What is the difference between 51G and 51N?
What is the difference between 51G and 51N?
As for 51N and 51G, the way modern relay manuals proposes, 51G actually measures the current in neutral using a CT (residual CTs), where as 51N is where current in neutral is calculated by vector sum of the 3 phase over currents by the relay.
What is a 51G relay?
Similarly, the “G” suffix can denote a “ground”, hence a “51G” is a time overcurrent ground relay. The “G” suffix can also mean “generator”, hence an “87G” is a Generator Differential Protective Relay while an “87T” is a Transformer Differential Protective Relay.
What is a 49 relay?
The Type 49/50/51 overload relay provides three important functions for the protection of a motor. The Type 49/50/51 overload relay provides three important functions for the protection of a motor: Overload Protection (Function 49), Locked Rotor Protection (Function 51) and Phase Fault Protection (Function 50).
What is a 59 device?
55 – Power Factor Relay. 56 – Field Application Relay. 59 – Overvoltage Relay. 60 – Voltage or Current Balance Relay. 62 – Time-Delay Stopping or Opening Relay.
Can a 50 function be added to a 51 relay?
On electromechanical relays, the 50 function can be added as an instantaneous attachment to a 51 time-overcurrent relay. If a relay has both 50 and 51 functions present and enabled is referred to as a 50/51 relay.
How are 51 relays related to overcurrent magnitude?
All 51 relays are inverse in that the amount of time to trip varies inversely with overcurrent magnitude: the greater the sensed current, the less time to trip. However, the function of trip time versus overcurrent magnitude is a curve, and several different curve shapes are available for United States applications:
Why are there different curves in time overcurrent relays?
The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. Other overcurrent protection devices include fuses and additional 51 relays at different locations along the same line.
What is the pickup current on a 50 relay?
The amount of CT secondary current necessary to activate the 50 relay is called the pickup current. Its value may be varied by adjusting a movable magnetic pole inside the core of the relay.