thermal o/l and stalling relays...

[ycliff]

I have a bunch of data for various thermal o/l and stalling relays. can anyone tell me what it all means?

tapthis is the current tap setting i'm assuming)

time setting: stall:45 (what does this mean? is this just the time setting on the relay like any other relay that goes along w/ the current tap setting above?)

ground: (is the the current tap setting (cts) for the ground ct?) should it have it's own time setting associated with it?

% overload: these are all listed as either 100, 110, 135. is this the % overload of the motor, ie: % of full load amps? does this represent the 50/51 relay (phase time delay and phase instantaneous?) should this have it's own time delay setting?

 

[DanDel]

Just assumptions, but the 'tap' would indeed be the tap setting for pickup of the overload unit.
I would imagine that a 'stall' setting of 45 would be a time setting to trip upon a stall condition, i.e. LRA for 45 seconds?
'Ground' should be for ground fault current, I'm assuming it's a current setting from your statement. It may have a fixed time delay if there is no setting for it.
'% overload' is interesting if it is on the same relay as 'tap'. It may be a setting based on the tap for overload pickup.
I'm also assuming that you don't have access to any manuals for these relays. Can you tell us manufacturer/model data?

 

[ycliff]

Manufacturer/Model:
THERMAL O/L & STALLING RELAY
P&B GOULDS
Mn 5ALI-C53-5
-----------------------------
example:
tap - 74A (FLC of motor)
ct ratio - 100:5
time: curve 1 or 4
% overload - 1.05 * FLC

is the current tap setting = 1.05*(74A)*(5/100)?

 

[ycliff]

Are phase inbalance and ground essentially the same thing? ie: does phase inbalance imply that there is a gnd fault somewhere? or are they totally independent?

 

[dpc]

Phase imbalance protection primarily guards against the loss of a phase on a single phase motor.

 

[dpc]

Sorry - make that a "three-phase" motor. Wish this forum had an "edit" function.

 

[ycliff]

what is the ct config. for phase inbalance?

 

[DanDel]

It looks the the overload pickup setting would be the 'tap' setting times the '% overload' setting, which the relay would see as a ratio from the 100:5A CT. (74A * 1.05 * 5/100 = 3.885A at the relay).

Phase imbalance is not the same as ground fault. Typically, motor protection would be concerned about a voltage imbalance, since a 1% imbalance of the voltage applied to a three-phase motor can cause a 10% current imbalance, and resulting overheating and damage.

As long as there are three CTs for the three-phase, three-wire system, typically in a wye configuration, you can sense current imbalance.

 

[powerjunx]

ycliff,

phase imbalance and ground fault are totally independent where 5% imbalance voltage will lead to single phase scenario. Thus, phase imbalance relay is required.

I wonder why you dont have realy manuals?

Dandel,
1% imbalance voltage to 10% imbalance current is quite rough,
maybe 1%IV to 5-6%IC is a slim approximation.
GE motor management relay has 10% IC triggers the alarm while 15% IC triggers to trip.