CT Ratio C
Primary Characteristics as per IEC
Stage 1 (Calculation of Primary Service Current Ipn and Rated Primary Current Ips)
Primary Voltage
11
KVA / KW (For Motor Only)
2000
Power Factor (Input 1 if not motor)
1
Motor Efficiency (Input 1 if not motor)
1
Service Current Ipn
User Defined Value of Service current
104.975855553
0
Value to be used
104.975855553
Coorected Value
105
Stage 2 (Calculation of thermal Short Circuit Current Ith for 1s)
Rated Short Circuit Power in MVA
380
Thermal Short Circuit Current Ith
19945.4125551
Stage 3 (Checking of Surge Current Coefficient Ksi)
Surge Current Coefficient
190
Note: The lesser the Ksi, the easier it will be to produce CT.
For Normal conditions Ksi<100 otherwise it will be very difficult.
Ksi<300 as a thumb rule.
Correction in Short thermal Rating (If higher)
19945.4125551
Correction in Ksi
190
Rated Primary Current of CT Ipn
150
CT Ratio Calculation by Muhammad Ibad Alam as per IEC 60044-1
EC
Secondary Characteristics as per IEC
Rated Primary Current Ips)
Stage 4 (Selection of Primary Service Current Ipn)
(KV)
Rated Secondary Current
(KVA/KW)
Input Range of Use in Meters (loop)
Stage 5 (Selecting Accuracy Class)
(A)
CT Purpose
Accuracy Class
Safety Factor
(A)
(A)
(A)
urrent Ith for 1s)
(MVA)
(A)
fficient Ksi)
Stage 6 (Calculate the effective power VA in CT)
Consumption by copper cable (Burden 1)
Length of cable (Input/Output Loop) L
Select Section of Cable S
Value of k
Consumption by Equipment (Buerden 2)
Select type of Instrument
Nominal Burden of Equipment
User defined VA
Combined VA
Suggested VA
ult.
(A)
(A)
Rated Seconday Current of CT
Alam as per IEC 60044-1
istics as per IEC
Operating Characterstics for Relay (Optional)
ry Service Current Ipn)
Optional Stage 7
5
(A)
Overcurrent protection independent time
5
(Meters) Effective ALF of the CT
Set Point of relay Ir (Ir= x*In)
Accuracy Class)
Rated Secondary Circuit current of the CT
Metering
Operation
0.5
10
Overcurrent protection independent time
ective power VA in CT)
1
5
2.5
0.5
2
Electronic meter
2
0
3
5
(VA)
(Meters) Input Value
(mm2) Output value
Calculation Value
(VA)
(VA)
(A)
Output CT
Ith for 1 s Suggested as per Nominal rating
CT Ratio
CT for
Um
150/5 5VA cl0.5 FS10 12 KV It
20KA
Relay (Optional)
e7
2
10
5
5
OK
(A)
(A)
200
20
150/5
Metering
12
10 12 KV Ith
Secondary CT Voltage
5
1
CT Purpose
Protection
Metering
Cable
1.5
2.5
4
6
10
ALF
5
10
15
20
30
NA List
N/A
primary service current (Ips) pr Ips Low
10 < Ips < 15 15
15 < Ips < 20 20
20 < Ips < 30 30
30 < Ips < 50 50
50 < Ips < 75 75
75 < Ips < 100 100
100 < Ips < 150 150
