Testing a transformer is a vital step in making certain the protected and environment friendly operation {of electrical} tools. Transformers play an important function in energy distribution techniques, and their correct functioning is important for the dependable supply of electrical energy to properties, companies, and industries. By conducting common checks, technicians can determine potential issues early on, stopping expensive breakdowns and making certain the longevity of the tools.
There are a number of completely different strategies for testing transformers, every with its distinctive benefits and downsides. The most typical check strategies embrace insulation resistance testing, turns ratio testing, and excitation present testing. Insulation resistance testing measures the resistance between the transformer’s windings and the core, making certain that there are not any insulation defects that would result in electrical shorts. Turns ratio testing verifies the accuracy of the transformer’s winding ratios, which is important for correct voltage regulation. Excitation present testing measures the present drawn by the transformer when it’s linked to a voltage supply, offering details about the transformer’s core losses and effectivity.
Along with these commonplace checks, there are additionally a number of specialised checks that may be carried out on transformers. These checks could also be essential to diagnose particular issues or to confirm the efficiency of the transformer below particular working situations. For instance, a dielectric power check measures the transformer’s potential to resist excessive voltage, whereas a load check measures the transformer’s efficiency below load situations. By utilizing a mix of normal and specialised checks, technicians can get hold of a complete understanding of the transformer’s situation and guarantee its dependable operation.
Visible Inspection
Earlier than energizing a transformer, it’s essential to conduct an intensive visible inspection to determine any potential points that would result in tools failure. This inspection entails analyzing numerous elements of the transformer and its elements.
1. Exterior Examination
Start by inspecting the transformer’s exterior for any seen indicators of injury, akin to dents, cracks, rust, or corrosion. Test the insulation for tears, cuts, or discoloration. Be certain that the transformer is clear and freed from particles, which may accumulate moisture and create a possible brief circuit hazard. Pay shut consideration to the next elements:
| Part | Key Inspections |
|---|---|
| Bushings | Test for cracks, leaks, or unfastened connections. |
| Tank | Examine for dents, leaks, or rust. |
| Cooling System | Confirm correct operation of followers, radiators, or different cooling mechanisms. |
| Conservator | Test the oil degree and situation, and examine for leaks. |
| Grounding Connections. | Guarantee all grounding connections are safe and freed from corrosion. |
Resistance and Ratio Exams
Resistance Exams:
To find out the winding resistance and verify for any open or brief circuits, resistance checks are carried out. A precision multimeter or micro-ohmmeter is used to measure the resistance between every winding terminal and the impartial level, in addition to between phases.
The measured resistances needs to be near the desired values and balanced between phases. Deviations can point out attainable winding harm or damaged connections.
Ratio Exams:
Ratio checks are performed to confirm the transformer’s turns ratio and verify for any inside faults or incorrect connections. A variable transformer or voltage injection machine is used to use a voltage to the first winding whereas measuring the corresponding voltage on the secondary winding.
The calculated turns ratio ought to match the desired worth. If there’s a vital discrepancy, it could point out a shorted or open-circuited winding, misconnections, or a mismatch within the transformer’s design.
| Take a look at | Objective | Gear Used |
|---|---|---|
| Resistance Take a look at | Measure winding resistance and verify for open/brief circuits | Precision multimeter or micro-ohmmeter |
| Ratio Take a look at | Confirm turns ratio and verify for inside faults or misconnections | Variable transformer or voltage injection machine |
Winding Resistance Take a look at
The winding resistance check measures {the electrical} resistance of the transformer windings. It’s carried out utilizing a low-voltage ohmmeter or a megohmmeter. The check is usually carried out on each the first and secondary windings of the transformer.
Process
To carry out the winding resistance check, the next steps needs to be adopted:
1. Disconnect the transformer from all energy sources.
2. Discharge the transformer by shorting the terminals collectively.
3. Join the ohmmeter or megohmmeter to the transformer windings.
4. Measure the resistance of the windings between every terminal and the impartial terminal. Seek advice from the producer’s specs for the anticipated resistance values.
5. Evaluate the measured resistance values to the anticipated values. If the measured resistance values are considerably completely different from the anticipated values, it could point out an issue with the transformer windings.
