ที่นี่ V คือแรงดันไฟฟ้า และ N คือจำนวนรอบ H และ L ระบุขดลวดแรงดันสูงและแรงดันต่ำตามลำดับ เครื่องมือภาคสนามไม่ได้นับจำนวนรอบ แต่มันวัดอัตราส่วนแรงดันไฟฟ้าภายใต้การกระตุ้นทดสอบขนาดเล็ก และเปรียบเทียบผลลัพธ์กับอัตราส่วนที่คาดหวังจากแรงดันไฟฟ้าบนป้ายชื่อ ตำแหน่งแทป การกำหนดค่าขดลวด และกลุ่มเวกเตอร์.
Save raw results and restore the transformer. Remove test leads, return temporary disconnections and taps to the approved state, perform an independent check, and update the commissioning record.
Ratio results should be reviewed with other transformer tests and the approved factory baseline.
How to calculate ratio deviation
Many instruments calculate deviation automatically. For an engineering check:
Deviation (%) = (Measured ratio − Expected ratio) / Expected ratio × 100
Suppose the expected ratio for the selected tap is 20.000 and the instrument reports 20.060. The deviation is (20.060 − 20.000) / 20.000 × 100 = 0.30%. This arithmetic does not by itself determine acceptance. The correct expected ratio must reflect the actual winding connection and tap position, and the result must be judged against the applicable standard, manufacturer limits, factory report, instrument uncertainty, and project specification.
The current edition of IEEE C57.152 describes field diagnostic testing of liquid-filled power transformers and stresses combined interpretation of diagnostic results. Dry-type and special transformers may be governed by different standards and manufacturer procedures.
Interpreting patterns instead of one number
Similar deviation on all phases
A consistent offset may point to the wrong expected ratio, incorrect tap reference, a data-entry error, or a systematic connection issue. Confirm the nameplate voltages and whether the software expects line-to-line or phase values before assuming an internal defect.
One phase differs from the others
A phase-specific difference deserves investigation. Possible causes include poor lead contact, mislabeled terminals, an open or damaged winding connection, tap-changer contact problems, or winding damage. Repeat the test only after checking the setup; do not repeatedly energize a questionable test circuit without understanding the abnormality.
Ratio changes irregularly across taps
A smooth, expected progression is normally anticipated across tap positions. A discontinuity may indicate an incorrect mechanical indication, connection problem, or tap-changer issue. Compare the sequence with factory data and the tap-changer diagram.
Abnormal excitation current
Excitation current is sensitive to test voltage, connection, core condition, residual magnetism, and instrument method. It can support diagnosis, but it should not be interpreted without phase comparison, previous readings, and the test-set guidance.
ข้อผิดพลาดทั่วไปในการทดสอบ
Comparing a field result with the nominal ratio instead of the expected ratio for the actual tap.
Entering the wrong vector group or winding connection.
Leaving external circuits connected without checking their effect.
Using poor, contaminated, or mislabeled lead connections.
Recording only a pass/fail label and losing phase-by-phase raw data.
Applying one universal tolerance to every transformer and test purpose.
Treating a satisfactory TTR result as proof that insulation, core, bushings, and all mechanical parts are healthy.
How TTR fits into transformer commissioning
Ratio testing is one part of a coordinated commissioning package. The final scope may include insulation resistance, winding resistance, excitation current, power factor or dissipation factor, core ground checks, fluid tests for liquid-filled units, functional checks of alarms and cooling, protection testing, and verification of grounding and phase rotation. The exact combination depends on transformer type, voltage class, contract, applicable standard, and manufacturer instructions.
Procurement teams can reduce site uncertainty by requesting factory ratio results for every tap and ensuring that nameplate, vector group, and terminal diagrams are approved before shipment. Shenheng’s guide to transformer nameplate ratings helps teams identify the information needed for comparison, while the article on อิมพีแดนซ์ของหม้อแปลงและการทำงานแบบขนาน explains a separate parameter that TTR does not verify.
The following NPTEL IIT Delhi lecture explains the voltage and circuit relationships behind transformer measurements. It provides theory; it does not replace site safety rules or the test-set manual.
The ideal relationship is proportional, but three-phase line/phase relationships, connection groups, taps, measurement method, and real losses must be handled correctly when calculating the expected field result.
Include asset identity, nameplate data, vector group, taps, instrument and calibration details, test voltage, phase-by-phase results, deviation, excitation current when measured, observations, acceptance basis, and reviewer approval.
บริษัท เสินเฮิง พาวเวอร์ อีควิปเมนท์ จำกัด.
