The Omicron CPC100PTS is available for rent from TechRentals

 Application Notes:

Videos

CT Ratio Polarity and Burden

• The test measures the magnitude and angle of the secondary current, the ratio error in percent, and the assessment of the polarity of the CT. For nominal current tests, the burden of the CT can be measured using the same test setup. For this, the voltage drop at the burden is also taken into account. The burden is measured as complex impedance and displayed as the burden in VA with the power factor cosine phi. 

CT Burden

• The burden of a CT is measured with nominal current to rule out errors due to current dependent non-linearities. To take the resistance of the measuring leads for low-resistance burdens into account, the measurement is performed using a four-wire technique. The burden is measured as complex impedance. The result is displayed as apparent power in VA with the power factor cosine phi.

CT Current Booster

• For applications requiring up to 2000 Amps, the current booster CP CB2 can be used. The current booster is positioned close to the test object. The control cable to the CPC can be up to 30 m long. This enables the user to place the CPC conveniently on the ground and the CB2 near the cores. Testing several cores can be done quickly this way.

CT Winding Resistance

• The value of the secondary winding resistance needs to be known to determine the accuracy limit factor and the calculation of the CT time constant. The CPC is designed to measure small winding resistances with high accuracy. To eliminate the influence of the measurement leads, a four-wire technique is used. The difference between the present resistance value and the one measured 10 s ago is compared to the desired tolerance. For safety, the CT is discharged at the end of the test.

CT Excitation Curve

• For testing the excitation curve, the secondary voltage injection method is used, requiring only two leads. Voltage and current are measured with high accuracy according to ANSI or IEC standards. The CT core is demagnetized, then charged, and the excitation curve is recorded automatically. The calculation of the knee point voltage is done in compliance with ANSI or IEC standards.

CT Ratio V

• For a CT, the ratio of its windings can also be determined by the ratio of two voltages. To do this, a test voltage of around 100 Volts is applied to the secondary terminals of the CT and the voltage is measued back at the primary winding. This method is typically used for the ratio measurement of power transformer bushing CTs.

CT Rogowski Coil Ratio and Polarity

• In medium-voltage substations, the application of unconventional current transformers is increasing. An example of this is the Rogowski coil. An air core inductor is used here as opposed to conventional transformers with an iron core. The output signal is a voltage, which is proportional to the change of the current over time. Voltage levels are typically 150mV at nominal current rating.

Voltage Withstand Test

• The high voltage source built into the CPC allows for a voltage withstand test of up to 2000 Volts. Thus the voltage withstand capability of the secondary wiring of CTs and VTs can be tested. Detecting short current spikes or partial disruptive discharges is possible.

VT Ratio and Polarity

• The secondary terminals of the transformer are connected to the voltage measuring input of the CPC. Due to the high test voltage of 2000 Volts, a high measuring accuracy is obtained. From the resulting measurement, we get the test voltage injected to the primary side, the amplitude and phase of the secondary voltage, the ratio error in percent, as well as the assessment of the polarity of the VT.

VT Burden

• The burden is measured as complex impedance. The CPC injects the burden with the secondary nominal voltage, and measures the current for this test. The result is displayed as apparent power in VA with the power factor cosine phi.

Polarity Check

• The correct polarity of CTs and VTs and their secondary wiring is necessary for the proper operation of protection and measurement devices. The conventional measuring method with a battery and a galvanometer has significant disadvantages. The CPC allows for a unique new way of testing, due to state-of-the-art amplifier technology.

Electronic VT

• Electronic VTs normally provide small output voltages. The CPC provides precise measuring results for this type of transformer. The test unit provides high test voltages of up to 2 kV. This is combined with a low level measuring input which is calibrated to enable a high level of precision. We get the primary test voltage, the secondary voltage with amplitude and phase, the ratio error in percent, and the assessment of the polarity of the VT.

Power Transformer Winding 
Resistance Continuity of Tap 
Changer. 

• The impedance of power transformer windings can be measured with the CPC. The high no-load voltage of the current source allows for quick loading of high winding inductances. When testing a power transformer with tap changer, the transient tap changing operation is recorded by and analyzed with the CPC. Thus, the tap changer itself can also be diagnosed with this measurement.

Power Transformer Ratio per Tap

• The CPC allows for single-phase measuring of the ratio of power transformers of all vector groups. For power transformers with tap changers, the measurement values are recorded per tap and saved in a table.

Contact Resistance Measurement

• Because of its DC output, the CPC allows for the measurement of low-ohmic contact resistances, such as switching contacts, or clamp connections. With the high output current of up to 400 Amps, extremely low resistances of up to 0.5 micro ohms can be measured. The measurement is done using a four-wire technique.

