CTR HV: 500/1 CTR LV: 1250/1 Transformer Data : Power: 60 MVA HV voltage: 220 KV LV1 Voltage: 33 KV LV2 Voltage : 11kV Transformer percentage imp: 12.5 % Transformer vector group: YNyn0d11 Tap +15% & -5% at the rate of 1.25 % Recommended settings: Id> 0.2 Iref Id>> 7 Iref ( should be 10% more than max. inrush current) Id>>> 15 Iref m1 0.2 m2 0.8 IRm2 1.5 Iref
Supportive calculation to verify bias settings At normal condition current in HV bias circuit (Winding a): Primary current
= 60 MVA / (1.732 * 220 kV) = 157.46 A Current in CT Secondary = 157.46/ 500 A = 0.314 Required Ratio compensation = 1 / 0.314 = 3.18 (will be calculated by the relay)
At normal condition current in LV1 bias circuit (Winding b): Primary current
= 60 MVA / (1.732 *33 kV) = 1049.75 A
Current in CT Secondary
= 1049.75/1250 AREVA T&D AUTOMATION SUPPORT 19/1 GST Road, Pallavaram, Chennai -600043
Page 2
60MVA Transformer protn
APPLN07/Settings - Gomathinagar
Relay setting recommendations 25.03.2008
Rev-0
= 0.839A Required Ratio compensation = 1 / 0.839 (will be calculated by the relay) = 1.19 At +15 % tap condition current in HV bias circuit: Primary current
= 60 MVA / (1.732 * 253 kV) = 136.92 A Current in CT Secondary =136.92/500 = 0.273 As the adopted ratio correction is 3.18 the current to relay bias terminal = 0.273X 3.18 = 0.868 Amp
At - 5 % tap condition current in HV bias circuit HV Side current Current in CT Secondary With ratio compensation
Differential Current at Tap Extremities At -5% Tap Idiff1
= 1.054 -1 = 0.054 At +15% Tap Idiff2 = 1-0.868 = 0.132
Bias Current at Tap Extremities Ibias = IRHV + IRLV 2 IRHV – Relay HV Current IRLV – Relay LV Current AREVA T&D AUTOMATION SUPPORT 19/1 GST Road, Pallavaram, Chennai -600043 Page 3
60MVA Transformer protn
APPLN07/Settings - Gomathinagar
Relay setting recommendations 25.03.2008
Rev-0
Ibias1
= 1.054 + 1 2 =1.027 = 0.868 + 1 2 = 0.934
Ibias2
OPERATING CURRENT IOP At -5% Tap IOP1 = Is + (Bias setting x bias current)
Idiff1 Iop1
= 0.2+(0.2 X1.027) = 0.4054 = 0.054 = 13% 0.405
Since the differential current is not greater than 90% of the operating current at -5% tap the relay will operate satisfactorily. OPERATING CURRENT IOP At +15% Tap IOP2 = Is +(0.2 x Ibias2) = 0.2 +(0.2 x 0.934) = 0.387 Idiff2 = 0.132 = 34% Iop2 0.387 Since the differential current is not greater than 90% of the operating current at -15% tap the relay will operate satisfactorily. Bias setting shall be kept at m2
m1 = 20% up to × 1.5 ×Full load current.(IRm2=1.5Iref) = 80% for through fault stability.
Over Fluxing protection: AREVA T&D AUTOMATION SUPPORT 19/1 GST Road, Pallavaram, Chennai -600043 Page 4
60MVA Transformer protn
APPLN07/Settings - Gomathinagar
Relay setting recommendations 25.03.2008
Rev-0
Data Provided by Customer : Continuous over flux withstand capability : 110% Withstand capability at 120% : 1 minute Withstand capability at 150% : 1secs Recommended settings are as below: Alarms: Alarms will be generated if V/f value is 1.12 the nominal value after a time delay of 10 secs. Tripping chararateristic: Overfluxing tripping IDMT characteristics can be made as per the transformer withstand specifications . /Parameters/Function parameters/Parameter subset 1/V/f Address | Group | Description | Active value --------------+-------------+----------------------+---------------------------081.210 | V/f | Enable PS1 | Yes 081.211 | V/f | V/f> (alarm) PS1 | 1.12 Vnom/fnom 081.212 | V/f | V/f(t)> PS1 | 1.15 Vnom/fnom 081.213 | V/f | V/f>> PS1 | Blocked 081.214 | V/f | tV/f> PS1 | 10 s 081.217 | V/f | t at V/f=1.05 PS1 | 1000 s 081.218 | V/f | t at V/f=1.10 PS1 | 1000 s 081.219 | V/f | t at V/f=1.15 PS1 | 600 s 081.220 | V/f | t at V/f=1.20 PS1 | 300 s 081.221 | V/f | t at V/f=1.25 PS1 | 50 s 081.222 | V/f | t at V/f=1.30 PS1 | 45 s 081.223 | V/f | t at V/f=1.35 PS1 | 30 s 081.224 | V/f | t at V/f=1.40 PS1 | 15 s 081.225 | V/f | t at V/f=1.45 PS1 | 3 s 081.226 | V/f | t at V/f=1.50 PS1 | 0.5 s 081.227 | V/f | t at V/f=1.55 PS1 | 0.5 s 081.228 | V/f | t at V/f=1.60 PS1 | 0.5 s 081.230 | V/f | Reset time PS1 | 0 s 081.229 | V/f | tV/f>> PS1 | Blocked
(Note : 1. Out put relays, LED s, Opto inputs front panel etc, need to be configured at site during commissioning. AREVA T&D AUTOMATION SUPPORT 19/1 GST Road, Pallavaram, Chennai -600043 Page 5
R stab calculation Fault current at 220 kV side neglecting source impedance FLI/%imp = 157.46/ 0.125 = 1259 A IF in secondary : 1259/ 500 = 2.51 A RCT : 10 ohms (assumed) Lead resistance RL – 5 ohms ( provided by the customer) Vs = If (Rct+2 Rl) = 2.51 x (10 + (2× 5)) = 50.2 Volts
Rstab = Vs Is
= 502 ohm Hence recommended stabilising resistor value is 502 ohms AREVA T&D AUTOMATION SUPPORT 19/1 GST Road, Pallavaram, Chennai -600043 Page 6
