Load Flow Analysis

Power System Studies

When designing an Electrical distribution system, it is necessary that a power system study be performed before any equipment is specified or purchased. The analysis should always consist of a short circuit, load flow, motor starting, over-current coordination, and arc flash hazard study. The output from the analysis is then used to specify equipment ratings. The engineer should perform the analysis with a well-defined list of electrical distribution system performance criteria in mind, as follows:

  • To design an inherently safe system
  • To standardize equipment sizing practices and protection methods
  • To limit bus voltage drops to 5–8% under maximum load conditions and to 15–20% during large motor starting
  • To set overcurrent devices to protect equipment from damage and to selectively shut down sections of the power system in response to a system disturbance
  • To limit arc fault energy levels to 40 cal/cm2 or below.

When analysing an existing electrical distribution system, the need to perform a load flow or motor-starting study is diminished. At this point, unless there is an obvious loading or motor-starting problem such as transformers running hot, low voltage under normal or motor-starting conditions, or motors failing prematurely, the effort should be focused in the areas of short circuit, overcurrent coordination, and arc flash. These studies are all life safety related, and if problems are found, they must be rectified immediately.

Electrical Power System Studies that can be performed by iFluids are as below,

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Load Flow or Power Flow Analysis

The Load Flow study is the analysis of a power system in normal steady-state operation. A load flow study calculates the voltage drop on each feeder, the voltage at each bus, and the power flow and losses in all branch and feeder circuits. Load flow studies determine if system voltages remain within specified limits under normal or emergency operating conditions, and whether equipment such as generator, transformers and conductors are overloaded.

Life Cycle Transformer Management/ Residual Life Assessment (RLA) of Transformers

Capital spending on new and replacement transformers is at its lowest level in decades. The load on each transformer continues to grow, with power consumption increasing at a rate of about 2 to 5 percentage per year.Residual Life Assessment (RLA) of Transformers can be done to ensure the reliability and continuous operation of the transformers for next 10 years and to find out corrective actions to be taken to avoid any failures in future.

The below mentioned tests can be carried out for both HV and LV side for all the phases as applicable,

  • R and PI of all windings.
  • Tan – Delta and capacitance of all the bushings.
  • Tan – Delta and capacitance of all the windings.
  • Winding Resistance.
  • Measurement of turns ratio at all the taps of OLTC.
  • Sweep Frequency Response Analysis (SFRA).
  • Magnetic Balance Test.
  • Magnetising Current / Excitation Current.
  • Dirana or Furan Test to find out paper insulation condition or degree of polymerization.
  • Polarisation – Depolarisation Current Analysis.
  • Partial Discharge Analysis.
  • Oil Testing for Flash point, Neutralization value, BDV, dielectric dissipation factor (tan delta), water content, sludge content and pour point as per International Standard.

Medium and Long Term Load Growth Impact Study

Accurate models for electric power load forecasting are essential to the operation and planning of a utility company. Load forecasting helps an electric utility to make important decisions including decisions on purchasing and generating electric power, load switching, and infrastructure development. Load forecasts can be divided into three categories: short-term forecasts which are usually from one hour to one week, medium forecasts which are usually from a week to a year, and long-term forecasts which are longer than a year. iFluids Engineering use statistical techniques or artificial intelligence algorithms such as regression, neural networks, fuzzy logic, and expert systems for medium and long term forecasting.

Short Circuit and Protection Coordination Studies

A short-circuit study is an analysis of an electrical system that determines the magnitude of the currents that flow during an electrical fault. Comparing these calculated values against the equipment ratings is the first step to ensuring that the power system is safely protected. Once the expected short-circuit currents are known, a protection coordination study is performed to determine the optimum characteristics, ratings and settings of the power system protective devices.

Motor Start Transient Studies

Motor starting studies can vary from basic voltage drop on the system to a detailed waveform presentation of motor bus voltage, motor speed and motor torque, acceleration torque, load torque, power factor, rotor and stator currents, motor slip, real, reactive and total power. One of the most issues of starting large motors is a serious voltage dip on the buses throughout the facility. This voltage dip will cause other motors to slow down; in severe cases other motors may reach the stall point causing a domino effect to the voltage drop. Excessive starting current results in drop in terminal voltage and may result in the following:

  • Failure of motor starting due to low starting torques.
  • Unnecessary operation of under voltage relays.
  • Stalling of other running motors connected to the network.
  • Voltage dips at the power sources and consequent flicker in the lighting system.

iFluids Engineering can carry out Motor starting studies which can help in the selection of best method of starting, the proper motor design, and the proper system design for minimizing the impact of the motor starting. Analysis of motor starting methods can be performed by both static and dynamic simulation techniques.

Harmonics Penetration Studies

Distortion of sinusoidal voltage and current waveforms caused by harmonics is one of the major power quality concerns in electric power industry. Considerable efforts have been made in recent years to improve the management of harmonic distortions in power systems. Standards for harmonic control have been established. Instruments for harmonic measurements are widely available. The area of power system harmonic analysis has also experienced significant advancement. iFluids Engineering can carry out well accepted component models, simulation methods and analysis procedures for conducting systematic harmonic studies.

