PT.
ABB SAKTI INDUSTRI
CALCULATION
Project :
GI 150kV PELANGGAN
PT. STAR AJIBARANG PURWOKERTO
Title :
CT SIZING CALCULATION
Reference Drawing :
SLD START-EM-PRJ-001
Rev No Date Remarks Prepare Check Approve
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY TRANSFORMER
PT. STAR AJIBARANG PURWOKERTO
CT SIZING CALCULATION
SELECTION OF PARAMETER OF CURRENT TRANSFORMER FOR BAY TRANSFORMER
Maxsimum cable route length CT to relay panel located in switcyard control building 75 meters
Core 1
Purpose Transformer Differential Protection
Rasio 250/1 A
Primary Current Ipn 250 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class X
Burrden 30 VA
MVA Rated of the Transformer P 50 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 192.45 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency
1.604
that passed thru main CT and the power Trafo
Itf 1.604 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
Two way lead loop resistance RL 1.73 Ω
Relay Burden for RET650 (ABB make) Pb 0.25 VA
Rb Pb/(Isn)²=Ω 0.25 Ω
Total connected burden = Lead Burden + Instrumen Burden 1.98 VA
Current Transformer knee point voltage requirment
Equation 1 Vk 30 x Int x Isn/Ipn x (Rct+RL+Rb/Ir²) 91.93 V
Rct is current transformer secondary winding resistance at 75⁰C at selected ratio 2 Ω
Current transformer knee point voltage requirment Vk 91.93 V
Knee point volatge of CT
Vk = ALF x Is (VA/(Is²)+ (Is x Rct)) V
Vk 640 V
Required knee point voltage is less than selected,Hence CT selected is adequate.
where
RC is the corrected resistance
RM is the measured resistance
CF is the correction factor for copper (234.5) or aluminum (225) windings
CT is the corrected temperature (75°C or 85°C)
WT is the winding temperature (°C) at time of test
Page : 3 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY TRANSFORMER
PT. STAR AJIBARANG PURWOKERTO
Core 2
Purpose O/C & E/F Prot
Rasio 250/1 A
Primary Current Ipn 250 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class X
Burrden 30 VA
MVA Rated of the Transformer P 50 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 192.45 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency P
1.604
that passed thru main CT and the power Trafo V3xZxVnt
Itf 1.604 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
lead loop resistance RL 1.73 Ω
Lead Burden 1.73 VA
Relay Burden for REF615 (ABB make) Pb 0.05 VA
Rb Pb/(Isn)²=Ω 0.05 Ω
Total connected burden = Lead Burden + Instrumen Burden 1.78 VA
Current Transformer knee point voltage requirment
Equation 1 Vk 30 x Int x Isn/Ipn x (Rct+RL+Rb/Ir²) 87.31 V
Rct is current transformer secondary winding resistance at 75⁰C at selected ratio 2 Ω
Current transformer knee point voltage requirment Vk 87.31 V
Knee point volatge of CT
Vk = ALF x Is (VA/(Is²)+ (Is x Rct)) V
Vk 640 V
Page : 4 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY TRANSFORMER
PT. STAR AJIBARANG PURWOKERTO
Core 3
Purpose Metering
Rasio 250/1 A
Primary Current Ipn 250 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class 0.5
Burrden 30 VA
MVA Rated of the Transformer P 50 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 192.45 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency P
1.604
that passed thru main CT and the power Trafo V3xZxV
Itf 1.604 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
lead loop resistance RL 1.73 Ω
Lead Burden 1.73 VA
Metering Relay Burden Pb 0.3 VA
Rb Pb/(Isn)²=Ω 0.3 Ω
Total connected burden = Lead Burden + Instrumen Burden 2.03 VA
Required Burden is less than selected,Hence CT selected is adequate.
Page : 5 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY TRANSFORMER
PT. STAR AJIBARANG PURWOKERTO
Page : 6 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY OVER HEAD LINE
PT. STAR AJIBARANG PURWOKERTO
CT SIZING CALCULATION
SELECTION OF PARAMETER OF CURRENT TRANSFORMER FOR BAY OVER HEAD LINE
Maxsimum cable route length CT to relay panel located in switcyard control building 150 meters
Core 1
Purpose Line Differential
Rasio 600/1 A
Primary Current Ipn 600 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class X
Burrden 30 VA
MVA Rated of the Transformer P 100 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 384.90 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency
3.208
that passed thru main CT and the power Trafo
Imax 3.208 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
Two way lead loop resistance RL 3.46 Ω
Relay Burden for RED650 (ABB make) Pb 0.15 VA
Rb Pb/(Isn)²=Ω 0.15 Ω
Total connected burden = Lead Burden + Instrumen Burden 3.61 VA
Current Transformer knee point voltage requirment
Equation 1 Vk 30 x Int x Isn/Ipn x (Rct+RL+Rb/Ir²) 107.98 V
Rct is current transformer secondary winding resistance at 75⁰C at selected ratio 2 Ω
Current transformer knee point voltage requirment Vk 107.98 V
Knee point volatge of CT
Vk = ALF x Is (VA/(Is²)+ (Is x Rct)) V
Vk 640 V
Required knee point voltage is less than selected,Hence CT selected is adequate.
