Sub-Synchronous Frequency Detection Using SEL OGIC ® Control Equations SSF Relay ERCOT Workshop NPRR562 Subsynchronous Resonance Larry Gross

Founded in 2000 Protection and integration services company –Interconnection consultant –Standard designs –Custom designs –Commissioning Not associated with any relay manufacturer Improving Project Confidence

SSF Definition Sub-Synchronous Frequency (SSF): The frequency of an oscillation that is less than the nominal frequency (60 Hz in North America) of the power system. Not to be confused with confuse with power system fundamental frequency that temporarily becomes slightly lower (i.e Hz) than nominal.

System Fault Fault was cleared in 2.5 cycles Wind Systems became sourced only by a series compensated line Voltage reached 1.9 pu Turbine damage in 200 ms Series Capacitor was bypassed in 1.5 seconds 2009 SSF Event

2009 SSF Event Oscillography

2.5 Cycle Fault

2009 SSF Event Oscillography

Transmission Expansion Projects Series Compensation System Controls This Problem Will Become More Prevalent

Similar Philosophy to Typical Frequency (81) Protection Three Levels of Frequency Protection –Generator Control and Protection –Interconnection backup protection –System control and backup protection A Complete Solution

Three Levels of SSF Protection –Generator (Turbine) Control and Protection –Interconnection backup protection –System control and backup protection A Complete SSF Protection Solution

Three Levels of SSF Protection –Generator (Turbine) Control and Protection –Interconnection backup protection –System control and backup protection One Specific Solution

Microprocessor Based Solution Uses SEL-400 series relays Implemented using the SEL-421 Algorithm in SEL OGIC ® Control Equations One Specific Solution

SSF DETECTION ALGORITHM USING DIGITAL RELAY RAW INPUT VA, VB, VC COSINE FILTER ANALOG VALUES CALCULATE ROTATING PHASOR FIXED PHASOR DIGITAL FILTER Cont’d Lower Left Cont’d Upper Right MINIMUM PICK UP EMBEDDED RELAY ALGORITHMS USER LOGIC ALGORITHMS USER LOGIC ALGORITHMS, Cont’d ZERO CROSSING DETECTOR PEAK/GAIN CALCULATOR TRIP THRESHOLD AND TIMER LOGIC TRIP OR ALARM FREQUENCY CALCULATOR

SPECIFICATIONS Frequency supervision is calculated for each phase Frequency calculation range is 5 – 48 Hz Peak magnitude detection is acceptable down to 8 Hz Peak magnitude detection needs 100 ms to determine and verify the peak of a 10 Hz signal

ACTUAL EVENT PLAY BACK Trip time is 170 ms after fault clearing

A FLEXIBLE SOLUTION User selectable peak detector User selectable time delay Multiple set-points available User designated alarming and/or breaker tripping Event recording

WHAT IS NEEDED Identification that SSF may exist Determine locations SSF must be monitored Determine what level and timing could cause damage (SSF study if available) Specify alarm vs trip SEL-4xx Relay SSF Algorithm License from RAI SSF Installation and Commissioning

ECONOMICS SEL-421 Relay ~$7,500 SSF Algorithm (up to two licenses) ~$9,000 Other quantity licensing available Project specific settings ~$5,000 Firmware and Lab Testing ~$8,000 Installation (by site construction) ~$1,500 Commisioning (by relay commiss.) ~$2,000 Misc Support ~$2,000

SSF RELAY ALGORITHM (509)