140% Recloser Trip Coil

[mbrooke]

When would you use a 140% trip coil? What about a 200% for the matter?

Basic characteristics W-group reclosers are hydraulically controlled protective devices in which tripping is initiated by a series trip coil that releases the stored-energy trip mechanism when an overcurrent occurs. Current-carrying and interrupting capacities depend on the rating of the recloser series trip coil. Minimum-trip current is 200% of the coil rating, except X coil ratings which initiate tripping at approximately 140%.

https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/reclosers/w-wv27-wv38X-vw-vwv27-vwv38X-three-phase-hydraulically-controlled-recloser-catalog-ca280005en.pdf

 

[wbdvt]

I would think it would be to coordinate with downstream protective devices.

 

[mbrooke]

Could be- I'm clueless to be honest. 140% is kind of low... I can assume it would never be used for a feeder application?

 

[Hv&Lv]

Just found this...

let me try...

A recloser nameplate represents the continuous current carrying capacity. 200% is the minimum trip pickup on the coil.
so a 70A recloser doesn’t start curve timing until it gets ~140A, whether it be an A, B, C, or D curve. 200% is used almost industry wide from what I have seen. But then again, I haven’t been everywhere.

MANY years ago cooper had a large customer that asked for 140% rather than 200% because their overloads weren’t that high. The assumption was(or is) they could get their curves tighter and coordinate better.

who this customer is (or was) I have no clue...

 

[mbrooke]

I've noticed large customers have the ability to create entire product lines lol.

 

[mivey]

Several reasons.

Generally 200% allows for a decent cold load pick up. 140% may coordinate better (react faster) with upline devices. 140% also sees further out the line for min trips.

You may have a limited amount of overcurrent the supply can handle before overloading a source or causing upline devices to trip. 200% may blow an upline fuse or other mis-coordination.

Also consider the case when the recloser sees minimum line to ground faults for end points. Suppose the station breaker trips for 200 amp ground faults but you have some 135 amp minimum ground fault possibilities on a long tap with 40 amps of load. You need something beyond the station to see end faults.

For a 200% rating you need a 135 * 90% / 2 = 61 amp coil (10% fault safety factor) or smaller. This means you would select a 50 amp or smaller recloser to see end of line minimum ground faults. We like a 30% load safety factor so we want 40 / 70% = 57 amps of continuous rating.

For a 140% rating you need a 135 * 90% / 1.4 = 87 amp coil or smaller. This means you would select a 70 amp or smaller recloser coil to see end of line minimum ground faults. A 70 amp coil will handle the 40 amp load with the load safety factor we like.

 

[mbrooke]

This is the reply I was looking for!

I take you would never use 140% on a substation (output) feeder? 140% is nice to aid when you don't have a ground trip accessory- but just can't see it in practice.

 

[mivey]

Not for a general load mixed feeder. I normally like to allow for some cold load headroom. Today's digital relays make cold load coordination even better as you can get tighter during normal conditions and use temporary overload settings after longer outages.

I like 200-250% feeder head room above routine loads. This allows for some cold load or for picking up other feeders through the transfer bus when working on equipment (we try to do this in lighter load conditions). I might use 125-150% on specific industrial feeders but it depends on the load.

Some general mixed load feeders may require 250% or more and I have seen around 300% cold load for short periods. The problem then becomes overloading the supply and you could lose the station (been there too). Better in that case to stagger feeder energization and allow the loads to settle before adding more to the station.

Industrial and load specific feeders can have tighter coordination because startup can be managed better than some general commercial/residential load.

 

[mbrooke]

200-250% of the normal load or 200-250% of the max contingency load? By that I mean feeders are typically loaded to 50-70% of peak load to allow for picking up load though normally open ties.

Also, what type of time current curve (IEEE curve), multiplier and definite time magnitude do you use?

 

[mivey]

peak normal load. temporary load switching as well as extreme peaks would be considered.

I like an extremely inverse curve as it helps with fuse coordination.

I use a lower time dial for phase and much higher for ground. With the ground picking up to the left of phase (lower pick up amps) and top of phase (slower), it makes the composite curve even more inverse in nature and correllates better with a fuse curve.

