© ERLPhase Power Technologies Ltd. All Rights Reserved. Sub harmonic protection relay S-PRO Krish Narendra, P.hD. CTO ERL – Protection, Automation, Control & Smart Grid 09 Sept 2013 ERCOT Presentation, Austin, Texas

Outline Introduction Utility Event Microprocessor Based Sub harmonic (S-PRO) Protection Relay Test Setup and Real Event Playback Summary of S-PRO Capabilities S-PRO Upgrades Planned Conclusions Questions

Introduction : ERL Evolution, Vision, and Mission ERL’s Vision: ERL’s vision is to become technology leaders in providing solutions to the future Smart Grid and this is also reflected in our Mission Statement: Mission Statement We use the best in class technology to relentlessly provide Smart Solutions for our customers’ power system protection, monitoring and control needs.

Utility Event - System Single Line Diagram 4

Utility Event- Studies and Conclusions Radial connection of generation to the system would lead to sub synchronous frequency oscillation. Study was conducted to determine the impact of series capacitors installation on existing generators in the region. The study concluded that only the combustion turbines and the wind farm at Lakefield generation were impacted. Special Protection Scheme (SPS) was needed to bypass the capacitor under some system configuration. 5

Utility Event - Effect of Series Capacitors On Combustion Turbine The study concluded that the CT generator units are stable under base (normal) condition but with some potential for SSR under N-1 contingency. Since conclusion depended heavily on the actual mode shape of the turbine-generators and damping due to load, it was decided to determine the load damping and mode shape through actual measurement on one of the units. 6

Utility Event - Effect of Series Capacitors On Wind Farms Study concluded that the wind farm will be affected by what is known as SSR induction generation effect. In the case of Xcel Energy, it was determined that this can be mitigated by bypassing the series capacitor on loss of LFD- LAJ line. In addition, a study performed by Xcel Energy also concluded that failure to bypass should be backed up by suitable SSR protection that can recognize the electrical instability and trip the wind farm as a last resort. 7

Utility Event - Special Protection Scheme A special protection scheme was designed to bypass the series capacitor for the following conditions: At Lakefield Generation substation: –Any relay operation on the LFD-LAJ line –Breaker configuration at Lakefield Generation that leads to radial connection of wind farm or CT Generators At Lakefield Junction substation –Any relay operation on LAJ-LFD line –Any configuration of breakers at Lakefield Junction that leads to opening of the line towards Lakefield Generation. 8

1- Breaker 1 & 2 opened for regular system switching procedure 2- CT1,CT2, and W start feeding radially through series capacitor 3- Tripped the CT generator unit Line kV 345 kV 45 MVA Utility Event: What Happened? 9 15 MW (20% of total generation) To the System

Utility Event - TESLA DFR Capture 10 9 Hz & 13 Hz dominant sub harmonics High speed recording of 3 phase generator currents captured by the DFR

Utility Event – Slow Speed Event Analysis 11 Slow speed (swing ) recording of one of the phases

Utility Event – Sub harmonics In Wind Generators Phase currents of wind generators connected to the system during the second switching event had sub synchronous frequencies even when the series capacitor was not in service. The conclusion was to develop a back up protection device to detect sustained oscillations. 12

Utility Event : Need for Backup Protection for Wind Farm None available at that time to detect sub synchronous frequencies. Specification/Requirement: –Ability to detect any frequencies from 5-25 HZ with 1 HZ resolution. –Set points based on nominal, fundamental and THD frequency ratio. –Set points based on individual current or voltage input as well as summation of more than one current input. 13

Microprocessor Based Sub harmonic Protection Relay (S-PRO)

Microprocessor...Relay Functional Modules 15

Microprocessor…Sub Harmonic Detection Logic Diagram 16

Microprocessor…Sub Harmonic Detection 17 Trip or Alarm: = max (f2, f3, f4, f5, f6, f7) > Lset

Microprocessor…Operations/Minute Detection 18

Microprocessor…RMS Overcurrent and Overvoltage Backup Protection with S-PRO Overcurrent and Overvoltage Setting for the fundamental can also be determined by means of a power system study that should reveal the current and voltage levels that may appear in the system during an event. The overcurrent settings shall be coordinated with the other overcurrent relays being used to protect the transmission line. The overvoltage settings shall be coordinated with the regional reliability center requirements and the minimum insulation requirements for the equipment. 19

Microprocessor Based….Features Sub-harmonic detectors associated to each of the three phase AC analog phase currents and voltages –Two (2) detectors are provided for each three phase analog quantities. –Configurable alarming or tripping –An innovative “Operations/Minute” trigger monitors the sub-harmonic level to cope up with the statistical nature of wind turbine operations and availability Four (4) sets of configurable three phase current summation virtual channels suitable for ring bus configuration are also monitored

Microprocessor Based…Inputs/Outputs 4 sets of 3-Phase CT inputs (<0.25 VA) –5 A RMS – nominal (1 Amp nominal version available) –15 A RMS - maximum continuous –100 A for 1 second - maximum full scale without distortion –400 A for 1 second - maximum thermal rating 2 sets of 3-Phase VT inputs (<0.15 VA) –69 V RMS - nominal –138 V RMS – maximum continuous –207 V RMS for 10 seconds - maximum thermal rating 9 digital inputs, externally wetted 14 programmable output contacts, plus 1 relay inoperative output

Test Setup and Real Event Playback Real-time playback Field & Simulated waveforms –Case study-1: COMTRADE Files Generated Through RTDS system –Case study-2: Xcel Energy 22

Test Set Up…Detector Setting 23

Test Setup…Current Playback Results – Xcel Energy Event 24

Test Setup : Sub harmonic analysis of Xcel Energy Event 25

Summary of S-PRO Capabilities Protection against SSR problems in both Wind and Synchronous generator systems or any combined cycle plant. The current resolution of sub harmonic detection is 1 sec and can detect single sub harmonic or range of sub harmonics from 5 Hz to 40 Hz for both 60 Hz and 50 Hz system. Substation hardened and comes with 10 year warranty. ( ( for data sheet / full features / more details ) Installed and in operation at Xcel Energy Lake Field Substation with Wind Generation since Recent installation at Suzlon owned Wind farm in India. Future installations in a Series Compensated Synchronous generating station in Bahrain in Middle East, and in Mid India to detect SSR issues. More Upgrades Planned by end of the 2013.

S-PRO Upgrades Planned Faster Detection of sub harmonics – depending on the sub harmonic range – 5 Hz in 200 mS to 40 Hz in 25 mS, that is, the response time in the range of 25 mS – 200 mS depending the sub harmonic to be detected. Less than 1.3 cycle response for the fundamental Over current / voltage back up protections. Automation / SCADA Enhancements: –IEC station bus support – user selectable sub harmonics measurements, GOOSE, Report Control Blocks etc. –DNP3 – additional sub harmonic measurements through user selectable point map. Fault Summary – feature which summarizes sub harmonic fault current / voltage level under any trip conditions including the RMS over current / voltage protection function.

The new event captured at the Xcel Energy Utility lead to the development of a microprocessor based sub harmonic protection technique. With the increase use of wind generators (DFIGs) feeding HV and EHV utility networks with series compensation, it is necessary to ensure that sub harmonic oscillations are monitored, and that the electrical grid is protected from any resulting detrimental effects. 28 Conclusions

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