Extra Data
The winding resistance check can be utilized to determine a variety of issues with transformer windings, together with:
- Open circuits
- Quick circuits
- Floor faults
- Free connections
The winding resistance check is a comparatively easy and cheap check that may present priceless details about the situation of transformer windings.
| Sort of Transformer | Anticipated Resistance Values |
|---|---|
| Single-phase transformer | Lower than 5 ohms |
| Three-phase transformer | Lower than 10 ohms |
Turns Ratio Take a look at
The turns ratio check is a standard technique for testing the integrity of a transformer’s windings. It entails measuring the ratio of the variety of activates the first winding to the variety of activates the secondary winding. The ensuing ratio ought to match the producer’s specified worth.
Process:
- Disconnect the transformer from the facility provide.
- Determine the first and secondary windings.
- Join a voltmeter to the first winding and an ammeter in sequence with the secondary winding.
- Apply a recognized voltage to the first winding and file the corresponding present within the secondary winding.
- Repeat steps 3 and 4 for various voltage ranges.
Evaluation:
The turns ratio is calculated by dividing the secondary winding’s voltage by the first winding’s voltage. The calculated ratio needs to be in comparison with the producer’s specified worth. If the calculated ratio deviates considerably from the desired worth, it could point out an issue with the transformer’s windings.
Desk: Instance Measurement Outcomes
| Major Winding Voltage (V) | Secondary Winding Voltage (V) | Turns Ratio |
|---|---|---|
| 10 | 20 | 2 |
| 15 | 30 | 2 |
| 20 | 40 | 2 |
Dielectric Energy Take a look at
The dielectric power check assesses the insulation’s potential to resist excessive voltage with out breaking down. It determines the transformer’s resistance to insulation failure attributable to electrical stress.
Process:
1. Join the transformer’s terminals to a high-voltage tester.
2. Steadily enhance the voltage till a specified check degree is reached.
3. Monitor the present flowing by way of the transformer.
4. File any indicators of insulation breakdown, akin to sparking or arcing.
5. Cut back the voltage and disconnect the transformer from the tester.
6. Measurement and Interpretation:
The dielectric power check outcomes are analyzed within the following steps:
| Measurement | Interpretation |
|---|---|
| Breakdown Voltage | The voltage at which the insulation fails signifies the transformer’s dielectric power. A better breakdown voltage signifies higher insulation high quality. |
| Leakage Present | The present flowing by way of the insulation throughout the check needs to be minimal. Extreme leakage present suggests insulation degradation or contamination. |
| Insulation Resistance | The resistance provided by the insulation will be measured utilizing a megohmmeter. Excessive insulation resistance signifies good insulation high quality. |
The dielectric power check outcomes assist decide the transformer’s health for service and determine any potential insulation points.
Leakage Present Take a look at
The leakage present check is designed to measure the present that flows by way of the insulation of a transformer when it’s not energized. A excessive leakage present studying might point out an issue with the insulation, which might result in transformer failure.
To carry out the leakage present check, the transformer is remoted from all electrical sources and grounded. A voltage supply is then linked to the transformer winding, and the leakage present is measured. The leakage present studying needs to be in comparison with the producer’s specs for the transformer.
There are a number of completely different strategies that can be utilized to carry out the leakage present check, together with:
| Technique | Description |
|---|---|
|
DC leakage present check |
A DC voltage supply is used to cost the transformer insulation. The leakage present is then measured after a time frame. |
|
AC leakage present check |
An AC voltage supply is used to cost the transformer insulation. The leakage present is then measured on the frequency of the utilized voltage. |
|
Ratiometric leakage present check |
This technique makes use of a ratiometer to check the leakage present of a check transformer to the leakage present of a reference transformer. |
The leakage present check is a priceless device for assessing the situation of a transformer’s insulation. By frequently performing this check, it’s attainable to determine issues with the insulation early on and stop transformer failure.
Excitation Loss Measurement
Excitation loss measurement determines the no-load losses of a transformer. It entails making use of a voltage to the first winding whereas conserving the secondary winding open-circuited. The facility consumed by the transformer below these situations is the excitation loss, which is the sum of hysteresis and eddy present losses within the core.
Process:
- Join the transformer to a variable AC voltage supply.
- Measure the voltage (V) and present (I) on the major terminals.
- Calculate the facility (P) consumed by the transformer utilizing the system P = VI.
- Repeat steps 2-3 for various voltage ranges.
- Plot a graph of excitation energy (P) versus voltage (V).
- The excitation loss is the intercept of the graph on the facility axis (V = 0).
