AEMC 8500 - Tips for Making Precise Ratio Measurements; Ratio Test - 1:1

Digital Transformer Ratiometer DTR
®
Model 8500 19
4.8 Tips for Making Precise Ratio Measurements
NOTE: The DTR is designed to test step down transformers. It works
with low voltage on the primary, limited to 40V max. If the secondary
reaches 40V before the primary, a safety feature stops the mea-
surement. The recommended procedure to test step up transform-
ers is to reverse the low and high leads and read the reverse ratio.
• Alwaysverifytheintegrityoftestcableconnectionsandrepositiontest
clips as necessary. Inspect transformer terminals for dielectric coat-
ings, fungus and corrosion.
• DuringVT/PTModeoperation,selectContinuityTestwhenpossible.
Besidesbeingausefulwaytocheckwindingsandconnections,this
testhastheaddedbenetofreducingmagneticremnantsinthetrans-
former under test. This is important primarily in transformers with high
seriesresistance,andinlow-KVAtransformerswithextremelyhighpri-
mary-sideinductance.Itisnotrequiredinmosttap-changeandregula-
tor transformers.
• Whentestingpolyphasetransformers,keepinmindthatinsomecases,
measuredratiosmustbemultipliedordividedby√3.Referto§4.10for
polyphaseconnectionsdiagramsandassociatedratioequations.
4.9 Ratio Test - 1:1
A simple test can be conducted to test functionality of the DTR
®
. By
connecting HRED to XRED, and (separately) HBLACK to XBLACK, a 1:1
transformer is simulated. Operation of the DTR
®
 in this conguration
shouldyieldaratioverynearlyequalto1.000.Ifitdoesnot,theDTR
®
may
requirerepairorcalibration.
CONNECTIONS EQUIVALENT
H RED X RED
H BLACK X BLACK
1 : 1