Pd Phase Patterns And Pulses - General Examples April 2012

PD Phase Patterns and Pulses Summary PDGold Software Signal Recognition Guide Version 3 - April 2012 Copyright HVPD Ltd.

INTERNAL CABLE PD Phase Patterns

Segment Waveforms

Cable Cable PD 1,500 PD Magnitude (pC)

1,000 500 0 -500 -1,000 -1,500 0

90 180 270 Phase of Pow er Cycle (deg)

360

Risetime: 89 nSec Max Frequency: 1.10 MHz +ve PD Pulse

Comments • Pulses on both halves of power cycle. • Positive pulses on one half, negative pulses on other half. • Generally, magnitudes should be similar on both halves of the cycle, although one half can be bigger than other. • Number of pulses per power cycle can vary from two up to hundreds. • Sometimes wide inception window, if very active PD site. • Variation in pulse height is typical, i.e. not all pulses have same magnitude. • Pulses should have a reasonably monopolar shape, sometimes with a little oscillation. Source: Example1.PDG

Noise

Analysis Note Noise Events

8

Noise Magnitude (mV)

6 4 2 0 -2 -4 -6 -8 0

90 180 270 Phase of Pow er Cycle (deg)

360

Risetime: 3.7 uSec Max Frequency: 66 kHz

Pulse magnitude is determined by automatically integrating the area underneath the pulse relative to its baseline. Approximate to this is multiplying base by height.

NOISE Phase Patterns

Segment Waveforms

Comments • Noise can affect all measurements. • Can resemble PF very closely in phase and pulse characteristics. • Below shows the effect of local AM broadcast on overhead cables. • By selection of the appropriate filter, the source frequencies of noise can be minimised in measurements, revealing even significantly lower magnitude partial discharges.

Noise Noise Events 8

Noise Magnitude (mV)

6 4 2 0 -2 -4 -6 -8 0

90 180 270 Phase of Pow er Cycle (deg)

360

Risetime: 3.7 uSec Max Frequency: 66 kHz Source: Example1.PDG

Noise

Noise Waveform 8 6

Volts (mV)

10 5 0

Volts (mV)

Noise Events

Noise Magnitude (mV)

4

Noise Waveform 12 10 8 6 4 2

-4 -6

0 -2 -4 -6 -8

0

1

2

3

4

5

6

-10

90 180 270 Phase of Pow er Cycle (deg)

360

1

2

3

4

5

6

7 8 Time us

9

10

11

12

13

14

Risetime: 181.72 ns Max Frequency: 976.56 kHz 0

0

0 -2

-10

-5

2

Risetime: 23.86 ns Max Frequency: 12.70 MHz

7 8 Time us

9

10

11

12

13

14

15

Sources: Example1.PDG Example1b.PDG Castlemoate Fostertown Feeder.PDG - ESB FS 7763 LA’s Connected.PDG – Jemena

15

INTERNAL CABLE PD ON ALL THREE PHASES Phase Patterns

Segment Waveforms

• Pulses on both halves of power cycle. • 120 degree phase separation between pulse groups on L1, L2 and L3. • Phase-phase crosstalk is not necessarily present if the HFCTs are coupled onto cable with earth brought back through instead of commonly grounded earth sheaths.

Cable Cable PD 1,500 1,000 PD Magnitude (pC)

Comments

500 0

Risetime: 75.96 ns Max Frequency: 2.50 MHz

-500 -1,000 -1,500 0

90 180 270 Phase of Pow er Cycle (deg)

360

Source: Example2.PDG

Noise

Noise Waveform Noise Events

Noise Waveform 4

6

3

1 Vo lts (m V)

Noise Magnitude (mV)

2

4 2 0

0 -1 -2 -3 -4

-2

-5

-4 0

-6 0

90 180 270 Phase of Pow er Cycle (deg)

360

1

2

3

4

5

6

7 8 Time us

Risetime: 600.24 ns Max Frequency: 390.63 kHz

9

10

11

12

13

14

15

INTERNAL CABLE PD ON ALL THREE PHASES (Belted PILC) Phase Patterns

Segment Waveforms

• More than one phase grouping of pulses present across power cycle. • Different cable PD wave shapes observable (i.e. with different rise-times/fall times/pulse widths). • HFCT signal has mono-polar cable PD wave shapes.

