improved assessment of voltage dips with common monitoring devices

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



Voltage Dip Representation

Why Voltage Phasors?

Limitations of RMS-representation



Dip produced by single phase fault

Depth = 36 % Depth = 16 %

single phase dip 2-phase dip



Dip produced by single phase fault

D y

primary side trafo secondary side trafo

MAGNITUDE (PP)-U1 = 94%-U2 = 80%-U3 = 93%



Why phasors?

• indication about origin– fault type and characteristics

• dip propagation– through transformers– connection : star or delta

• depth: phase-to-ground phase-to-phase



Improved Dip Characterisation (M. Bollen)

Voltage Type: A, B, C, D, E, F & G

Characteristic Magnitude V

Phase Angle Jump



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)



Dip Type A

Origin: balanced three phase fault

« A »



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



Dip Type E, F & G

Connection: star

Origin: 2-phase to ground

Connection: delta Connection: delta

Behind Dy or Yd trafo

« E » « F » « G »



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 !



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



Voltage Dip Conversion Algorithms

RMS PHASORS



Why conversion algorithms?

Common power quality monitors only measure rms-voltages during dip

Voltage phasors interesting / required for analysis / statistics

conversion!



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



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



Step 1: determine dip type (2)

1 & 3 phase drops 2 & 3 phase drops



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



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



Conclusions



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



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



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



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



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



Thank You!

improved assessment of voltage dips with common monitoring devices

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