CT Testing Equipment for Hire

CT testing verifies that a current transformer will deliver an accurate, in-phase secondary current to its connected protection relays and metering circuits across the full operating range of the asset. Modern testing covers ratio accuracy, phase displacement, polarity, the excitation (saturation) curve, the knee point voltage, winding resistance, burden, and insulation resistance. For protection CTs the test programme also confirms accuracy class limits including composite error, instrument security factor (FS) and accuracy limit factor (ALF). For metering CTs the programme confirms compliance with revenue accuracy class requirements at the specified rated burden.

The dominant test method on Australian projects is low-energy secondary injection using the Omicron CT Analyser, which captures the complete CT performance characteristic in under a minute per CT and applies an automatic pass/fail assessment against the selected standard. Primary injection using a CPC 100 or CPX 200 is used where the project specification calls for end-to-end primary-side verification, where the CT design or installation does not permit secondary-side testing, or where critical protection schemes such as transformer differential, busbar protection and line differential require an independent primary check on top of the CT Analyser results. The two methods are complementary, not competing.

CT testing in Australia is governed by IEC 61869-1 (general requirements for instrument transformers) and IEC 61869-2 (current transformers), with IEC 60044-1 still referenced on legacy assets. IEEE C57.13 applies where the project specification calls for IEEE compliance, and AEMO metering CT requirements apply to revenue metering installations under the National Electricity Rules. Megavar’s commissioning engineers test CTs against all four standards from offices in Hobart, Launceston, Adelaide and Newcastle, with delivery Australia-wide.

CT testing is performed across the full project lifecycle, from factory acceptance through commissioning to periodic asset management. The right test programme depends on what the CT is being installed for, what the project specification calls for, and what evidence the asset owner needs at handover.

Substation commissioning

Greenfield and brownfield substation commissioning is the highest-volume CT testing scope on Megavar projects. Every CT in every bay is tested for ratio, polarity, excitation, winding resistance and burden against the nameplate, with the results compiled into the commissioning records that are handed back to the asset owner at energisation. The CT Analyser with the CT SB2 switch box is the standard tool for this work because it tests all secondary taps in a single automated run.

Revenue metering CT compliance

Revenue metering CTs must be verified against the accuracy class declared on the nameplate (Class 0.2, 0.2S, 0.5 or 0.5S) at rated burden. AEMO metering rules under the National Electricity Rules set out the test and verification regime for Type 1 to Type 7 metering installations, and the CT Analyser provides the documented evidence required for compliance. Where the metering installation has been disturbed, the test must be repeated and the result lodged before metering can be re-energised.

Protection scheme verification

Critical protection schemes including transformer differential, busbar protection, line differential and high-impedance restricted earth fault rely on accurate, in-phase CT secondary currents from multiple CTs on the same protected zone. CT verification for these schemes typically combines a CT Analyser pass against the protection class (5P, 10P, PX, TPX, TPY or TPZ) with a primary injection check using the CPC 100 to confirm correct wiring, polarity and end-to-end ratio. Megavar performs this combination of tests on every major protection commissioning.

CT excitation and knee point characterisation

The excitation curve plots the secondary voltage required to produce a given exciting current in the CT secondary. The curve identifies the knee point, above which the CT begins to saturate. Knee point voltage and the maximum exciting current at the knee point are critical inputs to differential and high-impedance scheme calculations, and to verification of CT adequacy under fault conditions. The CT Analyser captures the full excitation curve in seconds and reports the knee point automatically.

Periodic asset management and post-fault investigation

Asset owners increasingly include CT verification in their cyclic maintenance programmes, particularly for transmission-class CTs and HV bushing CTs where in-service degradation is a real risk. Tan delta measurement on the HV CT insulation using the CP TD1 accessory paired with a CPC 100 detects ageing and contamination of the bushing insulation system. After a major fault on a protected zone, CT testing forms part of the standard post-fault investigation to confirm that the CTs themselves remained within their declared performance class during and after the fault.

