CPECC - AGP
Electro Mechanical Co.LLC HABSHAN SS-7 AND SS-18 SWITCH
GEAR UPGRADE
1.3 METERING-CORE DIMENSIONING FOR METERING
GENERAL PROJECT DATA:
Customer: CPECC - AGP
Project: HABSHAN SS-7 AND SS-18 SWITCH GEAR UPGRADE
Station: SS-18
Feeder: 80-EE-1802
Issued by: Sivaraman A L
Our reference: EM272/22
Date: 10/01/2023
Remark:
GENERAL SYSTEM AND SUBSTATION DATA:
Nominal voltage: 0.415 kV
Nominal frequency: 50 Hz
Rated short-circuit current of station: 50 kA
Remark:
DATA OF MEASURING CT 2 (T5-T7) ACCORDING TO IEC:
CT type: IEC Class 1
Transformation ratio: 1600 A/1 A
Instrument security factor FS: 10
Rated output Sr: 10 VA
Secondary wiring resistance Rct: 7.8 Ω
Remark:
METER DATA:
Manufacturer: JANITZA HOBUT
Type: PQM-UMG 96 AMMETER - D96
Rated Current: 1A 1A
Rated short-time thermal current Imax: 60 A 30 A
Meter burden for rated current: 0.2 VA 0.7 VA
Remark:
CT REQUIREMENTS:
In general, the rated burden of the measuring CT shall be chosen as close as possible to the actual
connected burden consisting of metering instrument and the secondary wiring.
In order to protect the connected metering equipment in case of fault currents the connected metering
instrument shall be able to withstand the total RMS value of the secondary current at the operating
instrument security factor (FS').
S r Sct
I max I sr FS ' with FS ' FS (Requirement 1)
Stotal Sct
where
FS': Operating instrument security factor
FS: Instrument security factor
S r: Rated output
Sct: Secondary winding resistance
Electro Mechanical Co.LLC/EM272/22/Sivaraman A L 10/01/2023
Revision 0 80-EE-1802
© CTDim 3.7.1
CPECC - AGP
Electro Mechanical Co.LLC HABSHAN SS-7 AND SS-18 SWITCH
GEAR UPGRADE
Stotal: Total effective connected burden
Imax: Rated short-time thermal current
Isr: Nominal secondary current of CT
Moreover, in order to assure the measuring accuracy, the total effective connected burden has to be
between 25% and 100% of rated output of the current transformer.
25% S r Stotal Sr (Requirement 2)
where
Stotal: Total effective connected burden
S r: Rated output
CALCULATION OF TOTAL CT CONNECTED BURDENS:
The performance of the current transformer depends on the connected burdens at the secondary
terminals. The total burden includes the meter burden and additional burdens: the burden of cables
and, if used, the burden of a matching transformer.
CT 2 (T5-T7):
Name / transf. ratio Burden:
Meter burden: SPQM UMG 96-PA = 0.2 VA
Samm AMMETER - D96 = 0.7 VA
Sadd Resistor = 2.0 VA
The cable burden is calculated by the single length, the cross section, the specific resistivity and an
effective factor for the wire length. This factor kwire is 2 if the return wire is to be considered.
Cable burden:
Length: lwire =5m
Cross section: awire = 4 mm2
Spec. resistivity: ρ = 0.0225 Ω mm2/m (Cu at 75 OC)
Sec. wire current: Isr,wire =1A
Eff. wire length in p.u.: kwire =2
k wire
I sr ,wire
2
S wire wire = 0.056 VA
a wire
The total effective burden is given by the sum of all connected burdens:
Total burden: Stotal = Srelay + S amm + Sadd + Swire = 2.956 VA
CHECK OF CT REQUIREMENTS:
Operating instrument security factor FS':
The CT behaviour acc. to IEC will be described by the operating instrument security factor FS'. It
depends on the instrument security factor FS, the rated output S r, the secondary winding resistance of
the CT Sct and the total effective connected burden Stotal.
Sr Sct
FS ' FS = 16.549
Stotal Sct
where
Electro Mechanical Co.LLC/EM272/22/Sivaraman A L 10/01/2023
Revision 0 80-EE-1802
© CTDim 3.7.1
CPECC - AGP
Electro Mechanical Co.LLC HABSHAN SS-7 AND SS-18 SWITCH
GEAR UPGRADE
FS: Instrument security factor = 10
S r: Rated output = 10 VA
Sct: Secondary winding resistance burden = 7.8 VA
Stotal: Total effective connected burden = 2.956 VA
Total connected burdens:
The total effective connected burden has to be between 25% and 100% of the rated output of the
current transformer.
25% S r Stotal S r
where
Stotal: Total effective connected burden = 2.956 VA
S r: Rated output = 10 VA
CT-DIMENSIONING CHECK:
I max I sr FS ' (Requirement 1)
where:
Imax = 30 A
Isr · FS’ = 16.549 A
30 A 16.549 A Meets requirement
25% S r Stotal Sr (Requirement 2)
where:
25% Sr = 2.5 VA
Stotal = 2.956 VA
Sr = 10 VA
2.5 VA ≤ 2.956 VA ≤ 10 VA Meets requirement
The metering core is correctly dimensioned!
Electro Mechanical Co.LLC/EM272/22/Sivaraman A L 10/01/2023
Revision 0 80-EE-1802
© CTDim 3.7.1
