1. Describe the function of polarity marks on current transformers. 2. Transformer differential relays protecting a 50 MVA, 138 kV – 13.09 Y/7.56 kV transformer have been operating normally during the construction phase of a project. When the transformer is being brought up to full load it trips. There is no indication of a fault, as all tests on the transformer and cable …
People are easily distracted in a world filled with more distractions every day. In this day of modern technology, it is easy to get overwhelmed with the number of distracting devices out there, and these devices have encroached upon the driving environment. Cell phones are convenient means to communicate over long distances, but couple them with texting, email, internet, and …
“What are you doing here?” asked the manufacturer’s testing representative. “We are doing start-up of the gear, and your work seems redundant.” Redundant? That depends on what each of us is responsible for checking. That depends on who is going to ensure that all the known potential failures get checked and as needed, corrected. As an industrial or commercial buyer, …
Numerical protection relays offer the ability to alarm for many abnormal operating conditions, including the health of the relay. Below is a list of typical conditions to alarm for due to an abnormal condition: Overexcitation Phase undervoltage Loss of potential or blown fuse(s) Relay firmware or hardware failure Relay access Over or under station battery DC voltage Trip coil monitoring …
The National Fire Protection Association (NFPA) is best known for the 70 standard, which is a consensus standard reviewed and updated every three years. The NFPA produces many additional standards covering topics such as Aircraft Rescue and Fire Fighting, Finishing Processes, and Wastewater Treatment Plants. There are three standards that pertain directly to electrical workers and equipment: • NFPA 70 …
Ground testing is often thought of as ground electrode testing: the measurement of the resistance associated with a particular rod or grounding system. A useful corollary to this is soil resistivity testing. Resistivity is the electrical property of soil itself that determines how well it can carry current. It varies enormously (Table 1) depending on physical and chemical composition, moisture, …
The Tech Quiz questions for this issue concern medium-voltage power system components. FREE QUESTION! What is medium-voltage? Great question, as there are varying answers from NETA, NEMA, NFPA, and IEEE. NETA’s Standards Review Council has defined and classified medium-voltage within the NETA standards as “a class of nominal system voltages greater than 1,000 volts and less than 100,000 volts,” which …
When performing condition analysis on medium-voltage circuit breakers located in metal-clad switchgear, it is necessary to be aware of all potential hazards. The person performing the condition analysis must be qualified to perform the task and have a solid understanding of each possible hazard they may encounter as well as ways to minimize the risks. To better understand the hazards …
The technician’s job is usually to ensure the lights are on, but we often need to shut a facility down to perform much needed outage-based maintenance. This switching activity is often straightforward, but when the electrical system is complex and several issues exist, unexpected events can occur. Our team was recently fortunate to be awarded a major contract to provide …
Historically, CT connections compensated for the phase shift across a transformer when applying differential protection prior to the advent of numerical transformer protection relays. For example, a delta-wye transformer would have wye connected CTs on the delta side and delta connected CTs on the wye side. The delta connected CTs have the same connection as the transformer delta connected winding …