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This guide provides an introduction to transformer winding resistance test methods and procedures. Photo: TestGuy
Winding resistance measurements are an important diagnostic tool for assessing possible damage to transformers resulting from poor design, assembly, handling, unfavorable environments, overloading or poor maintenance.
Personal protective equipment (PPE), including arc flash rated clothing, provide additional safeguards against electrical hazards. Photo: PEO ACWA (Flickr CC)
Electricity has long been recognized as a serious workplace hazard, exposing employees to electric shock, electrocution, burns, fires, and explosions. Hundreds of deaths and thousands of injuries occur each year on the job due to electrical shock and arc flash, yet almost all of these tragic events are preventable.
In addition to being properly qualified for the task at hand, personal protective equipment (PPE), including arc flash rated clothing, can provide additional safeguards against the hazards posed by working around electrical energy.
This guide provides a general overview of the various PPE that may be necessary for safe electrical work, including insulated gloves or sleeves, face shields, footwear, eye or hearing protection, and other electrical protective equipment.
Mimic bus symbols accurately reflect the distribution system arrangement that they are producing. Photo: Sage Controls, Inc.
The primary function of the electric power distribution system in a building or facility is to receive power at one or more supply points and to deliver it to lighting, elevators, chillers, motors and all other electrical loads.
The best distribution system is one that will, cost-effectively and safely, supply adequate electric service to both present and future probable loads. The selection of a system arrangement has a profound impact upon the reliability and maintainability of the electrical system.
Determining the existing condition of power transformers is an essential step in analyzing the risk of failure. The following is a summary of testing and diagnostic techniques, and tools used to assess the condition of transformers.
It is essential to inspect and test current transformers and their connected instruments at regular intervals. Photo Credit: ABB
Current transformers play an important role in the monitoring and protection of electrical power systems. CT's are instrument transformers used for converting primary current into a reduced secondary current for use with meters, relays, control equipment and other instruments.
The field-testing and calibration of solid-state trip units can be performed by either primary current injection method or secondary current injection method. Photo: YouTube.
The Electronic Trip Unit is a microprocessor controlled, multifunction overcurrent protective device for application with low voltage power circuit breakers. The adjustment flexibility provided by the Electronic Trip Units allows users to easily accommodate load changes and other protective requirements while still assuring optimum coordination.
In addition to the adjustable protection functions, the trip unit is designed to use field interchangeable rating plugs. These rating plugs allow the ampere rating of the circuit breaker to be changed in order to meet specific applications.
Excellent maintenance is essential for reliability and safety of power circuit breakers. Maintenance programs must be tuned to the specific application, well planned and carried out consistent with both industry experience and manufacturer's recommendations.
Photo: Square D Masterpact
Drawout circuit breakers are equipped with safety interlock devices that are required by various Industry Standards and Certifying Authorities. Interlock systems are an integral part of keeping qualified personnel safe and protecting equipment from catastrophic damage.
Photo: epcc / shutterstock.
All transformers have an inherent sound level that varies with the size and style of the core/coil assembly. Depending upon the transformer operating conditions, sound level measurements at the installation site can be drastically different than those taken at the factory.
Switchgear maintenance is essential for continued reliable operation. Photo: Twins Chip Electrical Industry
Substations and switchgear in an electrical system perform the functions of voltage transformation, system protection, power factor correction metering, and circuit switching.
Electrical power aparatus, such as transformers, regulators, air switches, circuit breakers, capacitors, and lightning arresters comprise the components necessary to perform these functions.
This guide provides a general overview for the inspection, testing and maintenance techniques used on switchgear and switchboard assemblies, and their associated components.
Bushings in a high-voltage switchyard. Photo: Wikimedia
The primary function of a bushing is to provide an insulated entrance for an energized conductor into a high-voltage apparatus tank or chamber. A bushing may also serve as a support for other energized parts of the apparatus.
About 90% of all preventable bushing failures are caused by moisture entering through leaky gaskets, cracks, or seals. Moisture causes deterioration of the bushing insulation and can result in explosive failure, causing extensive transformer and other equipment damage, as well as hazards to personnel.
To prevent electrical catastrophes and optimize HV bushing service life, the following preventive maintenance and testing procedures should be performed at regular intervals.
A substation bus scheme is the arrangement of overhead bus bar and associated switching equipment. Photo: ENMAS GB Power Systems
The electrical substation is a junction point where two or more transmission lines terminate. In actuality, most EHV and HV substations can be the point where more than half a dozen of lines terminate. In many large transmission substations, the total numbers of lines terminating exceeds one or two dozen.
A substation bus scheme is the arrangement of overhead bus bar and associated switching equipment (circuit breakers and isolators) in a substation. The operational flexibility and reliability of the substation greatly depends upon the bus scheme.
