What Is an Electric Cutout?
Electric cutouts are small switchgear designed to cut off electricity.
It is often used especially for high voltage, such as 6,600V or 3,300V, and is also called a high voltage cutout. The Electric Cutout’s case is made of highly insulating porcelain, and opening the lid of this case opens the circuit.
A fuse is built inside to prevent the large current that flows in the event of a short circuit from spreading to the upper circuits.
Uses of Electric Cutouts
Electric cutouts are often used in high-voltage distribution lines. The following are examples of electric cutout applications:
- Upstream side of a pole transformer
- Upstream of indoor transformers
- Upstream of an arrester
- Upstream of phase advance capacitor
Cutouts are installed to interrupt the accidental current flowing upstream in the event of a failure of downstream equipment. Electric cutouts are also used to open the circuit during construction and maintenance to interrupt the voltage supplied to the equipment and prevent electric shock to workers.
Principle of Electric Cutouts
A box-type electric cutout, one of the most commonly used cutouts, consists of a main body, lid, and fuse/fuse links.
1. Main Body
Electric cutout bodies are made of porcelain, which has high insulation and weather resistance. Therefore, little deterioration occurs even after long-term use. The porcelain body has mounting bolts embedded in it, which are used to attach the cutout to a base or column.
The main body also has wire entry ports on the top and bottom, which are firmly connected to the fuse links with internal terminals.
2. Lid
The lid is connected to the main body with hinges. Hooks are attached to the surface of the lid, and the circuit can be opened with an operating hook rod or similar. A fuse or other device is mounted inside the lid and can be replaced by opening the circuit.
3. Fuses and Fuse Links
A fuse is a component installed to interrupt a circuit in the event of a short circuit in downstream wiring. The fuse contains a fuse element and silica sand. In the event of a short circuit, the fuse element breaks the wire and the silica sand quenches the arc to provide protection.
The fuse links are fitted with blades (contact blades), which are inserted into the fixed electrode terminals of the body to conduct the circuit.
Types of Electric Cutouts
Several types of electric cutouts are available, depending on the situation and installation location.
1. Double Fuse Type Cutout
Double fuse electric cutouts have two current-limiting fuses inside. If the first cutout is disconnected due to overcurrent, the second cutout is automatically connected. This can prevent power failure even in the event of a temporary overcurrent due to lightning or other causes.
2.Vibration-Resistant Cutout
Vibration-resistant electric cutouts are designed to be resistant to vibration. Electric cutouts are characterized by their ability to hold fuses and lids better than normal electric cutouts. They are used in locations where vibration is expected, such as on cranes. 3.
3. Salt-Resistant Cutout
Electric cutouts are used in areas where salt damage occurs, such as at the seaside. The withstand voltage value when salt adheres to the surface is called the stain resistance characteristic. The salt-resistant cutout is characterized by its high stain resistance.
The internal structure of electric cutouts is no different from that of ordinary cutouts. However, packing is installed at the wiring entry port and at the joints with the lid to prevent salt from entering.
4. Cylindrical Cutout
Cylindrical electric cutouts have a fuse inside the cylindrical insulator. It is used for feeding power to trains, etc. The current-limiting fuse can be pulled out from the bottom of the cylinder.
Other Information on Electric Cutouts
Life Span of Electric Cutouts
Electric cutouts deteriorate over time due to exposure to the elements and ultraviolet rays. The life expectancy over time is 10 to 15 years.
The number of times the load current can be opened and closed is limited to about 50 to 100 times, and the number of times the short-circuit current can be interrupted is limited to about 5 times. Therefore, it is recommended to open them under no-voltage or no-load conditions whenever possible for maintenance and other purposes.
Note, however, that the above is only a guideline, and the service life may vary depending on the installation environment and usage conditions.