In our last blog post we spoke about the work done by our services division ISOSCELES Commissioning of PMUs for a Central Transmission Utility. On popular demand, today we are doing knowledge sharing on PMUs and WAMS as well as technical information on our offering of Vizimax PMU.
The Indian Electricity Grid, following the policy of “One Nation One Grid” is among the most complex grid networks and is operating near to its stability limits. The Indian Power Grid is constantly upgrading to meet new generation and demand requirements such as integration of large scale intermittent & variable renewable generation as well as addition of new grid infrastructure for system strengthening to meet ever increasing demand for power.
To ensure planning efficiency, smooth grid operations and to avoid cascading trippings resulting in partial or complete grid blackout (such as 2012 Indian grid blackout), the Indian electricity grid established Wide Area Monitoring Systems (WAMS) consisting of Phasor Measurement Units (PMUs) at substations/generating stations and Phasor Data Concentrators (PDCs) at Load Dispatch Centres capable to acquire, analyse and act on stability related issues of the power grid network.
Phasors and Synchrophasors
A Phasor representation of a sinusoidal waveform (such as currents and voltages) and is written as a value of magnitude and phase angle. A timestamped phasor is known as a synchrophasor.
In the above diagram, the point V1 on the sinusoidal voltage waveform consists of magnitude (V1) and phase (‘d’1) which is the angular difference between peak voltage phase angle and voltage phase angle at time reference T=0. *Here the time reference T=0 is provided by the GPS signal.
Phasor Measurement Units
PMU is a device that produces the time synchronized measurements of Synchrophasors (i.e. its amplitude and phase), frequency, ROCOF (Rate of Change Of Frequency) from voltage and current signals based on a common and accurate time source typically provided by the Global Positioning System (UTC-GPS). These real time synchronised measurements enable the analysis of dynamic behavior for improved efficiency.
Three key Benefits of PMUs over other monitoring systems are:
- PMU provides phase angle value of the measured synchrophasor which indicates “system stress” at the monitoring node
- PMU provides high speed sampling (256samples/cycle) of synchrophasors and reporting (200framese/second) of data to central software. This high accurate and rapid sampled data provides critical information of dynamic behaviour of power system network
- Accuracy of time synchronisation (with microsecond precision) of PMUs enables analysis across a wide area
Wide Area Monitoring System (WAMS)
WAMS consists of PMUs at field substation end and PDC software at Central Load Dispatch Centre. The PDC software will collect time synchronised data from multiple PMUs located at different points on the grid and perform specific analytics. A number of software analytical functions have been identified and deployed in Indian Power Sector. Some of these analytics are:
● Vulnerability analysis of relay
● Dynamic/Linear State Estimator
● Supervised Zone-3 distance protection scheme to prevent unwanted tripping
● On line CVT parameter validation
● Emergency control schemes for controlling frequency and voltage instabilities
● Schemes for controlling angular instabilities i.e, out of step protection and adaptive islanding.
Benefits of WAMS Technology in Grid Operations
● In-depth insight in to Power System behavior & Elements
● Brings efficiency in operation as well as economy
● This will enable efficient calibration of measuring equipment.
● It would facilitate integration of large quantum of intermittent and variable renewable generation into the grid.
● Enables synchronous measurement of real time grid parameters across the widely spread grid with low latency in data transfer to control centers which would be very effective in reliable, secure and economical grid operation.
● Provides more intelligent/dynamic information to Special Protection Schemes which will be a step towards self-healing Grids.
● Further the WAMS data shall be used for Power System Planning and will help in better planning of the Power System in the Country.
SCOPE has partnered with Vizimax Inc (Canada) to provide Phasor Measurement Unit (PMU) to Indian customers.
Vizimax PMU is IEEE C37.118.1a-2014 Certified for high accuracy acquisition and reporting for HV and MV Power Grids.
Vizimax offers the PMU for substation applications with standard Current (1/5 Amp) and standard Voltage (110 Volt) Input
Vizimax also offers a PMU Variant with low voltage (10 Vrms) input range for the use of PMU for Real time simulation applications focused for Research & Development laboratories.