Important Aspects to Be Considered Dealing with Phase … · Centro de Pesquisas de Energia Elétrica - Cepel Synchrophasor measurement accuracy and the instrumentation channels –

Centro de Pesquisas de Energia Elétrica - Cepel 1

Centro de Pesquisas de Energia Elétrica

Departamento de Tecnologia de Distribuição – DTD

Distribution Technology Department

“Important Aspects to Be

Considered Dealing with

Phase Measurement Units and Applications"

Luiz Carlos Grillo de Brito (CEPEL)

Ricardo Penido D. Ross(CEPEL)

José Eduardo da R. Alves Júnior(CEPEL)

Glauco Nery Taranto (UFRJ)

Centro de Pesquisas de Energia Elétrica - Cepel

Synchrophasor measurement accuracy and the

instrumentation channels – a new approach.

2

CT

CCVT or VT

VP ø

IP θ

Secondary Circuits

PROTECTION

REVENUE

METERING

OPERATIONAL

METERING

PHASOR

METERING UNIT

V’p

I’p

ø’

θ’ It is necessary that the synchrophasors are

collected accurately through all measurement

chain, from instrument transformers to the

operations center.


– Off-line:

• Post event diagnostics.

– Real time:

• Monitoring, Protection and Control:

• Ex.: enhance state estimation, monitoring critical angles and

oscillations, FACTS equipment control, etc.

3

All applications require that synchronized phasors have an

accuracy considering the whole chain of signal acquisition,

not only PMU itself.



Applications for PMU:


CURRENT PHASORS

(STEADY STATE)

Ia

Ib

Ic

Metering

CT

Protection

CT

Accuracy linked to electrical

energy measurement (ratio error

and phase displacement error).

Accuracy linked to fault

conditions (current error, error in

phase displacement and

composite error).

Accuracy linked to

criteria of Total Vector

Error (TVE).

Phasor

Measurement

Unit (PMU)

Criteria of standards do not match !!




Main

Characteristics

(Standards)

Current Transformers

PMU Billing Operation Protection

Accuracy

≤ 0.3 % 0.5% to 5% 5% or 10 % 1%

Accuracy

Criteria

Power/Energy

Metering

Power/Energy

Metering

Fault

Conditions

Phasor

(TVE)

Current

Range

10% Irated to

Irated x TF(*)

10% Irated to

Irated. x TF(*)

Irated to

20 x Irated

10% to

2 x Irated

(*) TF : Thermal Factor (TIPICALLY FROM 1.2 TO 2.0)



Comparison of Accuracy Classes: CT’s and PMUs.

5


Some issues that arise in this context:

6

• How to correlate the definition of TVE (TOTAL VECTOR ERROR –

standards IEEEc37.118-2005 and IEEEc37.118.1-2011) and the criteria

of accuracy of metering and protection CT’s, which are also different

from each other?

• How to quantify, based on standards, the TVE produced by a

metering CT or a protection CT in a Synchronized Phasor

Measurement System?




P

M

U

X(n) = Xr (n) + j Xi (n)

Accuracy of PMU and its mathematics representations



IEEEc37.118.1-2011

REFERENCE:


TVE Fd

Fi

=

Fd

Fm

Fi

(Fi): True phasor.

(Fd): Difference phasor.

(Fm): Measured Phasor.

Accuracy of PMU and its graphical representations

β

Im

Re




TVE(%) = [ ( 1 + ε% ). cos (β) – 1]2 + [ ( 1 + ε% ). sen (β) ]2 * 100

100 100

The TVE equation can be rewritten as a function of the

magnitude (current) error and phase displacement error, to

compare and bring to the same basis, the different

accuracy criteria of Metering CTs, Protection CTs and

PMUs, as follows:

Where:

ε% : Percentage current error (ratio or magnitude error).

β : Phase displacement error (in minutes).



9


Three-Dimensional graphic representation of TVE(%) as a function

of ε% and β:



10

β (min.)

TVE(%)

ε (%)


Three-Dimensional Graphic Representation Accuracy Class of

Metering CT as a function of ε% and β:



11

ε (%)

β (min.)

Accuracy

Class

(%)


TVE - Amplitude Error(%) x Angle Error(min.)

Metering CTs - Accuracy parallelograms

-5

-4

-3

-2

-1

0

1

2

3

4

5

-150

-140

-130

-120

-110

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

110

120

130

140

150

Angle(min.)

Amplitude Error(%)

TVE= 1%TVE= 2%TVE= 3%TVE = 4%

Class 0.3

Class 0.6

Class 1.2

Current Range: 10% to 200%



Comparison between TVE (%) and the parallelogram accuracy for Metering CT.

12


Equipment Maximum angular

displacement

error(degrees)

Current

Error

TVE(%)

equivalent

PMU 0,573 0 1,00

Metering CT (Billing)

Accuracy Class 0.3

0,520 -0,6% 1,09

Metering CT

Accuracy Class 0.6

1,04 -1,2% 2,17

Metering CT

Accuracy Class 1.2

2,08 -2,4% 4,32



Comparison between accuracy criteria: TVE (%) and Metering CT.

