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 ¡ State estimation carried out to provide state of

system

¡ Load forecast carried out every 15mins ¡ AGC used balance power generation and load

demand

¡ Contingency analysis carried out ¡ OPF for transmission- constrained economic

dispatch

¡ Historical and forecasted data stored in storage

devices

¡ Various copies of data coordinated, synchronized

and merged in databases

¡ 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

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

• Provides 1 PPS signal
• Time- tagging

An architecture involving the following must exist in

• rder 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 < 31.8µs for 50 Hz system and 26.5µs

for 60Hz system

APPLICATIONS OF PMU

Real-time operations applications

¡

Wide-area situational awareness

¡

Frequency stability monitoring and trending

¡

Power oscillation monitoring

¡

Voltage monitoring and trending

¡

Event detection and avoidance

¡

Resource integration

¡

State estimation

¡

Dynamic line ratings and congestion management

¡

Outage restoration Planning and off-line applications

¡

Baselining power system performance

¡

Event analysis

¡

Power plant model validation

¡

Load characterization

¡

Special protection schemes and islanding

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