improved assessment of voltage dips with common monitoring devices
DESCRIPTION
Improved Assessment of Voltage Dips with Common Monitoring Devices. M. Bollen, A. Robert & P. Goossens Session 2 Paper No5. Voltage Dip Representation. Why Voltage Phasors? Limitations of RMS-representation. Dip produced by single phase fault. single phase dip. 2-phase dip. Depth = 36 %. - PowerPoint PPT PresentationTRANSCRIPT
1GOOSSENS (BE) Session 2 – Block 3
Barcelona 12-15 May 2003
Improved Assessment of Voltage Dips with Common Monitoring
Devices
M. Bollen, A. Robert & P. Goossens
Session 2 Paper No5
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Voltage Dip Representation
Why Voltage Phasors?
Limitations of RMS-representation
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Dip produced by single phase fault
Depth = 36 % Depth = 16 %
single phase dip 2-phase dip
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Dip produced by single phase fault
D y
primary side trafo secondary side trafo
MAGNITUDE (PP)-U1 = 94%-U2 = 80%-U3 = 93%
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Why phasors?
• indication about origin– fault type and characteristics
• dip propagation– through transformers– connection : star or delta
• depth: phase-to-ground phase-to-phase
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Improved Dip Characterisation (M. Bollen)
Voltage Type: A, B, C, D, E, F & G
Characteristic Magnitude V
Phase Angle Jump
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7 Dip Types
4 types of faults– 3-phase faults– 1-phase faults– 2-phase faults– 2-phase-to-ground faults
• propagation through transformers• delta or star connection
Seven types of voltage dips
AB (C, D)C (D)E (F, G)
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Dip Type A
Origin: balanced three phase fault
« A »
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Dip type B, C & D« B »
« C » « D »
origin: single phase faultstar connection
origin: 2-phase fault, star connectionor single phase fault, delta connection
2-phase fault, delta connection
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Dip Type E, F & G
Connection: star
Origin: 2-phase to ground
Connection: delta Connection: delta
Behind Dy or Yd trafo
« E » « F » « G »
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Propagation of voltage dips
Yd
Dy
I
II
III
Fault Type Dip Location
I II III
3-phase A A A
3-phase-to-ground A A A
2-phase-to-ground E F G
2-phase C D C
1-phase-to-ground B C D
line & phase voltages are swapped: rms-voltages changes !
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V
Characteristic Voltage
Characteristic Magnitude V & Phase Angle Jump A, C, D, F, G: MIN(3 UPN & 3 UPP) B, E: first remove U0
= Invariable of connection type (PP PG) and location (primary secondary trafo)
sincos jVVV V
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Voltage Dip Conversion Algorithms
RMS PHASORS
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Why conversion algorithms?
Common power quality monitors only measure rms-voltages during dip
Voltage phasors interesting / required for analysis / statistics
conversion!
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Rms phasors algorithm
2 STEPS:• step 1: determine type of dip
– from relation between the three rms-voltages– number of possible dips is limited
• step 2: determine dip characteristics & phasors– 3 rms-voltages & dip type the characteristic
voltage V and phase-angle jump can be estimated
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Step 1: determine dip type (1)
• A : three-phase drops• C, E and G: two-phase drops• B, D and F: single-phase drops
Umin
Umax Voltage Dip Type
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Step 1: determine dip type (2)
1 & 3 phase drops 2 & 3 phase drops
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Step 2: determine characteristic voltage & phase angle jump
3 rms voltagesU1, U2, U3
dip type
C
characteristic voltage
&
phase angle jump
voltage phasors
sincos jVVV
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RMS Voltage Phasorsfor PP measurements
• no zero-sequence component• 3 phasors makes up closed triangle
phasors can easily be estimated out of 3 rms voltages with trigonometry equations
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Conclusions
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Evaluation of algorithms
• check of twenty voltage dips in Belgium HV-stations
• accuracy better than 5% for 95% of dips: acceptable for statistical purposes
• fine tuning of algorithms in progress
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Monitor spec’s
Best solution: recording of rms & phasor evolution during voltage dip
Alternative: only rms recordings to be able to apply conversion algorithms
– all three rms-voltages must be recorded during voltage dip
– snapshot of three rms-voltages when maximum depth is reached
if necessary: adapt firmware of monitor
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Connection of monitor (rms)
phase-to-phase measurement (PP)• phasors can be calculated with trigonometry equations
(closed triangle)• propagation of voltage dips can be estimated
accurately • no indication about the origin
phase-to-ground measurement (PN)• often preferable because indication about origin• propagation can be estimated with proposed
algorithms
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Voltage dip statistics (depth & length)
• phase-to-ground phase-to-phase statistics
– not comparable & should never be mixed
– always mention which connection is considered in tables or statistics (PG or PP)
• avoid phase-to-ground statistics
– too pessimistic view
– especially in impedance grounded systems
– zero-sequence component is removed in Yd and Dy transformers
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Voltage dip statistics (depth & length)
• phase-to-phase statistics are preferable
– can be derived from phase-to-ground measurements with proposed algorithms
• alternative: statistics with characteristic magnitude
– characteristic magnitude can be estimated with proposed algorithms,
– remains invariable during propagation (primary or secondary side trafo)
– is independant of connection
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Thank You!