Relay Setting and Protection Co-ordination Studies

Where there are two or more series protective devices between the fault point and the power supply, these devices must be coordinated to insure that the device nearest the fault point will operate first. The other upstream devices must be designed to operate in sequence to provide back-up protection, if any device fails to respond. This is called selective coordination. To meet this requirement, protective devices must be rated or set to operate on minimum overcurrent, in minimum time, and still be selective with other devices on the system. When the above objectives are fulfilled, maximum protection to equipment, production, and personnel will be accomplished. Protection and coordination are often in direct opposition with each other. Protection may have to be sacrificed for coordination, and vice versa. iFluids Engineering over the years have developed experience in designing optimum coordination and protection.

Power Factor Improvement Studies

Power Factor is an efficiency measurement used in the electrical industry. By carrying out reliable power factor studies can help organization to avoid equipment damage, equipment failure and potential safety incidents. During a power factor study, iFluids Engineering will Monitor the secondary sides of all primary transformer banks, including the analysis of kW, kVA, kVAR, PF, voltage, current and harmonic voltage/current distortion and suggest the requirement for Power Factor Correction equipment. The benefits of Power Factor Correction are it will reduce demand charges, increase load carrying capabilities in existing circuits, improved voltage, and reduce power system losses, reduced carbon footprint. Relay Setting and Protection Co-ordination Studies.

Load Management and Load Shedding System Studies

Power supply to critical process loads is extremely important for all the industries not only for continuous production but also important for overall plant safety during severe disturbances. A sudden interruption in production may result in significant economic loss and raise safety concern. To prevent total blackout and to stabilize the system under any abnormal condition, appropriate Islanding and Load Shedding (LS) strategies must be developed for industrial system. The load shedding technique primarily can be classified as conventional load shedding technique and Adaptive or Intelligent load shedding technique. Conventional load shedding schemes, breaker interlock load shedding, under-frequency relay load Shedding, programmable logic controller-based load shedding are most common and easy way to isolate the excess amount of load during generation deficit in the islanded power system.

System Stability Analysis

The stability of a system refers to the ability of a system to return back to its steady state when subjected to a disturbance. Power system stability can be defined as the ability of the power system to return to steady state without losing synchronism. Usually power system stability is categorized into Steady State, Transient and Dynamic Stability.

Increase in load is a kind of disturbance. If increase in loading takes place gradually and in small steps and the system withstands this change and performs satisfactorily, then the system is said to be in Steady State Stability. Study of steady state stability is basically concerned with the determination of upper limit of machine’s loading before losing synchronism, provided the loading is increased gradually at a slow rate.

In practice, load change may not be gradual. Further, there may be sudden disturbances due to sudden change of load, switching operation, loss of generation or fault. Following such sudden disturbances in the power system, rotor angular differences, rotor speeds, and power transfer undergo fast changes whose magnitudes are dependent upon the severity of disturbances. For a large disturbance, changes in angular differences may be so large as to cause the machine to fall out of step. This type of instability is known as Transient Instability. Transient stability is a fast phenomenon, usually occurring within one second for a generator close to the cause of disturbance.

The ability of a power system to maintain stability under continuous small disturbances is investigated under the name of Dynamic Stability (also known as small-signal stability). These small disturbances occur due random fluctuations in loads and generation levels. In an interconnected power system, these random variations can lead catastrophic failure as this may force the rotor angle to increase steadily.

Grid Islanding Scheme and Auto Load Shedding Schemes

An Electrical Power System is a large interconnected electrical system made up of generation, transmission and distribution facilities and their control systems. In order to maintain power continuity and reliability service, a Power System must remain intact and be capable of withstanding a wide variety of disturbances. Therefore, it is essential that the system be designed and operated so that (i) more probable contingencies can be sustained with no loss of load (except that connected to the faulted element), (ii) the most adverse possible contingencies do not result in uncontrolled, widespread and cascading power interruptions. iFluids Engineering can provide technical consulting to develop an auto load shedding and islanding scheme which is the ultimate solution to restore system frequency and ensure availability of electrical power to critical loads in the plant and to prevent blackout and to stabilize the system under any abnormal condition.

Arc Flash Hazard Analysis

An arc flash is a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur.

Arc flash can be caused by many things including Dust, Dropping tools, Accidental touching, Condensation, Material failure, Corrosion, Faulty Installation. Three factors determine the severity of arc flash injury which is proximity of the worker to the hazard, Temperature and Time for circuit to break. Typical Results from an Arc Flash ranges from simple Burns (Non FR clothing can burn onto skin), Fire (could spread rapidly through building), Flying objects (often molten metal), Blast pressure (upwards of 2,000 lbs./sq.ft), Sound Blast (noise can reach 140 dB – loud as a gun) or Heat (upward of 35,000 degrees F).

The National Fire protection Association (NFPA) has developed specific approach boundaries designed to protect employees while working on or near energized equipment. These boundaries are Flash Protection Boundary (outer boundary), Limited Approach, Restricted Approach, Prohibited Approach (inner boundary).

iFluids Engineering can technical consulting and provide solutions to protect workers from the threat of electrical hazard. Some of the methods are for the protection of qualified employees doing work on electrical circuit and other methods are geared towards non-qualified employees who work nearby energized equipment. Few of the protective methods are De-energize the circuit, work practices, insulation, guarding, barricades, ground fault circuit interrupters (GFCI) and grounding (secondary protection).