Explain the monitoring methods of distribution in electrical power system
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Answer:
Distribution networks carry power the last few miles from transmission or sub-transmission to consumers. Power is carried in distribution networks through wires either on poles or, in many urban areas, underground. Distribution networks are distinguished from transmission networks by their voltage level and topology. Lower voltages are used in distribution networks, as lower voltages require less clearance. Typically, lines up to 35 kV are considered part of the distribution network. The connection between distribution networks and transmission or subtransmission occurs at distribution substations. Distribution substations have transformers to step voltage down to the primary distribution level (typically in the 4–35 kV range in the United States). Like transmission substations, distribution substations also have circuit breakers and monitoring equipment. However, distribution substations are generally less automated than transmission substations.
Distribution networks usually have a radial topology, referred to as a “star network,” with only one power flow path between the distribution substation and a particular load. Distribution networks sometimes have a ring (or loop) topology, with two power flow paths between the distribution substation and the load.
Direction-Coordinating Based Ant Colony Algorithm and its Application in Distribution Network Reconfiguration
Xiangping Meng, Zhaoyu Pian, in Intelligent Coordinated Control of Complex Uncertain Systems for Power Distribution Network Reliability, 2016
7.3.1 Distribution Network Reconfiguration Issue
Distribution network reconfiguration refers to the situation when, under the condition that all the constraints to ensure the safe operation of the power grid are satisfied – such as requirements for voltage drop, line heat capacity, etc. – power supply and lines are chosen by changing the opening and closing states of each segment switch and interconnection switches, aimed at forming eventually a radial network through this choice. This is so that it may make a particular index of the distribution network, such as the line losses, voltage capacity, load balancing, and so on, achieve the optimal state.
The distribution network reconfiguration problem studied in this chapter selects distribution network losses as the objective function, in order to apply the directional pheromone-based ant colony algorithm in distribution a network reconfiguration problem, for the purpose of reducing distribution network losses.
The distribution network reconfiguration problem is rendered abstract. The distribution transformer, feeder sections, and loads of the network are considered as nodes, and circuits as edges in the figure. As such, the distribution network is represented as an undirected connected graph G´= (V, E), where V represents a set of individual nodes, and E represents the set of edges in the network. Thus, the optimal solution that needs to be solved in the distribution network reconfiguration problem is rendered abstract, as searching a minimal spanning tree G that meets the minimal conditions of network losses under the premise that some constraints are satisfied, and the G generated is a directed graph.
The network losses of the distribution network include copper and iron losses of the transformers’ own consumption, and losses of line conductors, and so on, yet only line conductor losses can be changed through distribution network reconfiguration, so this chapter chooses loss minimum as an objective function, shown in expression (7.6):
(7.6)
In the expression, Nb is the number of branches in the distribution network; Ri is the resistance on branch i; Pi and Qi are the active power and reactive power on branch i, respectively; Ui is the node voltage at the end of branch i; ki is the discrete variable of 0 – 1 used to represent the opening and closing state of switch i, where 0 stands for open, 1 stands for closed; and Ii is the current on branch i.
When distribution network reconfiguration is carried out, the following constraints need to be satisfied:
1.
Network topology constraint. After the distribution network is reconfigured, the network formed must be radial.
2.
Power supply constraint. The reconfigured distribution network must satisfy the requirements of line loads, without any independent nodes in the distribution network at the same time.
3.
Inequality constraint. It includes constraint of node voltage [equation (7.7)], overload constraint of branch [equations (7.8) and (7.9)] and overload constraint of transformers [equation (7.10)], and so