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Open circuit test in a cable can be located by
BlavierтАЩs test
Capacity test
Varley loop test
Murray loop test
Capacity test
The capacity test is specifically used to locate an open-circuit fault in an underground cable by measuring the capacitance of the cable core. Since capacitance is proportional to the length of the cable section, the location of the break can be determined by comparing the measured capacitance with the known capacitance per unit length of the cable.
The capacity test is specifically used to locate an open-circuit fault in an underground cable by measuring the capacitance of the cable core. Since capacitance is proportional to the length of the cable section, the location of the break can be determined by comparing the measured capacitance with the known capacitance per unit length of the cable.
d=C0тАЛCтАЛ├ЧL тАФ formula to locate the fault distance d from the test end
The cable acts as a capacitor with the core as one plate and the sheath as the other. By measuring the capacitance C between the conductor and the ground/sheath using a bridge circuit or ballistic galvanometer, the distance d to the fault can be calculated using d=C0тАЛCтАЛ├ЧL, where C0тАЛ is the capacitance per unit length and L is the total cable length.
Used specifically for open-circuit faults where loop tests like Murray or Varley fail.
Requires knowledge of the capacitance per unit length (C0тАЛ) of the cable.
The cable acts as a shunt capacitor in the bridge circuit.
Requires high sensitivity instruments like a ballistic galvanometer or a Capacitance Bridge.
Suitable for open circuit faults where loop tests cannot be performed.
Simple mathematical relation for distance calculation.
Accuracy depends on the precise value of capacitance per unit length (C0тАЛ).
Affected by temperature and humidity which change dielectric properties.
Underground transmission line diagnostics.
Telecommunication cable maintenance.
Murray and Varley loop tests are exclusively used for short-circuit or earth faults, not open-circuit faults.
Blavier's test is used for determining the location of a fault to earth in a cable, not an open circuit.
B is correct тАФ The capacity test utilizes the linear relationship between capacitance and length to pinpoint the location of an open-circuit fault in an underground cable.
Always remember: Loop tests (Murray/Varley) are for low-resistance faults (short/earth), while Capacitance tests are for high-resistance/open faults.