ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 1 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

CT-Core Dimensioning for Protection Relay P632 (87T) GENERAL PROJECT DATA:

Issued by: Dimitry Taranenko Our reference: Date: 12.08.2011 Remark: GENERAL SYSTEM AND SUBSTATION DATA: Nominal voltage: 10 kV Nominal frequency: 50 Hz Power system time constant: 200 ms Rated short-circuit current of station: 31.5 kA Remark:

DATA OF CT 1 ACCORDING TO IEC:

CT type: IEC Class 5P Transformation ratio: 200 A / 1 A nominal accuracy limiting factor Knalf : 20

CT nominal burden Pn: 30 VA

Internal resistance Rct: 4.5 Ω

Remark: Max.Außenbürde 2 Ohm

DATA OF CT 1 ACCORDING TO IEC:

CT type: IEC class 5P Transformation ratio: 200 A / 1 A Kneepoint voltage Uknee: 530.769 V Mag. current Iknee at Uknee: 0.049 A Internal resistance Rct: 4.5 Ω Remark: Max.Außenbürde 2 Ohm

DATA OF CT 2 ACCORDING TO IEC:

CT type: IEC Class 5P Transformation ratio: 2000 A / 1 A nominal accuracy limiting factor Knalf : 20

CT nominal burden Pn: 30 VA

Internal resistance Rct: 4.5 Ω

Remark: Max.Außenbürde 2 Ohm

DATA OF CT 2 ACCORDING TO IEC:

CT type: IEC class 5P

ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 2 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

Transformation ratio: 2000 A / 1 A Kneepoint voltage Uknee: 530.769 V Mag. current Iknee at Uknee: 0.049 A Internal resistance Rct: 4.5 Ω Remark: Max.Außenbürde 2 Ohm RELAY DATA: Manufacturer: Areva Type: P632 Nominal Current: 1 A Relay burden: 0.1 VA Remark: CT REQUIREMENTS FOR P632 according to AREVA P63x technical description, publication P63X/EN M/B11 (AFSV.12.066661):

The transformer differential protection device is equipped with a saturation discriminator. This function will generate a stabilizing blocking signal if a differential current occurs as a consequence of transformer saturation with an external fault (in contrast to an internal fault). For the passing maximum fault current in the case of an external fault, overdimensioning is, therefore, obviated (k1=1).

In order to ensure correct operation of the connected relay, the knee-point voltage Uknee of the CT

should fulfill the following requirement:

( )pn

sn

thrtotalctsatkneeI

IIkRRUU ⋅⋅⋅+=≥

max,11,

(Requirement 1) where : Uknee : knee-point voltage of CT

Usat,1 : saturation voltage for internal fault

Rct : CT burden

Rtotal : total connected burden

k1 = 1 dimensioning factor

Imax,thr : non-offset maximum primary short circuit current for through faults

Ipn : CT primary rated current Isn : CT secondary rated current Moreover, for the maximum fault current with an internal fault, static saturation up to a maximum saturation factor of 4 is permissible. This corresponds to an overdimensioning factor k2 of 0.25. In

order to ensure correct operation of the connected relay, the knee-point voltage Uknee of the CT

should fulfill the following requirement:

( )pn

sn

ktotalctsatkneeI

IIkRRUU ⋅⋅⋅+=≥

max,22,

(Requirement 2) where : Uknee : knee-point voltage of CT

Usat,2 : saturation voltage for external fault

ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 3 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

Rct : CT burden

Rtotal : total connected burden

k2 = 0.25 dimensioning factor

Ik,max : non-offset maximum primary short circuit current for through faults

Ipn : CT primary rated current Isn : CT secondary rated current CALCULATION OF TOTAL CONNECTED BURDENS:

CURRENT TRANSFORMER 1

The performance of the current transformer depends on the connected burdens at the secondary terminals. The total burden includes the relay burden and additional burdens, the burden of cables and the burden of an eventually connected matching transformer.

Resistance [Ω] Transformation ratio

Relay burden: Rrelay = 0.1 Ω --- ---

Additional relay burdens:

Radd = 0 Ω --- ---

Burden of matching transformer:

Rmat,1 = 0 Ω trmat,1 = 1

Rmat,2 = 0 Ω trmat,2 = 1

CALCULATION OF CABLE BURDEN:

The cable burden is calculated by the single length, the cross section, the specific resistivity for copper and an effective factor for the wire length. This factor kwire is 2 if the return wire is to be considered.