where
RC is the corrected resistance
RM is the measured resistance
CF is the correction factor for copper (234.5) or aluminum (225) windings
CT is the corrected temperature (75°C or 85°C)
WT is the winding temperature (°C) at time of test
Page : 7 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY OVER HEAD LINE
PT. STAR AJIBARANG PURWOKERTO
Core 2
Purpose O/C & E/F Prot
Rasio 600/1 A
Primary Current Ipn 600 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class 5P20
Burrden 30 VA
MVA Rated of the Transformer P 100 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 384.90 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency
3.208
that passed thru main CT and the power Trafo
Imax 3.208 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
Two way lead loop resistance RL 3.46 Ω
Relay Burden for REF615 (ABB make) Pb 0.05 VA
Rb Pb/(Isn)²=Ω 0.05 Ω
Total connected burden = Lead Burden + Instrumen Burden 3.51 VA
Current Transformer knee point voltage requirment
Equation 1 Vk 30 x Int x Isn/Ipn x (Rct+RL+Rb/Ir²) 106.06 V
Rct is current transformer secondary winding resistance at 75⁰C at selected ratio 2 Ω
Current transformer knee point voltage requirment Vk 106.06 V
Knee point volatge of CT
Vk = ALF x Is (VA/(Is²)+ (Is x Rct)) V
Vk 640 V
Page : 8 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY OVER HEAD LINE
PT. STAR AJIBARANG PURWOKERTO
Core 3
Purpose Metering
Rasio 600/1 A
Primary Current Ipn 600 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class 0.2
Burrden 30 VA
MVA Rated of the Transformer P 100 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 384.90 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency
3.208
that passed thru main CT and the power Trafo
Itf 3.208 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
Two way lead loop resistance RL 3.46 Ω
Metering Relay Burden Pb 0.3 VA
Rb Pb/(Isn)²=Ω 0.3 Ω
Total connected burden = Lead Burden + Instrumen Burden 3.76 VA
Required Burden is less than selected,Hence CT selected is adequate.
Page : 9 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY OVER HEAD LINE
PT. STAR AJIBARANG PURWOKERTO
Core 4
Purpose SPARE
Rasio 600/1 A
Primary Current Ipn 600 A
Secodary Current Isn 1 A
Rated Current of the protection IED Ir 1 A
Accuracy Class X
Burrden 30 VA
MVA Rated of the Transformer P 100 MVA
impedance of the transformer Z 12 %
Rated Primary Current of the transformer Int 384.90 A
Rated primary Voltage of the transformer Vnt 150 kV
Maximum primary fundamental frequency
3.208
that passed thru main CT and the power Trafo
Imax 3.208 kA
Conductor cross-section 6 mm²
Conductor material Copper
Number of runs per phase 1
Conductor unit resistance 3.08 Ω/km
lead Resistance at 20⁰C CF+CT Rc 3.75 Ω
Rc = xR
lead Resistance at 70⁰C CF+WT
Two way lead loop resistance RL 3.46 Ω
Relay Burden for Spare Pb 0.25 VA
Rb Pb/(Isn)²=Ω 0.25 Ω
Total connected burden = Lead Burden + Instrumen Burden 3.71 VA
Current Transformer knee point voltage requirment
Equation 1 Vk 30 x Int x Isn/Ipn x (Rct+RL+Rb/Ir²) 109.91 V
Rct is current transformer secondary winding resistance at 75⁰C at selected ratio 2 Ω
Current transformer knee point voltage requirment Vk 109.91 V
Knee point volatge of CT
Vk = ALF x Is (VA/(Is²)+ (Is x Rct)) V
Vk 640 V
Page : 10 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI BAY OVER HEAD LINE
PT. STAR AJIBARANG PURWOKERTO
Page : 11 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI PT. STAR AJIBARANG PURWOKERTO
PARAMETERS OF CURRENT TRANSFORMERS
SELECTION OF PARAMETER OF CURRENT TRANSFORMER FOR ALL BAY
Bay Transformer
Selected Calculated Required Proposed
Ratio CT Rct
Core Class Burden Burden Vk Equiv. Vk Device
[A] [Ω] [VA] [VA] [V] [V]
1 250-500/1 X ≤2 30 1.98 91.93 640.00 RET650
2 250-500/1 X ≤2 30 1.78 87.31 640.00 REF615
3 250-500/1 5P20+0,5 - 30 2.03 - - Metering
Bay Line
Selected Calculated Required Proposed
Ratio CT Rct
Core Class Burden Burden Vk Equiv. Vk Device
[A] [Ω] [VA] [VA] [V] [V]
1 300-600/1 X ≤2 30 3.61 107.98 640.00 RED670
2 300-600/1 X ≤2 30 3.51 106.06 640.00 REF615
3 300-600/1 0.2 - 30 3.76 - - Metering
4 300-600/1 X - 30 3.71 109.91 640.00 N/A
Page : 12 of 13
GI 150kV PELANGGAN
PT. ABB SAKTI INDUSTRI PT. STAR AJIBARANG PURWOKERTO
Page : 13 of 13
