A 1 and a 1 similarly, A 2 and a 2 are the terminals with identical instantaneous polarities. To make the things more clear, consider the two winding single phase transformer shown in Fig. If at any instant, the emf E 1 acts from A 2 to A 1 in the h. The polarity test is carried out as a routine test on all the transformers newly manufactured. This test is carried out to find the terminals having the same instantaneous polarity, assuming that the terminals are not marked.
When viewed from the h. A 1 being on the extreme right. Terminals A 1 and A 2 are assumed to have arbitrarily positive and negative instantaneous polarities. Now, A 1 is connected to one end of the secondary winding and a voltmeter is connected between A 2 and other end of the secondary winding as illustrated in Fig. A voltage of suitable value, say V 1 is then applied across the terminals of the h.
For instance, for an Edison screw light holder, it is significant that the connection of line conductor should be to the center terminal as well as the neutral conductor is allied to the external conductor. Likewise, it is significant to verify that switches are situated within the line conductor, not the neutral conductor. The polarity can be defined as the induced voltage direction in the two windings of the transformer namely primary as well as secondary. If the connection of two transformers can be done in parallel, then the polarity must be identified for the good connection of the transformer.
The importance of the polarity test is to make sure that all single-pole devices like switches, circuit breakers, and fuses are allied only in the phase conductor. We cannot trust the electricians always, because sometimes they can connect the things in the wrong way. As ac fixings comprise a Neutral and a live conductor, which is very significant that these two conductors are associated in the right way approximately, in all electrical devices like plugs or wall sockets.
For ensuring this, the test of polarity is done on every significant point. There are four different situations need this test. The polarity testing can be done using polarity testing methods which include the following. By using a visual check-up, the exact execution of cables connecting to core colors can be established.
Save my name, email, and website in this browser for the next time I comment. Skip to content Polarity means the direction of the induced voltages in the primary and the secondary winding of the transformer.
Leave a Comment Cancel Reply Your email address will not be published. The multimeter type method of finding the polarity is shown in the figure below. One can find the resistance of the windings and can conclude the polarity.
The Earth wire has a lower resistance compared to the Line. Earth wire has to maintain low resistance compared to the Line L to divert surge currents in the case of a short-circuit. The voltmeters V1 and V2 are connected across the primary and secondary windings of the transformer.
The voltmeter V1 measures the voltage across the primary winding whereas voltmeter V2 measures the voltage across the secondary winding respectively.
Apart from these two voltmeters, a third voltmeter V3 is connected across both the windings I,e primary winding and secondary winding. If V3 reads voltage as the summation of both V1 and V2 then, it is an additive type.
The polarity of the primary winding and the secondary winding is different. The terminals A1 and B2 have the same polarity whereas A2 and B1 have the same polarity. The figure which explains the Additive type polarity is shown in the figure below. If V3 reads voltage as the difference of both V1 and V2 then, it is as subtractive type.
The polarity of the primary winding and the secondary winding is the same. The terminals A1 and A2 have the same polarity whereas B1 and B2 have the same polarity. The figure which explains the subtractive type polarity is shown in the figure below.
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