Implementation and applications of a Wide Area Frequency Measurement System synchronized using Network Time Protocol

A Wide Area Frequency Measurement System synchronized using Network Time Protocol (NTP) has been implemented at several locations in the Indian grid. Although the synchronization accuracy of a NTP-synchronized system cannot match that of a GPS system, it is adequate to accurately capture electro-mechanical transients like inter-area power swings. This system has been successfully used to monitor events occuring in the grid, including the loss-of-synchronism during the partial blackout of 30^th July 2012 in India. It has also been possible to apply power swing damping estimation algortithms to the data. The results match well with those obtained from GPS synchonized PMU data. For these applications, the NTP based system is a viable, low-cost and easy-to-deploy alternative to a PMU system.

I. Introduction

A typical Wide-Area Measurement System (WAMS) consists of Phasor Measurement Units (PMU) [1], which are time-synchronized using a Global Positioning System (GPS). The high synchronizing accuracy, which is provided by a GPS, is required for accurate relative phase angular measurements. Accurate measurement of relative phase angles are required for applications like state estimation and parameter estimation/calibration and protection/control schemes. Time synchronization using Network Time Protocol(NTP) [2] is less accurate than a GPS scheme, with the synchronization error typically around 1-20 ms. Although this is not suitable for phase angular measurement [3], it is adequate for applications like the monitoring of electro-mechanical power swings (0.2-2 Hz) and event detection, besides the analysis of disturbances. Interestingly, the authors of [4] suggest that NTP may be used as a back-up scheme to detect GPS spoofing in a GPS based WAMS.