Impacts of Imperfect Power Quality on Industrial Power Protection Relays and Pmus

Impacts of imperfect power quality on industrial power protection relays and PMUs

Interim Report

University of Strathclyde, Glasgow, Scotland, United Kingdom

Luca Santos Matzenbacher

Reg.: 201333243

Thiago Ghidoni Mantovan

Reg.: 201404777

12 June 2014

Abstract: Considering the increased need of an accurate protection system for modern power grids and “smart” grids this project will run tests to access the performance of commercial relays and PMUs. The signals that are going to be used on the tests represent imperfect power quality, being waveforms containing harmonic and interharmonics distortions or being off-nominal frequency. Also real fault data shall be used to evaluate the impacts on the relay.

1. Introduction

Modern power grids and “smart” grids increasingly rely on measurement and protection functions which have to give accurate readings in a timely manner. At the same time, decreasing system inertia, and the increasing use of power electronic & non-linear devices mean that there is a tendency for power quality to be degraded. The aim of this project is to inject test signals into commercial relays and phasor measurement units (PMUs), and assess their accuracy objectively and fairly. This will give a unique insight into potential problems that might be encountered in the next 20 years, as such equipment may still be in use that far into the future. The tests will be conducted using the rtX - a real-time system for hardware-in-the-loop simulation [1] - to generate the test signals, an amplifier to increase the magnitude of the signals and the relays and PMU that will be tested. The most important results for the analysis are the frequency and the rate of change of frequency (ROCOF) and their errors because they express the behaviour of the relays when there is a fault in the system.

1. Synchrophasor

To understand the concept of synchrophasors a definition of phasors is necessary.

Phasor representation of sinusoidal signals is commonly used in ac power system analysis. A sinusoidal signal can be written as:

  (1)[pic 1]

Where f0 is the nominal system frequency.

And its phasor can be represented as:

[pic 2]

         (2)[pic 3]

[pic 4]

Where  is the magnitude of the waveform, Xr is is the real part and Xi is the imaginary part of a complex value in rectangular components. This particular phasor is defined the angular frequency  and the value of  is dependent of the time scale.[pic 5][pic 6][pic 7]