PHASOR MEASUREMENT UNIT (PMU) AKANKSHA PACHPINDE INTRODUCTION - PowerPoint PPT Presentation

PHASOR MEASUREMENT UNIT (PMU) AKANKSHA PACHPINDE

INTRODUCTION

OUTLINE ¡ Conventional control centers ¡ Introduction to Synchrophasors ¡ A generic PMU ¡ Applications of PMU ¡ Role of GPS ¡ Cost profile of PMU with GPS ¡ PMU with IEEE 1588

TASKS PERFORMED BY CONTROL CENTER

¡ Data is acquired from SCADA every 2s or so ¡ OPF for transmission- constrained economic dispatch ¡ State estimation carried out to provide state of system ¡ Historical and forecasted data stored in storage devices ¡ Load forecast carried out every 15mins ¡ AGC used balance power generation and load ¡ Various copies of data coordinated, synchronized demand and merged in databases ¡ Contingency analysis carried out ¡ Control centers integrate horizontally & vertically

INTRODUCTION TO SYNCHROPHASORS

§ An AC waveform can be mathematically represented as: § In phasor notation it can be represented as: where: = rms magnitude of waveform = phase angle

A GENERIC PMU

- Provides 1 PPS signal - Time- tagging Communication links to higher level Current/voltage signal from Instrument Transformer Restricts bandwidth to Calculates positive- satisfy Nyquist criterion sequence estimates Analog-to-digital converter

An architecture involving the following must exist in order to realize the full benefit of the technology ¡ PMUs ¡ Communication links ¡ Data concentrators

MEASUREMENT ACCURACY REQUIRED BY SYNCHROPHASOR STANDARD

¡ The value of Total Vector Error (TVE) < 1% ¡ Possible sources of error- magnitude, angle and timing ¡ Only magnitude error < 1% ¡ Only phase error < 0.573º ¡ Only time error < 31.8 µ s for 50 Hz system and 26.5 µ s for 60Hz system

APPLICATIONS OF PMU

Real-time operations applications Wide-area situational awareness Planning and off-line applications ¡ Frequency stability monitoring and trending Baselining power system performance ¡ ¡ Power oscillation monitoring Event analysis ¡ ¡ Voltage monitoring and trending Power plant model validation ¡ ¡ Event detection and avoidance Load characterization ¡ ¡ Resource integration Special protection schemes and islanding ¡ ¡ State estimation ¡ Dynamic line ratings and congestion management ¡ Outage restoration ¡

ROLE OF GPS

¡ PULSE PER SECOND (PPS) SIGNAL This pulse as received by any receiver on earth is coincident with all other received pulses to within 1 microsecond ¡ PPS signal is used for sampling the analog data ¡ ¡ TIME – STAMP The GPS time does not take into account the earth’s rotation ¡ Corrections to the GPS time are made in the GPS receivers so that they provide UTC clock time ¡

COST PROFILE OF PMU WITH GPS

¡ Total installed cost of the technology includes cost of – device, design and engineering, labor and material, any needed construction ¡ Cost of the device – one-quarter of the total cost ¡ Upgrades cost considerably less than installing new PMUs ¡ Projects installing a greater number of PMUs or PDCs did not have lower average costs per device.

REASONS FOR HIGH COST ¡ GPS requirement ¡ Data storage needs ¡ Communication infrastructure requirement ¡ Changes required in substation like new busbars, additional CTs and PTs ¡ Downtime, labor cost, commissioning costs ¡ Limited experience ¡ Projects more about research, testing and demonstration

REASONS FOR HIGH COST ¡ GPS requirement ¡ Data storage needs ¡ Communication infrastructure requirement ¡ Changes required in substation like new busbars, additional CTs and PTs ¡ Downtime, labor cost, commissioning costs ¡ Limited experience ¡ Projects more about research, testing and demonstration

PMU WITH IEEE 1588

¡ Precision Time Protocol (PTP) was first defined in IEEE 1588- 2002 and upgraded in 2008 ¡ It is designed for local systems requiring accuracies beyond those attainable using Network Time Protocol ¡ Designed for applications that Cannot bear the cost of a GPS receiver at each node OR ¡ For which GPS signals are inaccessible ¡

IEEE 1588 has three types of clocks: ¡ Master clock- A clock which is controlled ideally by a radio clock or a GPS receiver ¡ Boundary/ Transparent clock- A clock in a transmission component like an Ethernet Switch ¡ Ordinary clock- A clock in an end device

¡ Assuming that the master-to-slave and slave-to-master propagation times are equal, the offset and propagation time can be computed as follows: ¡ Synchronization accuracies better than 1 sub-microsecond can be achieved ¡ PTP is supported by Ethernet and TCP/ IP

¡ Reallocation of time signals is done to bring the samples in their correct position ¡ The number of samples ‘N’ coming between two successive PPS edges is evaluated and the new sampling interval is calculated as inverse of ‘N’ ¡ After reallocation, samples are passed to the DFT block

¡ Does not require GPS at every node ¡ Communication costs lowered as based on Ethernet ¡ Eliminates the extra cabling requirements of 1PPS to propagate highly accurate timing signals ¡ Non-recurring engineering costs – firmware development ¡ Cost of goods sold – negligible as only requires modification in Ethernet physical layer to support IEEE 1588 ¡ High grade oscillators required which are expensive ¡ Lack of testing equipment supporting IEEE 1588 v2 protocol

QUESTIONS ?

THANK YOU