Reactance diagram of the power system is shown below. Reactance diagram is drawn by neglecting the effective resistance of generator armature, transformer winding resistance, transmission line resistance line charging and the magnetising circuit of transformers. The impedance diagram can further be simplified by making certain assumptions and reduced to simplified reactance. The three separate impedance diagrams are used in the short circuit for the studies of unsymmetrical fault. Three separate diagrams are also used for representing the positive, negative and zero sequence networks. It is also called positive sequence diagram. The diagram shown below is the balanced 3-phase diagram. Neutral earthing impedance does not appear in the diagram as the balanced condition is assumed. The load is assumed to be passive and are represented by a resistive and inductive reactance in the series. In impedance diagram, each component is represented by its equivalent circuit, e.g., the synchronous generator at the generating station by a voltage source in series with the resistance and reactance, the transformer by a nominal ∏-equivalent circuit. So for simplification, the impedance diagram is used for representing the power system components. It is difficult to draw the line diagram of the few components. The figure shown below represents the single line diagram of a typical block system. Generator and transformer connections, star, delta and neutral earthing are indicated by symbols drawn by the side of the representation of these elements.Ĭircuit breakers are represented by rectangular blocks. In the single line diagram, the system component is usually drawn in the form of their symbols. It is not necessary to show all the components of the system on a single line diagram, e.g., circuit breaker need not be shown in the load flow study but are the must for a protection study. The single line diagram of a power system is the network which shows the main connections and arrangement of the system components along with their data (such as output rating, voltage, resistance and reactance, etc.). Another box represents the power control center, motor control centers and connecting them with feeders.Ĭurrent transformers are shown in two places with indicators.Ī neutral ground resistor (NGR) is shown connected to a neutral line to provide protection to the generator against earth faults.Ĭircuit breakers are shown at various places for isolation of power for the transformer, PCC, and MCC.Single line diagram is the representation of a power system using the simple symbol for each component. The single line diagram is divided into two portions, from generation to substation are shown in a dotted grey line box. Greyline represents three-phase power in a single conductor. The blue circle overlapped represents the transformer from HT to LT power. The red box represents the circuit breakers. From the above one-line drawing, one can easily understand that the line shown from power generation, number breakers, HT/LT transformer, power control Center (PCC), then Motor control center, finally to feeders. The above single line diagram shows right from generation to distribution stage. The restoration of power can be possible by identifying.Įlectrical engineers: Use single line diagrams to understand system behavior and to make changes to the power system to improve performance.Įnd-users: Use the single-line diagrams to identify their electrical equipment, circuits, and protection apparatus.įamiliarity with electrical symbols helps one to understand the overall system connections. System operators: Use the single-line diagrams to identify the electrical placement of breakers, switches, transformers, regulators, and so on in substations that may indicate alarms. It shows how all alternate sources may be isolated. Line crew: Single line diagram drawing tells the worker at a glance where the disconnecting means is located. Helps to view the relationships between smaller sections of the power system and the overall system.Useful for switching orders to change system configurations.Helps in rerouting power after a fault.They are very useful for planning maintenance activities.It also includes the system protection schemes. The required information is added to give the engineer or a system operator the full picture of the electrical system. It is a simplified drawing of the whole system or a portion of the power system that shows the electrical placement of all major equipment.Ī single line diagram is a simplified explanation for representing a three-phase power system. An electrical single line diagram abbreviated as SLD is also referred to as a one-line diagram.

Define single line diagram