CLASSIFICATION OF POWER SYSTEM BUSES

LOAD BUS

A bus where there is only load connected and no generation exists is called a load bus. At this bus real and reactive load demand P_d and Q_d are drawn from the supply. The demand is generally estimated or predicted as in load forecast or metered and measured from instruments. Quite often, the reactive power is calculated from real power demand with an assumed power factor. A load bus is also called a P, Q bus. Since the load demands P_d and Q_d are known values at this bus. The other two unknown quantities at a load bus are voltage magnitude and its phase angle at the bus. In a power balance equation P_d and Q_d are treated as negative quantities since generated powers P_g and Q_g are assumed positive.

VOLTAGE CONTROLLED BUS OR GENERATOR BUS

A voltage controlled bus is any bus in the system where the voltage magnitude can be controlled. The real power developed by a synchronous generator can be varied b: changing the prime mover input. This in turn changes the machine rotor axis position with respect to a synchronously rotating or reference axis or a reference bus. In other words, the phase angle of the rotor δ is directly related to the real power generated by the machine. The voltage magnitude on the other hand, is mainly, influenced by the excitation current in the field winding. Thus at a generator bus the real power generation P_g and the voltage magnitude [V_g] can be specified. It is also possible to produce vars by using capacitor or reactor banks too. They compensate the lagging or leading vars consumed and then contribute to voltage control. At a generator bus or voltage controlled bus, also called a PV-bus the reactive power Q_g and δ_g are the values that are not known and are to be computed.

SLACK BUS

In a network as power flow from the generators to loads through transmission lines power loss occurs due to the losses in the line conductors. These losses when included, we get the power balance relations

Pg-P_d–P_L=O ---- (1)

Qg-Q_d-Q_L=0 ---- (2)

Where Pg and Qg are the total real and reactive generations, P_d and Q_d are the total real and reactive power demands and PL and QL. are the power losses in the transmission network. The values of Pg, Qg and P_d and Q_d are either known or estimated. Since the flow of currents in the various lines in the transmission lines are not known in advance, P_L and Q_L remains unknown before the analysis of the network.

But these losses have to be supplied by the generators in the system. For this purpose, one of the generators or generating bus is specified as 'slack bus' or 'swing bus'. At this bus the generation Pg and Qg are not specified. The voltage magnitude is specified at this bus. Further, the voltage phase angle δ is also fixed at this bus. Generally it is specified as 0° so that all voltage phase angles are measured with respect to voltage at this bus. For this reason slack bus is also known as reference bus. All the system losses are supplied by the generation at this bus. Further the system voltage profile is also influenced by the voltage specified at this bus.

Comments

PRIMARY SECONDARY AND TERTIARY FREQUENCY CONTROL IN POWER SYSTEMS

Primary, Secondary and Tertiary Frequency Control in Power Systems Author: Engr. Aneel Kumar Keywords: frequency control, primary frequency control, automatic generation control (AGC), tertiary control, load-frequency control, grid stability. Frequency control keeps the power grid stable by balancing generation and load. When generation and demand drift apart, system frequency moves away from its nominal value (50 or 60 Hz). Grids rely on three hierarchical control layers — Primary , Secondary (AGC), and Tertiary — to arrest frequency deviation, restore the set-point and optimize generation dispatch. Related: Power System Stability — causes & mitigation Overview of primary, secondary and tertiary frequency control in power systems. ⚡ Primary Frequency Control (Droop Control) Primary control is a fast, local response implemented by generator governors (dro...

ADVANTAGES AND DISADVANTAGES OF CORONA EFFECT IN TRANSMISSION LINES | ELECTRICAL ENGINEERING GUIDE

Advantages and Disadvantages of Corona Effect in Power Systems In high-voltage overhead transmission lines , the corona effect plays a critical role in system performance. Corona occurs when the air around a conductor becomes ionized due to high electric stress. While often seen as a drawback because of power losses and interference , it also provides certain engineering benefits . This article explains the advantages and disadvantages of corona effect in detail, with examples relevant to modern electrical power systems. ✅ Advantages of Corona Effect Increase in Virtual Conductor Diameter Due to corona formation, the surrounding air becomes partially conductive, increasing the virtual diameter of the conductor. This reduces electrostatic stress between conductors and minimizes insulation breakdown risks. Related Reading: Electrostatic Fields in High Voltage Engineering Reduction of Transient Surges Corona acts like a natural cushion for sudden ...

