RARF DATA for TYPES 3 & 4 WTGsFault Current Contribution for Current Limited ResourcesEd Geer, P.E.Network Model Engineer, Sr. SPWG MeetingJuly 17, 2014

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• Type 3 WTGs are Doubly-fed induction turbines (DFIG) where the power flows both directly to the grid and through an AC/DC/AC converter. The converter replaces any reactive compensation required in Type 1 and Type 2 generators.

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• Type 4 WTGs are variable speed full converter turbines that employ a AC/DC/AC frequency converter as the sole power flow path from the turbine to the grid. The Type 4 WTG does not directly connect to the grid.

• Visual descriptions of the four wind types are below.

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• The RARF forms require some information that does not fully apply to an asynchronous generator.

• An example of such is the request for synchronous impedance.

• In this case the values provided correspond to the impedance of the machine seen from the stator at an estimated rated slip for Type1 and 2.

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• For Type 3 and 4 the values provided correspond to an approximate equivalent impedance that reproduces the contribution to a remote short circuit.

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• For Type 3, if there is crowbar operation, as is the expected case from close short circuits, then the controls are by-passed then the machine behaves like an asynchronous generator…

• estimation that X’ is a good approximation for X” and negative sequence impedances equals 0.2 to represent 5 pu initial short circuit current

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RARF Project – Siemens PTI Report- Appendix A.3 WTGs

• For Type 3 without crowbar operation, if the controls operate, then the current is controlled and we provide typical values for just after the short circuit and various cycles afterward.

• As noted in Table A-4, the instantaneous Imax is 3.0 per unit, the Imax at 2-3 cycles following the fault equals 1.25 per unit and the Imax at 4+ cycles following the fault equals 1.11 per unit.

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RARF Project – Siemens PTI Report - Table A-4

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RARF Data for Type 3 & 4 WTG s

• Instantaneous Controlled Fault Current Magnitude (Multiple of full load current) for Turbine Types 3 & 4

• Maximum expected wind turbine fault current contribution immediately after a fault on the grid for Type 4 and Type 3 turbines, allowing for action of the controls (no crowbar operation) as a percent of full load current

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RARF Data for Type 3 & 4 WTG s

• Controlled Fault Current Magnitude At 2 to 3 cycles after fault (Multiple of full load current) for Turbine Types 3 & 4

• Maximum expected wind turbine fault current contribution at 2 – 3 cycles after a fault on the grid for Type 4 and Type 3 turbines, allowing for action of the controls (no crowbar operation) as a percent of full load current

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RARF Data for Type 3 & 4 WTG s

• Controlled Fault Current Magnitude At 4 plus cycles after fault (Multiple of full load current) for Turbine Types 3 & 4

• Maximum expected wind turbine fault current contribution at 4+ cycles after a fault on the grid for Type 4 and Type 3 turbines, allowing for action of the controls (no crowbar operation) as a percent of full load current

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RARF Data for Type 3 & 4 WTG s

• Currently RARF data for Type 3 WTGs range from 1.36 p.u to 4.96 p.u for instantaneous current contribution

• Currently RARF data for Type 3 WTGs range from 1.0 p.u to 3.0 p.u for current contribution at 2-3 cycles

• Currently RARF data for Type 3 WTGs range from 1.0 p.u to 3.0 p.u for current contribution at 4+ cycles

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RARF Data for Type 3 & 4 WTG s

• Currently RARF data for Type 3 WTGs range from 0.02 p.u to 0.383 p.u for subtransient reactance

• Currently RARF data for Type 3 WTGs range from 0.02 p.u to 0.38562 p.u for transient reactance

• Currently RARF data for Type 3 WTGs range from 0.02 p.u to 7.01 p.u for positive sequence reactance

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RARF Data for Type 3 & 4 WTG s

• RARF Validation Rules -

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RARF Data for Type 3 & 4 WTG s

• Type 3 WTG with RARF data outside typical Siemens PTI Report ranges

• crowbar activates for most faults• crowbar in the rotor about 5-6 cycles• initial current peak of about 5 to 6 times

the rated current reduced rapidly to values lower than the rated current

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RARF Data for Type 3 & 4 WTG s

• Type 3 WTG with RARF data outside typical Siemens PTI Report ranges

• rotor voltage returns to tolerable values for the converter, the crowbar is released and the converter retakes control, starting to command the injection of reactive current, in order to provide voltage support to the fault. The current that can be injected during this time is around 1.0 p.u.

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RARF Data for Type 3 & 4 WTG s

• Type 3 WTG with RARF data outside typical Siemens PTI Report ranges

• Ipeak = 5.8 p.u• I at 2-3 cycles = 0.8 p.u.• I at 4+ cycles = 0.45 p.u.

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RARF Data for Type 3 & 4 WTG s

• Type 3 WTG with RARF data outside typical Siemens PTI Report ranges

• Value for subtransient reactance of 0.17 p.u. (1/peak current of 5.8 p.u.)

• Values for transient reactance of 1.25 p.u. (1/current at 2-3 cycles of 0.8 p.u.)

• Once the crowbar is released, the WTG operates similarly to current source of 1.0 p.u.

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RARF Data for Type 3 & 4 WTG s

• Type 3 WTG with RARF data outside typical Siemens PTI Report ranges

• Considering changing the RARF Validation rule to show warnings rather than errors for the values of 5.8 p.u., 0.8 p.u. and 0.45 p.u. fault current contribution for instantaneous, after 2-3 cycles and 4+ cycles respectively.

SPWG MeetingJuly 17, 2014 21

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