Mike Dolt Enterprises
Mike Dolt Enterprises
User: OBI213, Location: Wisconsin
Asked on: Friday, April 8, 2011 at 1:51 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:57 am EDT
Question: What advantages do you get if you activate the overcurrent portions 50/51 on a multifunction relay when you already have trip units in the breaker?Should the settings be the same on the protection relays as the trip units?It is my understanding that multifunction relays are used for throwover schemes and that would be my reason to use them in leiu of discreet relays. However when it comes to selective coordination I am not sure if they should be the same trip settings or if they are even required as there is already protection in the form of trip units in the breaker.Can anyone provide insight on this?
Advantages of Activating Overcurrent Portions (50/51) on Multifunction Relays with Trip Units in Breakers Enhanced protection
Redundancy and increased reliability of overcurrent protection.
Selectivity improvement
Multifunction relays can provide faster and more precise tripping, improving selectivity over breakers with trip units.
Improved fault detection
Relays can complement the protection from trip units by providing additional detection methods (e.g., instantaneous, inverse, ground fault)
Remote monitoring and troubleshooting
Relays offer remote access for monitoring and diagnostics, allowing for early identification of potential issues.
Future-proofing
Multifunction relays can be easily programmed to meet evolving protection requirements, making them adaptable to changing electrical systems.
Settings Comparison
It is generally not recommended to use the same trip settings on both protection relays and breaker trip units. Reasons for different settings
Breaker trip units may be set for different modes (e.g., long time, short time), while relays provide more flexible settings. Relays can be set to provide faster tripping for protection coordination purposes, while breakers provide backup protection.
Use of Multifunction Relays for Selective Coordination
Multifunction relays are commonly used for selective coordination schemes, as they offer: Programmable time-current curves
Allows for precise coordination with other protective devices.
Fast tripping
Can isolate faults quickly, minimizing the impact on critical loads.*
Directional protection
Can identify the direction of fault current, enhancing protection selectivity.
Conclusion
Activating the overcurrent portions (50/51) on multifunction relays provides additional protection, improves selectivity, and facilitates remote monitoring and troubleshooting. While it is not necessary to have identical trip settings on both relays and breaker trip units, it is important to establish coordinated settings to ensure optimal protection and reliability. Flag for review