MRCT Relay And Current Transformer Test Set
The MRCT relay and current transformer tester is a lightweight, robust, portable unit used to perform demagnetisation, ratio, saturation, winding resistance, polarity, phase deviation, and insulation tests on current transformers. The MRCT can be configured to include functionality for performing an excitation test on CTs using DC voltage, allowing measurement of knee points on CTs up to 30 kV. Additionally, the MRCT can be configured to test VTs and single phase relays.
The MRCT simplifies testing by automatically calculating ratio errors, saturation curves, and knee points. It also provides a microprocessor-controlled variable voltage and current output, as well as precision instrumentation, for automatically testing single and multi-ratio CTs, ultimately reducing testing time and increasing productivity.
What’s more, the MRCT will directly connect to multi ratio CT’s and perform all tests – saturation, ratio, polarity, winding resistance, and insulation – on all taps with the push of a button and without changing leads. When the test is finished, your report is generated automatically.
The MRCT can be controlled via Megger’s Smart Touch View Interface (STVI) controller. The STVI is a full colour, high resolution, LCD touch screen that allows you to perform manual and automatic testing quickly and easily via the manual test screen, as well as by using preset test routines. The large display enables you to easily read all pertinent data while the test is being performed, and gives you the ability to view the current transformer’s saturation curve.
The unit can also be configured to come without a Megger STVI and can be controlled via a laptop with Megger’s PowerDB software.
The MRCT and PC are not communicating
Power off the MRCT and shut down your PC. Make sure that you have connected the ethernet cable to the MRCT and your PC. Power both units on with the cable connected.
I’m getting ratio errors. What can be causing this?
Ground/earth issues often cause ratio errors:
- The MRCT requires proper grounding through the power supply cord or through the chassis using the supplied grounding strap. The unit uses this ground as a reference, so for accurate testing, ensure that the MRCT is properly grounded using the supplied chassis ground strap.
- Testing large power transformers and autotransformers: The MRCT has a ground path inside the H1 (Primary 1) lead. We include this feature in the design of the MRCT for the dissipation of induced voltage typical in high voltage substations. This design allows the MRCT to test in environments other instruments cannot. However, you must take care when connecting the primary test leads on large transformers to ensure that a ground loop is not being created. When a transformer is grounded in such a way that both sides of the CT are grounded, you have a ground loop, and the MRCT cannot correctly measure any voltage. A ground loop will result in substantial ratio errors. To correct this, check all grounding on the transformer and ensure no ground loops have been created.
- Testing in high voltage yards such as 500 and 765 kV can also cause ratio errors. A sound safety practice requires grounding one side of the CT before connecting the primary test leads to it. We recommend leaving this ground in place during testing to improve ratio results. Since the H1P1 lead contains a ground path, you must be careful not to create a ground loop by grounding both sides of the CT. Therefore, external grounding should be on the same side of the CT where you connect the H1P1 lead. Additionally, the S1S/S1 (X1) connection point on the MRCT is also grounded internally, so verify that you do not have a ground loop here. Note: The MRCT has internal relays to disconnect the internal grounds when performing insulation resistance tests. When manually grounding the asset under test, you cannot perform insulation resistance tests. You will need to uncheck these on the setup screen.
- If testing CTs inside a power transformer, the windings not associated with the CT under test need to be shorted. For example, when testing a CT on the H1 to H3 primary delta winding, you would short the H3 and H2 bushings together. Separate from this, you would also short all secondary terminals (e.g., X1, X2, X3, and X0 if it is a WYE winding). Finally, you would short the tertiary terminals if the transformer has tertiary windings. See the appendix in the MRCT user guide for further information.
- To ensure the ratio error is not due to an internal fault, you can manually ground the H1 connection point to the side of the unit (safety ground).
- If the above recommendations don’t work, there is an option under the CT settings screen. Look for a button labelled “Primary Noise Filtration”. You should enable this setting only in extremely noisy environments where you cannot obtain accurate results. If used in a non-noisy environment, this can reduce the unit’s accuracy by approximately +/- 0.05 %.
Lead check failure error/message is appearing on screen
- Verify that leads are connected correctly. Make sure primary leads are connected to H1, H2, and Ground, and you are not connected to HI (high current), which is to the left of the ground connection plug.
- Verify that the red S1S (source) lead and S5S (source) leads are in the right spot, as well as the X1-X5 leads
- Check for any circulating ground connections. Both S1S and H1 points are grounded internally.
- Disable “Lead Check” in the settings menu and see if the test proceeds without the lead check enabled.
Ratios are correct, but the phase is approximately 180° out of phase, i.e., polarity is reversed
Check all connections and verify they are correct. Check under the Nameplate section in the software that “Simulated Primary Leads Swap” is not checked.
Why integrate a relay test set into a CT test set?
CTs are the communication points between the various assets in the substation and the relays so, if taking something offline in order to test the CTs, it is beneficial to have the ability to perform some standard relay tests, as needed. With the relay testing option, a simple CT tester can be turned into a troubleshooting and multipurpose tool.
If the MRCT has an onboard computer/display, can I still connect my laptop?
Yes. All versions of the MRCT, including those with built in displays, can be connected to your laptop and run via PowerDB.
Can CTs be tested when mounted in transformers, oil circuit breakers, or switchgear?
Yes. However, it is necessary for the parent asset to be completely isolated from the electrical system prior to testing.
Is the MRCT configurable?
Yes, whether you need a simple 2kV CT tester or advanced DC testing methods, VT testing, single phase relay testing, onboard or computer control, the MRCT can be customised to meet your unique testing needs.
Can I upgrade my MRCT in the future?
Yes, the MRCT includes the ability to upgrade testing capability. With various configurations and accessories, the MRCT system can be upgraded as new testing needs emerge.
How can i get technical support on this product ?
Information about Service / Repair / Calibration and Technical Support are available here
The test performs quickly, but my ratio readings are not accurate?
When you first boot up the MRCT, you may see an optional simulation mode that you can turn on. Ratio values for X1-X2 and X1-X5 are 505.047:5 and 3998.75:5, respectively, and resistance values are 0.260 and 2.100, respectively. If you have these values, you could be in simulation mode. If controlling the MRCT with your PC, disconnect and reconnect to the unit. If you have an onboard screen or are controlling the MRCT with an STVI, power down the MRCT and turn it back on.
I’m testing CTs inside of a circuit breaker bushing. On my older test unit, I would switch the H1 and H2 leads instead of switching the connection points when I moved to the next bushing CT. Can I do this with the MRCT?
Since the MRCT has an internal ground on the H1 lead, you cannot simply swap the leads. The software has an option under the Nameplate section called “Simulated Primary Leads Swap.” You can select this to let the software know that the H1 and H2 leads should be reversed so that the unit will measure the polarity based on this connection.
On the main testing screen, I see other options beside CT that are greyed out, e.g., “VT”, “CVT”, and “Relay”. How do I enable these?
These are optional features that certain MRCT configurations have. You can call technical support to see if your MRCT has this configuration and, if not, to see if you can upgrade your MRCT to use these functions. Note: some operations might need additional leads.
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