Cable Cable PD 3,000 PD Magnitude (pC)

Comments

2,000 1,000 0 -1,000 -2,000 -3,000 0

90 180 270 Phase of Pow er Cycle (deg)

360

Source: Example3.PDG

Noise

Noise Waveform Noise Events

8

Noise Magnitude (mV)

6 4 2

Risetime: 109 nSec Max Frequency: 315 kHz

0 -2 -4 -6 -8 0

90 180 270 Phase of Pow er Cycle (deg)

360

CABLE PD AT TERMINATION Phase Patterns

Segment Waveforms

Comments • Synchronous HFCT and TEV signals. • HFCT signal has rapidly oscillating PD wave shapes (10+ MHz)

Local Cable PD 1,500

PD Magnitude (pC)

1,000 500 0 -500 -1,000 -1,500 0

90 180 270 Phase of Pow er Cycle (deg)

360

Noise

Risetime: 40 nSec Max Frequency: 10.67 MHz

Noise Waveform Noise Events

20 Noise Magnitude (mV)

15 10 5 0 -5 -10 -15 -20 0

90 180 270 Phase of Pow er Cycle (deg)

360

Risetime: 423.89 ns Max Frequency: 427.25 kHz

Source: Example4.PDG

CABLE PD PHASE-TO-PHASE CROSSTALK Phase Patterns

Segment Waveforms

• Typically occurs when cable earth sheath are bonded to common point, e.g. at earth link box. • If HFCTs are installed with arrows pointing in same direction with respect to earth then PD crosstalk signals should be of opposite polarity to the source.

Cable

PD Magnitude (pC)

Cable PD 400 350 300 250 200 150 100 50 0 0

90 180 270 360 Phase of Pow er Cycle (deg)

Noise Magnitude (mV)

Noise

Comments

Risetime: 11.49 nSec Max Frequency: 18.5 MHz nSec

Falltime: 88 ns Pulse Width: 156

Noise Waveform

8 6 4 2 0 0

90 180 270 360 Phase of Pow er Cycle (deg)

Source: Example6.PDG

SURFACE DISCHARGE Phase Patterns

Segment Waveforms

Comments • Pulses on both halves of power cycle. • Often diagnosed as cable and local PD, due to pulse shapes being on the threshold between these two types (frequency range 3-10 MHz). • Larger magnitude pulses on one half than the other. • Typically detected when testing at outdoor terminations and metal-clad switchgear.

Local

Risetime: 2.21 nSec Max Frequency:6.25 MHz

Noise

Noise Waveform

Source: Example5.PDG

CORONA – SHARP POINTS ON HV OR GROUND CONDUCTORS Phase Patterns

Segment Waveforms

Comments • Pulses only on one half of the power cycle. • Pulses can be very large in magnitude (hundreds of mV). • Pulses occur over a narrow inception window that should remain fixed on each power cycle (assuming trigger source is synchronous). • Typically detected when testing at outdoor terminations.

Cable Cable PD 500 400 PD Magnitude (pC)

300 200 100 0 -100 -200 -300 -400 -500 0

90 180 270 Phase of Pow er Cycle (deg)

360

Noise Waveform Noise Waveform

8 10 8

6

6 4 V o lts ( m V )

Noise Magnitude (mV)

Noise

Risetime: 34 nSec Max Frequency: 3.29 MHz

4

2 0 -2 -4

2

-6 -8

0

-10

0

90 180 270 360 Phase of Pow er Cycle (deg)

0

20

40

60

80

100 120 Time us

140

160

180

200

220

Source: Example7.PDG

PD AT TRANSFORMERS Phase Patterns

Segment Waveforms

• Pulses on both halves of power cycle. • Positive pulses on one half, negative pulses on other half. • Sometimes wide inception window if very active PD site. • Variation in pulse height typical, i.e. not all pulses have the same magnitude. • Phase-to-phase crosstalk expected. • Large oscillation on pulse shapes expected.

Cable PD Magnitude (pC)

Comments

400 300 200 100 0 0

90 180 270 360 Phase of Pow er Cycle (deg)

Noise on Single HFCT

Risetime: 60 nSec Max Frequency: 3.42 MHz

Noise in TEV (Local) Channel

Source: Example8.PDG

Risetimes of PD

DISCHARGE DUE TO FLOATING METAL PARTICLES / UNEARTHED METALWORK Phase Patterns

Segment Waveforms

Comments • Pulses on both halves of the power cycle. • Pulses can be very large in magnitude (hundreds of mV). • Pulses have uniform height and wide inception windows that can vary between power cycles. • Typically detected when testing at outdoor terminations and gas insulated switchgear (GIS).

800

Volts (mV)

PD Magnitude (mV)

Local

600 400 200

600 400 200 0 -200 -400 -600 -800 4.8

4.9

5

5.1 5.2 Time uSec

5.3

5.4

0 0

Noise

90 180 270 360 Phase of Pow er Cycle (deg)

Risetime: 4.81 nSec Max Frequency: 58.6 MHz

Noise Waveform

Source: Example10.PDG