- To eliminate the effect of leads
- Guard the resistance against stray electrostatic fields
- Bypass the leakage current
- Guard the resistance against overloads
Answer: 3. Bypass the leakage current
Explanation:
- High resistances are provided with a guard terminal. This guard terminal used to Bypass the leakage current
- The guard wire runs along the top of the transmission line and it is earthed. The lightning strike or lightning induces voltage first strike this wire and the energy is transferred to the ground and no voltage is induced in the live conductor
- A guarding is provided for the safety of life, installation, and communication circuits.
- The guarding for 11 kV lines is provided at road crossings, canal crossings, railway crossings, crossing over lt lines, or communication lines.
- Regarding guarding line crossings or approaching each other IER 87 provides all-important guidelines, IER (Indian Electricity Rule) 88 provides that every guard wire shall be connected with the earth at each point at which electrical continuity is broken
- Every guard wire should have sufficient current-carrying capacity to ensure the circuit renders dead, without the risk of fusing of the guard wire or wires till the contact of any line wire has been removed. There are various other rules relating to guarding where lines cross trolley wires as mentioned in sub-rule (5) of IER 88.
- Cage guarding is provided on lt lines with vertical formation. The guard should be made of the same material as used for earth wire. In lt lines, the guard is connected with the neutral and insulated from the earth by means of a porcelain reel.
- Cradle guarding is provided when the conductors are in horizontal or delta formation as in the case of 11 kV lines. The cradle guard is directly connected to an earth wire. If a line conductor breaks, it will fall on the guard, thereby blowing the fuse or tripping the coil of a circuit breaker.
