How ETAP Helps in Modeling and Analyzing Generator Stability During Step Loading

My case study is based on an ETAP model prepared for a fertilizer plant on one of the industrial networks in India. We have tried to perform transient stability studies for the generator's step loading.
By Mr. Vedant Sonar, Electrical Engineer, L&T-Sargent & Lundy Limited

This study simulates the impact of step loading on the transient stability of a 2 x 25 MW GTG-based captive power plant at one of the Chemical Fertilizer Plants in Trombay, India. The variation of the generator's electrical frequency and terminal voltage during one generator unit's most conservative step loading is studied. The loads divided in steps are switched at certain time intervals to determine whether the frequency profile of the system is within the acceptable limit of ±5%. Load Flow and Short Circuit Studies are performed on the entire power plant distribution network of the fertilizer plant in advance to check the adequacy of equipment ratings during normal and short circuit conditions with all verified input data.

L&T-Sargent & Lundy Limited is a joint venture between Larsen & Toubro, India, and Sargent & Lundy L.L.C., USA. Established in 1995, it provides consultancy and engineering design services in Power and affiliated sectors. With a professional staff of about 500 engineers and designers, it has extensive experience in power plant engineering and consulting assignments. A unique feature of L&T-S&L’s engineering proficiency is the PLADES (Plant Design Software) modeling, which not only facilitates smooth project execution but also gives it an edge with enhanced quality.

Location: Vadodara, Gujarat, India

Year: 2022

To perform transient stability studies for the step loading of the generator using the ETAP model

Challenges

  • To find the methodology and criteria to analyze the stability of the plant using large Gas Turbine Generators (GTG) for power generation. Chemical plants are in continuous operation.
  • To assess the dynamic impact of loading one GTG (operating in isolation) in multiple load steps in definite time intervals.
  • To model the electrical industrial network of the fertilizer plant. The power system model should be flexible, with all electrical equipment like transformers, circuit breakers, buses, lines, motors, pumps, and many other loads used typically in the chemical industry.
  • The model should include gas turbine generators as a primary power source.
  • To find modeling software that simulates different generator work modes, especially the islanded mode, when the generator is the only power source.
  • The speed-governing and excitation systems models should be considered in the dynamic model of the gas turbine generators.
  • To check the electrical network's adequacy concerning the power flows, the voltage magnitude at all the buses, and the short circuit levels at different plant locations.
  • To create relevant scenarios for the electrical network, enable analyses according to the customer's needs, and confirm the system's stability.

 

Which solutions did they choose?

Selected applications

They chose ETAP Digital-Twin to model the network and perform generator stability studies.

They use ETAP Predictive Simulation of events, which allows them to predict the generator's behavior during startup and other operations. 

Why do they use ETAP?

Main Customer Benefits

  • L&T-S&L engineers created the Electrical Network model using ETAP Digital Modeling. The plant electrical network model, which is a One-Line Diagram, consists of two generators, utility connections, the buses, the number of switchgears, transformers, and other equipment symbols needed to reflect the analyzed situations. They used actual equipment parameters to maintain the quality of the analysis.
  • The possibility of using different network variations was crucial. The ETAP model was flexible. Engineers used a variation with the utility grid out of service, all LV (low voltage) loads 80% dynamic and 20% static with less than 37 kW, an exciter with constant parameters, a speed governor with continuous parameters, and a conservative step load of the generator.
  • Embedded in the ETAP IEEE standards were used for calculations. They could set up a frequency variation of ±5%, and a voltage variation of ±10%. These were the main criteria used for analysis.
  • Engineers can divide the load process into eight steps. The loads were switched at specific intervals to determine the system's frequency and voltage profile within the steady state acceptable limits. Creating a scenario is a profitable benefit when users must analyze complex electrical systems.
  • They obtained study results in relevant tables according to the chosen methodology. The first table includes the occurrence of events (steps 1 to 8), description of loads, loading in kW, and time intervals in seconds. The total time is 107 seconds. The second table includes events, frequency, and voltage drop in percentage.
  • Thanks to the ETAP analysis tool, engineers found the worst case in step 7, when loading the methanol switchboard. The voltage drop on the bus was 94,69%.
  • Using ETAP, many generator parameters were plotted, including generator speed, generator active power, reactive power, mechanical power, and especially bus voltage and bus frequency. The last two parameters determine the transient stability.
  • The main benefit was the conclusion that the electrical network of the surveyed plant is stable, and the customer can keep the plant without changes to the electrical network.

What do they think about ETAP?

Opinions

As part of this contract, we performed the Generator Step Load Response Study using the transient stability analysis module of ETAP for the complete distribution network. For this, the dynamic modelling of GTGs with respect to the automatic voltage regulation and the turbine governor of the GTG was detailed based on the inputs given from the GTGs' original equipment manufacturer.
By Mr. Vedant Sonar, Electrical Engineer, L&T-Sargent & Lundy Limited

The client shared the parameters for the exact modeling of this ETAP model, and the same data was used to perform the study. Similarly, the client shared the exciter or AVR model, an IEEE AC8B type model, and the client also gave the parameters.
By Mr. Vedant Sonar, Electrical Engineer, L&T-Sargent & Lundy Limited


Videos

How to dynamically model & analyze generator stability during step loading using ETAP software

This study simulates the impact of step loading on the transient stability of a 2 x 25 MW GTG-based captive power plant at one of the Chemical Fertilizer Plants located at Trombay, India. The variation of electrical frequency and terminal voltage of the generator during the most conservative step loading of one generator unit is studied. The loads divided in steps are switched at certain time intervals to determine whether the frequency profile of the system is within the acceptable limit of ±5%. Load Flow and Short Circuit Studies are performed on the entire power plant distribution network of the fertilizer plant in advance to check the adequacy of equipment ratings during normal and short circuit conditions with all verified input data. The step load response study is carried out with only one GTG unit running in isolation, feeding only the critical emergency loads. Transient behavior of the GTG unit is simulated with IEEE transfer function dynamic models, viz. AC8B model of excitation system (AVR) and IEEE GGOV1 model for turbine governing system using the in-built standard library in ETAP software version 16.1.0. Various parameters of the generator like speed, active and reactive power, bus voltage, and frequency are plotted for determining the transient performance of the GTG unit.


Solutions


Packages/Products