POWER SYSTEMS

GENERATION

TRANSMISSION

DISTRIBUTION

COMPONENTS

SMART GRID

HISTORY

FUN ZONE

Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment and household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level.

A distribution substation is located near or inside city/town/village/industrial area. It receives power from a transmission network. The high voltage from the transmission line is then stepped down by a step-down transformer to the primary distribution level voltage. Primary distribution voltage is usually 11 kV, but can range between 2.4 kV to 33 kV depending upon region or consumer.

A typical power distribution system consists of:
* Distribution substation
* Feeders
* Distribution Transformers
* Distributor conductors
* Service mains conductors
Along with these, a distribution system also consists of switches, protection equipment, measurement equipment etc.

Distribution feeders: The stepped-down voltage from the substation is carried to distribution transformers via feeder conductors. Generally, no tappings are taken from the feeders so that the current remains same throughout. The main consideration in designing of a feeder conductor is its current carrying capacity.

Distribution transformer: A distribution transformer, also called as service transformer, provides final transformation in the electric power distribution system. It is basically a step-down 3-phase transformer. Distribution transformer steps down the voltage to 400Y/230 volts. Here it means, voltage between any one phase and the neutral is 230 volts and phase to phase voltage is 400 volts. However, in USA and some other countries, 120/240 volts split-phase system is used; where voltage between a phase and neutral is 120 volts.

Distributors: Output from a distribution transformer is carried by distributor conductor. Tappings are taken from a distributor conductor for power supply to the end consumers. The current through a distributor is not constant as tappings are taken at various places throughout its length. So, voltage drop along the length is the main consideration while designing a distributor conductor.

Service mains: It is a small cable which connects the distributor conductor at the nearest pole to the consumer's end.

Primary Distribution
It is that part of an AC distribution system which operates at somewhat higher voltages than general residential consumer utilization. Commonly used primary distribution voltages in most countries are 11 kV, 6.6 kV and 3.3 kV. Primary distribution handles large consumers such as factories and industries. It also feeds small substation from where secondary distribution is carried out. Primary distribution is carried out by 3-phase, 3-wire system.

Secondary Distribution
This part directly supplies to the residential end consumers. Domestic consumers are fed with single phase supply at 230 volts (120 volts in USA and some other countries). Three phase supply may also be provided at 400 volts for big properties, commercial buildings, small factories etc. Secondary transmission in most countries is carried out by 3-phase, 4-wire system.

The key of successful power delivery to the load center is to design and implement a reliable and stable distribution network. Power provision to individual customer’s premises can be enhanced through a proper and efficient electrical power distribution system. Distribution network are vulnerable by natural disaster, such as earthquake and cyclone. As each system is designed under natural disaster rated units, the damages sustain can affect the restoration of power network prolongs based on the design, control and management of that particular network.

Many electric distribution organizations are presently evaluating their approach to integrating three key operational systems – SCADA (Supervisory Control and Data Acquisition), OMS (Outage Management System) and DMS (Distribution Management System). SCADA, which has long been prevalent throughout transmission systems, is finding increased applications on distribution systems. Modern OMS, utilizing GIS-based connectivity models, is now well established and a key component of many organizations’ outage management business processes. The implementation of DMS functionality is a relatively recent trend. While a DMS can include and improve the traditional outage management functions, a DMS also typically includes applications that assist in the improved operation of the electric distribution system, as well as functionality for improving planned work on the system.

Recently, renewable energy sources are widely being used to meet the energy demand. Energy generation in the distribution levels provide benefits for both the user and the electricity provider as generation in distribution network can reduce the transmission losses, as well as costs for power generation. To provide good power quality and reliability to the customers, we require new technologies in electric utilities.

The paradigm of passive distribution networks, with a sole aim of transporting energy from transmission grid to the end-customers is rapidly fading away. With a significant rise in proliferation of distributed energy resources (DERs) around the globe, we are witnessing a shift of this paradigm as we enter the world of highly complex distribution systems. Dynamically changing distribution grid, means that its conditions are changing in real-time. This can be caused by EVs, volatile nature of renewable DERs, and so on. Active and dynamically changing distribution grid is the most complex case, when there are all types of DERs connected to the distribution level, that cause a dynamically changing environment in real-time.