Progress Report on Failures of High Voltage Bushings with Draw Leads By Jim McBride and Larry Coffeen, JMX Services / NEETRAC 7/26/2010

Transcription

1 The Team: Jim McBride: IEEE Member Larry Coffeen: IEEE Senior Member President, JMX Services, Inc. Senior Research Engineer, NEETRAC BS EE Georgia Tech BS EE Georgia Tech Testing, DAQ, and Measurement Substation Testing and Research 26 Years 43 Years 7/26/2010 IEEE PES July 26,

2 Transients from 345/138 kv & 230/115 kv Substation Apparatus Recorded by NEETRAC/JMX On-line FRA Equipment Sensors located at H & X transformer bushing taps & across transformer neutral bushing Sensor Connection Neutral Bushing Sensor Bushing Tap 7/26/2010 IEEE PES July 26,

3 OLFRA & OLRPF Cabinets 7/26/2010 IEEE PES July 26,

4 OLRPF OLFRA 7/26/2010 IEEE PES July 26,

5 OLFRA Cabinet 7/26/2010 IEEE PES July 26,

6 Typical bushing tap + high pass filter + cabling frequency responses compared to laboratory reference divider (red trace in left column) 345kV System, Lapp POC, 2000A, Bottom Conn.,1999 yr 230kV System,Trench COTA 750,1400A,Draw Lead,1999yr 7/26/2010 IEEE PES July 26,

7 Pre-strike of the 345 kv OCB contacts on energizing 345 kv transformer from high side The top trace is the magnitude vs. time overlay of the H1 bushing tap, the X1 bushing tap, & the Neutral bushing waveforms for the 345kV OCB prestrike transients on energizing the transformer. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the H1 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

8 Zoom-in on highest burst from left upper waveform set. 2 usec. / big division. Blue = H1 bushing tap. (Bushing input max. approx. 10kV pk.) Red = X1 bushing tap. Green = Neutral bushing & represents pulse travel through H1 transformer winding / insulation combination from H1 to neutral. 7/26/2010 IEEE PES July 26,

9 Picking Up Load with 138kV, SF6, Low Side Bank Breaker The top trace is the magnitude vs. time overlay of the H3 bushing tap, the X3 bushing tap, & the Neutral bushing waveforms for the transformer as the SF6 LS PCB picks up load (176 MW, 37MV, 740A on 138kV). The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the X3 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

10 Zoom-in on second burst from left upper waveform set. Blue = H3 bushing tap. Red = X3 bushing tap (bushing input max.approx. 5kV). Green = Neutral bushing & represents pulse travel through X3 transformer winding / insulation combination from X3 to neutral. 7/26/2010 IEEE PES July 26,

11 Opening a 345 kv energized air disconnect switch to drop short bus & bushing capacitive load The top trace is the magnitude vs. time overlay of the H1 bushing tap, the X1 bushing tap, & the Neutral bushing waveforms for the transformer as a 345kV disconnect switch is opened to obtain a working clearance for 345kV line CCVTs. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the H1 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

12 Zoom-in on first burst from left upper waveform set. Blue = H1 bushing tap (bushing max. input approx. 5kV). Red = X1 bushing tap. Green = Neutral bushing & represents pulse travel through H1 transformer winding / insulation combination from H1 to neutral. 7/26/2010 IEEE PES July 26,

13 Pre-strike of the 230kV Air Disconnect Switch on Energizing 230kV Transformer from High Side The top trace is the magnitude vs. time overlay of the H1 bushing tap, the X1 bushing tap, & the Neutral bushing waveforms for the 230kV Air Disconnect Transients on energizing the transformer. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the H1 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

14 Zoom-in on highest burst from left upper waveform set. 2 usec. / big division. Blue = H1 bushing tap. (Bushing input max. approx. 30kV pk.) Red = X1 bushing tap. Green = Neutral bushing & represents pulse travel through H1 transformer winding / insulation combination from H1 to neutral. 7/26/2010 IEEE PES July 26,

15 230/115kV, 300MVA, Auto with 230kV High Side Air Disconnect Switch 230kV High Side Air Disconnect Switch OLFRA & OLRPF Equipment 7/26/2010 IEEE PES July 26,

16 Fast transient currents entering top of bushing see an inductive draw lead in series with a large capacitance at winding to case with most all initial voltage drop across the bushing draw lead. 7/26/2010 IEEE PES July 26,

17 Opening a 115kV, 58.5MVAR, Capacitor Bank OCB The top trace is the magnitude vs. time overlay of the H2 bushing tap, the X2 bushing tap, & the Neutral bushing waveforms for the transformer as a 115kV cap. bank OCB is opened. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the X2 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

18 Zoom-in on first burst from left upper waveform set. Blue = H2 bushing tap Red = X2 bushing tap (bushing max. input approx. 6kV). Green = Neutral bushing & represents pulse travel through H2 transformer winding / insulation combination from H2 to neutral. 7/26/2010 IEEE PES July 26,

19 115kV, 58.5MVAR, Capacitor Bank 7/26/2010 IEEE PES July 26,

20 Pre-strike of 230kV SF6 PCB on Energizing 230kV, 180MVAR Capacitor Bank The top trace is the magnitude vs. time overlay of the H2 bushing tap, the X2 bushing tap, & the Neutral bushing waveforms for the 230kV SF6 PCB prestrike transients on energizing the cap bank. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the H2 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

21 Zoom-in on highest burst from left upper waveform set. 2 usec. / big division. Blue = H2 bushing tap. (Bushing input max. approx. 7kV pk.) Red = X2 bushing tap. Green = Neutral bushing & represents pulse travel through H2 transformer winding / insulation combination from H2 to neutral. 7/26/2010 IEEE PES July 26,

22 230kV, 180MVAR, Capacitor Bank 7/26/2010 IEEE PES July 26,

23 Opening a 230kV Energized Air Disconnect Switch to Clear Up 230kV, 180MVAR Capacitor Bank for Maintenance The top trace is the magnitude vs. time overlay of the H3 bushing tap, the X3 bushing tap, & the Neutral bushing waveforms for the transformer as a 230kV disconnect switch is opened to obtain a working clearance for 230kV cap bank after the SF6 cap breaker is opened. The waveforms are sampled at 12 bit, 20MHz w/ 64K records. The 60 Hz is filtered out to increase transient dynamic range of measurement. The bottom purple graph is the FFT of the H3 tap waveform that indicates frequency energy well into the MHz range. The FFT full scale is 5MHz. 7/26/2010 IEEE PES July 26,

24 Zoom-in on first burst from left upper waveform set. Blue = H3 bushing tap (bushing max. input approx. 2.5kV). Red = X3 bushing tap. Green = Neutral bushing & represents pulse travel through H3 transformer winding / insulation combination from H3 to neutral. 7/26/2010 IEEE PES July 26,

25 Summary 1. Air disconnect switches and power circuit breakers are examples of devices that produce a significant number of medium voltage and/or current, fast transients as a result of normal switching operations. 2. These fast transients have rise times in the sub-microsecond range with frequencies well into the megahertz region. 3. The fast transients are characterized as they reach the high side, low side, and neutral bushings of the auto-transformer using the NEETRAC OLFRA equipment built by JMX Services, Inc. 7/26/2010 IEEE PES July 26,