CT testing splits between two test methodologies, and a complete project usually uses both. The right method for a given test depends on what the project specification calls for and what level of end-to-end verification is required.

Secondary injection (CT Analyser method)

Secondary injection uses a low-voltage, low-energy signal applied to the CT secondary winding, with the CT Analyser deriving the complete equivalent-circuit model of the transformer from the measured response. From this model, ratio, phase displacement, excitation curve, knee point, polarity, burden and winding resistance are all calculated and assessed against the selected standard. Test voltage is typically below 120 V which makes the method significantly safer than legacy high-current primary injection, the test runs in under a minute per CT, and the demagnetisation cycle at the end of the test leaves the CT ready for service. This is the dominant method for substation commissioning in Australia and is accepted by all major asset owners as the primary CT acceptance test.

Primary injection (CPC 100 method)

Primary injection applies a known current through the CT primary, typically the busbar or primary conductor, and measures the resulting secondary current at the relay terminals. This verifies the entire CT, wiring, terminal connections and relay path in one shot, which is the strongest possible end-to-end check on protection scheme integrity. Primary injection is mandatory under some asset-owner specifications, is the established method for verifying critical schemes such as transformer differential and busbar protection, and is the test of last resort where secondary-side access is restricted or where the CT design does not support secondary injection. The Omicron CPC 100 is Megavar’s standard primary injection toolkit, with the Omicron CPX 200 (and its HVX10 high-voltage attachment) available where a second multifunction set or a higher test voltage is needed.

How they fit together

Most major commissioning projects use both methods. The CT Analyser handles the bulk volume of CT acceptance testing, providing a fast, documented pass against the nameplate class for every CT. The CPC 100 then handles end-to-end primary injection on critical protection schemes, on revenue metering installations where the project specification mandates it, and on any CT where the CT Analyser result is ambiguous or contested. Megavar’s engineers run this combined workflow as routine.

CT testing equipment is a sensible candidate for hire on most project profiles. The Omicron CT Analyser and CPC 100 are class-leading instruments and the cost of ownership reflects that. Hire makes economic sense for project-driven workloads; ownership only makes sense for organisations with year-round high-volume CT testing demand.

• You need a CT Analyser for a project window from a single day to several months
• You need a primary injection set for a one-off scheme commissioning
• Your team handles CT testing on commissioning projects but not as a year-round activity
• You want results interpreted by engineers who test CTs every month
• The project specification calls for both secondary and primary injection across multiple bays
• You need the CT SB2 switch box for a multi-bay substation but only on this project

• Your team performs CT testing as a year-round routine activity
• You commission more than 200 CTs per year across multiple sites
• You have qualified protection engineers in-house with current CT testing competency
• You can commit to ongoing manufacturer training and software updates
• Your asset register justifies a multi-year programme of CT condition monitoring
• Your organisation can absorb 3 to 5 year obsolescence on the measurement platform

CT testing is one of the highest-volume disciplines in HV commissioning and one of the most consequential. A wrongly tested CT produces a false-positive acceptance record that the asset owner relies on for years afterwards, and the protection scheme it feeds may never function as intended until a real fault occurs. Megavar’s commissioning engineers test CTs to IEC 61869 every month on transmission and distribution projects, including BESS step-up CTs, transmission line CTs, transformer bushing CTs, distribution switchgear CTs and revenue metering installations.

When you hire CT testing equipment from Megavar you receive: current calibration with traceable certificates, the matched accessories and software licences for the asset class you are testing, and the manufacturer's manuals. Where the project requires CT testing done end-to-end rather than equipment alone, we can quote a turnkey commissioning service with our protection engineers operating the equipment, running the test programme and producing the commissioning records. This is the most common arrangement on substation commissioning, scheme verification, revenue metering compliance and post-fault investigation.

Hire periods are flexible from single-day commissioning checks through to multi-month project rentals. Delivery is Australia-wide. Call 1300 730 499 or email rentals@megavar.com.au.