The National Grid Flashcards
What is the national grid?
The National Grid is a system of cables and transformers linking power stations to consumers.
How electrical power transferred from power stations?
Electrical power is transferred from power stations to consumers (anywhere on the grid/supply) using the National Grid.
Throughout the day electricity usage changes, what does this mean for the role of power stations?
The usage changes and therefore, the demand also changes. This means that power stations have to produce enough electricity for everyone to have it when they need it.
When will demand be higher?
in the morning when people wake up. When people come home from school or work, when it starts to get darker and colder outside, when popular events are taking place like on a TV.
Why do Power stations often run at well below their max power output?
Power stations will often run at well below their max power output so there’s spare capacity to cope with a high demand even if there’s an unexpected shut down of another station. Lot’s of smaller power stations that can start up quickly are also kept in standby just in case.
What is needed to transmit the huge amount of power needed?
Either a high current or a high pd.
What’s the disadvantage of using a high current to transport the huge amount of power needed?
A high current causes the wires to heat up and energy is therefore transferred to the thermal energy store of the surroundings. This means that, a high current means you lose loads of energy.
How does the national grid transmit the huge amount of power efficiently?
So a high pd is used. A high pd also means a lower current so there’s less energy by heating the wires and the surroundings. This makes the national grid an efficient way of transferring energy.
What are used to increase the pd?
To get the pd to 400 000V in order to transmit power, requires transformers as well as bug pylons with huge insulators - but its still cheaper.
What do transformers do? Why?
They have to step up the pd at one end for efficient transmission then bring it back down to safe usable levels at the other end.
What do step up transformers do?
Step-up transformers are used to increase the potential difference from the power station to the transmission cables.
What do step down transformers do?
Step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.
How efficient are transformers?
Almost 100% so you can assume the input power = output power
Input power = output power
V(s) I(s) = V(p) I(p)
V(s) = pd across secondary coil
I(s) = current thru secondary coil
V(p) = pd across primary coil
I(p) = current thru primary coil
