Basics of transformer technology
Measuring transformers are the basis for precise energy measurement in power grids. These technical components transform high voltages and currents into measurable quantities for downstream measuring instruments. The use of transformers enables the reliable recording of electrical parameters in high-voltage systems without exposing the measuring instruments directly to the high-voltage potential.
The accuracy of the transformers is particularly important. Even minimal deviations can lead to significant financial differences in energy billing. The technical design is based on the respective operating conditions – from the low-voltage range to the extra-high voltage level.
The way they work is based on the induction principle. Magnetic coupling enables the low-loss transmission of measured values. The latest converter technology also uses electronic components for signal processing and error correction.
Definition and operating principle of converters
Measuring converters work according to the transformer principle. The primary circuit records the variable to be measured, while the secondary circuit provides a proportionally reduced signal. The winding conditions and the magnetic properties of the core material are crucial for the measurement accuracy.
Current transformers convert high primary currents into low secondary currents. Voltage transformers reduce high voltages to measurable values. The transformation ratios are defined by standardised values. Typical secondary values are 1A or 5A for current transformers and 100V or 110V for voltage transformers.
The magnetic transfer behaviour is a decisive factor for the measurement accuracy. Non-linearities of the core material lead to amplitude and phase errors. Modern ferromagnetic materials minimise these effects by optimising the magnetic properties.
Types of transformers in energy supply
Protective transformers are used to quickly detect faults. They must provide a proportional output signal even at high overcurrents. Accuracy in the nominal range plays a subordinate role. What is crucial is the behaviour at short-circuit currents.
Measuring transformers for billing purposes require the highest precision in the nominal range. The accuracy classes range from 0.1 to 0.5 for precision measurements. Combined transformers combine protection and measurement functions in a single device, but require separate winding systems to do so.
Optical transformers use the Faraday effect for contactless measurement. They are particularly suitable for high-voltage applications, as there is no galvanic connection to the high-voltage potential. Digital signal processing enables additional diagnostic functions.
Normative basis for transformer testing
The technical requirements for instrument transformers are regulated by standards. Test specifications define standardised procedures for verifying measurement accuracy. International standards ensure comparability of measurement results across national borders.
Quality standards define minimum requirements for instrument transformers. Regular tests ensure compliance with the specified accuracy. Accredited testing laboratories perform calibration according to specified procedures.
Technical progress requires continuous adaptation of the standards. Working groups from industry and research develop new test specifications. Digital transformers require extended test procedures for the electronic components.
IEC standards for instrument transformers
IEC standards form the international framework for instrument transformers. The IEC 61869 standard defines the fundamental requirements for current and voltage transformers. Specific sub-standards cover various transformer types and applications.
Test specifications govern the performance of accuracy measurements. Tolerances for amplitude and phase are precisely defined. Environmental conditions during the test must be documented.
Standardisation also takes safety aspects into account. Insulation coordination and partial discharge measurements ensure safe operation. Type tests also include mechanical and climatic tests.
National regulations and standards
National standards supplement international standards. Technical connection requirements of grid operators define additional requirements. Calibration regulations govern use for billing purposes.
Test intervals are based on operational experience. Random sample tests supplement regular calibrations. Maintenance specifications ensure long-term measurement accuracy.
Certification bodies monitor compliance with the standards. Conformity assessments document standard-compliant design. Test reports form the basis for official approvals.
Test procedures and measurement technology
Modern test procedures use automated measurement sequences. High-precision reference converters serve as a comparative standard. Computer-aided evaluation enables direct error calculation.
Calibration equipment must be regularly traced. The measurement uncertainty is determined by statistical methods. Environmental influences on the measurement are mathematically corrected.
Test procedures follow defined work instructions. Measurements are carried out by qualified personnel. Plausibility checks ensure the quality of the results.
Routine tests
Routine tests ensure the quality of each individual transducer. The verification of the transformation ratio is carried out under various load conditions. Tolerance limits must be observed over the entire measuring range.
Standardised test procedures ensure reproducible results. Measuring the polarity prevents connection errors during operation. Insulation tests verify the electrical strength.
Test logs document all relevant measured values. Deviations from the target values are analysed. If limit values are exceeded, corrective measures must be initiated.
Type tests
Type testing validates new converter models. Comprehensive test series verify the behaviour under extreme conditions. Climatic tests simulate various environmental conditions.
Mechanical stress tests demonstrate the robustness. Short-circuit strength and thermal behaviour are examined. Partial discharge measurements show weak points in the insulation.
Additional tests are required for the development of digital converters. Electromagnetic compatibility must be verified. Software tests validate the implemented functions.
Measuring instruments and test equipment
Precision measuring instruments are at the heart of modern test equipment. Computer-controlled measuring systems enable automated test sequences. Climatic chambers simulate various environmental conditions.
High-precision reference transducers serve as a comparative standard. Calibration certificates document the traceability to national standards. Regular maintenance ensures the measuring accuracy of the test equipment.
The measurement data is recorded digitally at a high resolution. Special software automatically analyses the measurement results. Graphical representations make it easier to interpret the data.
Test parameters and limit values
Test parameters are based on the operating conditions. Measurement accuracy must be ensured throughout the entire operating range. Temperature effects are taken into account by means of correction factors.
Limit values define the maximum permissible deviations. Statistical evaluations reveal systematic errors. Control charts document long-term changes.
Linearity testing requires several measuring points. Hysteresis effects are recorded by means of upward and downward measurements. Repeat measurements increase statistical certainty.