For instantaneous, one high fault to stop reclosing into hard or close-in faults, one normal to see 80% of main line or just above first downline device, one hotline to pick up at 2x normal pickup, and one at 70% of ground pickup to write an event and/or create alarm for circuit unbalance but not in trip equation.

 

[mbrooke]

peak normal load. temporary load switching as well as extreme peaks would be considered.

I'm curious what the theory is behind using normal peak load vs contingency peak load.

A feeder loaded at 50% or 250 amps would be 500amp picking up another feeder through a tie. 500-625 amps is kind of close...

I like an extremely inverse curve as it helps with fuse coordination.

We are freinds here on in

I use a lower time dial for phase and much higher for ground. With the ground picking up to the left of phase (lower pick up amps) and top of phase (slower), it makes the composite curve even more inverse in nature and correllates better with a fuse curve.

For instantaneous, one high fault to stop reclosing into hard or close-in faults, one normal to see 80% of main line or just above first downline device, one hotline to pick up at 2x normal pickup, and one at 70% of ground pickup to write an event and/or create alarm for circuit unbalance but not in trip equation.

Aka drive to lock out or block re-closing close in faults? Either way, respectable

 

[mivey]

Cost and reliability are concerns. Better to take the 250 amps and share between two or more other feeders (even better if some from other substations) when possible. Better reliabilty because you spread risk.

If your only source contingency is the one feeder from the same substation then you may be stuck with high cost or load shedding.

We can't fix everything but try to balance money, safety, reliability, service.

 

[mivey]

We don't really want to reclose on a bolted fault inside the station fence. Somebody needs to get eyes on.

 

[mbrooke]

Cost and reliability are concerns. Better to take the 250 amps and share between two or more other feeders (even better if some from other substations) when possible. Better reliabilty because you spread risk.

If your only source contingency is the one feeder from the same substation then you may be stuck with high cost or load shedding.

We can't fix everything but try to balance money, safety, reliability, service.

I know- but when you pick up another 250 amp feeder thats 500amps. 200-250% of 250amps sound to low. Would not 200% of 500amps make more sense?

 

[mbrooke]

We don't really want to reclose on a bolted fault inside the station fence. Somebody needs to get eyes on.

Yup- I'll agree with this.

 

[mivey]

I know- but when you pick up another 250 amp feeder thats 500amps. 200-250% of 250amps sound to low. Would not 200% of 500amps make more sense?

If money is no object.

It is not just setting the relay at 1000 amps but making sure you can deliver and control 1000 amps. That requires a bigger source and beefier equipment. So higher cost at a poor utilization factor means higher cost per delivery unit.

 

[mbrooke]

If money is no object.

It is not just setting the relay at 1000 amps but making sure you can deliver and control 1000 amps. That requires a bigger source and beefier equipment. So higher cost at a poor utilization factor means higher cost per delivery unit.

Obviously. But my point is design, along with switching procedures prevent the feeder from going over 500amps during contingency switching. Setting the pickup to 500amps in that case doesn't seem right to me. Any hot load inrush could trip the relay.

 

[mivey]

Higher settings lose sensitivity. Maybe uneccessarily so. But you should set it for what works for you. Protection is an art, not an exact science.

 

[mbrooke]

Yup- but negative sequence helps

 

[mbrooke]

Not for a general load mixed feeder. I normally like to allow for some cold load headroom. Today's digital relays make cold load coordination even better as you can get tighter during normal conditions and use temporary overload settings after longer outages.

I like 200-250% feeder head room above routine loads. This allows for some cold load or for picking up other feeders through the transfer bus when working on equipment (we try to do this in lighter load conditions). I might use 125-150% on specific industrial feeders but it depends on the load.

Some general mixed load feeders may require 250% or more and I have seen around 300% cold load for short periods. The problem then becomes overloading the supply and you could lose the station (been there too). Better in that case to stagger feeder energization and allow the loads to settle before adding more to the station.

Industrial and load specific feeders can have tighter coordination because startup can be managed better than some general commercial/residential load.

Don't know if you are still following this thread- but does a 200X hydraulic pickup setting change overhead conductor sizing?

I'm thinking: a tree wire or spacer cable conductor comes down producing fault current in excess of the conductor rating- such as 900 a amp ground fault- 400amp above the feeder's setting- but below the 1000amp pickup- exceeding the 100*C emergency limit.

Is this realistic to consider?