13


Accuracy Class for CT Protection (Standards):

• The limits of ratio (current or magnitude) error are higher than CT

metering;

• The angular error is not considered in most cases;

• In addition to the current error and angle error, introduces the

concept of Composite Error, as follows:



14


Accuracy Class for CT Protection (Standards):



Class Current

range

Current

(Magnitude) Error

(%)

Composite Error (%)

Angular

Displacement Error

(degrees)

IEC IEEE ABNT IEC IEEE ABNT IEC IEEE ABNT

5 Irated 1,0 1,0 2,0

(*) 1,0

5 20 x

Irated 5,0 5,0 5,0

10 Irated 3,0 3,0

10 20 x

Irated 10,0 10,0 10,0 10,0

15 (*) Calculated


It can be demonstrate that the indicator of criteria

accuracy of PMU (TVE%) and accuracy criteria of

protection CTs (ERROR COMPOSITE %) have the same meaning, considering sinusoidal signals.



TVE(%)= [ ( 1 + ε% ). cos (β) – 1]2 + [ ( 1 + ε% ). sen (β) ]2 * 100

100 100

TVE (%) = εc (%)

16




-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Angle error (min.)

TVE=1% (PMU accuracy limit)

Protection CT –Accuracy class limit

5% (Composite error and TVE (%))

Protection CT –Accuracy class limit

10% (Composite error and TVE (%))

(sinusoidal signals)

Comparison of TVE (%) and the composite

error (%) of protection CTs.

17

Protection CT –Accuracy class

limit 5% (Composite error and

TVE (%)) – at rated current

point. (IEC)




Comparison between accuracy criteria: TVE (%) and Protection CT.

Equipment Composite

Error εc (%)

Angular

Displacement

Error(degrees)

PMU 1 0,573

Protection CT

5% accuracy

class

5

2,85

Protection CT

10% accuracy

class

10 5,70

18

Current

Error (%)

TVE (%)

0 1

0

1(*)

5

2(*)

0 10

(for sinusoidal signals)

(*) At rated primary current, as IEC.




Gráphic TVE(%) X Primary Current (A)

Metering CT - DIFFERENT BURDENS

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

0 200 400 600 800

Primary Current (A)

TV

E (

%)

NO BURDEN

2,5 VA

5 VA

12,5 VA

22,5 VA

TVE=1

Curves TVE (%) x Primary Current (A) - CT Metering

0.3 Accuracy class for different secondary burden.

0,3C12,5 VA

19




Graphic TVE(%) X Primary Current (A)

Protection CT - Isn = 5A - DIFFERENT BURDENS

0

1

2

3

4

5

6

7

8

9

10

0 100 200 300 400 500 600 700 800

Primary Current (A)

TV

E (

%)

200 VA

100 VA

50 VA

25 VA

12,5 VA

SEM CARGA

TVE=1 %

Curves TVE(%) or Composite Error(%) x Primary Current (A)

CT Protection (Isn = 5 A) for different secondary burden.

C400/100 VA/4Ω

20




Graphic TVE(%) X Primary Current(A)

Protection CT - Isn = 1 A - DIFFERENT BURDEN

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

1,60

1,80

2,00

0 200 400 600 800

Primary Current (A)

NO BURDEN

8 VA

4 VA

TVE = 1 %

TV

E (

%)

Curves TVE(%) or Composite Error(%) x Primary Current (A)

CT Protection (Isn = 1 A) for different secondary burden.

5 VA / 5Ω

21


PMUs Application - Harmonic Assessment

using PQ Analysers

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• Measurement of Harmonic Currents

Synchronized on distant “bays”

• Evaluation of TC errors

• Excellent tool to evaluate the network

elements involved in a ressonance condition

TL –

Terminal A TL –

Terminal B

I 5A I 5B


Cepel’s Synchrophasor Laboratory (LabPMU)

1. Study performance of PMUs standalone.

2. Study performance of a system comprising PMUs and PDC within an electric power system

3. R&D related to PMU applications.

MME Project sponsored by WORLD BANK

1. PMUs and PDC: bidding process already done.

2. Auxiliary instrumentation: bidding process already done.

3. PMU test bed instrumentation: international bid (under WB analysis).

4. Real time simulator: international bid (under WB analysis).


Standards accuracy’s aspects of the metering and protection CTs have qualitative and quantitative discrepancies in relation to the correspondents criteria of PMUs, and may have values well away from their limits.

A new expression for the TVE, based on amplitude and phase angle errors, was established, to analyze, with the same comparative basis, their effects in Syncrophasor Metering Systems.

Perform similar analysis for voltage transformers is necessary, mainly when dealing with harmonics components.

Review the accuracy requirements of Instrument Transformers standards for PMU applications is an important target.



CONCLUSIONS

25


Thanks Questions?

Contact:

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[email protected] www.cepel.br

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Important Aspects to Be Considered Dealing with Phase … · Centro de Pesquisas de Energia Elétrica - Cepel Synchrophasor measurement accuracy and the instrumentation channels –