scope:

This guide provides background information and general recommendations of instrumentation, circuitry, calibration, and measurement techniques of no-load losses (excluding auxiliary losses), excitation current, and load losses of power and distribution transformers. The test codes, namely, IEEE Std C57.12.90^TM, IEEE Std C57.12.91^TM, and the test code section of IEEE Std C57.15^TM, provide specifications and requirements for conducting these tests.¹ This guide has been written to provide supplemental information for each test. More technical details of the measuring instruments and techniques presented in this guide can be found in the document developed by So [B16].² This guide applies to liquid-immersed-power and distribution transformers, dry-type transformers, and step-voltage regulators. Additionally, it applies to both single- and three-phase transformers.

Purpose

The purpose of the guide is

a) To describe the basis and methodology by which the accuracy requirements of (Clause 8 and Clause 9) of IEEE Std C57.12.90 for liquid-immersed transformers and IEEE Std C57.12.91 for dry-type transformers can be achieved.

b) To explain why the test code specifies certain procedures and limits.

c) To explain advantages and disadvantages of different test methods where alternative methods are available.

d) To explain practical limitations and valid means of overcoming them.

e) To give theoretical basis for interpolation/extrapolation of tested data and valid limits.

f) To explain test anomalies-how they result, what they mean, and how to handle them.

g) To give procedures for calibration, certification, and traceability of measurement processes to reference standards.

h) To discuss procedures for grounding, shielding, safety precautions, etc.

i) To provide schematics and examples to clarify concepts and demonstrate methodologies.

¹ Information on references can be found in Clause 2.

² The numbers in brackets correspond to those of the bibliography in Annex A.