SMART GRID MEASUREMENTS

Saikat ChakrabartiProfessor

Department of Electrical Engineering

Indian Institute of Technology Kanpur

UP 208016

Email: saikatc@iitk.ac.in

1

Characteristics of modern power systems

Wide geographical spread

Large number of interconnections

Rapid growth in the demand of electricity

Power system components operated closer to their

designed limits

High penetration of renewable energy sources

Competitive electricity market

2

Need for monitoring the system3

To take preventive and corrective control actions to

avoid any potentially dangerous operating condition

To analyse the vulnerability of the system against credible

contingencies

To facilitate economic operation of the system by

controlling the generator outputs and line flows based on

the information obtained from the monitoring system

To ensure acceptable quality of the power supplied to

the consumers

Need for real-time monitoring4

Power system is dynamic, and the operating conditions

are changing continuously

System topology (network interconnections) also may

change

Uncertainties in the demand for electricity

Power system components are being operated closer to

their designed limits

High penetration of renewable energy sources adds to

power quality and control problems.

How do we monitor?5

Remote terminal units (RTUs) and intelligent electronic devices (IEDs) placed at substations

Measurements from these RTUs and IEDs are telemetered to the control centre

Dedicated communication channels, such as optical fibre network are typically used for transmitting the measurements

Above monitoring mechanism is a part of the so-called

supervisory control and data acquisition (SCADA) system

Source: A. Abur and A. Exposito,

“Power System State Estimation: Theory

and Implementation"

What do we measure?6

In SCADA, two types of measurements are collected by

the RTUs and the IEDs, and telemetered to the control

centre:

Analog measurements (power flow, power

measurement, voltage magnitude, and current

magnitude)

Logic measurements (status of circuit breakers,

switches etc.)

What is done with the measurements?7

Measurements are telemetered to

the control centre

A state estimator constructs the

single line diagram of the system,

and estimates the states, after

detecting, identifying, and

processing bad data, if any, in the

measurements

By states, we usually mean the magnitude and phase angle

of the bus voltages

Control centre: source: internet

Measurement systems8

Two measurement technologies are revolutionizing the way

we monitor and control the power system

At the distribution level:

Advanced metering infrastructure (AMI), including smart meters and

the associated ICT infrastructure

At the transmission level:

Wide area measurement system (WAMS), including phasor

measurement units (PMUs) and the associated ICT infrastructure

Wide area measurement system (WAMS)

Measurements

from widely

dispersed

locations are

synchronized

with respect to a

common clock

9

Source: Internet

Synchrophasor measurements 10

1 pps time signals are obtained from GPS

Phase angle of a sinusoidal signal 𝑥(𝑡) will be taken as 0°, if the

peak of the signal coincides with the UTC seconds rollover

The phase angle is taken as 90° if the positive zero-crossing of the

signal coincides with the UTC seconds rollover.

Convention for

synchrophasor

representation

Phasor measurement units (PMUs) 11

Phasor represents a sinusoidal signal with a magnitude and a phase

angle (with respect to a reference)

Phasor measurement technology enables measurement of voltage

and current phasors with respect to a reference signal from a

satellite clock.

Source: http://www.phasor-rtdms.com/

Potential applications of WAMS12

Real-time visualization of power systems

Improved state estimation

Online estimation of load models

Online monitoring of power system stability

Analysis of the causes of a total or partial blackout

Real-time congestion management

Design of an adaptive protection system

Detection of faults on transmission lines

Advanced metering infrastructure (AMI) 13

AMI is comprised of the state-of-the-art electronic/digital hardware and software, which combine interval data measurement with continuously available remote communications

AMI typically refers to the full measurement and collection system that includes:

meters at the customer site

communication networks between the customer and a service provider, such as an electric, gas, or water utility

data reception and management systems that make the information available to the service provider

AMI components 14

Source: EPRI, the USA

AMI components…contd. 15

Meters: electricity/gas/water meters

Fixed network: commonly available networks are Broadband over Power Line (BPL), Power Line Communications (PLC), Fixed Radio Frequency (RF) networks, and public networks (e.g., landline, cellular, paging)

The AMI host system (servers) that receives the meter data and sends to the Meter Data Management System (MDMS)

MDMS manages data storage and analyses to provide useful information to the utility

Functional requirements of AMI 16

The main objectives of AMI are:

to enable two way communication between smart

energy meter and Head End System (HES)

to enable remote reading, monitoring & control of

electrical energy meters (consumer, feeder, DT meters

etc.)

to serve as repository of record for all raw, validated and

edited data.

The sanitized data may be subscribed by other utility

function for higher order analysis, billing, and collection.

AMI system requirement 17

Smart Meter at consumer end: Single phase whole current, Three phase whole current, CT & PT operated three phase meters and CT operated three phase meters

Smart meter network: usually Radio Frequency (RF) mesh in license free frequency band/ Power Line Carrier Communication (PLCC) or GPRS/3G/4G communication technology or combination of these technologies as per the site requirement

Data Concentrator Units (DCUs): The smart meter data using RF mesh/PLCC is collected by DCUs or Access points

Head End System (HES): data collected by the DCUs transported to HES through Wide Area Network (WAN); data from smart meters using GPRS/3G/4G technology may be transported directly to HES through WAN

AMI system requirement…contd. 18

Meter Data Management System (MDM): required for managing, analyzing, reporting, and securing the meter data

Web application: updated on-line data of consumers, consumer portal etc.

Mobile app: to enable consumer to log in through android/iOS/Window based mobile app to see information related to his/her energy consumption. App should also provide platform for implementation of peak load management functionality by providing existing tariff & incentives rates, participation options etc.

The AMI Implementing Agency (AIA): responsible for proper data exchange among Smart meter, DCU, MDM, HES and other operational/requisite software as part of fully functional AMI system.

Distribution system state estimator (DSSE) 19

Deployment of SE at the distribution level needed for:

handling massive penetration DGs

managing demand response

manage EVs and storage

Challenges in DSSE:

Unbalanced system – requiring 3-phase formulation

High R/X ratio

Large number of nodes

Incomplete observability – possibility of utilizing smart meter

data along with SCADA measurements

Conclusion 20

Measurement and sensing technologies are going to play

a major role in smart grids.

In the distribution systems, AMI including smart meters will

be a key enabler for efficient operation.

In generation and transmission segment, WAMS is going

to play a major role.

Managing the large amount of information and ensuring

its security will be a big challenge. Cyber-security and

cloud computing applications are bound to get

increased importance.