{"id":27,"date":"2019-07-04T10:51:56","date_gmt":"2019-07-04T14:51:56","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/?post_type=chapter&p=27"},"modified":"2020-01-22T15:05:04","modified_gmt":"2020-01-22T20:05:04","slug":"additive-and-subtractive-polarity","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/chapter\/additive-and-subtractive-polarity\/","title":{"raw":"Additive and Subtractive Polarity","rendered":"Additive and Subtractive Polarity"},"content":{"raw":"

It's All about the Instantaneous Polarity!<\/h2>\r\nPolarity in an AC circuit is constantly changing direction and magnitude. When we talk about the polarity of a transformer, we mean an instantaneous polarity.\u00a0<\/span>\r\n\r\nThe high-voltage windings are always referred to as H1<\/sub> and H2<\/sub>.\u00a0<\/span>The low-voltage windings are always referred to as X1<\/sub> and X2<\/sub>.\u00a0<\/span>If we take an instantaneous polarity, H1<\/sub> and X1<\/sub> will always have the same polarity.\u00a0<\/span>\r\n\r\nTransformers are referred to as having either\u00a0additive<\/em>\u00a0polarity or\u00a0subtractive<\/em>\u00a0polarity. What this refers to is the relative position of high-voltage terminals with respect to the low-voltage terminals as they are brought out of the transformer case. Observing the transformer from the side where the low voltage terminals are brought out, H1<\/sub>\u00a0is always located on the left-hand side of the transformer, as shown in Figure 4. Then:<\/span>\r\n
    \r\n \t
  • If the X1<\/sub>\u00a0terminal is directly across from the H1<\/sub>\u00a0terminal, the transformer has subtractive polarity.<\/span><\/li>\r\n<\/ul>\r\n
      \r\n \t
    • If the X1<\/sub>\u00a0terminal sits diagonally across from the H1<\/sub>\u00a0terminal, the transformer has additive polarity.<\/span><\/li>\r\n<\/ul>\r\n[caption id=\"attachment_71\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 4. Additive and subtractive polarities[\/caption]\r\n\r\nSometimes we must determine the polarity of a transformer (the markings have worn off, for example).<\/span>\r\n
      AC Voltmeter Test<\/strong>\r\n<\/span><\/div>\r\n
      \r\n
        \r\n \t
      1. Identify which leads are H leads and which are X leads. This can be done from the gauge and insulation of the windings. High voltage (H), thinner wire, thicker insulation. Low voltage (X), thicker wire, thinner insulation.<\/span><\/span><\/li>\r\n \t
      2. Pick one terminal of the H windings and mark it as H1<\/sub>. The other terminal will be H2<\/sub> (Thanks to Captain Obvious!).<\/li>\r\n \t
      3. Place a jumper between H1<\/sub> and the adjacent X terminal.<\/li>\r\n \t
      4. Apply a voltage to the high side of the transformer. To be safe, keep the value relatively low.<\/li>\r\n \t
      5. Place a voltmeter between H2<\/sub> and the other X terminal. If the voltmeter has a subtractive polarity, the voltmeter will read the difference between the high-side voltage and low-side voltage. If the transformer has an additive polarity, the voltmeter will read the sum of the high-side voltage and low-side voltage.<\/li>\r\n<\/ol>\r\n \r\n\r\n[caption id=\"attachment_72\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 5. AC voltmeter test[\/caption]\r\n

        In summary:<\/span><\/p>\r\n\r\n

          \r\n \t
        • Using the turns ratio, we can put a lower voltage than rated on the primary.<\/span><\/li>\r\n \t
        • Place a jumper from one H lead to an X lead.<\/span><\/li>\r\n \t
        • Read the voltage across the two leads not jumped.<\/span><\/li>\r\n \t
        • If the voltage is the sum of the primary and secondary, then the transformer is additive.<\/span><\/li>\r\n \t
        • If the voltage is the difference of the primary and secondary, then the transformer is subtractive.<\/span><\/li>\r\n<\/ul>\r\n<\/div>","rendered":"

