59N vs 50G/51G
59N vs 50G/51G
(OP)
Hi all,
when protecting a 600V alternator against ground faults (high resistance grounded, 5A); is there an advantage of using a 59N protection over using a 50G/51G with a sensitive CT?
I see common practice is 59N, but basic motor relays don't have this function. I'd use 50G/51G with sensitive CT (0.25 to 25 A primary).
Thanks for your comments.
when protecting a 600V alternator against ground faults (high resistance grounded, 5A); is there an advantage of using a 59N protection over using a 50G/51G with a sensitive CT?
I see common practice is 59N, but basic motor relays don't have this function. I'd use 50G/51G with sensitive CT (0.25 to 25 A primary).
Thanks for your comments.






RE: 59N vs 50G/51G
RE: 59N vs 50G/51G
What Dave said.
Regards.
Slava
RE: 59N vs 50G/51G
You're probably aware of this, but just thought I'd mention this since I've seen this done in quite a few installations.
RE: 59N vs 50G/51G
RE: 59N vs 50G/51G
Thanks for the clarification.
Dave
RE: 59N vs 50G/51G
The system is delta on low voltage side, so high resistance grounding will protect the stator of the generator.
JL
RE: 59N vs 50G/51G
A 51N relay connected to a CT with a primary rating of 50% of the expected ground fault should provide sensitive operation. So if you expect 100A of ground fault select a CT ratio of 50/5
RE: 59N vs 50G/51G
A generator neutral grounded with a properly sized distribution transformer can be incorporated with a 59N relay to detect ground faults. Since the ground fault currents of such a grounding system are very low you cannot use 50G or 51G.
But a motor does not have its star point grounded. So you cannot have 59N. If the motor is connected to a high resistance grounded system, then you can use 51G (actually 51GS) sensitive ground fault protection to detect low level ground fault currents.
Therefore motor relays donot have 59N.
Two different issues.
Kiri
RE: 59N vs 50G/51G
in my case, it's a 1MW induction generator (almost same thing than induction motor)...
we will use Multilin 369 (motor relay) with 51GS function, with 50:0.025 sensitive CT. This GE CT can read currents as low as 0.25A, which will be OK with a 5A grounding resistor...I guess.
Thank you