Secondary resistance measurement
Protection CT secondary resistance= 0.3 Ω
Measuring CT secondary resistance= 0.4 Ω
Primary current flow is from P2 → P1
Secondary current flow when,
Switch ON S2 → S1
Switch OFF S1 → S2
Protection CT secondary current= 0.6 A
Measuring CT B secondary current= 0.57 A
Secondary voltage(V)| Secondary current(A)|
Secondary voltage(V)| Secondary current(mA)|
Primary Current: 50 A
Secondary voltage (V): 0.39
Secondary voltage (V): 0.371
Magnetizing curve for measuring CT
The knee point of an excitation curve is defined as the point at which a further increase of 10% of secondary e.m.f. would require an increment of 50% of exciting current.
Knee point voltage = 12.72 V
Magnetizing curve for protection CT
Knee point voltage = 17.7 V
1) Reason out as to why the secondary resistance of a protective transformer is low compared to that of a measuring transformer
* Measuring transformers are used to measure the currents at normal operation normally flows small current, used in small range of currents. * Protective transformers are used to measure currents at fault conditions. At fault conditions the drown current is several times higher than the normal operation condition. * So protection transformer should be able to handle a high current than the measuring CT. * Therefore the secondary resistance of the protection transformer needs to be a lower value compared to measuring transformer in order to handle high currents and to reduce power dissipation.
2) Explain the significance of knee point voltage of the...