Death or severe injury can occur if the appropriate safety instructions are not observed.
The COMPANO 100 test set can output life-hazardous voltages and currents.
Before operating any such electrical equipment, carefully read the Safety Instructions chapter in this manual (see Safety instructions).
When injecting current into the CT's primary winding, make sure that no secondary windings are open.
If a shunt is used to measure the current on the secondary side of a CT, check if the shunt if working properly before connecting it to the CT. A damaged shunt may have a high resistance and can lead to dangerous voltages.
If possible, us a current clamp to measure the current on the secondary side of a CT, as it does not require to open the secondary circuit.
This chapter provides you with examples how to perform tests on a CT (current transformer) and its secondary wiring all the way to the protection relay, the meter, or to the control room display. If you check the wiring of a CT, the CT ratio or measure the CT burden with COMPANO 100, it is not necessary to open the secondary wiring.
Connect COMPANO 100's output I OUT to the CT's primary terminals P1/H0 and P2/H1 using the high current cables.
Connect the CT's secondary terminals S1/X1 and S2/X2 to the current input of the relay and to COMPANO 100's input IN 1.
Configure COMPANO 100's input IN 1 to be a voltage input: press the IN 1 key below the actual input. Press the following soft keys sequentially: Analog ► Voltage ► AC ► Auto ► Accurate.
Verify that the CT’s secondary loop is closed and check the CT polarity
Inject an I OUT AC current of 1 A for a few seconds, and read out the voltage on IN 1. You should get to see a few millivolts, only.
If you see a voltage value of say more than 1 V, the secondary loop of the CT might be not closed, which is a safety issue. You should stop the test in that case.
Now set a timeout to 2 seconds, and inject an I OUT AC of say 100 A into the CT.
The interesting result of this test is the phase angle of the voltage:
If it is between 0 ° and 90 °, the CT's polarity is correct.
If it is between -90 ° and -180 °, the polarity is not correct.
This first step now has verified that the secondary circuit of the CT is closed, and that the polarity of the CT is correct.
Connect the current clamp to the COMPANO 100 input IN 2.
Note: perform a DC current offset calibration on the current clamp before carrying the measurement.
At the current clamp, set a suitable current range, for example, 100 mV/A or 1 V/A, depending on the current clamp type and setting.
Configure COMPANO 100's input IN 2 to be a current input. Press the IN 2 key below the actual input. Press the following soft keys sequentially: Analog ► Clamp ► 100 mV/A* ► AC ► Auto ► Accurate.
*Select the value corresponding to the current clamp. Use the jog dial wheel to set a value differing from the preset.
Press the Calculated measurement key . Then press the jog dial wheel to turn it On.
Configure the calculated measurement by using the output current I OUT as operand 1, and the input current at IN 2 as operand 2.
Because both operands currents, the Calculation setting provides the ratio options Ratio:1 and Ratio:5. Select the proper ratio setting according to the secondary circuit 1 A or 5 A.
Return to the QUICK application module, inject a current of 100 A for 2 seconds, and read the ratio from the display.
If the measurement result does not match the expected outcome, make sure that the current clamp range is sufficient for the expected current in the secondary circuit.
So far you have verified CT ratio and CT polarity. Now change from primary injection to secondary injection in order to obtain higher secondary currents for a longer period of time.
Connect the current output I OUT to the CT's secondary terminals S1/X1 and S2/X2. For your convenience, you can use standard measurement cables this time instead of the high current cables.
Note: perform a DC current offset calibration on the current clamp before carrying the measurement.
In the QUICK application module at I OUT, set the nominal secondary current of your choice.
Press the Calculated measurement key . Then press the On soft key.
Configure the calculated measurement for apparent power by using the voltage at IN 1 as operand 1, and the input at IN 2 as operand 2.
Because one operand is a current and the other one a voltage, the Calculation setting provides an apparent power S option.
Now return to the QUICK application module, and inject the nominal secondary nominal current for 2 seconds. The measurement shows the secondary burden of the CT.
Apply the current clamp to the wire that grounds the CT between the actual grounding point and the relay.
Note: perform a DC current offset calibration on the current clamp before carrying the measurement.
You should read approximately the nominal current. If you only read a portion of the nominal value, there might be an unwanted ground connection on the high side of the wiring. If you only read approximately a third of the nominal value, the grounds of the other current transformers could be linked via connected grounds in the relay.
Now temporarily ground the high side of the CT:
Now, the current reading should approximate zero. If this is not the case, the ground connection (in this example on S2/X2) might be missing. Remove the temporary ground then.
In case the secondary CT wiring incorporates a relay test switch with a make-before-break functionality to shorten out the CT before disconnecting the relay, you can test this by using a function that detects short interruptions. The moment the make-before-break contact interrupts the current path, the trigger will occur and deactivate the COMPANO 100. This is easy to detect, even on the other end of the substation: there is no more polarity check signal. Operate the switch several times to ensure proper operation.
Note: perform a DC current offset calibration on the current clamp before carrying the measurement.
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 switches1. 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.
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.
While injecting the nominal current, operate the make-before-break switch in the path several times.
If an interruption is detected, the Polarity Check application module will shows 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.
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, or 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.
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.
1 Other commonly-used names for such "change-over make-before-break switches" are "relay test switch", "relay test connector", "shorting devices, or "superior switches".
. Then press the jog dial wheel to turn it 
