How To Check Transformer Primary And Secondary?

Tools and Equipment Needed To Check Transformer Winding

Transformer windings are a very simply designed part of the transformer and they do not need much to check and inspect. You only need a 

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• Multimeter to check the voltage and current values across the winding.
• Insulation resistance tester to measure the insulation resistance between winding layers.
• Safety gear like electrically insulated gloves, and clear hard plastic goggles to protect yourself while working.

Safety Precautions Before Checking Winding

Your safety is the first and most important thing followed by the safety of the equipment and surrounding area. So only do the process after you have complete knowledge on how to check transformer primary and secondary winding and have all the necessary tools. Ensure following things before starting checking the transformer winding.

First, initially disconnect the transformer from its power source. This will eliminate the risk of any accidental electrical shocks or equipment damage during the checking process. 

Second, do a zero voltage check using a multimeter. Use a standard multimeter and check every input and output terminal of the transformer. There should be zero voltage reading on each of the terminals. 

Third, make sure of the proper grounding. Whether you remove the winding or keep it inside the transformer for check, make sure that the winding or the transformer has been properly grounded. Grounding redirects stray currents away from personnel, reducing the risk of accidents.

Fourth, never touch transformer parts without proper knowledge. Avoid all types of unnecessary touch of all transformer parts, specially live parts. With even power off, some parts can retain a residual charge or have capacitive effects. Always treat electrical equipment with caution and use insulated tools for added safety.

How To Identify Primary And Secondary Of Transformer

The primary and secondary winding of the transformer can be identified in a number of ways. Most easy and authentic way of checking this is to check the name plate attached to the winding. Most manufacturers have attached a name plate of primary or input on the primary winding and secondary or output to the secondary winding of the transformer. 

If your transformer winding is still connected to the transformer, then observe which winding is connected with the power source, that one will be primary winding and other will be secondary winding. 

If you have a winding from step down transformer which is most of the case in domestic appliances and installations. Then primary winding will be bulkier than the secondary winding. If you check the resistance with a multimeter, primary winding resistance will be higher than the secondary winding as primary has more wire turns than secondary.

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How To Check Transformer Primary And Secondary With Multimeter

Checking the transformer primary and secondary using a multimeter is very easy and requires the following steps. First make sure you have taken all safety steps mentioned above. 

• First step is to set up the multimeter to the resistance or continuity mode. Depending on the type of your multimeter, you either need to rotate the selection switch or place the red terminal in the resistance slot.
• Make sure the transformer winding is not connected to any power source.
• Place the terminals of the multimeter on the terminals of the winding. It does not matter which terminal is connected to which terminal of the winding. Just one terminal of the multimeter, one terminal of the winding and another with another terminal. 
• If you have selected the continuity mode, then if you hear a beep from the multimeter, then it's an indication that the winding circuit is closed.
• If you have selected resistance mode, then observe the resistance reading you see on the multimeter. 
• A functioning primary or secondary winding will show a moderate resistance value, depending on its design
• If the multimeter screen shows an infinite resistance value on the screen, then the winding has a broken wire, open circuit and needs repair.
• If a multimeter screen shows very low resistance that is resistance near to zero, then winding has a short circuit in it.

Advanced Techniques for Transformer Testing

Insulation Resistance Test

Insulation resistance test is done to check insulation between windings and between winding and core. This is a crucial test that ensures whether windings are good enough to work or need repair. To perform an Insulation resistance test follow the below mentioned steps.

• First make sure that the transformer is not connected to the power source.
• Make sure that all terminals of the winding are clean from any type of dust, oil or grease.
• Make sure that the insulation tester is working properly and has its terminal cleaned.
• To check the insulation between any of the winding and core.
• Take an insulation tester aka megohmmeter and connect its one terminal with the terminal of the winding you need to check.
• Connect the other terminal of the meter with either the core or the ground. 
• To perform inter-winding insulation testing, connect the probes between different winding terminals (e.g., primary to secondary).
• Now set the voltage of the meter according to the transformer specification. 
• Start the test by applying the specific voltage for a fixed duration that is for one minute.
• Megohmmeter will show the reading of resistance between the selection two connections.
• Value of this resistance will be Mega Ohm and should lie above the manufacturer's minimum acceptable insulation resistance standards.
• A resistance value in the range of hundreds of megohms indicates healthy insulation with minimal current leakage. This suggests the insulation is dry, intact, and capable of withstanding the applied voltage.
• A low resistance value (e.g., below 1 MΩ) indicates potential issues, such as moisture ingress or contamination.

More resource: How to test a power transformer?

Testing for Winding Polarity

Transformer winding polarity testing is important to check the phase relationship between primary and secondary winding. Winding can either be in phase or out of phase with each other and only in phase relationship between the winding is required. 

Follow the following steps to check the transformer winding polarity.

• First make sure the transformer and its winding is disconnected from all power sources.
• Label terminals of the winding, label P1 and P2 to the two terminals of the winding and S1 and S2 to the two terminals of the secondary winding.
• Set the multimeter to measure voltage.
• Now apply a low AC voltage to the two terminals of the primary winding. 
• Now use a multimeter to measure voltage at both primary winding and at secondary winding. To measure the voltage, attach a voltmeter in parallel to the winding terminal. Never attach it in series for measuring voltage. 
• Note down the primary and secondary winding voltage.
• You also need to measure the combined voltage of the transformer winding. To measure that, attach a red terminal to the incoming terminal on primary winding, let say P1 and black terminal to the outgoing terminal of secondary winding let say S2. 
• Note down the combined winding voltage.
• If the combined voltage of the winding is equal to the sum of the primary and secondary voltage, then your transformer windings are in phase.
• If the combined voltage of the winding is equal to the difference of the primary and secondary voltage, then your transformer windings are out of phase.

Importance of Checking Transformer Windings

As transformers work as the backbone of our electrical systems and their failure has to be prevented at every cost. Checking transformer winding offer following benefits

• Continuous checking of transformer winding helps detect and remove issues at early stages thus ensuring reliability in performance and operations.
• Addressing all issues at early stages prevent catastrophic failure of transformer or transformer explosion that can be dangerous for surrounding and connected equipment. 
• Continuous checking of transformer winding increases safety and reduces risk of hazards like electrical shock, fire, and short circuit between windings.
• Regular monitoring and maintenance of transformer windings prolong their service life, protecting your investment and avoiding the need for frequent replacements.

Conclusion

Transformers are vital components of electrical systems. Their regular winding checks ensure their reliability, safety, and longevity. Using tools like a multimeter and insulation tester, one can diagnose issues like open circuits, short circuits, or insulation breakdowns. Proper maintenance prevents catastrophic failures, enhances operational safety, and extends the transformer's service life.

Follow Up

Windings are the transformer's most crucial part and need continuous inspection and maintenance. Dealim’s offer best quality transformer windings of all types, sizes and capacity by following standards like ANSI, IEEE, CSA, AS, GOST, IEC, EU, and DIN/VDE. 

We have fully functional distribution and facility centers and a strong customer base in the USA, Europe, Canada, Australia, and all others around the globe. If you have any query about transformers, just Contact Us and we will talk you through the process.

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