Stabilizing Resistor Calculation

Parameter description Symbol Value Unit Remarks

Rated Power Pnm = 160 kW

Rated Voltage U_nm = 0.415 kV

Length of cable connecting CT to Relay L = 10 m L&T to verify the value

DC Resistance of the cable Rcable = 8.82 Ω/km L&T to verify the value

CT Primary Rated Current I₁ = 300 A

CT Secondary Rated Current I₂ = 1 A

Peak factor for during motor starting = 7.2

-Maximum earth fault current Imax = 400 A

Relay input impedance R_r = 0.1 Ω

Rated Current I_nm = 290 A

Internal Resistance of the CT R_ct = 0.28 Ω L&T to put the value

Magnetizing current of the CT at the voltage Ukn Iekn = 100 mA L&T to put the value

Knee point voltage of CT U_kn = 20 V L&T to put the value

Motor earth fault setting = 15 %

CT Ratio n = 300

-Startup current (primary value) of the motor Istart = 2088 A

Resistance of the longest loop of the CT secondary circuit R_m = 0.18 Ω

Primary current at which relay starts I_prim = 43.5 A

Start current(secondary value) of the earth fault protection Is = 0.09735 A Magnetizing current of the CT at the voltage Us Ie = 15.88 mA

Relay setting = 0.09735

-Stabilizing voltage U_s = 3.176544 V

Maximum voltage across relay duting fault (ignoring CT saturation) Uf = 44.25 V

Should be less than Relay Permissible Voltage Peak voltage across relay during fault (considering CT saturation) Upeak = 62.29 V Should be less than Relay _{Permissible Voltage}

Stabilizing resistance R_s = 32.63 Ω Result

Parameter description Symbol Value Unit Remarks

Rated Power Pnm = 132 kW

Rated Voltage Unm = 0.415 kV

Length of cable connecting CT to Relay L = 10 m L&T to verify

DC Resistance of the cable Rcable = 8.82 Ω/km L&T to verify

CT Primary Rated Current I1 = 300 A

CT Secondary Rated Current I₂ = 1 A

Peak factor for during motor starting = 7.2

-Maximum earth fault current I_max = 400 A

Relay input impedance R_r = 0.02 Ω

Rated Current I_nm = 240 A

Internal Resistance of the CT R_ct = 0.28 Ω L&T to put the value

Magnetizing current of the CT at the voltage Ukn Iekn = 100 mA L&T to put the value

Knee point voltage of CT Ukn = 20 V L&T to put the value

Motor earth fault setting = 15 %

CT Ratio n = 300

-Startup current (primary value) of the motor I_start = 1728 A

Resistance of the longest loop of the CT secondary circuit R_m = 0.18 Ω

Primary current at which relay starts I_prim = 36 A

Start current(secondary value) of the earth fault protection I_s = 0.08 A Magnetizing current of the CT at the voltage U_s I_e = 13.14 mA

Relay setting = 0.08

-Stabilizing voltage Us = 2.628864 V

Maximum voltage across relay duting fault (ignoring CT saturation) Uf = 44.14 V Should be less than Relay _{Permissible Voltage} Should be less than Relay Calculation of Stabilizing Resistance for Motor Earth Fault Protection (For SPACOM & RE series Relay)

Parameter description Symbol Value Unit

Rated Power Pnm = 110 kW

Rated Voltage U_nm = 0.415 kV

Length of cable connecting CT to Relay L = 10 m

DC Resistance of the cable Rcable = 8.82 Ω/km

CT Primary Rated Current I₁ = 250 A

CT Secondary Rated Current I₂ = 1 A

Peak factor for during motor starting = 7.2

-Maximum earth fault current Imax = 400 A

Relay input impedance R_r = 0.02 Ω

Rated Current I_nm = 200 A

Internal Resistance of the CT R_ct = 0.28 Ω

Magnetizing current of the CT at the voltage Ukn Iekn = 100 mA

Knee point voltage of CT U_kn = 20 V

Motor earth fault setting = 15 %

CT Ratio n = 250

-Startup current (primary value) of the motor Istart = 1440 A

Resistance of the longest loop of the CT secondary circuit R_m = 0.18 Ω

Primary current at which relay starts I_prim = 30 A

Start current(secondary value) of the earth fault protection Is = 0.08 A

Magnetizing current of the CT at the voltage Us Ie = 13.14 mA

Relay setting = 0.08

-Stabilizing voltage U_s = 2.628864 V

Maximum voltage across relay duting fault (ignoring CT saturation) Uf = 52.97 V

Peak voltage across relay during fault (considering CT saturation) Upeak = 72.63 V

Stabilizing resistance R_s = 32.63 Ω

Remarks

L&T to verify L&T to verify

L&T to put the value L&T to put the value L&T to put the value

Should be less than Relay Permissible Voltage Calculation of Stabilizing Resistance for Motor Earth Fault Protection (For SPACOM & RE series Relay)

Parameter description Symbol Value Unit

Rated Power Pnm = 90 kW

Rated Voltage U_nm = 0.415 kV

Length of cable connecting CT to Relay L = 10 m

DC Resistance of the cable Rcable = 8.82 Ω/km

CT Primary Rated Current I₁ = 200 A

CT Secondary Rated Current I₂ = 1 A

Peak factor for during motor starting = 7.2

-Maximum earth fault current Imax = 400 A

Relay input impedance R_r = 0.02 Ω

Rated Current I_nm = 165 A

Internal Resistance of the CT R_ct = 0.28 Ω

Magnetizing current of the CT at the voltage Ukn Iekn = 100 mA

Knee point voltage of CT U_kn = 20 V

Motor earth fault setting = 15 %

CT Ratio n = 200

-Startup current (primary value) of the motor Istart = 1188 A

Resistance of the longest loop of the CT secondary circuit R_m = 0.18 Ω

Primary current at which relay starts I_prim = 24.75 A

Start current(secondary value) of the earth fault protection Is = 0.08 A Magnetizing current of the CT at the voltage Us Ie = 13.56 mA

Relay setting = 0.08

-Stabilizing voltage U_s = 2.711016 V

Maximum voltage across relay duting fault (ignoring CT saturation) Uf = 66.21 V

Peak voltage across relay during fault (considering CT saturation) Upeak = 85.99 V

Stabilizing resistance R_s = 32.63 Ω

Remarks

L&T to verify L&T to verify

L&T to put the value L&T to put the value L&T to put the value

Should be less than Relay Permissible Voltage Calculation of Stabilizing Resistance for Motor Earth Fault Protection (For SPACOM & RE series Relay)