Length: lwire = 100 m

Cross section: αwire = 2.5 mm2

Spec. resistivity (Cu): ρcu = 0.02171 Ω mm2/m at 75 °C

Eff. wire length in p.u.: kwire = 2

wire

wireCuwire

wire

lkR

αρ ⋅⋅

=

= 1.7368 Ω

The total effective resistance is given by the sum of all resistances:

Total resistance:

++++=

2

2,

2,1,

1

2

,

1

mat

addrelay

matmatwire

mat

totaltr

RRRRR

trR

= 1.8368 Ω

CURRENT TRANSFORMER 2

ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 4 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

The performance of the current transformer depends on the connected burdens at the secondary terminals. The total burden includes the relay burden and additional burdens, the burden of cables and the burden of an eventually connected matching transformer.

Resistance [Ω] Transformation ratio

Relay burden: Rrelay = 0.1 Ω --- ---

Additional relay burdens:

Radd = 0.1 Ω --- ---

Burden of matching transformer:

Rmat,1 = 0 Ω trmat,1 = 1

Rmat,2 = 0 Ω trmat,2 = 1

CALCULATION OF CABLE BURDEN:

The cable burden is calculated by the single length, the cross section, the specific resistivity for copper and an effective factor for the wire length. This factor kwire is 2 if the return wire is to be considered.

Length: lwire = 100 m

Cross section: αwire = 2.5 mm2

Spec. resistivity (Cu): ρcu = 0.02171 Ω mm2/m at 75 °C

Eff. wire length in p.u.: kwire = 2

wire

wireCuwire

wire

lkR

αρ ⋅⋅

=

= 1.7368 Ω

The total effective resistance is given by the sum of all resistances:

Total resistance:

++++=

2

2,

2,1,

1

2

,

1

mat

addrelay

matmatwire

mat

totaltr

RRRRR

trR

= 1.9368 Ω

CHECK OF CT REQUIREMENTS:

CT side 1

Check of requirement 1: Required saturation voltage Usat,1:

( ) =⋅⋅⋅+=≥pn

sn

thrtotalctsatkneeI

IIkRRUU

max,11,

38.338 V

where Usat,1: saturation knee-point voltage

Imax,thr: non-offset maximum primary short circuit current for through faults

= 1.21 kA

Rct: CT burden = 4.5 Ω

Rtotal: actual connected total burden = 1.837 Ω

ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 5 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

k1 : dimensioning factor = 1

Ipn: primary CT current rating = 200 A Isn: secondary CT current ratio = 1 A

Check of requirement 2: Required saturation voltage Usat,2:

( ) =⋅⋅⋅+=≥pn

sn

ktotalctsatkneeI

IIkRRUU

max,22,

249.513 V

where Usat,2: saturation knee-point voltage

Ik,max non-offset internal fault current = 31.5 kA

Rct: CT burden = 4.5 Ω

Rtotal: actual connected total burden = 1.837 Ω

k2 : dimensioning factor = 0.25

Ipn: primary CT current rating = 200 A Isn: secondary CT current ratio = 1 A

CT side 2:

Check of requirement 1: Required saturation voltage Usat,1:

( ) =⋅⋅⋅+=≥pn

sn

thrtotalctsatkneeI

IIkRRUU

max,11,

41.84 V

where Usat,1: saturation knee-point voltage

Imax,thr: non-offset maximum primary short circuit current for through faults

= 13 kA

Rct: CT burden = 4.5 Ω

Rtotal: actual connected total burden = 1.937 Ω

k1 : dimensioning factor = 1

Ipn: primary CT current rating = 2000 A Isn: secondary CT current ratio = 1 A

Check of requirement 2: Required saturation voltage Usat,2:

( ) =⋅⋅⋅+=≥pn

sn

ktotalctsatkneeI

IIkRRUU

max,22,

10.46 V

where Usat,2: saturation knee-point voltage

Ik,max non-offset internal fault current = 13 kA

Rct: CT burden = 4.5 Ω

ELPRO E&U/ /Dimitry Taranenko 12.08.2011

Revision 6 31.5MVA-Trafo / Schutz

© CTDim3.4 P632

Rtotal: actual connected total burden = 1.937 Ω

k2 : dimensioning factor = 0.25

Ipn: primary CT current rating = 2000 A Isn: secondary CT current ratio = 1 A CT-DIMENSIONING CHECK:

For the protection relay P632 the following requirement has to be fulfilled.

1,satknee UU ≥ (Requirement 1)

2,satknee UU ≥ (Requirement 2)

Check of CT 1: Uknee = 530.769 V

Usat,1 = 38.338 V

Usat,2 = 249.513 V Meets requirement

Check of CT 2: Uknee = 530.769 V

Usat,1 = 41.84 V

Usat,2 = 10.46 V Meets requirement

The current transformers are correctly dimensioned!