Power System Protection Components

Let us dig deeper into knowing what are the components involved in power system protection. For now it is not necessary to master them in minute details. We only need to know how it works and what are the limitations of each component. 

Here are the main components in power system protection:

1. Relays - it is a protection device which senses the system currents during normal and abnormal condition of the power system. Protection relays are multifunction devices that permanently compare the electrical variables of networks such as current, voltage, frequency, power and impedances with predetermined values, and then automatically send signals for action usually the opening of a circuit breaker or give off an alarm when the monitored value goes above the threshold. 


2. Voltage Transformers (VT) - a voltage transformer is a transformer connected to a very high impedance. It is designed to give the secondary a voltage proportional to that applied to the primary. VT's are also used in metering and indicators. By using voltage transformer all secondary equipments (relays, metering devices, voltmeters etc) are rated to a standard voltage level of 110V. Usually the voltage transformer are denoted by mainly ration and output VA.


3. Current Transformers (CT) - they provide a current proportional to the current flowing through the cable in order to perform energy metering or to analyze this current through a protection device. Usually a current transformer has a secondary value of 1A or 5A.




Summary of the functions instrument transformers (CT, VT):

* To transform currents, or voltages from a high value to a value easy to handle for relays and instruments.
* To isolate the metering circuit from the primary high voltage.
* To provide possibilities of standardization, concerning instruments and relays of rated currents and voltages.

I'll discuss in detail on protection relays in the next following blogs.