The polarity markings on a CT specify the comparative instantaneous directions of the currents. The polarity examination proves that predicted way of secondary CT latest (making) is proper for confirmed movement of major current (penetrating).

Taking good care to observe the proper polarity is important whenever using and connecting recent transformer to power metering and protective relays. In one immediate of time, the major latest was going into the primary terminal the corresponding second present needs to be making the go to my blog likewise marked second terminal.

A CT under test try presumed to possess appropriate polarity if instantaneous current way for main and supplementary current is actually other to one another. CT Polarity is critical when CT’s are being utilized collectively in single-phase or three-phase software.

Most contemporary time CT examination products can perform executing the proportion test automatically making use of a simplified test contribute build and will display polarity as proper or wrong. CT polarity are verified manually with the use of a 9V battery and analog voltmeter aided by the appropriate examination therapy:

Marks on existing transformers have been occasionally misapplied by the plant. You’ll confirm the polarity of a CT on the go with a 9V power supply. Photo: TestGuy.

CT Polarity Test Process

1. Disconnect all-power prior to tests and hook the analog voltmeter on secondary terminal of CT to get analyzed. The positive terminal for the meter was linked to terminal X1 of this CT whilst unfavorable terminal are attached to X2.
2. Manage an article of line through highest side of the CT windows and fleetingly speak to the positive 9-volt power supply on the H1 side (often marked with a mark) therefore the bad conclusion toward H2 part. It is very important stay away from continuous call, which will short circuit the battery.
3. If polarity is correct, the momentary contact leads to a small deflection in analog meter from inside the positive course. If deflection is actually adverse, the polarity of this recent transformer is actually reversed. The terminals X1 and X2 need to be reversed together with test can be carried out.

Note: Polarity is certainly not important when hooking up to ammeters and voltmeters. Polarity is very important only if hooking up to wattmeters, watt-hour yards, varmeters, and induction-type relays. To maintain polarity, the H1 side of the CT must certanly be toward the foundation of electricity; then the X1 supplementary terminal is the polarity connection.

3. Excitation (Saturation) Test

When a CT try “saturated”, the magnetized course within the CT functions like this short circuit regarding the transmission line. Almost all of the fuel supplied by the main winding are shunted from the secondary winding and it is made use of write a magnetic area in the CT.

Saturation tests for an ongoing transformer recognizes the ranked knee point against IEEE or IEC expectations, the point where the transformer no longer is able to result present in proportion to their given proportion.

Excitation reports become done by applying an AC voltage with the second winding for the CT and raising the voltage in actions up until the CT is within saturation. The “Knee” aim depends upon watching a tiny current increase leading to a large escalation in latest.

The test current try slowly reduced to zero to dea€?magnetize the CT. The test answers are plotted on a logarithmic (loga€?log) graph and evaluated using the change cycle between typical procedure and saturation.

Excitation reports are sang through the use of an AC voltage into additional winding for the CT and raising the voltage in steps before the CT is in saturation. Pic: TestGuy.

The excitation bend round the information in which current jumps up for a small boost of current; is essential for review of shape with released shape or similar CT figure. The excitation test results must be weighed against published manufacturer’s facts or previous recordings to find out any deviations from previously received curves.

IEEE describes the saturation as “the point where the tangent is at 45 qualifications for the additional interesting amperes”. Also referred to as “knee” aim. This examination confirms your CT is of correct accuracy status, does not have any shorted changes during the CT without short circuits can be found inside biggest or secondary windings in the CT under examination.

4. Insulation Opposition Test

The insulation between your current transformer windings and windings to floor needs to be checked for dielectric energy while carrying out a comprehensive CT examination. Three reports were sang to discover the situation for the insulation from the CT under examination:

1. Primary to additional: Checks the healthiness of the insulation between large to reduced.
2. Primary to surface: Checks the healthiness of the insulation between highest to soil.
3. Second to crushed: Checks the healthiness of the insulation between low to ground.