Protection Relay Setting Calculations

Protection relays are the brain of the power system, monitoring  operating parameters of the power system. When a fault is detected or there is a change in the monitored parameters, the relays respond to protect the power system by sending a tripping signal to the connected breaker isolating that part of the power system.

The selection of protective devices is based on:

• The safety of personnel and equipment (sensitivity of detection and response time).

• The quality and continuity of the electrical supply (fault determination, special directional protection, automatic transfer and fast clearing times to improve/ensure system stability).

The optimisation of the power system’s reliability and safety dictates the use of independent stand-alone relays located close to the power circuit breakers that they control. In some cases, improvements in the overall protection performance are possible by transmitting the relay status to a remote location (known as “acceleration”) or to an automation unit. It is, however, important to ensure that these additional functions do not jeopardise the inherent integrity of the local relays’ performance.

In recent years, technological progress has led to the use of microprocessors in protective relay manufacture. This has led to:

• A significant increase in the amount of information that is processed by the relays.

• Easy calculation of electrical quantities such as harmonics.

• Secure and reliable exchange of digital information with remote locations.

• Continuous monitoring of protection relay integrity by self-supervision and auto-diagnostics.


Protection relays are to be set for operation at the required level of the monitored parameter  and the time delay for operation.  Load flow and Short circuit studies  ( Power system fault studies) are conducted to determine the parameter levels and calculate the settings. We have recently done protection relay setting calculations and supplied the actual setting files to Cheetham Salt Ltd, Bajool, Qld for their 22KV and LV reticulation system. Please do not hesitate to contact us on 0423087897 for protection setting calculations anywhere in Brisbane or Australia.





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Date published: 02/17/2016
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