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Current Limiting Reactors vs. Current Limiting Fuses

Current Limiting Reactors vs. Current Limiting Fuses

Current Limiting Reactors vs. Current Limiting Fuses

(OP)
We are undergoing an expansion of our industrial facility (islanded system in USA) and adding a significant amount of captive generation (130 MW) and load. The substation containing the new power generating equipment will be connected to an existing substation on our generating system. This will bring our total from (6) to (8) onsite generators for a plant-wide total of about 220MW.

The existing switchgear that the new substation is to be tied to is rated for 63kA interrupting current, and with the new substation tied in it will push that total up to 80-90kA. The existing fault current is in the neighborhood of 50kA. Our system runs at 13.8kV. So far as I can tell we basically have two choices:

1. Install CLRs between the two substations to keep fault current limited
2. Install current limiting fuses for the feeders connecting the substations

I'm wondering what would be the better solution in your minds? I like the CLR solution just because I feel like it actually solves the problem vs. the fuse solution which doesn't eliminate the problem but tries to mitigate it. That's just my initial gut reaction though.

Any opinions?

RE: Current Limiting Reactors vs. Current Limiting Fuses

In my opinion, CLR is a better solution. Fuses will not give you any coordination. I am not sure on series rating on the MV equipment and if you will be able to achieve the correct ratings with the fuses.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

RE: Current Limiting Reactors vs. Current Limiting Fuses

Perhaps you should consider upgrading the existing switchgear as another option.

Anyway, just some thoughts:

CLR:
Advantage: Guaranteed to lower fault current
Disadvantage: May cause poor voltage regulation
-Possibly could be mitigated by auto tap changing transformer

Disadvantage: Will limit maximum power output of your generator
Disadvantage: May cause transient stability issues

CLF:
Advantage: No voltage problems
Advantage: Power output of generator isn't limited
Disadvantage: Not always guaranteed to lower fault level to an acceptable value
Disadvantage: May cause coordination issues with other protective devices
Disadvantage: Fuses allow for the possibility of single phasing


These are my inexperienced opinions, not facts.

RE: Current Limiting Reactors vs. Current Limiting Fuses

Go with the series reactors if the constant losses are acceptable, it is cheaper and faster solution, then you have the old plant and the new plant.

RE: Current Limiting Reactors vs. Current Limiting Fuses

Or you can do as many utilities do, and split the load.

Some utilities have fewer substations (conversions from a higher voltage to lower voltage) because they have sized there equipment to handle higher fault current. This is expencive.

What other utilities do is have more substations with limited capacity because each smaller substation has lower fault currents. The other advantage is the loss of a single substation effects fewer customers.

130 MW is a sizable generation capacity, and I would think distributing that much power at or below a typical distribution voltage (15 kV class, I am assuming) will only happen if you have some very large conductors, and large losses. At this point you should consiter steping the voltage higher to transport it about. So having step down points, or we call substations is not that far off. The step down transformer sizes and impedance is the best way to control your fault current levels so you don't have to purchase new switchgear for your existing plant. You will have to purchase new gear for the new part of the plant, but here again you can optomise switchgear cost by controlling your transformer impedance levels.

But what do I know about industrial plants, I'm a utility guy.

RE: Current Limiting Reactors vs. Current Limiting Fuses

(OP)
Thanks all for your responses so far. I did not consider the coordination issues with fuses so that's a good point that was brought up. Another consideration pointed out that I need to keep on top of are the losses in the reactors due to power flow between the old and new substations.

The generation for the new substation is designed to support the entire load of the new expansion during normal operations, so there will be very little flow to-from the old system in typical configurations. However, on start-up of the new system, we will need to "import" 25MW from the old system in order to power the starting motors for some Frame-7 gas turbines. The new generation consists of STGs and uses waste heat from the frame-7s + boilers.

Regarding a higher distribution voltage...it is certainly an option, however the added expense of all the stepping transformers will likely be a bit much. This is a very large and expansive industrial project where the power system is just but a small part. Luckily the bulk of the load is directly off the new primary generating substation in the form of 3-4 large 20-25MW motors, so there really isn't much distribution happening outside of the busbar in the switchgear, and cabling costs aren't as crucial as could be.

Interestingly enough, one of the competing EPCs in an earlier phase of the project did up the new distribution voltage to 34kV, though their design was even more power hungry than the winner (not them!).

RE: Current Limiting Reactors vs. Current Limiting Fuses

A duplex reactor might work for the interconnection. Imagine a center tap reactor with the generation feeding the middle and about equal loads on each end. The load currents in opposite directions cancel the magnetic field and reduce voltage drop. During a fault, current is in the same direction, inserting the impedance needed. Look up Paul Hamer's IEEE- IAS paper on the duplex reactor application.

Option 2 is to do both fuses and current limiting reactors. Use the high current ClIp fuses to short out the reactors, eliminating the voltage drop and power losses. If a high level fault occurs, the di/dt and overcurrent detection on the ClIp fuse trigger the fuse (explosive charges) inserting the reactor in the circuit in less than 1/2 cycle (usually 1/4 cycle if their literature and testing is to be believed). That keeps currents within downstream equipment ratings and allows current flow through the reactors for coordinated fault clearing. Only the affected portion of the plant is tripped.

RE: Current Limiting Reactors vs. Current Limiting Fuses

rcwilson,
have you seen an installation with your option 2?

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