1.
0 OVER FLUXING PROTECTION (V/F PROTECTION):(P632)
VT References for V/F Protection:
HV PT Rating - Primary kV = 16.50
HV PT Rating - secondary V = 110
Assumed as Transformer continous withstand capacity as 120% and 160% as short time
withstand capacity.
Over fluxing setting for Alarm = 1.2
Time delay for V/f alarm = 5 sec
Over fluxing setting for Tripping = 1.60
Time delay for V/f trip = 1 sec
2.0 Over Head Differential Protection
Transformer load in MVA = 315
Voltage level in kV = 400
Transformer HV Side (765kv) current in = 315 x 1000 / (√3 x 400)
Amps = 454.68
MinimumPick up current Id> = 10 %(to achieve maximum sensitivity,
0.20
The first slope for the differential for fault hence the value is set to 0 or no bias
=
currents
The pickupnear to theatrated
setting whichcurrent
bias is (m1)
changed assuming no stand alone differential
= 200.00%
50 % (toisachieve
current flowing)clear discrimination for
to higher
The slopeslope
of bias(IRM2)
characteristics to take
= minor unbalances caused during external
care of severe faults (m2)
The recommended setting in the MiCOM P633 faultrelay
condition)
is as follows :
Idiff> = 0.2
m1 = 0.1
m2 = 0.5
IR,m2 = 2
Idiff>> = 4 Iref
Idiff>>> = 5 Iref
Vector Group ends a-b = 0
Vector Group ends a-c = 0
Zero seq filter end a = yes
Zero seq filter end b = yes
Zero seq filter end c = yes
Op. mode rush restraining = not phase selective
Rush I(2f0)/I(f0) = 20%
Ov I(5f0)/I(f0) = 20%
3.0 Over All Differential protection:
Relay type used = MiCOM P633
Transformer capacity in MVA = 315.000
Gen. Neutral side voltage in kV(winding -c) = 16.500
Gen. Neutral side C.T Ratio primary = 12500.000
Gen. Neutral side C.T Ratio secondary = 5.000
UAT-1 side voltage in kV(winding-b) = 16.500
UAT-1 side C.T Ratio primary = 12500.000
UAT-1 side C.T Ratio secondary = 5.000
G.T Phase side voltage in kV(winding-a) = 420.000
G.T Phase side C.T Ratio primary = 2000.000
G.T Phase side C.T Ratio secondary = 1.000
%Impedance = 14.500
Vector Group = YNd11
Tap = +5% to -5%
Voltage @ min tap = 399
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Voltage @ max tap = 441
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Supportive calculations:
At Normal condition current in HV Bias circuit:(winding a- GT HV side)
= 315MVA/(1.732*420kV)
Full load Primary Current in Amps
= 433.025
= 433.025/2000)
Equivalent Current in CT Secondary
= 0.217
Required Ratio Compensation = 4.619
At Normal condition current in HV Bias circuit:(winding b - UAT - 1 HV side)
= 315MVA/(1.732*16.5kV)
Full load Primary Current in Amps
= 11022.465
= 11022.465/(12500)
Equivalent Current in CT Secondary in Amps
= 0.882
Required Ratio Compensation = 1.134
At Normal condition current in LV Bias circuit:(winding c- Generator Neutral
side)
= 315MVA/(1.732*16.5kV)
Full load Primary Current in Amps
= 11022.465
= 11022.465/(12500)
Equivalent Current in CT Secondary in Amps
= 0.882
Required Ratio Compensation = 1.134
At -5% Tap condition current in HV Bias circuit:
The Transformer Differential protection relay MiCOM P633 has the following
parameters for setting:
1) Pick up value of Differential current, Idiff>. (Operate value of the differential protection
function as referred to the reference current of the relevant transformer end).
2) Slope-1 of tripping characteristic, m1. (Gradient of the tripping characteristic of
differential protection in the range).
3) Slope-2 of tripping characteristic, m2. (Gradient of the tripping characteristic of
differential protection in the range).
