Sample Setting Calculation for REF Protection

Sample Setting Calculation for REF Protection (MCAG Relay) Substation

: 220 kV GSS HISSAR

Transformer Name : BHEL Relay Name : MCAG, EE

Calculation: Transformer Name: BHEL MVA = 100 Voltage Ratio = 220/132 Rated Voltage in kV (HV Side) = 220 Rated Voltage in kV (LV Side) = 132 Vector Group = YNA0d1 % Impedance of the transformer=0.1132 Relay Operating Current

= 0.2A

Magnetizing Current of the Ref (Ct) = 60mA Knee Point Voltage of the Ref (Ct) = 1000 V Relay Burden

= 1VA

CT Ratio (HV Side) = 500/1 CT Ratio (Neutral Side) = 500/1 CT HV Side Vector Group = Star/Star CT Ratio (LV Side) = 500/1 CT LV Side Vector Group = Star/Star CT resistance (Rct) =5Ω Lead Resistance value=2.5 Ω Rated Current (HV Side) = MVA / (√3*kV) =100*10^6/ (√3*220*10^3) =262.43 A

Maximum fault current contributed =Rated current /Percentage Impedance =262.43/0.1132 =2318.286A Maximum fault current contributed secondary=2318.286/500 = 4.636 A

I Operating Current

=If *(Irelay Operating +n*Imag) = 4.636 /1000 (0.2 /1000+4*60) =1.112 mA

Operating Voltage Vs

= If*(Rct+2*Rl) =4.636*(5+2*2.5)

Vs

=46.36V

=Vs/I operating – R burden/Ioparating2

R stable

=(46.36/0.2)-(1/0.22) R stab =206.8 Ω

Stability Check

:

Stable If 2*Vs
 2*46.36<1000  Relay setting is stable.  Setting is in order.