Pagsulay sa Polarity sa Transformer – Diagrama sa Circuit ug Pamaagi sa Pag-obra

Polarity sa mga Two-Winding Transformers

Sa mga two-winding transformers, usa ka terminal sa winding adunay positibo sa uban sa tanang oras. Ang polarity sa transformer nagrefer sa relative direction sa induced voltages tali sa high-voltage (HV) ug low-voltage (LV) windings. Sa praktikal nga transformers, ang mga terminal sa winding ginaadto isip leads, ug ang polarity nagdefine kung pano niini gi-connect ug labeled.

Importansya sa Transformer Polarity

Ang pag-ila sa polarity kay importante para sa daghang operational ug engineering tasks:

• Instrument Transformer Connection (CTs and PTs):Ang maayo nga polarity nagpadayon sa accurate measurement sa current ug voltage sa power systems.

• Protective Relay Coordination:Ang maayo nga polarity importante aron moadto ang relays sa mga faults ug operasyon sa reliable way.

• Three-Phase Transformer Construction:Ang polarity nagdetermina kung pano gi-interconnect ang single-phase windings aron makabuo og three-phase configurations (e.g., delta o wye).

• Parallel Operation of Transformers:Ang mga transformers sa parallel operation kinahanglan na magka-identical ang polarity aron malikayan ang circulating currents ug magnetic flux cancellation.

Terminal Markings ug Polarity Identification

Kadaghanan mas clear ang paggamit og H1/H2 alang sa primary (HV) windings ug X1/X2 alang sa secondary (LV) windings aron mapakita ang polarity:

• H1 and H2: Markers sa primary winding terminals, nagsiling sa start ug end sa HV winding.

• X1 and X2: Corresponding markers sa secondary winding terminals (LV side).

Sa panahon sa polarity testing, ang mga labels niini makatabang identipikar:

• Ang instantaneous voltage relationship tali sa HV ug LV windings (e.g., ang H1 ug X1 "in-phase" kon additive ang polarity).

• Kon additive (series-aiding) o subtractive (series-opposing) ang polarity, na may impact sa pana sa pag-connect sa windings sa circuits.

Key Consideration

Ang sayop nga polarity makatabang sa:

• Faulty measurements sa instrument transformers.

• Malfunctioning protective relays.

• Excessive circulating currents o overheating sa parallel-connected transformers.

Sa pag-standardize sa clear terminal markings (H1/H2 ug X1/X2), ang mga engineers ug technicians makatabang sa proper transformer polarity, na nag-enhance sa safety, reliability, ug efficiency sa power systems.

Transformer Polarity
Ang dot convention (o dot notation) usa ka standard method gamiton aron mapakita ang polarity sa windings sa transformer.

Transformer Polarity ug Dot Convention

Sa Figure A, duha ka dots gitukod sa sama nga bahin sa primary ug secondary windings. Kini nagpakita nga ang current nga mosulod sa dotted terminal sa primary winding adunay sama nga direksyon sa current nga mogawas sa dotted terminal sa secondary winding. Kasagaran, ang voltages sa dotted ends in phase—kon positive ang voltage sa dotted point sa primary, positive usab ang voltage sa dotted point sa secondary.

Sa Figure B, ang dots gisugdan sa opisito nga bahin sa windings, nagpakita nga ang windings gipasabot sa opisito nga direksyon sa core. Ania, ang voltages sa dotted points out of phase: ang positive voltage sa primary’s dotted terminal naka-correspond sa negative voltage sa secondary’s dotted terminal.

Additive vs. Subtractive Polarity

Ang transformer polarity mahimong classify isip additive o subtractive. Aron matukod kung unsa ang applicable, iconnect ang usa ka terminal sa primary winding sa usa ka terminal sa secondary winding ug ibutang ang voltmeter sa remaining terminals sa both windings.

Additive Polarity

• Voltmeter Reading: Measures the sum of the primary voltage VA and secondary voltage VB, denoted as VC.

• Formula: VC = VA + VB.

• Winding Configuration: The windings are oriented such that their magnetic fluxes oppose each other when currents flow into the dotted terminals.

The circuit diagram of additive polarity is shown in the figure below.

Subtractive Polarity

In subtractive polarity, the voltmeter measures the difference between the primary voltage and the secondary voltage. Denoted as VC, the voltmeter reading is expressed by the equation:

The circuit diagram of subtractive polarity is shown in the figure below.

Circuit Diagram of Polarity Test

The circuit diagram of the polarity test is shown in the figure below.

Polarity Testing of Transformers

The primary winding terminals are denoted as A1, A2, and the secondary winding terminals as a1, a2. As shown in the figure, a voltmeter VA is connected across the primary winding, VB across the secondary winding, and VC between the primary terminal A1 and secondary terminal a1.

An autotransformer is used to provide a variable AC supply to the primary winding. All voltmeter readings are recorded under this configuration:

• If the voltmeter VC reads the sum of VA and VB, the transformer exhibits additive polarity.

• If VC reads the difference between VA and VB, the transformer exhibits subtractive polarity.

Polarity Test Using a DC Source (Battery)

The AC voltage method described above can be impractical for determining the relative polarity of two-winding transformers. A more convenient approach uses a DC source (battery), a switch, and a DC permanent-magnet voltmeter. The connection diagram for this method—including the correct battery polarity—is shown in the figure below.

A switch is connected in series with the primary winding. When the switch is closed, the battery is connected to the primary winding, allowing current to flow through it. This generates flux linkage in both windings, inducing electromotive force (EMF) in both the primary and secondary windings.

The induced EMF in the primary winding has a positive polarity at the end connected to the battery's positive terminal. To determine the secondary winding's polarity:

• If the DC voltmeter connected across the secondary winding shows a positive reading at the moment the switch is closed, the secondary terminal connected to the voltmeter's positive probe has the same polarity as the primary's positive terminal (i.e., the dotted terminals are correctly identified).

• If the voltmeter deflects to the negative side, the secondary terminal connected to the voltmeter's positive probe has opposite polarity to the primary's positive terminal.