Power Transformer Load Loss Measurement
Transcript of Power Transformer Load Loss Measurement
Power Transformer Load Loss Measurement
Gert RietveldErnest HoutzagerMilos AcanskiDennis HoogenboomEnrico MohnsHenrik BaduraIlija Pecelj
ELPOW workshop, 31 Aug 2016
• Power transformers - losses
• Why loss measurements?
• Transformer loss measurement systems
• ELPOW: TLMS calibration systems
• Summary
Outline
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Power transformers are used toscale voltages in the grid
High Voltage low losses
Power Transformers
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Loss mechanisms:1. No load losses (Zb = ), caused by iron core, continuous2. Load losses (Zb = 0 ), copper loss, depends on current3. Stray losses depend on design
Power transformer losses
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Why loss measurements (1)
• Cost of losses in power transformers are comparable to the productcost TCO (total cost ownership)
• Environmental impact is significant
Cost of (no-)load loss equals product costs
Consequence: regulations - EcoDesign Directive:“improve environmental performance of energy-
related products through better design”
Why loss measurements (2)
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Saving potential in use phase through more efficient designsestimated as 16 TWh/year ( 17 % of present losses)3.7 Mt of CO2 emissions (50 % of total Danish electricity consumption)
Consequence: more requirements in standardsIEC 60076-19 (uncertainty calculation), and upcoming IEC 60076-20:
Why loss measurements (3)
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Tier 1: 1 July 2015Tier 2: 1 July 2021
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0 20 40 60 80 100 120
Min
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PEI
[%]
Rated Power [MVA]
Liquid immersed - Tier 1Liquid immersed - Tier 2Dry-Type - Tier 1Dry-Type - Tier 2
Consequence: customers (utilities) put fines on losses in excess ofguaranteed maximum losses
Example calculation for a large transformer (100 MVA)• Guaranteed maximum losses: Pgar = 500 kW (0.5 % loss)• Fine for excess losses: 10.000 €/kW
Why loss measurements (4)
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Reliable loss measurement with low uncertaintygives confidence and less discussions
3 % measurement uncertainty (150 ppm) corresponds to500 kW · 3 % · 10.000 €/kW = 150.000 €
(manufacturer and customer have to decide who pays for uncertainty)
Prob
abili
ty
Loss
Uncertainty matters! (compliance)
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Actual loss
Ecodesign limit
Test resultfails to detectcompliance
Accurate test
Inaccurate test
Ecodesign allows no tolerance: if measured loss is above the limit,the transformer is not in conformity
High accuracy =low risk of incorrectdecisions
TLMS typical measurement range: 0 – 100 kV, 0 – 2 kAUncertainty: 3 % - 5 % (IEEE C57.12.00, IEC 60076-19, Ecodesign)
Traceable to international measurement standards
Transformer Loss Measurement
Power supply P = V · I · cos
Power: P = U · I · cos with 90
P = U · I · cos (90 - ) = U · I · with = (90 - ) 0
Measurement challenge
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phase accuracy, not amplitude accuracy required!!
U and I are large numbers 1 % uncertainty is very easyis a very small number:for PF=0.01, = 0.57 1 % uncertainty is a big challenge!
(6 m , 0.34 min, 100 µrad)
TLMS consists of high-quality components
1 % losses
Only a calibrated TLMS system, traceable to national standards, givesproven, reliable quality in load loss measurements
TLMS calibrations
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Two approaches in TLMS calibrations• Component calibration (< 0.5 %; at PF=0.01 0.2 min, 3 m )
Easier to perform, larger overall system uncertainty• System calibration (< 3 %; at PF=0.01 1 min, 17 m )
Difficult to perform, low uncertainty, all effects included
Increased measurement challenge: TUR = 3 – 10
Reference measurement accurate to < 0.15 min (50 µrad, 3 m )
Aim: system calibration of TLMS up to 100 kV and 2 kA, with anuncertainty of better than 50 µW/VA
ELPOW aim for TLMS calibration
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Two approaches:
• Simultaneous generation of voltage V and current I
• Phase lock current I to externally applied voltage V
• Realise feedback loop
LMS for testing power trafos
Generating part Measuring part
• “voltage and current up to 150 kV and at least 2 kA…”• “uncertainties better than 50 ppm…”
Generation: phantom power
30 kVA0 V - 250 V
10 kVAR1: 0 A – 50 AR2: 0 A – 25 A
To do:• Stability transconductance amplifier must be optimized• Assessment of the phantom power source
2 channel source• 16 bit DACs• 10 VPK• phase lock• external synchronization
or 15 Hz … 60 Hz intern DACor 50 Hz line
Measuring system
Voltage TransformerClass 0.02
Current TransformerClass 0.002
Power ComparatorClass 0.01
U, I, , P, Q, S
I = 2 kA
U = 150 kV
LabView Software
To do overview:1. Optimization of the software
• timing to read the comparator• automatic correction of the transformer error
2. Uncertainty calculation3. Assessment of the system
Challenge: lock I to Vwithin 0.3 m (5 µrad)
TLMS system calibration
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V I
DSP is a key element2nd reference CT + RD22 watt meter as check
Actual VSL implementation
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Control (DSP)
Power amplifier (G)
Transformer /current generator
Power reference (RD22 watt meter)
CTs(3-stage compensated)
VT (CC-based capacitive divider)
Generation:• Rohrer wideband amplifier (20 A, 150 V) + step-up transformer
Measurement:• VT: HV capacitor (100 pF, 100 kV) + CC-based LV divider
– Uncertainty: 15 – 25 ppm (phase / magnitude)• CT: 3-stage wideband; errors < 1 ppm (uncertainty 5 ppm)
– Wideband 5 A shunt for conversion to voltage• Power: two 24-bit ADCs (NI)Expected overall phase uncertainty: < 25 ppm (25 µrad)
Verification: RD22 power meter (< 10 ppm) + CT + VT
Components of VSL system
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The control loop has 2 main parts:
First part: high speed. Second part: high accuracy ( feedback)(NRC analogue system needs accurate 90 reference signal)
Results:• Extensive testing with different voltage signals; different phase
shifting blocks studied• Low noise: 4 – 5 µrad; agreement with power meter < 10 µrad
Control loop
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ADC
90°
V [n] DAC
I
Q
I [n-m]
Phaseshifting
Z-n
• Much more noise than in lab (30 µrad vs 5 µrad)• Agreement VSL LL and RD22 reference: within 15 ppm• Agreement with NRC better than 25 ppm
First on-site trial
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Power transformer losses are significant– Economically: TCO and fines– Environment: CO2 emissions
Requirements from EU regulations,IEC / IEEE on both the actual lossesand measurement accuracy
Conclusion
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Transformer Loss Measurement Systems need calibration– Proven, validated accuracy < 3 % @ PF = 0.01– ELPOW: System calibration < 0.5 % @ PF = 0.01
– simultaneous generation– current phase locking
(promising first results < 0.3 %!)