Insulation Co-ordination Studies

Insulation Coordination is the process of determining the proper insulation levels of various components in a power system as well as their arrangements. It is the selection of an insulation structure that will withstand voltage stresses to which the system or equipment will be subjected to, together with the proper surge arrester. The process is determined from the known characteristics of voltage surges and the   characteristics of surge arresters.

        The following standards are used by consultants, while performing the insulation coordination:

• Insulation Co-ordination, Part 1: Definitions, principles and rules IEC 71-1, standard.
• Insulation Co-ordination, Part 2: Application guide IEC 71-2, standard.
• IEEE Guide for the Application of Insulation Coordination. IEEE Std 1313-2-1999

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Evaluation of Load Shedding Schemes

The existing and proposed load shedding schemes will be evaluated using the transient stability simulation, with dynamic models of generators, controllers and loads. The following factors will be considered in evaluating the load shedding schemes and providing the recommendations

• Governor/prime mover controllers will be modeled in simulation
• Spinning reserves will be modeled appropriately in the governor/prime mover model
• Frequency deviation, Rate of change of frequency deviation, Bus voltage variations as function of time will be considered
• The power balance factor will also be considered in designing and evaluating the load shedding schemes.

Load shedding is essential only during under conditions with frequency still decreasing and never to be used when frequency is recovering or increasing. This factor will be considered appropriately while designing load shedding schemes.

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Contingency Studies

Contingency Studies

Maintaining power system security is one of the most important requirements for any utility and this includes planning for various contingency situations like outage of transmission lines; loss/recovery of generators and loads; changing/setting of switched shunts; injection groups; as well as opening/closing of buses and equipments. Contingency evaluation is carried out by using static as well as dynamic analytical tools such as load flow analysis and transient stability analysis. Real time control and monitoring solutions in energy control centers or energy management systems or load dispatch centers usually use an algorithm called contingency ranking algorithm to shortlist credible contingencies for real time evaluation and control of power systems. Often contingency ranking algorithm will use some approximate and fast load flow type algorithms from a list of contingencies and rank them in the decreasing order of severity. This ordered or ranked list will normally be considered for a detailed contingency evaluation to assess system security. Often contingency ranking algorithm will use some approximate and fast load flow type algorithms from a list of contingencies and rank them in the decreasing order of severity. This ordered or ranked list will be considered for a detailed contingency evaluation to assess system security.

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Power Flow Studies

Power flow/Load flow calculations provide active & reactive power flows, bus voltage magnitude and their phase angle at all the buses for a specified power system and operating conditions. These values are typically subject to various factors like regulating capability of generators, synchronous condensers, static VAR compensator, HVDC controls, FACTS controllers, tap changing under-load transformers and specified net interchange between individual operating systems (utilities). Power flow information is essential for the continuous evaluation of the current performance of a power system and for analyzing the effectiveness of alternative plans for system expansion to meet increased load demand. These analyses require the calculation of numerous power flow cases for both normal, and emergency (contingency) operating conditions.

Applications of Power Flow Study and Analysis

• Transmission expansion planning ,operation planning 
• Distribution expansion planning , operation planning 
• Industrial/Commercial distribution system planning, operational planning 
• Network interconnection, Grid interconnection studies 
• Evaluation of energy transactions between various stake holders 
• Energy audit to accurately determine network losses and estimate billing losses if any 
• Sizing of transformers, cables, overhead lines, transformer tap ranges, shunt capacitors, shunt reactors, reactive power management, FACTS devices, HVDC operation 
• System security assessment via static contingency studies 
• Decision making tool in operation planning and operation of the system in load dispatch center 
• Motor starting studies using load flow type analysis, where the starting impedance of the Induction motor is modeled as constant impedance model with starting impedance. 
• Evaluation of static voltage stability using load flow technique

The following general criteria of acceptability of design is used in power flow studies

1.  Voltage Drop at all buses should be within +/- 5% of the nominal rating for all operating conditions considered 
2. No over load conditions of any electrical circuits for all operating conditions considered 
3. Reactive power generation/import/export to be within specified limits for all operating conditions considered 
4. Ensuring quality power supply to all loads, under specified contingency conditions, as per design philosophy adopted.

The following study cases/ power flow outputs are generally considered in power flow studies

1. Extreme operating conditions of maximum and minimum loading conditions will be considered to check the adequacy of the network, even though some of these conditions may not exist during normal operation 
2. Contingency conditions such as outage of lines, transformers and generators will be considered and network adequacy for power evacuation will be assessed 
3. Operating solutions such as transformer taps, generator excitation, shunt reactive power compensations will be provided as needed. 
4. Recommendations for strengthening and equipment upgradations will be provided to meet specific operating requirements. 
5. Summary of load flow studies and concise reports in tabular formats and single line diagram formats will be provided, along with the summary of recommendations

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Overview of Power System Analysis

An electric power system is a network of electrical components used to generate, transmit and use electric power. This could be the elaborate network that supplies power to a region’s home and industry through an electrical grid transmission system from generating plants located faraway or even a captive power plant/microgrid which generates and consumes power within the same premises itself. The planning, design, and operation commercial and industrial power systems require indepth engineering studies to evaluate existing and proposed system performance, reliability, safety, and economics. Due to high risk of human life and costly equipments associated with any power systems, properly conceived and conducted power system studies and simulations are the only cost-effective way to prevent surprises and to optimize equipment selection. These power system studies identify and help avoid potential deficiencies in the system before it goes into operation. In the case of existing systems, the studies help locate the cause of equipment failure and misoperation, and determine corrective measures for improving system performance. 

In power engineering, an oneline diagram or single-line diagram (SLD) is a simplified notation for representing a three-phase power system. The one-line diagram has its largest application in power flow studies and in engineering design. Electrical elements such as circuit breakers, transformers, capacitors, bus bars, and conductors are shown by standardized schematic symbols. It is a form of block diagram graphically depicting the paths for power flow between entities of the system. Instead of representing each of three phases with a separate line or terminal, only one conductor is represented.  Elements on the diagram do not represent the physical size or location of the electrical equipment, but it is a common convention to organize the diagram with the same left-toright, top-to-bottom sequence as the switchgear or other apparatus represented. A typical SLD is illustrated below for reference:

Today, with the advent of digital computers, Power System Simulations are the basis of modern design of power systems for all industries. Typical studies most likely needed are load flow studies, ground mat design, harmonic measurements, cable ampacity studies, short-circuit studies, switching transient studies, coordination studies, and motor starting studies. The responsible engineer for system design must decide which studies are needed to ensure that the system will operate safely, economically, and efficiently over the expected life of the system. 

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