Overview

Safe Harbor Statement
I really don’t know what I am doing. The following is based on searching the internet and talking to those that have worked the industry. The problem is that I am trying to translate this to a model. Just how successful I am at that is up to discussion.

Note: My understanding of this subject is very slight. This is a WordPress page which means people can make comments. You can make corrections, link or add better drawings. You can tell me what is wrong and make CORRECTIONS. Please do so.

The idea for this is simple. We modelers are not going to be sending current through our miniatures of course . .but it would make me happy to wire up our models correctly.

I simply want .. as a modeler .. to logically wire transformers to my structures. I found this YouTube page – Northwest Lineman College – which has what looks to me like really good information. If someone who is “in the know” .. could translate this into simple diagrams that we modelers could use and even understand would be a ‘good thing’. I suppose what I really would like is a matrix showing wires coming in .. single, dual, triple, quad primary and then the various secondary lines .. why we might want different primary lines .. what we need for the secondary’s.

Single-phase transformer to 7200V primary with 120/240V secondary

Fig_4-1 – Single-phase transformer connected to 7200V primary and neutral (connected to H2) with three-wire 120/240V secondary.

The neutral can be below the transformer or in some areas with lots of lightening above the primary to act as a lightening arrestor.

Single-phase transformer to 7200V primary with 120/240V secondary

Fig_4-2 – Single-phase transformer with one bushing that connects to one single-phase primary 7200V.
Center tap grounded to earth ground.

Provides three-wire 120/240V to the system

One reason I like this is because I managed to break a bushing off of a couple of the transformers.

Single-phase transformer to a three- phase 2,400-volt three-wire ungrounded delta primary voltage system

Single-phase distribution transformers are manufactured with one or two primary bushings. The single-primary-bushing transformers can be used only on grounded wye systems if they are properly connected.

Figure 4-16 schematically shows the connections of a single-phase transformer to a three- phase 2,400-volt three-wire ungrounded delta primary voltage system to obtain l20-volt single-phase two-wire secondary service.

The connections for similar systems operating at other primary distribution voltages such as 4,800, 7,200. 13,200, and 34,400 would be identical.

Single-phase transformer to a three-phase three-wire ungrounded delta primary voltage system to obtain120/240-volt single-phase three-wire service

Figure 4-17 shows the proper connections for a single-phase transformer to a three-phase three-wire ungrounded delta primary voltage system to obtain 120/240-volt single-phase three-wire service.
Normally the wire connected to the center low-voltage bushing will be connected to ground. Grounding the wire connecting to the center bushing limits thevoltage above ground to 120 volts, even though the wires connecting to the outside secondary bushings have 240 volts between them.

Single-phase distribution transformer connections to a three-phase four-wire wye grounded neutral primary system rated 4,160Y/2,400 volts to obtain 120/240-volt single-phase secondary service

Figure 4-18 schematically shows the single-phase distribution transformer connections to a three-phase four-wire wye grounded neutral primary system rated 4,160Y/2,400 volts to obtain 120/240-volt single-phase secondary service.
The three-phase four-wire wye grounded neutral system has voltage between phases equal to the phase or line to neutral voltage multiplied by 1.73.

In figure 4-18, the primary system line to neutral voltage is 2,400 vots, and the voltage between phases is 1.73 times 2,400, or 4,160 volts.

This system is designated as a 4,160Y/2,400-volt system. Other standard three-phase four-wire wye grounded neutral primary system voltages are 8,320Y/4,800, 12,470Y/7,200, 13,200Y/7,620, and 13,800Y/7,970.

Three single-phase distribution transformers connected to a three-phase three-wire ungrounded delta primary-voltage system to obtain three-phase three-wire delta secondary service

Figure 4-21 shows the proper connections for three single-phase distribution transformers connected to a three-phase three-wire ungrounded delta primary-voltage system to obtain three-phase three-wire delta secondary service.
The illustration is for a 2,400-volt primary system and voltages would be connected the same. Single-phase transformers with secondary windings constructed for voltage of 240/480 should be used to obtain 480-volt three-phase secondary service.