Free Expert Guides on Power Systems, Circuit Design & Electrical Troubleshooting

Surge Arresters and Their EvolutionA surge arrester is always connected in parallel with the electrical equipment it protects. It does not interfere with the equipment's normal operation at system voltage. However, when a dangerous overvoltage appears on the equipment, the arrester conducts first, diverting the overvoltage safely into the ground.The earliest and simplest form of surge arrester consisted of two metal rods separated by a gap and connected in parallel across electrical equipment. W

Mechanical Endurance TestingThe mechanical endurance of circuit breakers is tested according to IEC 62271-100, requiring 10,000 operations (M2 class). During testing at an overseas laboratory, the first prototype failed at 6,527 operations due to a trip spring fracture. The lab accepted this isolated failure, attributing it to spring installation issues. A second prototype was tested but similarly failed after over 6,000 operations due to another trip spring breakage. Consequently, the test lab

The power outage and work scopes must be clearly inspectedCollaborate with the site survey leader to confirm the equipment to be maintained and the work area involved. Consider requirements such as the use of special vehicles and large machinery, and safe distances from adjacent energized equipment. Verify on-site whether the proposed power outage scope is sufficient to meet the operational needs.On-site safety measures must be clearly inspectedCollaborate with the site survey leader to verify s

How should a surge arrester with cracked or exploded porcelain housing be handled?Answer:Handling of Cracked Porcelain Housing: Under normal weather conditions, apply to the dispatcher to de-escalate and replace the damaged phase arrester with a qualified unit. If no spare parts are available, paint or epoxy resin may be applied to the crack to prevent moisture ingress, with replacement scheduled as soon as possible. During thunderstorms, avoid taking the arrester out of service if possible; def

1. What is accident handling? What are the common types of operations used in accident handling?Answer: Accident handling refers to a series of operational actions taken in response to an emergency that endangers personal, power grid, or equipment safety, or when a power grid or equipment accident occurs. The goal is to quickly rescue personnel, isolate faulty equipment, adjust operating modes, and restore normal operation as soon as possible.Common operation types include: test energizing, forc

In plugging or reverse current braking, the armature terminals or the supply polarity of a separately excited or shunt DC motor is reversed while the motor is running. As a result, during plugging, the supply voltage V and the induced armature voltage Eb (also known as back EMF) act in the same direction. This causes the effective voltage across the armature circuit to become (V + Eb), nearly twice the supply voltage. The armature current reverses, producing a high braking torque. To limit the a

A single-stack variable reluctance stepper motor features a salient-pole stator with concentrated windings mounted directly on the stator poles. The number of phases is determined by the connection configuration of these windings, typically comprising three or four windings. The rotor is constructed from ferromagnetic material and contains no windings.Both the stator and rotor are made of high-quality, high-permeability magnetic materials, requiring only a small exciting current to produce a str

Most power transformers are oil-immersed, as the use of oil as both a cooling and insulating medium has proven highly effective in the electrical industry. Below are the primary reasons for using oil in power transformers:Cooling: Oil possesses excellent cooling properties. It absorbs heat generated during transformer operation—particularly from the windings and core due to electrical losses—and transfers it away, effectively dissipating thermal energy and preventing overheat

The efficiency of a power transformer is influenced by a variety of factors, including its design, size, and operating conditions. In general, power transformers are highly efficient, with typical efficiencies exceeding 95%, and often reaching 98% or higher. However, actual efficiency can vary depending on load levels, voltage ratings, and specific design characteristics.Transformer efficiency (η) is defined as the ratio of output power to input power, expressed as a percentage:η

1. Type Test System and StandardsType testing verifies the design rationality and safety of eco-friendly insulated ring main units (RMUs), based on IEC 62271-200 and GB/T 3906, and includes: Insulation Performance: For 12kV RMUs, power frequency withstand voltage is 42kV (1 min) for main circuits and 48kV for breakers. Lightning impulse withstand is 75kV (12kV system) or 125kV (24kV system), with 15 standard impulses (1.2/50μs) per polarity. Partial discharge must be ≤10pC at 1.2&a