Hello, first time poster here.
Can somebody please tell me what the numbers next to 'Taps' mean. 2.5% means there is a 2.5% increment between taps, but what does the 4 and 2a, 2b mean?
https://gyazo.com/d6c949ad55d91e47c92297a06db98e63
p.s i dont know how to insert an image, when i click the insert image button it asks me for a url...
Thank you!!
What it means for there to be taps on a transformer, is the option to decide how many windings to engage on the primary coils. Suppose there are 40 windings (arbitrary number, that makes the math easy for us) that are engaged on the primary coil, at the nominal 600V primary voltage. Your transformer ratio between each pair of windings is from 600 to 120, which is 5:1. This means there are 8 windings on each secondary coil in this example. Each winding corresponds to 15 Volts, on both the primary and secondary in this example. You don't have taps on the secondary, so it will always be 8 windings. The primary by contrast, has the ability to adjust.
At the +5% tap setting, you engage two additional windings, to have 42 primary windings engaged. These windings are dead-end circuit sections which carry no current if you select a lower tap setting. The ratio becomes 42:8 instead of 40:8, so that you can compensate for the primary voltage being 630V instead of 600V like it is supposed to be.
Likewise, the +2.5% tap setting, engages just one additional winding beyond the nominal amount, for 41 windings engaged. The ratio becomes 41:8, to work with 615V primary voltage.
The -2.5% tap setting, disengages a winding, to get 39 windings engaged. The ratio becomes 39:8, to work with a 585V primary voltage.
Finally, the -5% tap setting, disengages a winding, to get 38 windings engaged. The ratio becomes 38:8, to work with a 570V primary voltage.
In all of the above cases, the secondary voltage is still 120V phase-to-neutral, with the taps allowing you to fine-tune the transformer to adapt to primary voltages that deviate from nominal.