TPI Phase / Motor / Transformer Testing Description
Phase / Motor / Transformer Testing is a general category for Motor Phase and Rotation Meters plus Transformer Turns Ratiometer (TTR).
Phase Sequence and Motor Rotation Testers…A small cost to protect equipment and your reputation
Phase Sequence and Motor Rotation Testers have two primary functions. Both are necessary to ensure that a motor will rotate in a prescribed direction when energized.
Determine the rotation direction of motors, clockwise or anticlockwise/counterclockwise, before connecting line voltage. Running motors backwards/wrong direction may damage expensive machinery. In these cases, motors are tested on a bench or temporary power is run to uncoupled motors for a rotation test. This can be costly, time-consuming, and hazardous, especially with high voltage motors. Using a motor and phase rotation tester, an electrician can make the final motor connections on the first attempt.
Determine phase rotation or sequence of energized power circuits. The load side (i.e. unpowered motor) and also the supply side should be checked. The phases of the line voltage must also be properly identified so that they can be connected to the motor for the desired rotation. This is true in a new or replacement motor situation, but also when working on switchgear, such as transformers, disconnects, and breakers. Utility crews or plant personnel working on switchgear must correctly connect or the result might be many backward rotating motors at different locations when power is re-applied. This can be very dangerous, plus possibly damage equipment.
Additional uses for Phase Sequence and Motor Rotation Testers
How to select a phase and motor rotation meter?
Identifying polarity and phase of motor windings where the terminal markings have been destroyed or where connection diagrams are lost
Determine polarity of instrument and power transformers
Continuity tester in checking electrical circuits
Make sure to have the right CAT safety rating for the voltages of live circuits being tested. Potential transformers (step-down transformer) are required for measurements on systems above the common CAT IV 600 V // CAT III 1000 V limit of many phase and motor rotation testers. Click here to learn more about CAT safety ratings.
Dedicated Phasing Testers are available for utility work in the kV range. Applications include checking high voltage fuses, testing for correct phase connections, and testing for absence of high voltage on de-energized lines.
Each varies slightly in the layout of buttons/switch, LED’s, and operation. Some have a buzzer in addition to LED. Our site has instruction manuals (ask if not posted).
Look for a model that is easy to learn.
Hioki has a dedicated Phase Detector with non-contact clips, reducing risk of electric shock and short circuit hazards. The clips do not have any exposed metal to contact the conductor. Clip right over 10-40 mm insulated wires. Similar to voltage detectors, it uses the principle of electrostatic induction.
Non-contact phase detectors offers safe and correct phase detection based on the basic understanding that a closed circuit is formed between the conductor, detecting device and the operator with reference to the earth.
Transformer Turns / TTR
Transformer Testers / Transformer Turns Ratiometer (TTR) measure the turns ratio, excitation current and polarity of windings in single and three phase distribution and power transformers (tested phase by phase), potential and current transformers, and tapped transformers. The applicable test method is IEEE C57.12.90 Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.
Why is it important to test Transformers?
Transformers can provide a long service life if well maintained. They are also the single most costly item in any substation. The proper operation of a transformer relies almost entirely on the electrical properties of its windings. To ensure continued proper operation, transformers are tested to verify that their electrical properties have not changed from design specifications. TTR’s are extremely useful instruments for testing transformer windings because it can help locate several types of problems within single and three phase transformers. Transformer ratio can change due to several factors, including physical damage from faults, deteriorated insulation, contamination, and shipping damage. If a transformer ratio deviates more than 0.5% from the rated voltage ratio, it may not operate reliably.
A TTR is ideal for meter shops. It can be used for inspection purposes to determine the no-load accuracy of most CTs and PTs. It also can be used to determine the need to test potentially faulty CTs and PTs
For additional related testing equipment see Products > Transmission Line/Station Testing
Selection Considerations for TTR’s
Single Phase and/or Three Phase. Single Phase only models will be less expensive. For three phase testing look at the model from Phenix
Hand-crank vs. battery/AC power to operate the unit. The Megger Hand-Crank model, while more expensive, cancels out various potential errors, such as leakage plus convenience of not needing batteries or AC power
The battery/AC powered units perform no-load test, so it does not see potential sources of error and can give an influenced reading. The benefit, however, is faster testing on complex transformers and lower cost
Full Automation. Phenix Three Phase model can automatically detect 130 different transformer types defined by ANSI, CEI/IEC, and Australian standards. In addition to measuring a transformer’s turns ratio it also measures a transformer’s excitation current and its phase angle. Users can also create and save a test plan for a specific transformer. The test plan comprises transformer nameplate voltages for each tap setting. Computed turns ratio is based on nameplate voltages and used later to compare with measured turns ratio