Electrical Circuits Transmission Haroon Junaidi Types Transmission Rectifiers

Electrical Circuits & Transmission Haroon Junaidi

Types • • Transmission Rectifiers Full Bridge Rectifiers Ballast Loads

Transformer The ratio of primary to secondary coil winding dictate the output voltage

Energy Losses in Transformer • Energy is dissipated in the windings, core, and surrounding structures • Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%.

Full Bridge Rectifier

Full Bridge Rectifier

Three Phase Rectification

Electrical Transmission • Power is transmitted at various voltages and both is AC and DC • HVDC offer greater efficiency over longer distances • No insulation is used on the wire • Power lines connecting UK to France and Northern Ireland are HVDC • Transmission voltages are in the range of 500 -138 KV: • In Scotland 275 k. V is the transmission voltage for bulk of the country

Electrical Transmission

Grid Facts Network Size The following figures are taken from the 2005 Seven Year Statement (SYS) • Maximum demand (2005/6): 63 GW (approx. ) (81. 39% of capacity) • Annual electrical energy used in the UK is around 360 TWh (1. 3 EJ) • Capacity (2005/6): 79. 9 GW (or 80 GW per the 2008 Seven Year Statement) • Number of large power stations: 181 • Length of 400 k. V grid: 11, 500 km (circuit) • Length of 275 k. V grid: 9, 800 km (circuit) • Length of 132 k. V (or lower) grid; 5, 250 km (circuit)

Grid Facts - Network Losses Figures are again from the 2005 SYS. • Joule heating in cables: 857. 8 MW • Fixed losses: 266 MW (consists of corona and iron losses; can be 100 MW higher in adverse weather) • Substation transformer heating losses: 142. 4 MW • Generator transformer heating losses: 157. 3 MW • Total losses: 1, 423. 5 MW (2. 29% of peak demand) • Although overall losses in the national grid are low, there are significant further losses in onward electricity distribution to the consumer, causing a total distribution loss of about 7. 7%. • Losses differ significantly for customers connected at different voltages; connected at high voltage the total losses are about 2. 6%, at medium voltage 6. 4% and at low voltage 12. 2%

Corona Discharge

Transmission Wire • Transmission wire are predominantly made up of Aluminium • Voltages less than 33 k. V are usually used for distribution • In the UK transmission costs are about 0. 2 p/k. Wh compared to a delivered domestic price of around 10 p/k. Wh • Burying underground cables (UGC) is the secondcheapest way of transmitting power but lifetime costs are £ 10. 2 m–£ 24. 1 m per km, compared to £ 2. 2 m– £ 4. 2 m per km for overhead lines (OHL), the government-commissioned report found.

Pylons

Pylons • Pylons are a source of visual pollution • Underground cables can cost as high as 18 time more than overhead counter parts • Find out the cost per km of laying pylons on a flat terrain?

HVDC • • • Large amount of power to long distances Small amount of power to small distances http: //www. youtube. com/watch? v=g 17 f 9 J 1 -r-k http: //www. youtube. com/watch? v=_DRMk. N 6 ew. VU Have lower foot print for the same amount of power Lower losses Terminal station and reconversion is costly Less Corona Discharge Thyristors are used for conversion

Transmission Losses • Electronics Use DC • Transmission Uses AC • Every electronic device has an adopter where power is lost

Smart Grid • Grid makes use of feedback • http: //www. youtube. com/watch? v=Yrcq. A_cq. R D 8 • What are the savings expected from a smart grid