How are the deviation values of transformer parameters and the parameters using peak values specified?

The specifications for evaluating the performance parameters of transformers are determined by technical conditions, and each standard value has corresponding deviation values, which can be categorized into several types:

(1) Parameters with only a lower limit specified, without an upper limit, where larger values are better:

a. Absorption ratio, insulation resistance; b. Distance between bushings with voltage; c. Insulation withstand capability; d. Local discharge test time and frequency, AC withstand voltage test time and frequency; e. Electrode surface; f. Number of impulse short-circuit tests; g. Number of impact tests; h. Electrical and mechanical lifespan of on-load tap changers.

(2) Parameters with only an upper limit specified, without a lower limit, where smaller values are better:

a. No-load losses, load losses; b. No-load current; c. Total losses; d. Temperature rise of windings and top oil surface; e. Dielectric loss ratio; f. Noise level; g. Local discharge quantity; h. Winding hotspot temperature rise; allowable temperature during short circuit; i. Over-excitation capability; j. Water and gas content in oil, oil dielectric strength; k. Power factor of wattmeter during loss measurement.

(3) Parameters with both upper and lower limits specified:

a. Impedance voltage; b. Voltage ratio; c. Waveform and peak value of impulse voltage; d. Unbalanced resistance.

(4) Parameters with no deviation requirements:

a. Zero-sequence impedance; b. Harmonic analysis of no-load current; c. Power consumption of auxiliary fan motors and pumps; d. Inrush current.

(5) Standard values that are allowed to be calibrated:

a. High altitude temperature rise limit; b. Impedance voltage and load loss measured at non-rated current (but at least 50% of rated current); c. Temperature rise at non-rated current or non-rated loss (but at least 90% of rated current); d. High-voltage side voltage during impulse test or applied voltage during pressure test with air gap correction.

(6) Precision-required quantities:

a. Voltage waveform during testing of no-load losses and no-load current; b. Frequency of AC power supply.

When determining the qualification of a product, the assessment should be based on the above requirements. Additionally, in the performance parameters of transformers, some use root mean square (RMS) values, while others use peak values. Parameters using peak values include:

a. Impulse voltage values, including full-wave, chopped-wave, and operating-wave test voltages; b. Excitation inrush current; c. Magnetic flux density; d. Short-circuit dynamic stable current, including the first peak of asymmetrical short-circuit current.

For AC frequency test voltage, the RMS value is obtained by dividing the peak measured value by √2. When there is waveform distortion, the peak value is not equal to √2 times the RMS value. When approaching saturation magnetic flux density, the ratio of peak value to RMS value of no-load current is much greater than √2. Therefore, for parameters using peak values, they must be evaluated based on peak values.

LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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