Testing a transformer is a vital step in making certain the secure and environment friendly operation {of electrical} gear. Transformers play a significant function in energy distribution methods, and their correct functioning is important for the dependable supply of electrical energy to houses, companies, and industries. By conducting common exams, technicians can establish potential issues early on, stopping expensive breakdowns and making certain the longevity of the gear.
There are a number of totally different strategies for testing transformers, every with its distinctive benefits and drawbacks. The commonest check strategies embody 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 aren’t any insulation defects that might 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 related to a voltage supply, offering details about the transformer’s core losses and effectivity.
Along with these normal exams, there are additionally a number of specialised exams that may be carried out on transformers. These exams could also be essential to diagnose particular issues or to confirm the efficiency of the transformer below particular working circumstances. 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 circumstances. By utilizing a mixture of ordinary and specialised exams, technicians can acquire 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 establish any potential points that might result in gear failure. This inspection entails inspecting numerous facets of the transformer and its elements.
1. Exterior Examination
Start by inspecting the transformer’s exterior for any seen indicators of harm, equivalent to dents, cracks, rust, or corrosion. Verify the insulation for tears, cuts, or discoloration. Make sure that the transformer is clear and freed from particles, which may accumulate moisture and create a possible quick circuit hazard. Pay shut consideration to the next elements:
| Part | Key Inspections |
|---|---|
| Bushings | Verify 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 | Verify the oil stage 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 examine for any open or quick circuits, resistance exams 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 ought to be near the required values and balanced between phases. Deviations can point out doable winding injury or damaged connections.
Ratio Exams:
Ratio exams are performed to confirm the transformer’s turns ratio and examine for any inside faults or incorrect connections. A variable transformer or voltage injection gadget 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 required worth. If there’s a vital discrepancy, it might point out a shorted or open-circuited winding, misconnections, or a mismatch within the transformer’s design.
| Check | Objective | Tools Used |
|---|---|---|
| Resistance Check | Measure winding resistance and examine for open/quick circuits | Precision multimeter or micro-ohmmeter |
| Ratio Check | Confirm turns ratio and examine for inside faults or misconnections | Variable transformer or voltage injection gadget |
Winding Resistance Check
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 often carried out on each the first and secondary windings of the transformer.
Process
To carry out the winding resistance check, the next steps ought 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. Consult with the producer’s specs for the anticipated resistance values.
5. Examine the measured resistance values to the anticipated values. If the measured resistance values are considerably totally different from the anticipated values, it might point out an issue with the transformer windings.
Extra Info
The winding resistance check can be utilized to establish various 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 beneficial 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 Check
The turns ratio check is a typical 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.
- Establish the first and secondary windings.
- Join a voltmeter to the first winding and an ammeter in sequence with the secondary winding.
- Apply a identified voltage to the first winding and report 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 ought to be in comparison with the producer’s specified worth. If the calculated ratio deviates considerably from the required worth, it might point out an issue with the transformer’s windings.
Desk: Instance Measurement Outcomes
| Main Winding Voltage (V) | Secondary Winding Voltage (V) | Turns Ratio |
|---|---|---|
| 10 | 20 | 2 |
| 15 | 30 | 2 |
| 20 | 40 | 2 |
Dielectric Power Check
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 improve the voltage till a specified check stage is reached.
3. Monitor the present flowing via the transformer.
4. Report any indicators of insulation breakdown, equivalent 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. The next breakdown voltage signifies higher insulation high quality. |
| Leakage Present | The present flowing via the insulation in the course of the check ought 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 establish any potential insulation points.
Leakage Present Check
The leakage present check is designed to measure the present that flows via the insulation of a transformer when it’s not energized. A excessive leakage present studying could point out an issue with the insulation, which may 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 related to the transformer winding, and the leakage present is measured. The leakage present studying ought to be in comparison with the producer’s specs for the transformer.
There are a number of totally different strategies that can be utilized to carry out the leakage present check, together with:
| Methodology | 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 beneficial software for assessing the situation of a transformer’s insulation. By commonly performing this check, it’s doable to establish issues with the insulation early on and forestall 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 holding the secondary winding open-circuited. The facility consumed by the transformer below these circumstances 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 formulation 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 formulation Rc = V/Ie.
The excitation loss and core loss resistance are essential 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 beneath.
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 beneath. |
| 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 often within the vary of 1-3% of the rated output energy.
Impulse Check
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.
- Establish weak factors or defects within the insulation.
- Make sure the transformer’s reliability and security.
Process
1. Preparation:
The transformer is related to a check circuit comprising an impulse generator, surge arrester, and measuring gear.
2. Voltage Utility:
The impulse generator produces a high-voltage pulse with a selected waveform and amplitude. The heart beat is utilized throughout the transformer terminals, and its results are monitored.
3. Measurements:
Measurements are taken to find out the transformer’s voltage stand 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 needed.
Check Sorts
Completely different impulse check varieties will be carried out relying on the transformer’s software and necessities:
1. Full Wave:
The total wave impulse check simulates the results of a lightning strike. A constructive and destructive polarity pulse is utilized to the transformer terminals.
2. Chopped Wave:
The chopped wave impulse check is a modified model of the total 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.
Check Parameters
Essential check parameters embody:
- Voltage Amplitude: The utmost voltage of the utilized pulse.
- Waveform: The form and period of the utilized pulse.
- Polarity: The path of the voltage pulse (constructive or destructive).
Acceptance Standards
The transformer passes the impulse check if it meets the next standards:
- No insulation breakdown or flashover happens.
- The transformer’s voltage stand up to functionality meets the required necessities.
- The insulation resistance stays inside acceptable limits.
How To Check A Transformer
To check a transformer, you have to the next gear:
- A multimeter
- A voltage supply
- A set of check leads
Upon getting gathered your gear, 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 widespread terminal on the multimeter.
- Join the crimson 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 crimson 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 crimson 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 totally different from the secondary voltage, then the transformer could also be defective.
