1.05 Model validation for accurate representation of ......Model Aggregation • Incorporating entire RPP models with complete collector networks into a large electrical network –unpractical

Electricity Supply to Africa and Developing Economies: Challenges and Opportunities

Johan SmithTNEI Africa

Paper Number 1.05

Session Number 1

15 November 2017

Model validation for accurate

representation of renewable power

plant technologies in developing

utilities to free up capacity


Agenda

• Introduction• Problem Statement• Case Study

– Steady state study– Dynamic capacity simulation

• Model Validation Examples– Full inverter coupled technologies– Synchronous generator technologies

• Model Aggregation• Conclusions


Introduction

• Abundance of renewable resources in Africa• Grid integration study is required to investigate

sufficient grid capacity

– Steady state study– Dynamic study

• Steady state load flow studies are the first and sometimes the only factor taking into

consideration – equipment loading and voltage

violations


Introduction (contd…)

• Dynamic studies require the existing and new generation, as well as the existing T&D network

to be accurately represented

• Safety margins needs to be introduced when integrating renewable generation:

– Capacity can be remaining– False capacity which places the network at risk


Problem Statement

• Using non-validated simulation models to determine network capacity can produce

unreliable results, which could lead to under- or

over-utilisation of the existing network


Case Study – Existing study case network

• Existing study case network63% OHL loading for

existing network


Case Study – Steady state simulation

• Renewable plant connected to base case

100% OHL loading with

new 116MW RPP

Theoretical spare capacity = 115MW


Study Case – Dynamic capacity simulation

• Network subjected to fault at 132 kV busbar

Dynamic spare

capacity = 45MW


Study Case – Input data errors

• Network with additional 45 MW is used and the inertia time constant of the generators are

changed to represent a 10% error in input data


Model Validation – Inverter technologies

Full inverter coupled technologies:

• Model validation focus– Active and reactive current injection for system

events and control modes

• Accurate plant measurements are required to validate RMS and EMT models


Model Validation – Inverter technologies (contd…)

• Reactive power control – measured vs. simulated (RMS model)



• Open Loop Reactive Power Validation for +2% Voltage Reference Change (RMS Model)



• Open Loop Reactive Power Validation for Tap Change Operation with Fixed Voltage Reference

(1p.u.) and 4% Droop (RMS Model)



• EMT model – system event required for RPP to go into grid support mode thus injecting or

absorbing reactive current


Model Validation – Synchronous technologies

• Data requirements:– Sampling rate: 5µs (20kHz)

• Lower resolution acceptable (1-10ms) for RMS models

– Measured quantities:• Field voltage• Field current• Terminal voltage• Active and reactive power

– Validation focus• Accurate representation of generator which includes AVR,

governor and PSS



• Typical tests:– AVR:

• Open circuit test• Closed circuit test• Limiter tests

– Governor:• Generator test: open circuit saturation curve, power

rejection test

• Governor test: high and low frequency excursion test, load ramp rate test.

– Power System Stabiliser (PSS): • white noise test


Model Aggregation

• Incorporating entire RPP models with complete collector networks into a large electrical network – unpractical and cumbersome

• Model aggregation required by utilities and forms part of overall validation process

• During major network disturbance it is possible for a portion of the generators to experience voltages beyond protection limits – not possible to capture these as the aggregated model represents the “average” generator in the RPP


Model Aggregation (contd…)

• After aggregation, the model is compared to the full validated model

• Simulation study to compare reactive current contribution at the POC

– Aggregate model is sufficient for studying impact on larger electrical network


Conclusions

• Case presented highlight the need for using validated models for representing generation to calculate remaining capacity

• Validation process was described for both inverter and synchronous generator technologies

• To validate simulation models – simulation results are compared to site measurements

• Model aggregation is integral part of model validation – provides accurate model to represent RPP in larger power system study


Conclusions (contd…)

• Dynamic and steady state simulations are required in order to determine available capacity

• Model validation ensures the accurate model representation of renewable technologies in

order to determine the “safe” available capacity

Documents

1.05 Model validation for accurate representation of ......Model Aggregation • Incorporating entire RPP models with complete collector networks into a large electrical network –unpractical