The Bureau of Reclamation is a provider of wholesale water and hydroelectric power in the U.S. The Reclamation was created to distribute water to the 17 western states and is best known for constructing dams, power plants, and canals. The Reclamation maintains a series of manuals entitled Facilities Instructions, Standards, & Techniques (FIST), which pertains to the operation and maintenance of hydroelectric equipment. We listed several sections of the FIST below, which are relevant to testing.
FIST 3-30 is a Bureau of Reclamation manual that is specific to transformer maintenance testing for the power plant industry. The Bureau of Reclamation is a provider of wholesale water and hydroelectric power in the U.S. The purpose of the Bureau of Reclamation FIST 3-30 is to provide guidance to power plant personnel in maintenance, diagnostics, and testing of transformers and associated equipment.
The FIST 3-30 defines power transformers as transformers rated 500 kilovolt amperes (kVA) and above. The Reclamation has hundreds of power transformers with voltages as low as 480 volts (V) and as high as 550 kilovolts (kV). All generator step-up transformers, and many station service and excitation transformers are considered power transformers because they are rated 500 kVA or larger.
Because transformer maintenance is vital to the power plant industry, procedures must exist to determine proper functioning of transformer-related equipment. Transformer maintenance tests ensure that power plant facilities continue to run smoothly with the proper equipment. Heat is one of the most common destroyers of transformers, which is why frequent maintenance is crucial for the successful operation of power plants. FIST 3-30 details the maintenance procedure and tests for dry type and liquid-immersed type transformers. These tests include infrared imaging, winding resistance tests, turn ratio/polarity tests, insulation resistance tests, power factor (tan delta) tests, partial discharge tests, and de-energizing/demagnetization tests, motor load tests, and more.
Manufacturers for transformer maintenance testing equipment in the power plant industry include Doble, OMICRON, Megger, Haefely Hipotronics, Vanguard, and others. These manufacturers have partnered their services with Advanced Test Equipment Rentals (ATEC) to provide the best transformer test equipment available to rent. Many of these manufactures specialize in these individual test, while some transformer test systems are designed to do multiple tests.
These products are:
Thermal imaging cameras/infrared cameras are able to identify hot points, leakage, and other thermal issues by using infrared radiation as opposed to visible light. According to the Reclamation FIST 3-30, an infrared scan with a thermal imager should be taken once after energizing and stabilizing the new transformer and a week later. An infrared image should also be taken annually before de-energizing or demagnetizing to show consistency with the temperature gage to catch any excess heat. Read more…
Two of the more popular brands of thermal imagers are manufactured by FLIR and Fluke.
Winding Resistance Tests
Power transformers require winding resistance tests to measure the applied DC voltage and current. Winding resistances are tested in the field to check for loose connections, broken strands, and high contact resistance in tap changers. Obvious faults and subtle problems can be detected by measuring a transformer's winding resistance from one transformer bushing to another. The integrity of all these components can be verified with the use of transformer resistance test instruments. Read more…
A variety of manufacturers make winding resistance test equipment:
Transformer Turn Ratio Tests / Polarity Tests
Transformer Turn Ratio tests are able to verify the operating principle of a power transformer, and identify any shorted turns or open-circuited conditions. With a low voltage AC test, transformer turns ratio equipment measures the ratio of high voltage to all other winding at no-load. A TTR device then displays measured ratio variations, which should fall within 0.5% of the nameplate markings. Values that fall outside of this range indicate a shorted or open transformer winding. Read more…
Power Factor / Tan Delta / Doble Tests
Power factor, tan delta or Doble testing is the process of measuring capacitance and dissipation to help determine the condition of a system’s insulation in bushings or between windings. The insulation of a system can degrade over time, and impurities like dirt and moisture can also start to compromise the insulation. This will create a conductive path to the current, consequently leaking electric current flowing through the system and reducing capacitance. The goal is to keep the ratio of resistive component to capacitive component of an insulator low. This ratio is known as tan delta, or dissipation factor (power factor). A high power factor indicates the dielectric loss of oil leading to the need for a Doble test or power factor test. Read more…
The Doble M4000 is specifically called out in FIST 3-30, and can be rented from ATEC along with other power factor test sets.
Insulation Resistance & Ground Tests
The transformer’s core requires two types of test, insulation resistance and ground tests. Insulation resistance testers can be used to determine the integrity of windings or cables in transformers. Transformer insulation resistance deterioration is one of the most common causes of transformer failure. Insulation is subject to many effects which can cause it to fail – excessive heat or cold, vibration, dirt, mechanical damage, oil, corrosive vapors, moisture from processes, and weather. If you fail to maintain your transformer with regular insulation resistance testing, then it can be a costly replacement with long downtime and a shortened lifespan.
Ground tests are required to test the conducting connection between the transformer core and the earth. Testing for grounding is indispensable to maintaining uptime, verifying an installation site, avoiding deterioration, and preventing corrosion. Read more…
Several popular Insulation resistance testers include:
Partial Discharge Tests
Partial discharges (PD), also known as corona, are the small electrical sparks found within the insulation of electrical systems and are caused by electrical breakdown and discontinuities. Over time, insulation is weakened from aging and electrical stress, and partial discharges erode the insulation, and may even cause insulation failure. Proper maintenance and partial discharge tests can help avoid total electrical failure. Read more…
Reclamation FIST 3-30 recommends partial discharge testing to be done on winding and bushings. OMICRON manufactures on of the top equipment for PD tests.
Short-Circuit Impedance Test
A short-circuit impedance test is useful for determining loose or high-resistance connections and can indicate if the core and coils have been shifted, either by mechanical or electrical damage. A short-circuit impedance test is the short-circuiting of one set of the transformer windings while energizing the other. Typically, you will look to short-circuit the higher voltage windings and energizing the lower voltage winding.
De-energizing / Demagnetizing Test
Demagnetizing the core of a power transformer is essential for eliminating the source of potential problems like erroneous diagnostics, inrush current at start-up, inaccurate measurements, and incorrect operation of protective relays. Demagnetizers provide alternating current (AC) for demagnetizing the transformers’ core by changing the polarity of a controlled DC current.
Motor Load Test
Motor load testing is recommended to ensure reliability, verify performance, ensure system compatibility, identify faults, and validate repairs. Optimal peak efficiency of a motor ensures the motor does not overheat and performs at ideal capacity. Read more…
The full Bureau of Reclamation FIST 3-30 manual is available in the pdf document.
Click here to view manual