- Measure the excitation present (Ie).
- Calculate the core loss resistance (Rc) utilizing the system Rc = V/Ie.
The excitation loss and core loss resistance are necessary parameters for evaluating the effectivity and thermal stability of a transformer.
Desk: Excitation Loss Measurement Outcomes
| Voltage (V) | Present (I) | Energy (P) |
|---|---|---|
| 100 | 0.1 | 10 |
| 200 | 0.2 | 40 |
| 300 | 0.3 | 90 |
Load Loss Measurement
Load loss is the sum of copper and stray losses within the transformer. It’s measured by making use of a rated load to the secondary and measuring the facility enter to the first. The distinction between the enter and output energy is the load loss.
The next steps are concerned in load loss measurement:
1. Join the transformer as proven within the diagram under.
2. Apply a rated load to the secondary.
3. Measure the facility enter to the first.
4. Calculate the load loss because the distinction between the enter and output energy.
| Step | Description |
|---|---|
| 1 | Join the transformer as proven within the diagram under. |
| 2 | Apply a rated load to the secondary. |
| 3 | Measure the facility enter to the first. |
| 4 | Calculate the load loss because the distinction between the enter and output energy. |
The load loss will be expressed as a proportion of the rated output energy:
“`
Load loss (%) = (Enter energy – Output energy) / Rated output energy * 100
“`
The load loss is usually within the vary of 1-3% of the rated output energy.
Impulse Take a look at
The impulse check is a high-voltage check used to guage the insulation power of transformers. It entails making use of a high-voltage, short-duration pulse to the transformer’s terminals, simulating the results of lightning strikes or different transient overvoltages.
Objective
The impulse check goals to:
- Confirm the insulation’s potential to resist high-voltage surges.
- Determine weak factors or defects within the insulation.
- Make sure the transformer’s reliability and security.
Process
1. Preparation:
The transformer is linked to a check circuit comprising an impulse generator, surge arrester, and measuring tools.
2. Voltage Utility:
The impulse generator produces a high-voltage pulse with a selected waveform and amplitude. The heartbeat is utilized throughout the transformer terminals, and its results are monitored.
3. Measurements:
Measurements are taken to find out the transformer’s voltage face up to functionality, insulation resistance, and different parameters.
4. Evaluation:
The check outcomes are analyzed to guage the transformer’s insulation power and detect any potential defects. If defects are discovered, repairs or insulation upgrades could also be mandatory.
Take a look at Varieties
Completely different impulse check sorts will be carried out relying on the transformer’s utility and necessities:
1. Full Wave:
The total wave impulse check simulates the results of a lightning strike. A constructive and unfavorable polarity pulse is utilized to the transformer terminals.
2. Chopped Wave:
The chopped wave impulse check is a modified model of the complete wave check. The voltage pulse is truncated or chopped at a selected time, offering further details about the transformer’s insulation power.
3. Switching Impulse:
The switching impulse check is used to guage the transformer’s potential to resist the transient overvoltages that happen throughout switching operations.
Take a look at Parameters
Necessary check parameters embrace:
- Voltage Amplitude: The utmost voltage of the utilized pulse.
- Waveform: The form and length of the utilized pulse.
- Polarity: The route of the voltage pulse (constructive or unfavorable).
Acceptance Standards
The transformer passes the impulse check if it meets the next standards:
- No insulation breakdown or flashover happens.
- The transformer’s voltage face up to functionality meets the desired necessities.
- The insulation resistance stays inside acceptable limits.
How To Take a look at A Transformer
To check a transformer, you will want the next tools:
- A multimeter
- A voltage supply
- A set of check leads
After getting gathered your tools, you’ll be able to comply with these steps to check a transformer:
- Set the multimeter to the AC voltage setting.
- Join the black check result in the frequent terminal on the multimeter.
- Join the purple check result in the AC voltage terminal on the multimeter.
- Join the black check result in one of many major terminals on the transformer.
- Join the purple check result in the opposite major terminal on the transformer.
- Learn the voltage on the multimeter. That is the first voltage.
- Disconnect the black check lead from the first terminal of the transformer.
- Join the black check result in one of many secondary terminals on the transformer.
- Join the purple check result in the opposite secondary terminal on the transformer.
- Learn the voltage on the multimeter. That is the secondary voltage.
If the first voltage is considerably completely different from the secondary voltage, then the transformer could also be defective.
