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Polarity check

Use the Polarity Check application module to output a sawtooth-shaped signal for testing the secondary wiring of current transformers and voltage/power transformers. Correct polarity of instrument transformers is essential; it determines the direction of the secondary current values in relation to the primary current values.

Typical setup when injecting at the primary side of a CT: COMPANO 100 injects a current, say 50 A, from I OUT positive to the primary terminal P1/H0 of the current transformer, and I OUT negative to P2/H1. To test the polarity, connect the OMICRON polarity checker CPOL, CPOL2 or CPOL3 to any contact pair of the secondary wiring.

Because a high current cannot be injected permanently, it makes sense to output the current for a certain time, and then give COMPANO 100 some time to cool down. Such an on/off time ratio for injecting a 50 A sawtooth signal would be, for example, ton = 5 s, toff = 55 s.

Typical setup when injecting at the secondary side of a CT: COMPANO 100 injects a current, say 5 A, from I OUT positive to the secondary terminal S1/X1 of the current transformer, and I OUT negative to S2/X2. To test the polarity, connect the OMICRON polarity checker CPOL, CPOL2 or CPOL3 to any contact pair of the secondary wiring.

When injecting a 5 A sawtooth signal, there is no on/off time ratio required. COMPANO 100 provides 5 A continuously (ton = 60 s, toff = 0 s).

Some self-supplied relays cause heavy distortions on the voltage as they are internally using a switched-mode power supply. CPOL, CPOL2 and CPOL3 are not able to detect such a distorted sawtooth signal.
For CPOL2 and CPOL3, a solution for this problem is using a current clamp to measure the current instead of the voltage (shown below).

Interruption detection

As additional function, the Polarity Check application module provides an interruption detection, that is, it can detect short interruptions of the secondary path of a current transformer. Its purpose is to detect defective make-before-break switches. (Other commonly-used names in the English language for such "change-over make-before-break switches" are "relay test switch", "relay test connector", "shorting devices", or "superior switches".) Such devices short-circuit the current transformer, then disconnect it from the relay. The order of “making before breaking” is of utmost importance because if there is an interruption, even a very short one, high voltages will occur as long as there is a primary current on the CT.

  1. To use the interruption detection, inject a current as close as possible to the CT on the secondary side. We recommend you permanently inject nominal current by setting for example, 1 minute/3600 cycles on time, and 0 seconds/cycles off time. Inject at least 1 A nominal current.

  2. While injecting the nominal current, operate the make-before-break switch in the path several times.

  3. If an interruption is detected, the Polarity Check application module will show its time span at TMax. open. Detected interruptions between 0.1 ms and 5 ms are displayed as such. If an interruption longer than 5 ms is detected, Polarity Check displays a value of > 5ms.

Setting a trigger

In case the make-before-break switch is physically far from the COMPANO 100 test set, set a trigger to disable the output in case an interruption is detected. That way, even being away from the test set, you become aware that such an interruption occurred by noticing the absence of the test signal after operating the make-before-break switch. To do so, turn the jog dial wheel until the focus is on the option field below Interrupt trigger. Press the jog dial wheel to toggle the Interrupt trigger option. Alternatively, use the Off/On soft keys.

Note: two limitations apply to that test.

  1. In case the inductance of the circuit behind the test switch is very high (due to an extensive wiring or a heavily inductive electro-mechanical relay, for example), a very short interruption may be detected even though the switch is operating properly.
    Such wrongly detected interruptions are generally very short, below 1 ms. If you are in doubt whether you have such a wrongly detected interruption, shorten the CT while the rest of the circuit is connected in parallel. If you then still detect such interruptions, you know that this is the cause for the detection.

  2. If the CT connected to the I OUT output is extremely small, say, in the range of 1 VA, it could happen that not the entire 5 ms of interruption time are detected. Reason: before that time has elapsed, the current starts flowing through the CT again. In such cases, longer interruptions could be shown with values slightly smaller than 5 ms. To find out if that is the case, open the secondary circuit, and read out the display of COMPANO 100.

Note: The Polarity Check application module supports a special open/close detection function. Very fast changes of the output load are detected as open/close transition, temporarily limiting the output driving voltage and control parameters for about 100 ms to optimize the output behavior for sudden changes between the three states: open circuit, normal load, and short circuit.