CASCADED TRANSFORMERS METHOD FOR GENERATING AC HIGH VOLTAGE

High-Frequency AC High Voltage Generation Using Cascaded Transformers Author: Engr. Aneel Kumar Figure 1: Infographic representation of cascaded transformers method for generating high AC voltages. Introduction In high voltage engineering , generating very high alternating current (AC) voltages is essential for testing equipment like insulators, circuit breakers, power cables, and other apparatus. One common and effective method for producing such voltages is the cascaded transformers method . This technique uses a series connection of specially designed test transformers , where the secondary of one transformer feeds the primary of the next. In this way, voltages are built up step by step, achieving levels in the range of hundreds of kilovolts (kV) or even megavolts (MV). Working Principle The principle of cascaded connection relies on the fact that each...

ADVANTAGES OF INTERCONNECTED GRID SYSTEM

Interconnected Grid System: Working, Advantages, Disadvantages, and Comparison with Isolated Grids Author: Engr. Aneel Kumar Figure 1: Infographic showing key advantages of an interconnected grid system. Introduction An interconnected grid system refers to a network of multiple power generation sources, transmission lines, substations, and distribution systems that are linked across regions, states, or even countries. Unlike an isolated grid (or islanded grid) which operates independently, an interconnected grid allows electricity to flow between interconnected nodes, enabling numerous benefits and some trade-offs. In today’s energy landscape—where demand, renewable generation, reliability, and cost pressure are all increasing—understanding how an interconnected grid works, what factors are essential, and what its advantages and disadvantages are is critical for utility planners, reg...

REVERSING DIRECTION OF ROTATION OF UNIVERSAL MOTOR

The direction of rotation of a universal motor can be changed by either: (i) Reversing the field connection with respect to those of armature; or (ii) By using two field windings wound on the core in opposite directions so that the one connected in series with armature gives clockwise rotation, while the other in series with the armature gives counterclockwise rotation. The second method, i.e, the two field method is used in applications such as motor operated rheostats and servo systems. This method has somewhat simpler connections than the first method. For simple applications like portable drills etc. manual switches are frequently used for reversing the direction of rotation of the motor. Figure 1 (a and b) shows how a DPDT (Double Pole Double Throw) switch and a three position switch may be used for reversing the direction of rotation of single field and double field type of motors respectively. Figure 1 Reversing of a universal motor (a) Armature re...

Factors Affecting Corona in Overhead Transmission Lines

Factors Affecting Corona in Overhead Transmission Lines Author: Engr. Aneel Kumar Figure 1: Infographic illustrating the factors influencing corona discharge in transmission lines. Introduction The corona effect in overhead transmission lines is a phenomenon that occurs when the electric field intensity around conductors exceeds a critical value, causing ionization of the surrounding air. This ionization produces bluish light, hissing sound, power loss, and ozone gas. While corona may seem undesirable, it also has a few advantages such as reducing overvoltages by absorbing surges. Corona directly impacts power system efficiency, transmission losses, equipment life, and design cost . Therefore, engineers must understand the factors affecting corona in detail to ensure efficient and reliable design of high-voltage transmission systems. 1. Conductor Size (Diameter) ...

Control Strategies for TCSC: Techniques for Dynamic Power Flow Management

Introduction As power transmission networks grow more complex, real-time voltage and impedance control becomes essential for ensuring grid reliability. Thyristor Controlled Series Capacitors (TCSC) play a key role in dynamically adjusting transmission line reactance, but their effectiveness depends on advanced control strategies . Different control methodologies —ranging from open-loop and closed-loop systems to AI-driven predictive models —allow TCSC to optimize power flow, improve stability, and enhance energy efficiency . In this article, we will explore: ✅ Different types of TCSC control strategies ✅ The role of real-time monitoring in optimizing power flow ✅ How AI and machine learning improve TCSC performance Keywords: AI-Based Power Flow Control, TCSC Dynamic Impedance Regulation, Real-Time Voltage Stabilization, Smart Grid FACTS Controllers Understanding TCSC Control Strategies A TCSC regulates transmission line reactance by adjusting thyristor switch...

ENGINEERING ARTICLES

Search This Blog