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Pole mounted distribution transformers are manufactured with additive polarity, while instrument transformers are made with subtractive polarity. Where markings have been obscured or are suspect, a test can be made by interconnecting the windings and exciting the transformer, and measuring the voltages. [4]
An insulation resistance test (IR test) measures the electrical resistance of insulation by applying a voltage between two locations, and measuring the resultant current flow. Proper safety precautions must be taken when doing this test, such as exclusion zones, making sure no wires are exposed, and personal protective equipment is worn.
A quick supplemental screening test for these simple miswiring errors can be performed using a non-contact voltage tester (NCVT) or non-contact voltage detector. [4] If a problem is thus identified, it can be investigated further using more-advanced equipment, or the outlet in question can be de-energized and disassembled for careful scrutiny. [4]
to test series and interpoles (commutating) fields from a DC motor; to determine phasing and polarity in multiwinding armatures; to test rotors in rotating frequency changers, as well as in wound rotors; to test shorts between turns in taped coils before installation into an armature or a stator; as a low voltage isolation transformer
This is determined by the polarity of the voltage on the highly curved electrode. If the curved electrode is positive with respect to the flat electrode, it has a positive corona; if it is negative, it has a negative corona. (See below for more details.) The physics of positive and negative coronas are strikingly different.
A leakage current test is an alternative to the insulation resistance test. A deficiency of the insulation resistance test is that the DC voltage will not activate electromagnetic switches or internal relays etc. that are common in many modern power tools, computers, and TVs, etc. and therefore it can only test the appliance up to those components.
Modifying the polarity of a weakly ionic group (e.g. carboxyl) on the surface is easily accomplished by adjusting the pH to be within two pH units of that group's pKa. For strongly ionic functional groups of the surface (i.e. sulfates or phosphates) one could instead use a lower amount of buffer so the residual charge is not completely ion paired.
A 120:120 instrument isolation transformer showing two polarity marking conventions. Voltage transformers (VT), also called potential transformers (PT), are a parallel-connected type of instrument transformer. They are designed to present a negligible load to the supply being measured and have an accurate voltage ratio and phase relationship to ...