, kg

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What is the SI unit and symbol of temperature?

Kelvin, K

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What is the SI unit and symbol of electric current?

Ampere, A

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What are the units and alternative SI expression of Force?

Newton(N)
kg.m/s²

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What are the units and alternative SI expression of Energy?

Joule(J)
N.m

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What are the units and alternative SI expression of Electric charge?

Coulomb(C)
A.s

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What are the units and alternative SI expression of Power?

Watt(W)
J/s = N.m/s

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What are the units and alternative SI expression of Voltage?

Volt
W/A = N.m/s/A

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What are the four parts of the basic electrical system?

The source
The load
The transmission/distribution system
The control apparatus

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How does an electrical system transmit energy?

Due to the movement of electric charge

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What is current?

The rate of flow of charge

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What happens when 1C of charge crosses an area in 1 second?

A current of 1A flows

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What are the conditions for continuous current flow?

Complete circuit
Presence of a driving influence

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Define electromotive force(EMF)

The energy expended during the passing of a unit charge through a source

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Define potential difference(PD)

The energy expending during the passing of a unit charge between two points of a circuit

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How is current measured?

At one point and has a direction

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How is voltage always measured?

Across two points and has a polarity

What is the link to electrons and conventional current?

Electrons move in the opposite direction to conventional current

Define power

The rate of change of energy with time

State Ohm's Law

For a given material, voltage is directly proportional to current at a constant temperature

What is conductance?

The reciprocal of resistance

What is the symbol for conductance?

What is the units for conductance?

Siemens(S)

Define a short circuit

Direct connection between two points in a circuit, with zero resistance

Describe the types of short circuit

- Deliberate short circuit: Normally a connecting wire - Accidental short circuit: Usually very bad as they cause very high currents and destruction of components

Define an open circuit

- No connection between two points in a circuit, i.e infinite resistance - Sometimes caused by a bad solder joint

Define load

The power dissipated in a load resistor

What happens when there is no load?

- No load = No load power - Current = 0 - Infinite resistance, i.e an open circuit

What is a node?

Any point where two or more circuit elements are connected together

What is a branch?

A circuit element between two nodes

What is a loop?

A collection of branches that form a closed path returning to the same node without going through any other nodes or branches twice

Define Kirchoff's Current Law(KCL)

At any instant, the algebraic sum of all the currents at a node in a circuit is equal to zero

Define Kirchoff's Voltage Law(KVL)

At any instant, the algebraic sum of all the voltages around a closed path in a circuit is equal to zero

What is a closed path?

A loop traced through connecting elements, starting and ending at the same node and encountering each intermediate node only once

State the equation that displays the experimental relation between current and capacitance

I ≈ C dv/dt

What is the role of the resistor?

To limit the flow of electrical current in a circuit

State 2 features of conventional generation

- Dispatchable - Simple power flow in one direction

What is the role of a switchgear?

Connect and disconnect under normal and fault conditions

Define parasitic capacitance

Capacitance caused by the space between cables connecting conductors

Define 1 Farad

Capacitor is able to store one coulomb of charge when the voltage across it is one volt

What is an inductor?

Circuit element able to store electromagnetic energy in its magnetic field

What is the unit of inductance?

Henrys(H)

What is the equation for energy stored in an inductor?

W = ½L²

What is the equation for energy stored in a capacitor?

W = ½CV²

What is the equation for capacitors in series?

1/Ceff = 1/c1 + 1/c2

What is the equation for capacitors in parallel?

Ceff = c1 + c2

How does an ideal voltage source work?

- Always supplies the same voltage - The current delivered by it, changes with the load

Define power

The rate of change of energy over time

What does a positive sign on a circuit element indicate?

Power is absorbed

What does a negative sign on a circuit element indicate?

Power is supplied

How does an ideal current source work?

- Always supplies the same current - The voltage delivered by it, changes with the load

State the voltage divider rule equations

- v1 = V x r1/r1+r2 - v2 = V x r2/r1+r2

State the current divider rule equations

- i1 = i x r2/r1+r2 - i2 = i x r1/r1+r2

What is the equation for resistors in series?

Reff = r1 + r2 + r3

What is the equation for resistors in parallel?

1/Reff = 1/r1 + 1/r2 + 1/r3

What is the equation for TWO resistors in parallel?

Reff = r1 x r2/r1 + r2

What can an ideal voltage source be replaced with, and why?

- A short circuit - As the internal resistance is zero

What can an ideal current source be replaced with, and why?

- An open circuit - As the internal resistance is infinite

What is the relationship between voltage and inductance?

V = L di/dt

State superposition theorem

In any network containing more than one source, the current in or the voltage across any branch can be found by considering each source separately and adding their effects

Year 1 Power and Energy: AC Circuits Flashcards

(68 cards)