4) Base point for slope-2 characteristic, IR,m2. (This setting defines the second knee of
the tripping characteristic. Above this knee, the gradient is m2).
5) Threshold value of the differential current for deactivation of the inrush stabilization
function (harmonic restraint) and of the overfluxing restraint, Idiff>>. (If the threshold is
set too high, it is possible for the P63x not to trip in the presence of internal faults with
transformer saturation).
6) Threshold value of the differential current for tripping by the differential protection
function independent of restraining variable, harmonic restraint, overfluxing restraint and
saturation detector, Idiff>>>. (If the threshold is set too low, the P63x can trip in the
presence of external faults with transformer saturation).
The following setting in the MiCOM P633 relay is recommended as below:
Idiff> = 0.2
m1 = 0.2
m2 = 0.8
IR,m2 = 1.5
The slope characteristics are defined to provide a stable operation using normal condition
(e.g. tap changing, out of zone fault, branch out of zone fault).
The setting is started with the above recommended setting of Idiff>, m1 , m2 ,IRm2 .
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The stability check is performed for the following cases :-
A. The GT is at -5% tap and the Generator generation is at rated capacity
B. The GT is at +5% tap and the Generator generation is at rated capacity
The Generator rating in MW = 250
Rated PF = 0.85
= 250/0.85
Generator MVA
= 294.118
= 294.1*10^3/(√3*16.5)
Full load current of the Generator in Amps
= 10291.8
Considering that the Generator is at full generation and the UAT are in service with its
rated load and the GT is carrying the balance load generated by the Generator.
Considering the above condition the load on = 294.1-(35)
GT in MVA = 259.118
A. Stability of OAD protection when GT at -5% tap at the above load:
Transformer load = 259.118
Transformer HV Side (420kV) current in = 259.118 * 1000 / (√3 * 399)
Amps = 375
Equivalent secondary current at HV Side = 375 / (2000)
(420kV) in Amps = 0.187
Transformer HV Side (420kV) current in Iref, = 0.187*4.619
Amp = 0.87
Transformer UAT Side (16.5kV) current in = 35* 1000 / (√3 * 16.5)
Amps = 1224.72
Equivalent secondary current at UAT Side = (1224.72 /12500)
(16.5kV) in Iref, Amps = 0.098
= 0.098*1.134
Transformer UAT(16.5kV) current in Iref
= 0.111
= 294.1*1000/(√3 *16.5)
Generator neutral side current in Amps
= 10291.75
= 10291.75/(12500)
Equivalent secondary current in Amps
= 0.82
= 0.82*1.134
Generator neutral side current in Iref
= 0.93
Differential current @ -5% tap position = 0.154
Restraining current @ -5% tap position = 0.955
Considering the above refered setting the operating current calculation.
The differential current = 0.154A & the Bias current = 0.955A
The Differential current required for the relay to operate = Idiff> (1-0.5 * Bias setting) +
(Bias Setting * Bias Current)
The Differential current required for the = 0.2 * (1-0.5 * 0.2) + (0.2 * 0.997)
relay to operate in Amps = 0.371
As the restraining current is 0.995, and the differential current is 0.154A the operating
point lies below the characteristic curve
Idiff> = 0.2
m1 = 0.2
m2 = 0.8
IR,m2 = 1.5
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B. Stability of OAD protection when GT at +5% tap at the above load:
= 224.18 * 1000 / (√3 *441 )
Transformer HV Side (420kV) current
= 339.24
Equivalent secondary current at HV Side = 339.24/(2000)
(420kV) in Amps = 0.170
Transformer HV Side (420kV) current in Iref = 0.170*4.619
in Amps = 0.78
Transformer UAT side (16.5kV) current in = 35 * 1000 / (√3 * 16.5)
Amps = 1224.72
Equivalent secondary current side (16.5kV) = 1224.72 (12500)
in Amps = 0.098
Transformer UAT side (16.5kV) current in = 0.098*1.134
Iref = 0.11
= 294.1*1000/(√3 *16.5)
Generator neutral side current in Amps
= 10291.75
= 10291.75/(12500)
Equivalent secondary current in Amps
= 0.82
= 0.82*1.134
Generator neutral side current in Iref
= 0.93
Differential current @ +5% tap position = 0.039
Restraining current @ +5% tap position = 0.914
Considering the above refered setting the operating current calculation.
