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1. April
2016
4
Protection Settings
Calculations
PROTECTION SETTINGS CALCULATIONS
Useful information
- Base MVA = 100MVA
- Rating of the TX 2 = 7.5MVA
- Percentage Impedance of the TX 2 at Tap 9 and Tap 17 is 7.70% and 7.47%
respectively
- Fault MVA at Chemosit 33kV bus = 0
62.10426.258 −∠
- Conductor size of the 33kV Kericho feeder and length from Chemosit is 2
75mm
ACSR and 20KM respectively
- Settings for 5L5 at Chemosit (Back up O/C & E/F);
 O/C : PSM = 300A, & TMS = 0.3
 E/F: PSM = 50A, & TMS = 0.4
Source Impedance`Calculation
0
62.104
26.258
100
)33( ∠=
MVA
MVA
kVZs
.3747.0098.0 puj−−=
Total Z p.u of the 33kV Kericho feeder upto the 33kV bus at Kericho 33/11kV s/s
)0365.00375.0(20)33(2
75
jxkVZ mm
+=
puj 73.075.0 +=
Impedance p.u. of the 7.5MVA TX 2 as expressed to the new MVA base (Tap 17)
= upj .996.0
The resultant Total impedance p.u. upto 11kV bus
)2()33()( 5.77511 2 TXZkVZZbusZ MVAmmskV ++=
= puj 3513.16523.0 +
Resultant fault MVA
= MVA0
23.6464.66 −∠
Fault Current at the 11kV bus
7.5MVA TX 2 – Kericho 33/11kV s/s
Calculations by: afanda rodgers
)3513.16523.0(
100
j
MVA
MVAf
+
=
1005.7
10047.7
)2(5.7
xMVA
MVAx
jTXZ MVA =

2. April
2016
4
Protection Settings
Calculations
A
kVx
MVAx
I f
113
100064.66
=
= A89.3497
Protection relays/equipment operating times calculations on the 11kV fault current of
3497.89A (ph – ph)
1. 5L5 O/C relay
sec
1)
3003
89.3497(
3.014.0
)/( 02.055
−
=
x
x
cot L
=1.5260 sec
2. New 7.5MVA TX 2 HV O/C relay
sec
1)
1503
89.3497(
35.014.0
)/( 02.0
−
=
x
x
cotHV
=1.1704 sec
Operating margin between the two units above is 0.357 sec
3. New 7.5MVA TX 2 LV O/C relay
sec
1)
396
89.3497(
25.014.0
)/( 02.0
−
=
x
cotLV
=0.7860 sec
Operating margin between LV and HV over current is 0.385 sec
4. All 11kV feeder reclosers
sec
1)
300
89.3497(
14.014.0
)/( 02.011
−
=
x
cot recloserskv
7.5MVA TX 2 – Kericho 33/11kV s/s
Calculations by: afanda rodgers

3. April
2016
4
Protection Settings
Calculations
=0.3893 sec
Operating Margin between TX 2 LV O/C and 11kV reclosers is 0.397 sec
Operating times of protection units on 11kV Earthfaults of 1165.96A
1. 5L5 E/F relay
sec
1)
50
6.388(
3.014.0
)/( 02.055
−
=
x
FEt L
=1.3376 sec
2. 7.5MVA TX 2 SBEF relay
sec
1)
80
96.1165(
38.014.0
)/( 02.0
−
=
x
FEtSBEF
= 0.9664 sec
Operating margin between 5L5 and the 7.5MVA TX 2 SBEF is 0.3712 sec
3. TX 2 LV E/F
sec
1)
45
96.1165(
3.014.0
)/( 02.0
−
=
x
FEtTX
=0.6245 sec
Operating margin between the TX 2 SBEF and TX 2 LV E/F is 0.3420 sec
4. 11kV feeder reclosers
7.5MVA TX 2 – Kericho 33/11kV s/s
Calculations by: afanda rodgers

4. April
2016
4
Protection Settings
Calculations
sec
1)
15
96.1165(
15.014.0
)/( 02.011
−
=
x
FEt recloserskV
= 0.2310 sec
Operating Margin between the TX 2 LV E/F and the 11kV reclosers is 0.3936 sec
Table
Protection Relay/Equipment Over Current Settings Earthfault settings
1 33kV Feeder 5L5 PSM =300A, TMS = 0.3 PSM = 50A, TMS = 0.4
2 7.5MVA TX 2 HV PSM = 150A, TMS = 0.35 Not Enabled
3 7.5MVA TX 2 LV PSM = 396A, TMS = 0.25 PSM = 45A, TMS =0.3
4 TX 2 SBEF ------------------------- PSM = 80A, TMS = 0.38
5 11kV Feeder Reclosers PSM = 300A, TMS = 0.14 PSM = 15A, TMS = 0.15
7.5MVA TX 2 – Kericho 33/11kV s/s
Calculations by: afanda rodgers