Accuracy classes
Accuracy classes categorise transformers according to their precision. Classification is based on maximum errors under nominal conditions. Careful selection of the accuracy class reduces measurement uncertainties in energy billing.
Class 0.1 precision transformers are used for energy billing. Protection transformers tolerate larger measurement errors in favour of better overcurrent behaviour. Combined transformers combine different accuracy requirements in separate winding systems.
Climatic influences affect the measurement accuracy. Temperature coefficients describe the dependence on the ambient temperature. Compensation methods minimise temperature-related measurement errors.
Transformation errors and phase angles
Transformation errors describe the amplitude deviation from the nominal value. Phase angles quantify the phase shift between primary and secondary quantities. Both parameters influence the active power measurement.
Magnetic non-linearities cause load-dependent errors. Saturation effects occur particularly at high primary currents. Optimised core materials reduce magnetic losses.
Stray inductances influence the transmission behaviour. Capacitive couplings lead to phase errors at high frequencies. Design measures minimise parasitic effects.
Burden and burden influence
The burden describes the secondary load of the converter. High burdens worsen the measurement accuracy due to increased voltage drops. Electronic measuring instruments reduce the burden through high input impedances.
Burden-dependent errors arise from voltage drops. Long connecting lines increase the secondary burden. Correct dimensioning of the connecting lines minimises ohmic losses.
Standardised loads make it easier to compare test results. Test specifications define standardised load conditions. Real operating conditions must be taken into account during the design.
Documentation and certification
Structured documentation ensures that the tests can be reproduced. Digital archiving enables quick access to historical data. Audit-proof storage meets legal requirements.
Comprehensive documentation forms the basis for certification. Quality management monitors compliance with processes. External audits confirm standard-compliant implementation.
Standardised report formats simplify evaluation. Graphical representations clearly visualise measurement results. Trend analyses enable early error detection.
Test logs and reports
Test logs document all relevant measurement parameters. Unique identification of the test objects through serial numbers ensures traceability. Environmental conditions during the test are included in the evaluation.
Detailed measurement recording enables later analyses. Automatic plausibility checks detect measurement errors early on. Graphical evaluations clarify the relationships between different parameters.
Test reports provide a clear summary of the results. Deviations from target values are specially marked. Recommendations for corrective measures are based on the measurement results.
Certification process
Certifications confirm compliance with defined standards. Accredited test laboratories carry out independent assessments. Regular surveillance audits ensure consistent quality.
Conformity assessments verify compliance with standards. Technical documentation proves that the product has been manufactured in accordance with the standards. Certificates document successfully completed tests.
Quality management systems monitor the processes. Internal audits identify potential for improvement. Corrective measures are implemented systematically.
Safety aspects of transformer testing
Safety concepts minimise hazards during testing. High voltages require special protective measures. Trained personnel consistently follow safety regulations.
Test stations have redundant safety systems. Automatic shutdown prevents hazards. Warning devices signal active high voltage.
Work approval procedures regulate test procedures. Safety training is provided to employees on a regular basis. Emergency plans define measures to be taken in the event of an incident.
Personal protective equipment
Insulating protective equipment protects against electrical hazards. Voltage-resistant gloves enable safe working. Face protection prevents injuries caused by electric arcs.
Regular testing of protective equipment ensures functionality. Damaged equipment is replaced immediately. Documented visual inspection before each use.
Ergonomic design facilitates longer work. Climate-controlled protective clothing prevents overheating. Freedom of movement is maintained despite protective equipment.
Occupational safety guidelines
Occupational safety guidelines define mandatory safety standards. Hazard assessments systematically identify potential risks. Protective measures are based on the level of risk.
Operating instructions govern safe workflows. Employee training is documented. Regular refresher courses keep knowledge up to date.
Safety officers monitor compliance with the regulations. Reporting systems record near-miss incidents for prevention. Sharing experiences continuously improves safety standards.
Maintenance and servicing
Scheduled maintenance ensures reliable operation of test equipment. Calibration intervals are based on manufacturer specifications. Wear parts are proactively replaced.
Maintenance concepts take operational requirements into account. Maintenance plans coordinate necessary work. Spare parts management ensures quick repairs.
Documented maintenance enables traceability. Digital maintenance calendars remind you of work that is due. Test equipment monitoring ensures availability.
Maintenance intervals
Maintenance intervals are based on operating experience. Load-dependent maintenance optimises intervals. Condition-based maintenance uses diagnostic data.
Preventive maintenance avoids unplanned downtime. Wear indicators signal the need for maintenance. Trend analyses enable forward-looking planning.
Documented maintenance history supports fault analysis. Empirical values are incorporated into maintenance optimisation. Cost efficiency through adapted intervals.
Fault detection and elimination
Systematic fault finding uses structured procedures. Diagnostic tools support localisation. Fault documentation enables statistical evaluations.
Experienced technicians recognise error patterns. Checklists standardise the error search. Repair instructions describe the necessary steps.
Spare parts supply minimises downtime. Quality control after repairs ensures functionality. An error database provides support in similar cases.
Conclusion and recommendations
Transformer testing ensures a reliable energy supply. Standardised implementation guarantees valid results. Qualified personnel are the basis for successful testing.
Regular training courses keep expertise up to date. Exchanging experiences promotes continuous improvement. Documented processes ensure traceability.
Investments in modern testing technology pay off. Automation sustainably increases efficiency. Future-oriented concepts take technological developments into account.