150 < Ips < 200 200
200 < Ips < 250 250
250 < Ips < 300 300
300 < Ips < 400 400
400 < Ips < 500 500
500 < Ips < 600 600
600 < Ips < 750 750
750 < Ips < 1000 1000
1250 < Ips < 1500 1500
1500 < Ips < 2000 2000
2000 < Ips < 2500 2500
2500 < Ips < 3000 3000
3000 < Ips < 3150 3150
10
15
20
30
50
75
100
150
200
250
300
400
500
600
750
1250
1500
2000
2500
3000
Ips High
Ipn
15
20
30
50
75
100
150
200
250
300
400
500
600
750
1250
1500
2000
2500
3000
3150
15
20
30
50
75
100
150
200
250
300
400
500
600
750
1000
1500
2000
2500
3000
3150
Safety factSafety Factor protection
10
5
10
15
20
30
r protection
Accuracy class
Error @ 0,05In
Error @ 0,2In
Error @ 0,5In
0.1
0.40%
0.20%
0.2
0.75%
0.35%
0.5
1.50%
0.75%
3%
1.50%
3%
Ratio errors accuracy classes
Accuracy class
Phase displ.@ 0.05In
Phase displ.@ 0.2In
Phase displ.@ In
0.1
15'
8'
5'
0.2
30'
15'
10'
0.5
90'
45'
30'
180'
90'
60'
Phase displacement accuracy classes
Accuracy class
Error @ 0.01In
Error @ 0.05In
Error @ 0.2In
0.2S
0.75%
0.35%
0.20%
0.5S
1.50%
0.75%
0.50%
5P
10P
Ratio errors classes S and protection
Accuracy class
Phase displ.@ 0.01In Phase displ.@ 0.05In Phase displ.@ 0.2In
0.2S
30'
15'
10'
0.5S
90'
45'
30'
5P
10P
Phase displacement classes S and protection
Error @ In
Error @ 1,2In
0.10%
0.10%
0.20%
0.20%
0.50%
0.50%
1%
1%
3%
Phase
displ.@ 1.2In
5'
10'
30'
60'
-
Error @ In
Error @ 1.2In
Composite error at
rated accuracy limit
current
0.20%
0.20%
0.50%
0.50%
1%
5%
3%
10%
Phase displ.@ In
Phase
displ.@ 1.2In
10'
10'
30'
30'
60'
protection
ection
Lead
Burde
ns
Is = 5A
1m
2m
3m
4m
5m
6m
7m
1.5 mm2
0.6
1.19
1.79
2.38
2.98
3.57
4.17
2.5 mm2
0.36
0.71
1.07
1.43
1.78
2.14
2.5
4 mm2
0.22
0.45
0.67
0.89
1.12
1.34
1.56
6 mm2
0.15
0.3
0.45
0.6
0.74
0.89
1.04
10 mm2
0.09
0.18
0.27
0.36
0.44
0.54
0.63
Losses VA. loop lengths in m.
Is = 1A
10m
20m
30m
40m
50m
60m
70m
1.5 mm2
0.24
0.48
0.72
0.96
1.19
1.43
1.67
2.5 mm2
0.14
0.29
0.43
0.57
0.72
0.86
4 mm2
0.09
0.18
0.27
0.36
0.45
0.54
0.63
6 mm2
0.06
0.12
0.18
0.24
0.3
0.36
0.42
10 mm2
0.04
0.07
0.11
0.14
0.18
0.21
0.25
Losses VA. loop lengths in m.
8m
9m
10m
4.76
5.36
5.95
2.86
3.21
3.57
1.79
2.01
2.24
1.19
1.34
1.49
0.71
0.8
0.89
80m
90m
100m
1.91
2.15
2.38
1.14
1.29
1.43
0.71
0.8
0.89
0.48
0.54
0.6
0.29
0.32
0.36
Instrument Burdens
Type of instrument
Burden
Amp-meter
0,5 to 4 VA
Volt-meter
2 to 5 VA
Frequency-meter
1 to 5 VA
Phase-meter
0,5 to 5 VA
Wattmeter - VARmeter
1 to 5 VA
Electromechanical meter
2 to 5 VA
Electronic meter
0,5 to 2 VA
Measure converter
0,5 to 1 VA
Recorder
5 to 20 VA
Protection relay
Other
0,2 to 30 VA
4
5
5
5
5
5
2
1
20
30
