Please explain power districts

Feed your 2 blocks with one power source or transformer, and that's all that it feeds, it would be one power district.

I would consider a power district as one loop of track powered by one transformer like a PowerHouse 180, or one handle of a ZW-L or Z-4000. Blocks would be sections of track in that loop that are isolated from the other sections of track in the same loop.

Example for DCS wiring, you have one handle of your Z-4000 feeding one channel of your TIU and one loop of track that is 48 sections of track. Per the guide lines for DCS wiring you have 12 sections of track per block and four blocks in that one loop, isolated from the other blocks within that loop to form one power district.

I'm not an expert here, but this is the way I understand it, and I'm thinking in terms of MTH's DCS system which is what I started out with a few years ago. The two railers using DC and DCC may have different ideas?

OK, so let's add a second loop of track inside the first one.  If I power that with the other handle of the ZW or Z4000, that becomes power district number 2.  If I want to, I can divide that into 2 or 3 or whatever number I want blocks.  Am I getting it?

Yes, that's the way I understand it. I have exactly the same thing on my layout, two loops of track isolated from each other and each powered by a PH-180. Those are my power districts. On my layout each loop is divided into four blocks instead of two. It could be further complicated I'm sure, but I think that is the simple form of things.

Tom,

I believe a power district can be described as any section of track that is powered by its own power source. A power district can be made up of one long block or multiple blocks to ensure power is distributed evenly over the district or to support DCS. 

Lets say you have a large loop of track and you want to run several passenger trains at once on it.  If all these trains add up to more than 10 amps, one PH180 will not be enough to power all of them.  So if you try to run multiple trains on this loop and the PH180 CB keeps popping, you need to do something different. 

You can fix this two ways.  One is to get a transformer that puts out more than 10 amps.  Large single transformers are out there, but some do this by paralleling two PH180s to get a total of 20 amps to run the trains.  The problem is 20 amps is a lot and may damage your trains and/or electronic circuits in a derailment.  This is why, even with the new circuit protection that is available, some folks say to never use more than 10 amps.

The second way to run your multiple trains is to break the loop up into 3 or more power districts, each district powered by its own PH180.   For simplicity lets look at running two trains on the same track.  Break up the loop into three even length sections and power each section with its own PH180 (3 power districts).  These three power districts should be good enough to run two trains without getting both trains into the same power district at the same time, popping a PH180's CB.

Anyway, that is how I believe power districts are used to run our trains.

Tom,

The point of power districts is to distribute your power around the layout so that 1 or more power consuming trains (dual-motor locomotives, lit passenger cars, etc.) are not all hitting 1 power source.

Example 1:  Your mainline is divided into 4 districts.  You have 4 transformers or transformer taps.  You would power each district with a separate tap.

Example 2:  Your mainline is divided into 4 districts.  You have 2 transformers or transformer taps.  You power districts 1 & 3 with transformer 1.  You power districts 2 & 4 with transformer 2.  That way a train straddling two districts is receiving power from two sources.

Does that make sense?

George

Just reading the responses I've learned a lot.

This is valuable information as I plan my layout. 

I never gave this much thought until now.  I like the idea of a train straddling two districts receiving power from two sources.  This may be my best bet in order to run some of the long passenger trains I have planned.

Thank you all for the great information!

Yes, very valuable information!  But I seem to recall from other discussions that as the engine bridges two adjoining districts, they must be set to almost exactly the same voltage.  Otherwise, there will be an abrupt change in speed, and possible damage to electronics.

How true is this and is it important?

Tom H.  This only becomes a  problem if you stop the loco or illuminated cars so they bridge the gap, or if there is a major difference in voltage, or if there is a short in one of the districts (which will overload wires in the loco or car.  When there is such a bridge across power districts,  and voltages are different, there is in fact a short between the two hot outputs of the transformer.  Usually, it is for such a bried poeriod and with such a low voltage that there is no untoward result.  BUT, an operator should be aware of it and try to keep voltages as close as possible.

Power districts have another purposes besides distribution.  When operating conventionally, they permit independent control of trains.

If you are operating in Command as opposed to Conventional, crossing/bridging the insulator between two power districts is not a problem. In Command you have a fixed 18 volts in both power districts[or 16 volts,etc, if desired]. 

Not quite...see below.

Excellent description...

BINGO - give that man a cigar!

Visualize a large loop of track. On that loop you want to run TWO passenger trains with lighted cars and dual locomotives. That's going to be around 20 amps of total current to run both trains. You can't safely do that from a single power source. 20 amps is a LOT of current. If you have a derailment, something is going to be welded to the rail or melted before the breaker trips.

Now, divide that loop up into four equal length segments and power EACH SEGMENT with a SEPARATE power supply. That could be two Z-4000's, or four PH 180's or a mix of whatever you have. Each power supply should be capable of delivering 10 amps of power if needed. You now have four POWER DISTRICTS which is different from FOUR BLOCKS. You could have four blocks with each one powered from the SAME power source. This is different - you have four Power Districts and each district is powered from its own power source.

What happens when you run the trains? Let's start by assuming that the engines for train 1 are in Power District 1 (PD1) and the cars stretch back into PD4. As you run the train, the locomotive will eventually move into PD2, but the cars are all still in PD1. So the current load is now split between the PD1 and PD2 power sources. As the train moves along, more and more cars move into PD2, so the current load on the PD2 power source gradually goes up as more of the lighted cars enter PD2. However, before we reach the point where the whole train is in PD2, the engine moves into PD3. This drops the load on PD2 because the engine is now getting its power from PD3. The cycle is repeated and before the whole train is in PD3, the engine moves into PD4, etc. The other train is doing the exact same thing, moving from one PD to another as it moves around the loop, constantly dividing the load among the four power sources.

You should plan the length of your power districts to be about 2/3 of the length of your longest, lighted passenger train. If set at that length, you will never have more than 2/3 of a train being fed from a single power source.

Make sure all your power sources (ZW, Z4000, etc.) are all properly phased as well.  Click here to see more on phasing transformers.

Dewey, one caveat in command operation, if there is a hort in one district, excessive current will flow thorugh the internal wiring of any car or loco straddiling districts.  Internal wiring may be fine enough to restrict current enough that breakers don' open quickly, but they will get hot, as will roller springs.

Do you need phasing if you are running only command control?

Whenever you have 2 or more transformers on a layout, they must be phased regardless of what you're running.

thanks.