METHODS OF REDUCING SHORT CIRCUIT CURRENT
An electrical circuit in which a very low resistance path has been accidentally opened. When the resistance in a circuit decreases the current in the circuit increases drastically, which can damage the circuit and cause fires. As a result, we have used certain equipment and other concepts in order to reduce the short circuit current.
Increasing the cable length:
There are numerous approaches available to minimize the fault current in a low voltage system. Increasing the cable length is one technique.
The fault current in bus 03 is 24.997 kA, and the cable length is 30 meters. However, because the breaking current of a low voltage circuit breaker is 20 kA, increasing the cable length from 30 to 50 meters. reduces the fault current to within 20 kA. The fault current on bus 03 is now 19.024kA. The fault current will decrease when the cable length is increased. that is shown the Figure 1: ETAP simulation for different cable length
Lighting transformers:
A lighting transformer is nothing but a 1:1 transformer. The transformer turns ratio is the number of turns of the primary winding divided by the number of turns of the secondary coil
The fault current in bus 03 is 24.997 kA, and the cable length is 30 meters. However, because the breaking current of a low voltage circuit breaker is 20 kA, we have installed a lighting transformer between the cable and bus 03. The fault current is now within20 kA of the safe limit. The fault current on bus 03 is now 10.707 kA. The fault current will be reduced shown in figure 2.
Current limiting reactor:
limiting fault current. Although the CLR introduces impedance into the circuit degrading the voltage profile during normal operation, it can be a cost-effective solution obviating the need for upgrading switchgear in the system due to increase in the fault level. A current limiting reactor (CLR) is a series reactor connected into the circuit for limiting fault current. Above the result is fault current limit the some values .
Disadvantages
Voltage drop
Increasing power loss
Reduce the grid power factor
High space require
The system bus 03fault current is 19.318 kA in normal conditions. However, as the system power is increased to 15 MW for internal purposes by employing one generator, the fault current has increased to 24.672 kA, as shown in figure. How to reduce the fault current? Whenever we have use some methods.
Unit ratio transformer:
The number of turns on a transformer’s secondary divided by the number of turns on its primary is known as the turns ratio. If the unit ratio transformer is connected between generator bus 02, Previously, the fault current of bus 02 was 24.672 kA. The fault current is now reduced from 24.672 kA to 19.874 kA.