Download - Transmission n Distribution Basic
Transmission and Distribution
Lecture Outline
• The electricity supply chain• Components of an electrical power system• Power Lines
– Standard voltages– Equivalent circuit, voltage regulation and
power transmission capability– Choosing the line voltage
• Substation Equipment
The Electricity Supply Chain
Generation
Transmission
Distribution
Retail
National Electricity Market
Principal components of an electrical power system
Power Station Substation
System Loads
SubstationTransmission Lines
Distribution Lines
• Step-up transformers & switchgear
• Step-down transformers & switchgear
• lighting
• heating
• appliances
• motors
Power Lines
Power LinesConsiderations in the design of a power line:• The amount of active power it has to transmit• The distance over which the power must be
carried• The cost of the power line• Aesthetic considerations, urban congestion,
ease of installation, expected load growth
Types of Power LinesPower Station Substation
System Loads
Transformer
Substation
High voltage (HV)
Medium Voltage (MV)
Low Voltage (LV)
e.g. Swanbank
e.g. Tennyson
e.g. Pole-mount
e.g. House
Standard Voltages
132kV, 275kV, 400kV, 750kV
> 100kVHV
3.3kV, 6.6kV, 11kV, 33kV, 66kV
1kV – 100kVMV
415V (3-phase)240V (1-phase)
< 1kVLV
Standard levelsRangeClassification
HV Power Line ComponentsConductors• Normally bare• Stranded copper or steel-reinforced aluminium cable (ACSR)
Insulators• Support and anchor conductors and insulate them from ground• Ceramic or glass• Must withstand mechanical and electrical stress
Support Structures (towers etc.)• Wooden poles / H-frames for lower voltages, galvanized steel
towers for higher voltages
Equivalent circuit of a line
Distributed impedance of a line
Lumped model
Inductive impedance is normally low
Capacitive impedance in normally high
Resistance varies with transmission voltage and power…
Voltage Regulation and Power Transmission Capability of Transmission Lines:
Resistive Line
0%10%20%30%40%50%60%70%80%90%
100%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Vload / Vsupply
P /
Pm
ax
Load
R
Supply
RV
P ply
4
2sup
max =
Load has unity power factor
Voltage Regulation and Power Transmission Capability of Transmission Lines:
Inductive Line
Load
L
Supply
L
ply
XV
P2
2sup
max =
Load has unity power factor
0%10%20%30%40%50%60%70%80%90%
100%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Vload / Vsupply
P /
Pm
ax
Choosing the Line Voltage• The voltage should remain as constant as
possible over the entire length of the line – from source to load – for all loads between zero and rated load.
• The line losses must be small so as to attain a high transmission efficiency and not overheat the conductorsThere is a trade-off between capital cost and
transmission losses in the choice of line voltage for a given power transmission capability
Substations
Substation Equipment• Transformers• Circuit breakers• Switches (horn-gap, disconnect & grounding)• Surge arrestors• Current-limiting reactors• Relays and protective devices• Instrumentation• See text for more info and examples