Quick Standard Test Card for multiple applications

• Quick mode allows manual controlling of all basic functions of the CPC. The outputs and the measurement inputs can be selected by pressing a few keys. Measurement results can be saved in tabular form. Output ranges can be selected, the output frequency can be set, triggers can be defined, and measurement channels can be set.

Quick CT Ratio Measurement

• We measure a CT with a ratio of 400/5 Amps. To do this, we select the ouput current in the first measuring window, and the current measured on the secondary side in the second. In the third column, we select a Ratio:5. We can inject this CT with different primary currents.

Quick CB Contact Resistance Measurement

• To measure the circuit breaker's contact resistance, we select the range 400 A DC and set the measuring channels. We want to measure the direct current we put out and measure the direct voltage back and calculate the impedance using these two quantities.

Quick Measuring the Threshold of a Primary Relay

• To measure the threshold of a primary relay, we select the range 800 Amps and set the test to stop with an overload condition. During the measurement we increase the current until the switch trips. The last measurement before the switching contacts open is automatically saved.

Quick Primary Testing of IDMT Relays without Trip Contact

• To determine the current tripping characteristic of a switch, we select the range 800 Amps and set overload as trigger condition. We have the CPC switch off when the contacts open. We set 400 Amps as the first current value. After the switch is put into operation again, we measure with 500 Amps and finally with 600 Amps. Later in the office, we analyze the measurement.

Quick Power Transformer Short Circuit Impedance Measurement

• To measure the short-circuit impedance of a power transformer, we select the 3 Amp current output and a measuring current of one amp. As measuring channels, we select the current through the impedance, as well as the voltage drop, which is measured using a four-wire technique, which eliminates any influence of the measurement leads. In the third column, we select the resistance and inductance as calculated values. We test at different frequencies from 15 to 400 Hz to establish consistency of the measurements.

Reporting

• An interface to an external PC, or to PC networks, allows uploading of saved test results unto the PC for further processing. All test cards, such as ratio, burden or winding resistance measurements, are stored in the report. An additional comment card allows for the reporting of e.g. test object nominal data. This test sequence can also be used as a template for another measurement with all basic settings stored. The report can be edited and printed from the PC.

Test Templates

Template pairs facilitate and speed up testing and the evaluation of results. Templates are pairs of XML documents and Microsoft Excel templates designed by OMICRON for designated applications. XML templates are predefined test procedures, often with comments, that run on the CPC 100 and guide the user through the test. Once completed, the XML file is saved, downloaded to the PC using CPC Explorer and then loaded into the corresponding Microsoft Excel template. The results are post processed and a final test report is generated.

The  template usage (PDF, 356 KB) requires the CPC Explorer software to be installed on your PC. CPC Explorer enables you to transfer files (templates and test results) between the PC and CPC 100.

OMICRON Templates

OMICRON provides several templates for various applications. They can be found in the "Templates" folder on the "CPC Explorer" CD or can be downloaded below. To use these templates download the corresponding .zip archive and extract it to your local PC. The files will start to download immediately. If not, right click on the link and select "save target as". Choose a place on your local PC to save the .zip archive. After downloading extract the archive with WinZip^®.

Templates for download (.zip Archives)
Power Transformers (ZIP, 8.6 MB)	Templates for PF/DF, Ratio, Tap Changer, ZK, ...
Rotating Machines (ZIP, 1.2 MB)	Templates for Power Factor/Dissipation Factor
Instrument-Transformers (ZIP, 3.5 MB)	Templates for PF/DF, Accuracy Limiting Factor, ...
Cables Transmission Lines (ZIP, 6.3 MB)	Templates for Line Impedance, Mutual Coupling, ...
Grounding-Systems (ZIP, 2.7 MB)	Templates for Ground Impedance, Step & Touch, ...
Other (ZIP, 1.5 MB)	Templates for other applications

Template Usage

To run a test procedure according to a template:

1. Upload the XML template (extension .xmt) for the intended application from the PC to the CPC 100 using CPC Explorer
2. Open the template on CPC 100
3. Run the test procedure according to the template
4. After completing the test procedure, save the test in a new file
5. Download the test results form the CPC 100 to the PC in your preferred working directory
6. Open the corresponding Microsoft Excel template by double-clicking the *.xlt file. A Microsoft workbook appears
7. Click the Load XML-File button and open the *.xml file saved in your preferred working directory before, to load the test results.
8. After all worksheets are filled with data, the test results are calculated