{"id":38,"date":"2019-07-04T10:57:48","date_gmt":"2019-07-04T14:57:48","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/?post_type=chapter&p=38"},"modified":"2019-10-11T14:23:10","modified_gmt":"2019-10-11T18:23:10","slug":"multi-tap-transformers","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/singlephasetransformers\/chapter\/multi-tap-transformers\/","title":{"raw":"Multi-Tap Transformers","rendered":"Multi-Tap Transformers"},"content":{"raw":"

Some transformers compensate for line drop and percent voltage regulation by having multiple taps by which the volts\/turn ratio can be adjusted.<\/span><\/p>\r\n

In the image below, we have a transformer whose secondary is open. For all intents and purposes, there is very little current flowing in the primary (in this case we will say it is negligible). The .25\u03a9 resistance in the primary is the resistance of the winding. In this example, the supply voltage and the terminal voltage will be the same value. There is a potential secondary voltage of 120 volts but there is no current flowing in the secondary.<\/p>\r\n\r\n\r\n[caption id=\"attachment_122\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 17. Fully loaded open circuit[\/caption]\r\n

When current flows in the secondary circuit, things start to change. Total line drop in the primary circuit is 150 V due to the volt drop across the resistance of the primary circuit (75 V+ 75 V). This means that the terminal voltage applied to the primary of the transformer is only 1050 V. With the 10:1 turns ratio on the transformer, the secondary voltage is 105 V. This is 15 V lower than is desired.<\/span><\/p>\r\n\r\n\r\n[caption id=\"attachment_124\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 18. Fully loaded transformer[\/caption]\r\n

To compensate for the line drop, it would be lovely if we could reduce the turns ratio of the transformer to 9.5:1. Some transformers provide taps to do that.<\/span><\/p>\r\n\r\n\r\n[caption id=\"attachment_125\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 19. Multi-tap transformer[\/caption]\r\n