Polarity Test of Transformer and Lighting Circuit

The term polarity refers to the conductors in a DC circuit like positive or else negative conductors. In an electrical circuit, the flow of current direction is called as electrical polarity.  The flow of current will be from positive terminal to negative terminal, whereas electrons flow from the negative terminal to the positive terminal. In a DC circuit, the flow of current will be in one direction only where the one terminal is positive and other terminal is negative always. In an AC circuit, the two terminals change among positive and negative and the direction of electron flow sometimes turns around. A Polarity Test is used in the situation of electricity fixing to verify the exact line connection as well as neutral conductors. 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.

What is Polarity Test?

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.

Why do a Polarity Test?

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.

  • All the single-pole apparatus are connected only in the phase conductor.
  • This conductor should be allied to the center terminal of the lamp holder.
  • Every one polarity of socket channels like radial and ring should be confirmed.
  • The mains supply polarity must be right, by a tester of standard voltage.

How is Polarity Testing Done?

The polarity testing can be done using polarity testing methods which include the following.

1) Polarity Testing through Visual Inspection

By using a visual check-up, the exact execution of cables connecting to core colors can be established. It is necessary that polarity is verified visually throughout the procedure of fitting, particularly in cases where verifying with testing is not practical.

2) Polarity through Continuity Testing

If the above testing is not achievable, you must utilize an ohmmeter with low-resistance for this test. While you continually check radial as well as ring final circuits, a fraction of the procedure is to check and visually examine the polarity of permanent apparatus &outlets of the socket.

3) Live Testing of Polarity

If the above two methods are not potential due to necessity we can execute live testing of polarity with the standard GS38 voltage.

  • Check among LINE terminal as well as NEUTRAL terminal.
  • Check among LINE terminal as well as EARTH terminal.
  • Check among NEUTRAL terminal well as EARTH terminal.

The test device must specify full voltage among line neutral conductor & line earth conductor. No-voltage is noticed between Earth and Neutral.

Polarity Test of Transformer

There are two kinds of polarity test of transformer namely additive polarity as well as subtractive polarity.

Additive-Polarity

In this type of polarity, the voltage among the primary coil as well as the secondary coil of the transformer will be the sum of these two voltages. Here the voltage is denoted with Vc, whereas the primary coil is Va (high-voltage) and the secondary coil is Vb (low-voltage). Addictive polarity can be used for small-scale distribution transformers. The total voltage for an additive-polarity, we can get the following equation.

Vc = Va + Vb

Additive Polarity
Additive Polarity

 

Subtractive-Polarity

In this type of polarity, the voltage among the primary coil as well as the secondary coil of the transformer will be the subtraction of both the voltages. Here the voltage is denoted with Vc, whereas the primary coil is Va (high-voltage) and the secondary coil is Vb (low-voltage). Subtractive polarity can be used for large-scale transformers. The total voltage for a subtractive-polarity, we can get the following equation.

Vc = Va – Vb

Subtractor Polarity
Subtractor Polarity

Polarity Test of Transformer Circuit

Each terminal of the primary and secondary windings in a transformer are positive and negative as shown in the below circuit. The positive and negative terminals of the primary winding are A1, and A2, whereas the positive and negative terminals of the secondary winding are a1, and a2. The A1 terminal is connected to one part of the secondary winding, as well as a V3 voltmeter is connected among A2 and a2.

Polarity Test of Transformer
Polarity Test of Transformer
  • The polarity test diagram of transformer circuit is shown above; connect the circuit according to the above circuit with a Va-voltmeter across the primary winding, Vb-voltmeter across the secondary winding.
  • Note down the transformer ratings as well as the turn ration if accessible.
  • Connect a Vc-voltmeter among primary winding as well as secondary windings.
  • Give the voltage at the primary winding side, by checking the Vc-voltmeter value we can tell whether it is additive polarity or subtractive polarity.
  • If the analysis of the Vc-voltmeter shows the sum of the values of Va and Vb that is Vc = Va+Vb then the connection of this is said to be additive polarity.
  • If the analysis of the Vc-voltmeter shows the subtraction of the values of Va and Vb that is Vc = Va-Vb then the connection of this is said to be subtractive polarity.

Polarity Test of Lighting Circuit

A polarity test for lighting circuit must be done when new or after a change has been made. This test is to make sure that the phase-conductor is linked to the MCB or FUSE, & only pole switches, alternately the neutral. In the above figure, any type of Edison-Screw light holder must be verified for ensuring that the phase-conductor is associated with the center contact as well as the neutral to the contact of the screw.

polarity test of lighting circuit
Polarity Test diagram of a lighting circuit

Detach the fuse from the circuit or release MCB (miniature circuit breaker). Take away all lamps from the related circuit. Attach one finish of the long trailing terminal to the departing terminal of the MCB circuit.

By another end in combination by the test meter terminals, note down the readings from the phase lead at all the ends in the region of the circuit. For example, ES light holders stability at every end ensures that polarity is accurate. If the power supply is detached from the setting up, the long trailing terminal may be allied to the phase busbar & the miniature circuit breaker must be left in the position of ‘ON’.

polarity test of lighting circuit (2)
polarity test of a lighting circuit (2)

Thus, this is all about polarity test for transformer as well as a lighting circuit. We hope that you have got a basic idea about this concept. Furthermore, any queries on the topic of the polarity test please get back to us by commenting in the comment section below. Here is a question for you, what is the importance of the polarity test?

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