What is the difference between 50 and 51 relay?
50 and 51 are types of overcurrent relays (relays driven by a current transformer). Type 50 is an “instantaneous off” relay, whereas type 51 has an inbuilt time delay. The N, G, etc depicts not what the relay is, but how it is wired up.
What is 50N and 51N?
ANSI 50N/51N or 50G/51G – Earth fault Earth fault protection based on measured or calculated residual current values: ANSI 50N/51N: residual current calculated or measured by 3 phase current sensors. ANSI 50G/51G: residual current measured directly by a specific sensor.
What are the numbers on a relay?
Numbers of a Relay Note that each pin is numbered. 85 and 86 are the coil pins while 30, 87, and 87a are the switch pins. 87 and 87a are the two contacts to which 30 will connect. If the coil is not activated, 30 will always be connected to 87a.
What is the difference between 50G and 50N?
In most SEL relays, there are two different ways to measure ground fault current. One way (SEL relay word 50N) uses the current as measured by a core-balance CT physically wired to the In terminals. The other (50G) uses the mathematical summation of the three phase CT’s.
What is 50P protection?
50 (or 50P) – Instantaneous overcurrent phase relay. 51Q – Time delay Negative Sequence overcurrent relay. 52 – AC circuit breaker. IEEE Device Designations commonly used in Distribution Protection. Avista sometimes adds letters to these such as F for feeders, T for transformers, B for bus and BF for breaker failure.
What is 50G relay?
In industrial power systems, a sensitive overcurrent relay connected to a zero-sequence CT (50G) is often used for ground fault protection of the feeder conductors and the high- voltage delta winding of a delta-wye transformer (Fig. 1).
What is the difference between 4 and 5 pin relays?
The difference between a 4 and 5 pin relay is that a 4 pin relay is used to control a single circuit, whereas a 5 pin relay switches power between two circuits. 4 pin relays use 2 pins (85 & 86) to control the coil and 2 pins (30 & 87) which switch power on a single circuit.
What are the parameters of a digital 51 relay?
It is an amusing anachronism that even in digital 51 relays containing no electromagnets or induction disks, you will find parameters labeled “pickup” and “time dial” in honor of legacy electromechanical relay behavior.
Can a 50 relay provide instantaneous overcurrent protection?
A single 50 relay sensing current on a single line would not provide adequate instantaneous overcurrent protection for all three lines. The amount of CT secondary current necessary to activate the 50 relay is called the pickup current.
How to calculate trip time in Schweitzer sel-551 relay?
The trip time formulae programmed within a Schweitzer Engineering Laboratories model SEL-551 overcurrent relay for inverse, very inverse, and extremely inverse time functions are given here: t = T (0.18 + 5.95 M 2 − 1) Inverse curve t = T (0.0963 + 3.88 M 2 − 1) Very inverse curve t = T (0.0352 + 5.67 M 2 − 1) Extremely inverse curve