Instrument Transformer
Field Testing

Current Transformer (CT) & Potential Transformer (PT) Testing

Instrument transformers play an important role in revenue calculation. One small error can lead to significant revenue loss for a utility. That's why Instrument Transformer Testing is so important.

PowerMaster® site analyzers accurately perform instrument transformer testing using the following test methodologies:
  • Ratio
  • Ratio with Burden Added & Burden Measurements
  • Dead Site Testing With Load Boost


Customer load test consisting of direct simultaneous measurement of primary and secondary signals. Both amplitude and phase error measurements are verified and graphically plotted according to IEEE.

Ratio with Burden Added

This is an additional burden to the CT circuit. Both amplitude and phase error measurements are verified and graphically plotted according to IEEE. Adding burden in this manner stresses the CT to determine at what point it will become over-burdened and inaccurate.

Customers can perform a test with our transformer testing equipment on the burden measurements, which include secondary current signal of the CT and the voltage drop across its terminals. Accurately measuring these signals allows the calculation of the existing burden on the CT. This burden measurement is verified against the specification from the CT manufacturer.

Dead Site Testing with Load Boost

Our transformer testing equipment generate load tests that perform direct simultaneous measurement of primary and secondary signals while injecting additional current to the primary of the CT. This application can be performed both in the field and the lab.

Ray Gore Instrument Transformer Testing with High Voltage Probe


Most metering class instrument CTs are rated at 0.3% accuracy within their burden and temperature specifications at full rated load. There is also a new, more accurate class of CTs which are rated at 0.15%.

Because of the importance of CTs in the billing chain, it is imperative that the test equipment used to verify their accuracy has proven accuracy much greater than the CTs.

Faulty installation and overburdening are just a few instances that will reduce the accuracy of the CT installation. Because of the importance of CTs and PTs in the billing chain, it is crucial to have the right equipment to perform potential and current transforming testing.

Powermetrix PowerMaster® solutions give you functionality, portability, and accuracy in the field for exact readings even when the most complex testing is necessary.

PowerMaster® site analyzers provide ease of use in a compact and feature-rich package. They’re built into a rugged Pelican hard case, enabling them to stand up to the rigorous demands of field Instrument Transformer Testing.

Pelican Cases

This transformer test instrument has a true three phase reference standard. Additionally, this PT/CT analyzer has an optional three phase current and voltage sources for ANSI C12 phantom load meter testing. You also have the option to add an MTA-15Z accessory to facilitate ANSI C12 meter testing on self-contained meters at the customer’s site or in the lab.

This state-of-the-art PT/CT analyzer features a compact three phase reference standard for testing meters under customer load conditions. Technicians can also test CTs and PTs, and with CAT IV 600V and IEC-61010 safety compliance. This protects them more than anything else in its class.

instrument transformer testing