Transformer short-circuit testing

Transformer short-circuit testing setup

Transformer prototypes are performance tested prior to production (type testing). Once manufactured, transformers are tested before commissioning to confirm compliance with normative and regulatory requirements (acceptance testing). Load loss tests are part of routine and acceptance tests specified by the international standard IEC 60076.

Short-circuit testing determines the copper losses of a power transformer when operating under full load short-circuit conditions. The primary side of the power transformer is (apart from the AC source supply) connected to the power analyzer, while the secondary side (all phases) is short-circuited. A transformer that exhibits high copper loss is less efficient, dissipating energy by generating wasted heat. It is also at greater risk of failure due to overload and overheating.

Precise transformer copper loss measurement verifies whether a power transformer can perform as specified under the rated current.

Open-circuit testing of transformers under no-load conditions

While load losses only occur when a transformer is operating under load, no-load losses occur whenever it is powered, regardless of the load. In addition to performing a short-circuit test to obtain a transformer copper loss measurement, an open-circuit test measures the iron loss under no-load conditions. The power analyzer is connected on the primary, high-voltage side of the transformer, and the secondary side remains open, without any load connected.

Learn more about transformer open-circuit testing

Short-circuit testing for transformer load-loss determination

Copper losses occur whenever transformer windings are under load. These losses are primarily caused by their internal resistance increasing when load is applied. Measuring the total load (copper) loss at rated current determines a transformer’s efficiency and energy loss under full loads.

Multi-channel testing captures the following for each individual phase and the overall system in a single setup:

• Power: Measures short-circuit power, per phase and overall, to determine copper losses at full rated load
• Current: Measured the applied current, per phase, to confirm when the transformer's rated current is reached
• Voltage: Measures the operating voltage, per phase, as current is raised up to the rated value
• Impedance: Measures per-phase and total impedance across the full test range to characterize both individual and system-level behavior

Reasons for transformer copper loss

Load losses cannot be eliminated entirely, but transformer design can be optimized to maximize efficiency and minimize energy loss.

Copper loss is increased by:

• Resistance of the conductor: The purpose of the copper conductor is to conduct the electrical current. Conductor windings of higher resistance material, smaller cross-sectional area and longer length increase load losses.
• Magnitude of the load current: Since load losses grow proportionally to the square of the load, a higher current increases the copper loss.
• Operating temperature: A higher temperature of the windings increases resistance and load losses.

Challenges in transformer short-circuit testing

Manufacturers are continually improving their designs and adopting new materials to produce even more reliable transformers with lower losses. At the same time, standards, specifications and regulations are becoming increasingly demanding. The ongoing quest for more efficient transformers to support the global energy transition poses a multitude of challenges in short-circuit testing:

• Capturing a wide range of electrical parameters, including power, current, voltage and frequency, in one measurement setup
• Acquiring precise measurements through a multifunctional tool to enable detailed analysis in time and frequency domain
• Complying with international standards like IEC 60076
• Calculating corrected short-circuit power loss due to temperature variations from specified reference winding temperature
• Simultaneous measurement and evaluation of both phase-specific and total impedance
• Audit-compliant test documentation
• Data export compatible with third-party applications

Our solution for transformer short-circuit testing

Manufacturers and test laboratories rely on the LMG671 Precision Power Analyzer for precise and comprehensive short-circuit testing. It offers flexible multi-channel measurement and delivers standards-compliant data for accurate, comprehensive and time-efficient power transformer testing.

Manufacturers and test laboratories can use one precision power analyzer as a single measurement platform to measure all relevant and mandatory data that would otherwise require a series of several conventional instruments like a power meter, an oscilloscope, a digital multimeter and a data logger.

• Up to seven power measurement modules measure the voltages, currents and power of all phases for full connectivity.
• A process signal interface (PSI) collects additional data relevant to the environmental test conditions, such as temperature, humidity, and vibration.
• Measurements are highly accurate across a wide dynamic current range.
• Pre-configurable measurement menus for no-load and short-circuit tests can be loaded and customized by the user to simplify testing procedures.
• Optional star-delta computation software L6-OPT-SDC calculates accurately phase-specific power values for various transformer connection configuration
• Test results are standardized, reliable and comparable.