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Electrical Science > Year 1 > Flashcards

Year 1 Flashcards

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1
Q

What is extra low voltage

A

24v,12v,1.5v

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2
Q

What is the power equation

A

P
—
Ixv

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3
Q

What are the 4 transmission voltages

A

400kv, 275kv, 132kv, 66kv

Overhead lines

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4
Q

What are the 4 distribution voltages

A

11kv, 400v,230v,33kv

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5
Q

Name 5 renewable energy

A

Wind, solar, geothermal, water-tidal, biomass

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6
Q

What is periodic time

A

The time it takes to complete one full cycle

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7
Q

What equation do you use to work out XL (inductive reactance)

A

2x3.14xfxL(___ Henry’s )

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8
Q

How to work out impedance (z)

A

Square root of r2 (resistence)+ XL2 (squared)(inductive reactance)

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9
Q

How do you calculate periodic time

A

Periodic time= 1
—
F ( frequency)

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10
Q

What equation would you use to calculate numbers in a transformer question

A

Np Vp Is
— = — =. —
Ns Vs Ip

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11
Q

Explain the 4 step process of coal being used to generate electricity in power stations

A

Burn coal > heat water into steam > pressurise the steam to turn the turbine > turbine will rotate the generator.

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12
Q

How does a transformer work

A
  • Alternating voltage is applied across the primary coil
  • Which then produces a magnetic field that is continuously changing
  • This changing magnetic field cuts through the coils of the secondary coil
  • An alternating voltage is then induced across the secondary coil
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13
Q

Why is it important to make sure each load on 3 phases are balanced

A

Because if they are not there will be a current flow in the neutral at the supply transformer

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14
Q

Single phase power equation

A

I x v x p.f

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15
Q

Three phase power equation

A

Square roots 3 x I x v x p.f

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16
Q

4 x None renewable energy

A

Oil
Nuclear
Coal
Natural gas

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17
Q

Generator definition

A

Converts mechanical energy into electrical energy

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18
Q

What is a generation voltage in kv

A

25kv

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19
Q

Name 2 main losses in a transformer

A

Iron losses

Copper losses

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20
Q

What is copper loss

A

Energy lost through ‘heat’ generated by current

It can be reduced by using good quality copper

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21
Q

What are 2 losses in iron loss

A

Eddy currents and hysteresis loss

22
Q

How do you make a transformer as efficient as possible

A

Need core to reduce leakage flux

And use laminated sheet

23
Q

What are 3 types of cooling system transformer

A

Gas cooling transformer
Air/ fan cooling transformer
Oil cooling transformer

24
Q

Describe the phaser diagram for voltage and current connected to a pure resistence

A

Voltage and current are the same

25
Q

Describe the phaser diagram for voltage and current where connected to a pure inductor

A

Currents lagging (L) shape

26
Q

Describe the phaser diagram for voltage and current when connected to a capacitor

A

Current leading by 90 degrees

Upside down L

27
Q

How do you calculate the current flow in a circuit when inductance is given

A

Work out xl if poss

  VL ———— IL    X.   XL
28
Q

How do you calculate current in a circuit when capacitance is given

A

Vc
———
Ic. X. Xc

29
Q

What’s the equation to find XC

A

1
————
2x3.14xfxc

30
Q

When calculating the hypotenuse on a triangle such as Z or kva
What equation is needed.

A 
Z= square root of Rsquared + XL squared
Kva= square root of kw squared - kvar squared
31
Q

What is KW

A

True power

32
Q

What is kvar

A

Reactive power

33
Q

What is kva

A

Apparent power

34
Q

What causes low power factors (x4)

A

Inductive loads which include

Transformers
Induction motors
Fluorescent luminaire’s
Anything electrical with a coil

35
Q

How do you improve lagging power factors

A

Add capacitors in parallel to the motor

36
Q

State what happens to current if you remove a capacitor

A

Current will increase

37
Q

What is true power

A

The power that actually works, useful power

Measured in kw or watts

38
Q

What is reactive power

A

Not useful
It’s lost power and it won’t do any work

Measured in KVAR

39
Q

What is apparent power

A

This is your total power

Measured in kva

40
Q

How to work out p.f in the R and Xl theory

In the right ght angled triangle

A

Adjacent
—————
Hypotenuse

41
Q

How do you reduce energy loss in a transformer

A

Using a laminated sheet

42
Q

What is potential energy

A

Comes in forms that are stored

Chemical
Gravitational
Mechanical
Nuclear

43
Q

What is kinetic energy

A

Forms of doing work

Electrical
Heat
Motion
Sound

44
Q

Whats the 12 step sequence of power stations

A

Fuel>furnace(burn)>boiler( turns into steam)>turbine>cooling tower>generator>electricity cables>step up transformer>pylons>step down transformer>homes>appliances

45
Q

List items used in the substation relevent to the transmission and distribution of electricity

A

Transformer
Circuit breaker
Fuses
Capacitor

46
Q

Name 3 main effects of current flow

A

Chemical effect
Heating effect
Production of magnetic affect

47
Q

What affects the output on a generator

A

Size of magnet, conductor and speed

48
Q

How do you work out electromotive force

A

E= BLV

49
Q

How can u reduce eddy currebts

A

Using a magnetic material with a high resistivity

The iron core is laminated

50
Q

How to reduce hysteresis

A

Make the core less magnetic

51
Q

Efficiency equation for efficiency of a transformer

A

Efficiency = power out
—————-
Power in

52
Q

What is hysteresis loss

A

Loss of energy from heat due to hysteresis

Electrical Science (2 decks)

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