Brief Description about the Loop No B20-C27
No of Substations in Loop : 7 Nos
Type of substations : 11/0.415kv, 2x 1500kVA oil type transformer 7 nos.
Cable type : 3CX300SQM CU/XLPE Cable
Substation Feeder Protection Details : Loop in/Loop out feeder has no protection. Transformer feeder is protected by
over current & earth fault and standby earth fault protection.
NETWORK DATA
FAULT LEVEL AT 11 KV BUS OF Exist.RHBPRY4 (33/11KV)
Three phase max fault current: 11.96 KA
Single phase max fault current: 14.14 KA
Primary end CT and relay data
CT ratio: 600/1
Rely type: REF670
Op time: .5 sec at max fault current.
Cable impedance data
Positive sequence impedance: 0.08+.085 ohm per km ( Make: As per M/s. Ducab, UAE technical Data Sheet)
Zero sequence impedance: 0.53+0.065 ohm per km ( Make: As per M/s. Ducab, UAE technical Data Sheet)
Cable length data
From Substation To Substation Cable Length
Loop Name (Mtr)
Primary s/s RHB L13 350
RHB L13 RHBL12 453
RHBL12 RHBL11 712
RHBL11 RHBN09 624
B20-C27
RHBN09 RHBN08 265
RHBN08 RHBP07 1179
RHBP07 RHBP09 329
RHBP09 Primary s/s 3200
Transformer data
Transformer capacity : 1.5MVA
Vector group : Dyn11
Voltage Rating : 11/0.415KV
Positivesequence : 6.00%
Zero sequence impedance : Same as positive sequence
Transformer relay and CT data
CT ratio : 100/1
Relay type : FANOX- SIAC
Op time : 1 sec at max LV fault current
SBEF relay and CT data
CT ratio : 1000/1
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Relay type : FANOX- SIAC
Op time : 1 sec at max LV fault current
Protection philosophy and assumption
1. X/R Ratio=10
2. 250 ms minimum discrimination time considered between two breaker
3. IEC normal inverse time considered for coordination for all relay for over current and earth fault
4. Current transformer is assumed to saturate after 10 times of rated current .
5. SBEF Current transformer is assumed to saturate after 20 times of rated current .
Short circuit result
THREE PHASE FAULT IN KA SINGLE PHASE FAULT IN KA
Bus Ref. 11kv 0.415kV 11kv 0.415kV
Primary s/s 11.96 N/A 14.14 N/A
RHB L13 11.34 36.62 12.86 38.25
RHBL12 10.7 36.34 11.6 38.04
RHBL11 9.96 35.98 10.38 37.78
RHBN09 9.53 35.77 9.73 37.62
RHBN08 9.41 35.7 9.54 37.57
RHBP07 9.17 35.56 9.2 37.47
RHBP09 9.19 35.58 9.24 37.48
Relay setting calculation
Transformer Over current and earth fault setting calculation
Over current relay
CT ratio 100/1
Relay type FANOX- SIAC
1500 kVA TRANSFORMER
Selection of plug setting of Pick up of over current is selected at 120% of over load of
Over current relay for IDMT transformer i.e. (120*78.73)/100 which is equal to 94.47 amp.
element Therefore selected plug setting = 94.47/CT ratio
= 94.47/100
= 0.944
Selected curve IEC NI which follows the formula as given below
Operating time at = {.14/(If/Is)^.02-1)}
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Selection of TMS Desired TMS = Desired op time /op time for 1 TMS
Desired op time = op time for over current relay at HV side should be coordinated
with LV protection . To have sec operation time for LV fault ,TMS will be calculated .
LV 3 phase fault = 35310.9 amp
Reflected fault at 11 KV side=1332 AMP
PSM for 1332 AMP current= 1332/94.47=14.09
Operating time = {.14/(If/Is)^.02-1)}
= {.14/(14.09)^.02-1)}
= 2.57sec
Therefore,
Desired TMS = 1/2.57 =0.39
Selected TMS = .4
Selection of pick up of Instantaneous element pick up = 1.2*reflected fault at 11 for 3 phase
Over current relay for instantaneous fault at LV bus .
element = 1.2* 1332= 1598.4 amp
element Selected pick up =1598/100
= 15.98*In
Operating time of 0.05 sec
Instantaneous element
Earth fault Relay
CT ratio 100/1
Relay type FANOX- SIAC
Selection of plug setting of Pick up of over current is selected at 20% CT rated current
Overcurrent relay for IDMT i. e 0.2 *In. =0.2*78.73=15.74
element Therefore selected plug setting = 15.74/CT Ratio=15.74/100
=0.157
Selected curve IEC NI
Selection of TMS Transformer of Dyn11 earth fault relay need not be coordinated with
earth fault protection at LV side .
Therefore selected op time = 0.1
Selection of pick up of earth fault relay for 4*In=4*78.73=314 A
instantaneous element
Operating time of Instantaneous element 0.05 Sec
SBEF Relay
CT ratio 1000/1
Relay type FANOX- SIAC
Selection of plug setting of Pick up of over current is selected at 20% CT rated current
Overcurrent relay for IDMT i. e 0.2 *In. =0.2*2086.81=417.36
element Therefore selected plug setting = 417.36/CT Ratio=417.36/1000
=0.4
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Selected curve IEC EI
Selection of TMS Transformer of Dyn11 earth fault relay need not be coordinated with
earth fault protection at LV side .
Therefore selected op time = 0.8
Selection of pick up of Over current earth Disabled
fault relay for instantaneous element
Operating time of Instantaneous element Disabled
11 kV Remote end Over current and earth fault setting calculation
INPUT DATA RECEIVED FROM ADDC
CT ratio 600/1
Relay type REF670
11 kV 3 phase fault current at SWS 11.96kA
Over current Element
Characteristic curve Normal Inverse
CT ratio 600/1
Over current Element- IDMT-PMS 0.8*ln
Over current Element- IDMT-PMS 0.62
Over current Element- Highest Current disabled
Over current Element- Highest Time setting disabled
Earth fault Element
Characteristic curve Normal Inverse
CT ratio 600/1
Over current Element- IDMT-PMS 0.2*ln
Over current Element- IDMT-PMS 0.157
Over current Element- Highest Current disabled
Over current Element- Highest Time setting disabled
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