Power System Study

Power System Study

Load Flow Study

One of the most common computational procedures used in power system analysis is the load flow calculation. The planning, design and operation of power systems require such calculations to analyse the steady state performance of power system under various operating conditions and to study the effects of changes in equipment configuration. These load flow solutions are performed using computer programs designed specifically for this purpose. The basic question in the load flow analysis is: “Given the demand at all buses of a known electric power system configuration and the power production at each generator, find the power flow in each line and transformer of the interconnecting network and the voltage magnitude and phase angle at each bus.“ Analysing the solution of load flow analysis for numerous conditions helps ensure that the power system is designed to satisfy its performance criteria while incurring the most favourable investment and operation costs. Some examples of the uses of load flow studies are to determine,

  • Component or circuit loading.
  • Steady state bus voltages.
  • Reactive power flows.
  • Tap settings of transformers.
  • System losses.
  • Performance under emergency conditions.

Modern systems are complex and have many paths or branches over which power can flow. Such systems form networks of series and parallel paths. Electric power flow in these networks divides among the branches until a balance is reached in accordance with established circuit theory. Computer programs to solve load flows are divided into two types static (offline) and dynamic (real time). Most load flow studies for system analysis are based on static network models. Real time load flows (online) that incorporate data input from the actual networks are typically used by utilities in Supervisory Control And Data Acquisition (SCADA) systems. Such systems are used primarily as operating tools for optimisation of generation, var control, dispatch, losses, and tie line control. This discussion is concerned with only static network models and their analysis. A load flow calculation determines the state of the power system for a given load and generation distribution. It represents a steady state condition as if that condition had fixed for some time. In reality, line flows and bus voltages fluctuate constantly by small amounts because load changes constantly as lights, motors, and other loads are turned on and off. However, these small fluctuations can be ignored in calculating the steady state effects on system equipment.The load flow model is also the basis for several other types of studies such as short circuit, stability, motor starting, and harmonic studies. The load flow model supplies the network data and an initial steady state condition for these studies.

Short Circuit Study

Short circuit studies are conducted to determine the fault currents and fault MVA levels in the plant for single line to ground fault and three phase to ground fault. The study is done for various types of faults at different locations throughout the system. Two factors upon which the proper selection of circuit breakers depends are the current flowing immediately after the fault occurs and the current, which the breaker must interrupt. In addition, the results of the short circuit studies are used to determine the settings of relays, which control the circuit breakers.

Power System Stability Study

The stability of the power system is mainly reflected by the transient response of the system and hence machine models with greater sophistication have to be used to understand the swing of generators rotor angle, Voltage profile at different buses, Frequency fluctuations of generators and current shoot up and it's stabilization for different equipment etc are simulated for following abnormal conditions.

  • Earth faults (3-phase and single line to ground).
  • Earth faults on state grid.
  • Large load throw off (100% or part thereof).
  • Grid faults, frequency and voltage fluctuations on the grid.
  • Any other condition for which customer may like to evaluate system behaviour.

Scope of Work

Data Collection, Validation and Power System Modeling

  • Collection of all data pertaining to power system elements like generators, transformers, cables, switchgears and various types of loads required for power system studies is collected from client / site. The collected data is validated and in case of discrepancies the same will be resolved by interaction / discussions with customer.

Load Flow study

  • The load flow study brings out the real (MW) and reactive (MVAR) power flows and bus voltage profile with different load and supply conditions. The system study will be carried out using ETAP – "Computer aided power system analysis package" based on system component data and the load data of the cement plant.
  • Load flow studies are conducted to determine the voltage profile in the plant for minimum and maximum voltage conditions of the Grid to arrive at adequate tap positions for the plant transformers, real and reactive power losses in the plant and to determine the reactive power compensation requirements in the plant.
  • The load flow analysis will also determine the state of the power system for a given load & generation and operating mode of the distribution system.
  • The load flow analysis will be conducted for different operating modes of the distribution system within the plant.

Short Circuit Study

  • The study is simulated to determine the 3-phase and single line to ground faults currents up to PCC or secondary of distribution transformer. Short circuit studies (3 phase and single line to ground) will help in determining the adequacy of the equipment rating starting from the grid incomers to LT buses of PCC.
  • Short circuit studies is conducted for different operating conditions of the plant. The capability of the existing switchgears is reviewed in light of the proposed additional generation.

Transient Stability Study

The following studies is carried out under transient study

  • The behaviour of the captive generators in case of islanding from the grid and during grid faults.
  • Effect on the system and on the grid when plant generator / generators trips.
  • Calculation of critical fault clearing time.
  • Load shedding and islanding behaviour.
  • Effect of Fault on different buses of the plant like 0.415 kV, 6.6 kV, 11kV etc...