          It’s All about the Instantaneous Polarity!<\/h2>\n

          Polarity in an AC circuit is constantly changing direction and magnitude. When we talk about the polarity of a transformer, we mean an instantaneous polarity.\u00a0<\/span><\/p>\n

          The high-voltage windings are always referred to as H1<\/sub> and H2<\/sub>.\u00a0<\/span>The low-voltage windings are always referred to as X1<\/sub> and X2<\/sub>.\u00a0<\/span>If we take an instantaneous polarity, H1<\/sub> and X1<\/sub> will always have the same polarity.\u00a0<\/span><\/p>\n

          Transformers are referred to as having either\u00a0additive<\/em>\u00a0polarity or\u00a0subtractive<\/em>\u00a0polarity. What this refers to is the relative position of high-voltage terminals with respect to the low-voltage terminals as they are brought out of the transformer case. Observing the transformer from the side where the low voltage terminals are brought out, H1<\/sub>\u00a0is always located on the left-hand side of the transformer, as shown in Figure 4. Then:<\/span><\/p>\n

            \n
          • If the X1<\/sub>\u00a0terminal is directly across from the H1<\/sub>\u00a0terminal, the transformer has subtractive polarity.<\/span><\/li>\n<\/ul>\n
              \n
            • If the X1<\/sub>\u00a0terminal sits diagonally across from the H1<\/sub>\u00a0terminal, the transformer has additive polarity.<\/span><\/li>\n<\/ul>\n
              \"\"
              Figure 4. Additive and subtractive polarities<\/figcaption><\/figure>\n

              Sometimes we must determine the polarity of a transformer (the markings have worn off, for example).<\/span><\/p>\n

              AC Voltmeter Test<\/strong>
              \n<\/span><\/div>\n
              \n
                \n
              1. Identify which leads are H leads and which are X leads. This can be done from the gauge and insulation of the windings. High voltage (H), thinner wire, thicker insulation. Low voltage (X), thicker wire, thinner insulation.<\/span><\/span><\/li>\n
              2. Pick one terminal of the H windings and mark it as H1<\/sub>. The other terminal will be H2<\/sub> (Thanks to Captain Obvious!).<\/li>\n
              3. Place a jumper between H1<\/sub> and the adjacent X terminal.<\/li>\n
              4. Apply a voltage to the high side of the transformer. To be safe, keep the value relatively low.<\/li>\n
              5. Place a voltmeter between H2<\/sub> and the other X terminal. If the voltmeter has a subtractive polarity, the voltmeter will read the difference between the high-side voltage and low-side voltage. If the transformer has an additive polarity, the voltmeter will read the sum of the high-side voltage and low-side voltage.<\/li>\n<\/ol>\n

                 <\/p>\n

                \"\"
                Figure 5. AC voltmeter test<\/figcaption><\/figure>\n

                In summary:<\/span><\/p>\n

                  \n
                • Using the turns ratio, we can put a lower voltage than rated on the primary.<\/span><\/li>\n
                • Place a jumper from one H lead to an X lead.<\/span><\/li>\n
                • Read the voltage across the two leads not jumped.<\/span><\/li>\n
                • If the voltage is the sum of the primary and secondary, then the transformer is additive.<\/span><\/li>\n
                • If the voltage is the difference of the primary and secondary, then the transformer is subtractive.<\/span><\/li>\n<\/ul>\n<\/div>\n","protected":false},"author":422,"menu_order":4,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-27","chapter","type-chapter","status-publish","hentry"],"part":3,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapters\/27","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/wp\/v2\/users\/422"}],"version-history":[{"count":10,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapters\/27\/revisions"}],"predecessor-version":[{"id":244,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapters\/27\/revisions\/244"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapters\/27\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/wp\/v2\/media?parent=27"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/pressbooks\/v2\/chapter-type?post=27"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/wp\/v2\/contributor?post=27"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/wp-json\/wp\/v2\/license?post=27"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}