Power Distribution Systems (EE 448) Lecture Notes PDF

Power distribution systems EE 448 - Electrical Engineering Department Assis. Prof. Saud Alotaibi [email protected] 2024-2025 Lecture 2: Power distribution systems Simple Power System ► In general, the definition of an electrical power system includes: ❑...

Power distribution systems EE 448 - Electrical Engineering Department Assis. Prof. Saud Alotaibi [email protected] 2024-2025 Lecture 2: Power distribution systems Simple Power System ► In general, the definition of an electrical power system includes: ❑ Generation : source of power, ideally with a specified voltage and frequency. ❑ Transmission : transmits power; ideally as a perfect conductor. ❑ Distribution : distributes electrical power for local use. ❑ Load : consumes power; ideally with a constant resistive value. Figure 1: Power system diagram. 3 Distribution System ❖ The distribution system is the final stage in the delivery of electricity, responsible for carrying power from the transmission system to individual consumers. ❖ Key Characteristics: i. Voltage Levels: Operates at lower voltage levels than transmission systems, typically in the range of 11 kV to 415 V, considered safer for local distribution. ii. Network Structure: Comprises a web of overhead or underground lines branching out from substations to reach diverse customer locations. ❖ Purpose: a. Deliver electricity reliably and efficiently to customers. b. Maintain consistent voltage levels within acceptable ranges. c. Protect the system from faults and overloads. d. Facilitate integration of distributed energy resources like solar panels and wind turbines. 4 Distribution components: ► Distribution line generally consist of : 1) Sub-transmission system. The sub-transmission circuits deliver energy from bulk power sources to the distribution substations. The sub-transmission voltage is somewhere between 12.47 and 245 kV. 2) Distribution substations. It is made of power transformers together with the necessary voltage-regulating apparatus, buses, and switchgear, It reduces the sub-transmission voltage to a lower primary system voltage for local distribution. 3) Primary feeders. The three-phase primary feeder, which is usually operating in the range of 4.16–34.5 kV, distributes energy from the low-voltage bus of the substation to its load center where it branches into three-phase sub-feeders and single laterals. Figure 2: A typical distribution system. 5 Distribution components: 4) Distribution transformers They are in ratings from 10 to 500 kVA, are usually connected to each primary feeder, sub-feeders, and laterals. 5) Secondary circuits They are the path to distribute energy from the distribution transformer to consumers through service drops. They reduce the distribution voltage to the utilization voltage. 6) Service drops A service drop is generally a small cable, which connects the distributor to the consumer's meter. 6 Distribution components: What is Feeders and Distributors in Distribution System ? ❑ Feeders: A feeder is a conductor which connects the sub-station (generating station) to the area where power is to be distributed. Characteristics: ▪ Typically, overhead lines or underground cables. ▪ It is feed the electric power to the distributor. ▪ No tapings are taken from the feeder. So, the current in it remains the same throughout. ▪ The main consideration in the design of a feeder is the current carrying capacity. 7 Distribution components: What is Feeders and Distributors in Distribution System ? ❑ Distributors A distributor is a conductor from which tappings are taken for supply to the consumers. (AB, BC, CD and DA) are the distributors. Characteristics: ▪ Can be overhead or underground lines, but often smaller and lighter than feeders. ▪ It is distributing electric power among various consumers, thus several tapping pints are taken from the distributor ▪ The current through a distributor is not constant because tappings are taken at various places along its length. ▪ The main consideration in the design of a distributor is voltage drop along its length. 8 Classification Of Distribution System ❖ It can be classified under different considerations as; a) Number Of Wires: o Two Wire o Three Wire o Four Wire b) Scheme Of Connection:. o Radial Distribution System o Ring or Loop Distribution System o Interconnected Distribution System c) Nature Of Current: o AC Distribution System. o DC Distribution System. d) Type Of Construction: o Overhead System o Underground System 9 Connection schemes in distribution system i. Radial Distribution System Structure : Only one/single path is connected between each Distributor and substation is called Radial Distribution System. Description : Simplest and most widely used configuration. Advantages: Low cost, simple design, and easy maintenance. Disadvantages: power flows along a single path. If interrupted, results in complete loss of power to the customer. Figure 3: Radial distribution system. 10 Connection schemes in distribution system i. Radial Distribution System Figure 4: Radial Distribution System 11 Connection schemes in distribution system ii. Ring Distribution System Structure : Feeder covers the whole area of supply in the ring or loop fashion, makes a loop through the area to be served, and returns to the substation. Description : The distributors are tapped from different points M, O and Q of the feeder through distribution transformers. Figure 5: Ring distribution system. 12 Connection schemes in distribution system ii. Ring Distribution System Advantages: a. There are less voltage fluctuations at consumer's terminals. b. The system is very reliable as each distributor is fed via two feeders. In the event of fault on any section of the feeder, the continuity of supply is maintained. For example, Suppose that fault occurs at any point F of section SLM of the feeder. Then section SLM of the feeder can be isolated for repairs and at the same time continuity of supply is maintained to all the consumers via the Feeder (SRQPONM). 13 Connection schemes in distribution system ii. Ring Distribution System Advantages: c. Less conductor material is required as each part of the ring carries less current than in the radial system. d. There are less voltage fluctuations at consumer’s terminals. Disadvantages : Increased complexity of design and cost when compared to the radial system. 14 Connection schemes in distribution system ii. Ring Distribution System Figure 6: Ring distribution system. 15 Connection schemes in distribution system iii. Interconnected Distribution System Structure : The feeder is energized by two or more than two generating station or sub station. Description : i. the single line diagram of interconnected system where the closed feeder ring ABCD is supplied by two substations S1 and S2 at points D and C respectively. ii. Distributors are connected to points O, P, Q and R of the feeder ring through distribution transformers. Figure 7: Interconnected system. 16 Connection schemes in distribution system iii. Interconnected Distribution System: Advantages: i. There is more flexibility. ii. Reliability is more. If fault occur on one section, supply can be continued by another route. iii. Good voltage regulation is achieved. iv. Size of substation is less compared to the radial system. Disadvantages: Highest complexity and cost. 17 Connection schemes in distribution system iii. Interconnected Distribution System: Figure 8: Interconnected Distribution System 18 Connection schemes in distribution system According to connection scheme, three main types can be compared as follows: 19 20