Table of Contents
Why fuse is used in potential transformer?
A PT Fuse (Potential Transformer) is a medium voltage,, current limiting, fuse with a high interrupting rating,. The PT fuse is used to protect the primary windings of a potential transformer or control power transformers (CPT). Potential Transformer fuse voltage ratings are from 0.625 kV to 15.5kV.
Are Potential Transformers fused?
Potential Transformer (PT) fuses are current limiting fuses with high interrupting ratings designed for the protection of potential transformers.
How does fuse?
The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.
Why CT must be shorted?
Unless a burden (i.e. meters, relays, etc.) is connected to the CT, current transformers should always be shorted across the secondary terminals. The reason is very high voltages will be induced at the terminals. Think of the CT as a transformer, with a 1 turn primary and many turns on the secondary.
Why CT secondary never kept open circuited?
The secondary side of the current transformer is always kept short-circuited in order to avoid core saturation and high voltage induction so that the current transformer can be used to measure high values of currents.
Why does a current transformer need a fuse in the secondary?
A current transformer not connected to an indicator device, as would be the case were a fuse to be installed in the secondary, will cause very high voltages to appear in the secondary wiring that may be sufficient to break down insulation. So a fuse is neither necessary nor desirable in the secondary circuits of a current transformer.
What is a PT fuse on a power transformer?
A PT Fuse (Potential Transformer) is a medium voltage, current limiting fuse with a high interrupting rating. The PT fuse is used to protect the primary windings of a potential transformer or control power transformers (CPT). A PT fuse is a small dimension ferrule type fuse that mounts in standard clips.
What happens if a fuse is placed in the CT circuit?
Suppose a fuse (on a fuse carrier) is placed in the CT circuit, the contact resistance between the fuse and fuse base provides enough resistance to heat and also damage the complete circuits beyond repair. Probably because coils of a potential transformer can short circuit.
How much current can the primary fuse withstand?
Since the starting current can be of the order of 30-35 times higher than nominal current for a short period, it is important that the primary fuse is as slow-acting as possible. A handy rule for Noratel transformers is that the fuse must withstand 35 times nominal current for 5 milliseconds.