1. High speed biased differential relay The DMH type relay provides high speed biased differential protection for two or three winding transformers. The relay is immune to high inrush current and has a high degree of stability against through faults. It requires a max of two cycles operating time for current above twice relay rated …
Protection Of Generators And Transformers
As Generators and transformers are major components of a power system, so it is quite necessary to take all the preventive measures for the protection of transformers and generators. These are the following ways (ANSI codes) we use to protect transformers and generators from faults: 87/G1 Generator differential protection (87/G1): the protection is provided with …
Ceramic (Porcelain and Glass) Insulators
Materials Porcelain is the most frequently used material for insulators. Insulators are made of wet, processed porcelain. The fundamental materials used are a mixture of feldspar (35%), china clay (28%), flint (25%), ball clay (10%), and talc (2%). The ingredients are mixed with water. The resulting mixture has the consistency of putty or paste and …
Operation of potentially explosive installations – The directive 99/92/EC
99/92/EC Directive In addition to the 94/9/EC Directive, which regulates how explosion protected equipment and protective systems are placed on the market and the design, construction and quality require-ments to be met by them, the 99/92/EC Directive stating “Minimum requirements for improving the health and safety protection of worker potentially at risk from explosive atmospheres” refers to the operation of potentially explosive …
The Need for Breaker Failure Protection
Circuit breakers are strategically located in power systems to connect circuits and electrical apparatus. Circuit breakers are commanded to open and close by protection and control systems that monitor conditions on the power system. Protective relay systems detect abnormal conditions, most notably, system faults (short circuits), and direct one or more circuit breakers to open …
Transformer Protection – Abstract from NEC
NEC, Code 450.4 Calculate overcurrent Protection on the Primary According to NEC 450.4, “each transformer 600 volts, nominal, or less shall be protected by an individual overcurrent device installed in series with each ungrounded input conductor.” Such overcurrent device shall be rated or set at not more than 125% of the rated full-load input current …
Motor starting problem and high motor inrush currents
Electric motor protection device depends on the accurate and correct selection of overload(s), fuses and/or circuit breakers. Over the years the protective devices have been selected according to the applicable code requirements with only minimal nuisance tripping. However, in recent years, the problem of nuisance tripping due to the high motor inrush currents that occur …
Consequences of internal arc for personal safety and MV electrical equipment
The aim of this article is to describe the internal arc phenomenon, its consequences for safety, current methods of limiting them and current regulations in general for equipment used in medium-voltage electrical distribution networks. Internal arcs can occur in electrical equipment when the service conditions for which it was designed are not fulfilled or it …
What is HIPOT Testing (Dielectric Strength Test)?
Hipot Test is short name of high potential (high voltage) Test and it is also known as Dielectric Withstand Test. A hipot test checks for “good isolation.” Hipot test makes surety of no current will flow from one point to another point. Hipot test is the opposite of a continuity test. Continuity Test checks surety …
Transient Voltage Surge Suppressors
Transient Voltage Surge Suppressor (TVSS) is a device that every data center or mission critical facility should have. Why should every data center have one and what does it do you ask? The purpose of a TVSS is to eliminate or reduce damage to data processing equipment and other critical equipment by limiting transient surge …
