Year 1 Flashcards
What is extra low voltage
24v,12v,1.5v
What is the power equation
P
—
Ixv
What are the 4 transmission voltages
400kv, 275kv, 132kv, 66kv
Overhead lines
What are the 4 distribution voltages
11kv, 400v,230v,33kv
Name 5 renewable energy
Wind, solar, geothermal, water-tidal, biomass
What is periodic time
The time it takes to complete one full cycle
What equation do you use to work out XL (inductive reactance)
2x3.14xfxL(___ Henry’s )
How to work out impedance (z)
Square root of r2 (resistence)+ XL2 (squared)(inductive reactance)
How do you calculate periodic time
Periodic time= 1
—
F ( frequency)
What equation would you use to calculate numbers in a transformer question
Np Vp Is
— = — =. —
Ns Vs Ip
Explain the 4 step process of coal being used to generate electricity in power stations
Burn coal > heat water into steam > pressurise the steam to turn the turbine > turbine will rotate the generator.
How does a transformer work
- 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
Why is it important to make sure each load on 3 phases are balanced
Because if they are not there will be a current flow in the neutral at the supply transformer
Single phase power equation
I x v x p.f
Three phase power equation
Square roots 3 x I x v x p.f
4 x None renewable energy
Oil
Nuclear
Coal
Natural gas
Generator definition
Converts mechanical energy into electrical energy
What is a generation voltage in kv
25kv
Name 2 main losses in a transformer
Iron losses
Copper losses
What is copper loss
Energy lost through ‘heat’ generated by current
It can be reduced by using good quality copper
What are 2 losses in iron loss
Eddy currents and hysteresis loss
How do you make a transformer as efficient as possible
Need core to reduce leakage flux
And use laminated sheet
What are 3 types of cooling system transformer
Gas cooling transformer
Air/ fan cooling transformer
Oil cooling transformer
Describe the phaser diagram for voltage and current connected to a pure resistence
Voltage and current are the same
Describe the phaser diagram for voltage and current where connected to a pure inductor
Currents lagging (L) shape
Describe the phaser diagram for voltage and current when connected to a capacitor
Current leading by 90 degrees
Upside down L
How do you calculate the current flow in a circuit when inductance is given
Work out xl if poss
VL ———— IL X. XL
How do you calculate current in a circuit when capacitance is given
Vc
———
Ic. X. Xc
What’s the equation to find XC
1
————
2x3.14xfxc
When calculating the hypotenuse on a triangle such as Z or kva
What equation is needed.
Z= square root of Rsquared + XL squared Kva= square root of kw squared - kvar squared
What is KW
True power
What is kvar
Reactive power
What is kva
Apparent power
What causes low power factors (x4)
Inductive loads which include
Transformers
Induction motors
Fluorescent luminaire’s
Anything electrical with a coil
How do you improve lagging power factors
Add capacitors in parallel to the motor
State what happens to current if you remove a capacitor
Current will increase
What is true power
The power that actually works, useful power
Measured in kw or watts
What is reactive power
Not useful
It’s lost power and it won’t do any work
Measured in KVAR
What is apparent power
This is your total power
Measured in kva
How to work out p.f in the R and Xl theory
In the right ght angled triangle
Adjacent
—————
Hypotenuse
How do you reduce energy loss in a transformer
Using a laminated sheet
What is potential energy
Comes in forms that are stored
Chemical
Gravitational
Mechanical
Nuclear
What is kinetic energy
Forms of doing work
Electrical
Heat
Motion
Sound
Whats the 12 step sequence of power stations
Fuel>furnace(burn)>boiler( turns into steam)>turbine>cooling tower>generator>electricity cables>step up transformer>pylons>step down transformer>homes>appliances
List items used in the substation relevent to the transmission and distribution of electricity
Transformer
Circuit breaker
Fuses
Capacitor
Name 3 main effects of current flow
Chemical effect
Heating effect
Production of magnetic affect
What affects the output on a generator
Size of magnet, conductor and speed
How do you work out electromotive force
E= BLV
How can u reduce eddy currebts
Using a magnetic material with a high resistivity
The iron core is laminated
How to reduce hysteresis
Make the core less magnetic
Efficiency equation for efficiency of a transformer
Efficiency = power out
—————-
Power in
What is hysteresis loss
Loss of energy from heat due to hysteresis