The differential current = 0.039A & the Bias current = 0.914 A
The Differential current required for the relay to operate = Idiff> (1-0.5 * Bias setting) +
(Bias Setting * Bias Current)
The Differential current required for the = 0.2 * (1-0.5 * 0.2) + (0.2 * 0.951)
relay to operate = 0.363
As the restraining current is 0.914A, and the differential current is 0.039 A the operating
point lies below the characteristic curve
4.0 Backup O/C Protection on G.T HV side
Relay type used = P143
Transformer capacity in MVA = 315.000
HV Voltage rating in kV = 420.000
CT Ratio primary = 600.00
CT Ratio secondary = 1
= 315 MVA/(1.732 x 420kV)
Rate current in Amps
= 433.025
Maximum through fault Current in Amps = 2986.4
SETTING:
= 120% of rated current
Pick up Setting in Amps, I>1 = 1.2 x 433.025
= 519.63
Pick up Setting in secondary, I>1 = 0.866
Delay Type = IDMT-SI
Downstream relay operating time in sec = 0.500
Grading Margin = 0.250
Required operating time 'treq' in sec = 0.750
= (0.14 x TMS)/(Ifault/Ipu)^0.02-1
Operating time @ TMS=1, 't1'
= 3.933
= treq/t1
TMS to be set in the relay TMS>1
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TMS to be set in the relay TMS>1
= 0.19
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5.0 Earth Fault Protection
5.1 Stage 1: (IN>1)
= 20% Full load current
Earthfault pickup in Amps IN>1
= 86.61
Equivalent secondary current in Amps = 0.14
Delay Type = IDMT-SI
Down stream relay trip time in sec assumed = 0.50
Grading margin in sec = 0.25
Required operating time delay treq sec = 0.85
= 0.14*TMS/((IF/IN>1)^0.02-1)
Operating time delay @ TMS 1 "t1"
= 2.40
= treq/t1
TMS to be set in the relay
= 0.35
6.0 HV STANDBY EARTH FAULT
= 30% of Full load current
Earth fault pickup in Amps IN>2
= 130
Equivalent secondary currents in Amps = 0.22
Delay Type = DT
Time Delay = 1 sec
7.0 REF protection:
Relay type used = MiCOM P143
Transformer Capacity in MVA = 315.000
Transformer % Impedance = 14.500
HV Side Phase side CT - primary = 2500.000
HV Side Phase side CT - secondary = 1.000
HV Side Voltage reference in kV = 420.000
= 315MVA/(1.732*420*10^3)
GT HV full load current in Amps
= 433.0
7.1 HV REF Settings:
Maximum Fault
Equivalent FaultCurrent
CurrentininAmps
Secondary in = 2986.4
Amps = 1.19
= 30% of full load current
REF Pickup current in Amps = 0.30*433
= 129.908
= 43.303/(2500/1)
Equivalent secondary current in Amps Is
= 0.05
Note:As per ESI 48-3 standard the pickup setting should be 10% - 60% of the full
load current.
Note:This pickup setting shall be set more than the stand alone spill current in
the fileld.
Rstab calculation:
Rct value of CT in Ohms(from drawings) Rct= 3
Lead length of 300 mtrs 0f 2.5 sqmmof parallel run is assumed with cable
resistance of 8.71 Ohms/KM.
Lead resistance in Ohms RL = 0.4355
= Fault current * (Rct + 2RL)
Voltage developed during fault across the = 1.19*(3+(2*0.4355))
relay Vs in Volts
= 4.62
= Vs/Is
Stabalizing resisitor value in Ohms = 4.62/0.05
Rstab
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FOR NTPC - BONGEGAON
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Stabalizing resisitor value in Ohms
Rstab
= 89
Recommended Rstab valus in ohms = 110
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FOR NTPC - BONGEGAON
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