There are many problems that can be avoided during transformer installation simply by installing the transformer in the correct environment. Many safety hazards and difficulties can be avoided or minimized by taking certain factors into account when placing a transformer, before installing and connecting it. Also, the location can influence how the transformer should be configured and what precautions should be taken in the future.
Installing transformers in accordance with ANSI, NEMA, and IEEE standards is critical to ensuring a safe electrical installation as well as a reliable power supply system, especially for those applications where power quality is an issue. Transformer installation is one of the most common but complicated installation practices that causes considerable confusion when sizing overcurrent protective devices (OCPD) and grounding and bonding conductors.
Many electrical installations can be challenging in terms of NEC requirements, and transformers can take that challenge to a new level. A properly designed installation will ensure that conductors and equipment are properly sized, protected, and will also take care of the overriding problem of grounding. Incorrect installation can cause fires due to protection or improper conductor sizes, as well as electric shock due to improper grounding.
This article will provide a brief overview of important considerations to take into account during installation, for transformers located indoors and outdoors, and for dry versus liquid-filled transformers.
Installation Best Practices Some of the particularly important transformer installation best practices are listed below:
1. Permanent ground connection: Once the transformer is permanently placed, prior to further inspection and prior to assembly of the unit, the tank must be permanently grounded with a properly installed permanent ground connection and the correct size.
2. Humidity: Access to the liquid-filled compartment of the transformer should not be allowed in conditions of excessive humidity or rain. If the humidity exceeds 70%, for example, dry air must be continuously pumped into the gas space. Liquid-filled transformers that are shipped with nitrogen in the gas space must be purged by pumping dry air for at least 30 minutes before service personnel can enter the tank. Oxygen concentrations of 19.5% to 23.5% are recommended.
3. Fluid inspection: If it is necessary to remove the insulating liquid for inspection electrical transformer installation, make sure you have equipment to store the clean and dry liquid during the inspection and to filter the liquid before refilling the tank. It is very important that all associated equipment used in handling the fluid (hoses, pumps, etc.) is also very clean and dry. If this equipment was previously used with a different type of fluid, clean all contaminated items. When removing the liquid, its level should not drop below the top of the windings.
4. Pressure holding: Liquid-filled transformers can be stored outdoors upon delivery. Sufficient gas pressure must be maintained to allow a positive pressure of 1 psi to 2 psi at all times, even at low ambient temperatures. The pressure-vacuum gauge, if supplied with the transformer, will show pressure variations with ambient temperature. Pressure and ambient temperature readings should be recorded regularly. Manufacturer’s instructions for storage of accessories should be consulted.
5. Inspection and Filling – You must perform a final inspection of the transformer before it is energized, especially if any work has been done inside the tank. All electrical connections should be checked for tightness. All bushings must be checked for tightness, and all traction cable connections must be checked. The electrical spaces inside the tank must be checked. A final check should be done to make sure all tools have been removed.
6. Load: After applying full voltage, the transformer should be kept under observation during the first hours of operation under load. After several days, check the oxygen content and dielectric strength of the oil. All temperatures and pressures should be verified in the transformer tank during the first week of operation. Except in the case of special designs, the transformers can operate at their nominal kVA