TechRef_Imeas[1].pdf

8/10/2019 TechRef_Imeas[1].pdf

1/9

D I g S I L E N T T e c h n i c a lD o c u m e n t a t i o n

Current Measurement


2/9

C u r r e n t M e a s u r e m e n t 2

DIgSILENT GmbHHeinrich-Hertz-Strasse 9D-72810 GomaringenTel.: +49 7072 9168 - 0Fax: +49 7072 9168- 88http://www.digsilent.dee-mail: [email protected]

Current Measurement

Published byDIgSILENT GmbH, Germany

Copyright 2009. All rightsreserved. Unauthorised copyingor publishing of this or any partof this document is prohibited.

TechRef StaImea V1

Build 337 05.05.2009


3/9

T a b l e o f C o n t e n t s


Table of Contents

1 GENERAL DESCRIPTION................................................ ......................................................... .............................. 4

1.1 RMS EQUATIONS........................................................................................................................................................... 4

1.1.1 Balanced .................................................................................................................................................................... 41.1.2 Unbalanced ................................................................................................................................................................51.2 EMT EQUATIONS ........................................................................................................................................................... 5

2 INPUT/OUTPUT DEFINITION OF DYNAMIC MODELS ........................................ ................................................... 7

2.1 STABILITY MODEL (RMS)............................................................................................................................................... 7

2.2 EMT MODEL .................................................................................................................................................................. 8

3 INPUT PARAMETER DEFINITIONS............... .................................................. ....................................................... 9


4/9


5/9

1 G e n e r a l D e s c r i p t i o n


1.1.2Unbalanced

i, iiand irare positive sequence currents. The current magnitude for unbalanced RMS simulation is calculated as follows:

3-phase system:

}Im{

}Re{

2

3

2

1

2

3

2

1

3

1

ii

ii

ijijii

i

r

cba

=

=

+

++=

(2)

2-phase system:

( )ba iii +=2

1 (3)

Single-phase system:

aii= (4)

DC system:

0==

i

ar

i

ii (5)

1.2

EMT Equations

ir, iiand iare the phasor currents and ia, iband icare the instantaneous phase values in kA of the measured phase currents. The

phase currents are transformed to space vectors (phasor) in the --system. The factors of the -transformation are selected

in a way that the rated current corresponds to an RMS-value. E.g. a symmetrical three-phase current with an RMS-value of 1kA

(peak value of 2 kA) will result in an -current with a magnitude of 1=+ ii p.u., assuming a rated current of 1kA.

Hence, the output of RMS- and EMT-simulation is compatible, which is important for models that shall be used in bothsimulation modes.

The zero-sequence is neglected in the transformation. iis corresponding to the output irand ito the output iiof the current

measurement device. For 2-phase systems an analogous transformation is used.

The output currents for EMT simulation are calculated as follows:


6/9

1 G e n e r a l D e s c r i p t i o n


3-phase system:

( )

( )cbi

cbar

iii

iiii

=

=

333

1

23

1

(6)

2-phase system:

( )

0

2

1

=

+=

i

bar

i

iii (7)

Single-phase system:

0=

=

i

ar

i

ii (8)

DC system:

0=

=

i

ar

i

ii (9)

The current magnitude is in all cases defined as:

22

ir iii += (10)


7/9

2 I n p u t / O u t p u t D e f i n i t i o n o f D y n a m i c M o d e l s


2Input/Output Definition of Dynamic Models

2.1Stability Model (RMS)

Figure 1: Input/Output Definition of the current measurement for balanced stability analysis (RMS-simulation)

Figure 2: Input/Output Definition of the current measurement for unbalanced stability analysis (RMS-

simulation)

Figure 3: Input/Output Definition of the current measurement for balanced stability analysis (RMS-simulation)

in DC networks

Table 1: Input Definition of the RMS-Model (for internal use only)

ir_A ir

ir_A

ii_A

ir

ii

iir_B

ii_B

ir_C

ii_C

ir_A

ii_Air

ii

i


8/9

2 I n p u t / O u t p u t D e f i n i t i o n o f D y n a m i c M o d e l s


Parameter Description Unit

ir_A Input Current, Real Part, Phase A

(based on 1MVA and nominal voltage)

p.u.

ii_A Input Current, Imaginary Part, Phase A


p.u.

ir_B Input Current, Real Part, Phase B


p.u.

ii_B Input Current, Imaginary Part, Phase B


p.u.

ir_C Input Current, Real Part, Phase C


p.u.

ii_C Input Current, Imaginary Part, Phase C


p.u.

Table 2: Output Definition of the RMS-Model


i Output Current, Magnitude p.u.

ir Output Current, Real Part p.u.

ii Output Current, Imaginary Part p.u.

2.2EMT Model

Figure 4: Input/Output Definition of the current measurement for EMT analysis

Figure 5: Input/Output Definition of the current measurement for EMT analysis in DC networks

i_A ir

i_A

i_B ir

ii

i

i_C


9/9

3 I n p u t P a r a m e t e r D e f i n i t i o n s


Table 3: Input Definition of the EMT-Model (for internal use only)


i_A Input Current, Phase A


p.u.

i_B Input Current, Phase B


p.u.

i_C Input Current, Phase C


p.u.

Table 4: Output Definition of the EMT-Model


i Output Current, Magnitude p.u.

ir Output Current, Real Part p.u.

ii Output Current, Imaginary Part p.u.

3Input Parameter Definitions

Table 5: Parameter Definitions


loc_name Name

pcubic Measurement cubicle for current measurement

i_mode Used current rating

Inom User defined current rating kA

iAstabint A-stable integration algorithm

Documents

TechRef_Imeas[1].pdf