Power system protection

Oil temperature indidication and protection in power transformer Ansi code 26Q https://www.facebook.com/share/3DhhJ3w8WbDyEmfp/?mibextid=oFDknk

Vacuum Circuit Breaker: In vacuum circuit breakers, the fixed and moving contacts are housed permanently inside a sealed vacuumed ceramic bottle. The arc is quenched as the contacts are separated in vacuum. In the MV switchgear range, vacuum is the most predominant insulating medium for circuit breaking.

Relay micom p440

Switchgear CBM activities

Transformer Category According to IEC 60076-1, windings in transformer can be classified into high voltage (HV) or low voltage (LV) windings. HV winding is defined as the winding having the highest voltage whilst LV winding is defined as the winding having the lowest voltage. Referring to this definition, transformers in TNB distribution system can be categorized into four categories:  Category 1 – Free breathing power transformers with On-Load Tap Changer (OLTC). This category of transformer has capacity above 5 MVA up to 30 MVA.  Category 2 – Free breathing power transformers with Off-Circuit Tap Changer (OCTC). This category transformer has capacity of 3 MVA up to 5 MVA.  Category 3 – Small power transformers with Off-Circuit Tap Changer (OCTC). However, this category of transformers has capacity above 1 MVA but not larger than 3 MVA and can be either free breathing or hermetically sealed transformers.  Category 4 – Distribution transformer. It has primary and secondary windings designed to operate at high and low voltage or vice versa depending whether it is a step down or a step up transformer. This category of transformer has capacity not larger than 1 MVA and can either be a free breathing or hermetically sealed transformers.

Pressure Relief Device (PRD) in transformer (63)code ANSI: PRD is used to release overpressure build up in the transformer tank so that tank rupture can be prevented. It is a spring operatedself-resealing PRD that operate at absolute overpressure between 28 and 35 kPa (4 – 5 psi). PRD for power transformers are equipped with a micro-switch. The operation of the spring will in turn trigger the contacts of a micro-switch and trip the transformer. It should be noted that PRD is not used for alarm indication.

MV motor protection (micom p242)

Circuit Breakers

Low voltage earthing system

Voltage transformer Markings according to IEC 60044.2 1 - Rating plate markings All voltage transformers shall carry at least the following markings: a) the manufacturer's name or other mark by which he may be readily identified; b) a serial number or a type designation, preferably both; c) the rated primary and secondary voltage (e.g. 66/0,11 kV); d) rated frequency (e.g. 50 Hz); e) rated output and the corresponding accuracy class (e.g. 50 VA Class 1.0); NOTE When two separate secondary windings are provided, the marking should indicate the output range of each secondary winding in VA, the corresponding accuracy class and the rated voltage of each winding. f) highest system voltage (e.g. 72,5 kV); g) rated insulation level (e.g. 140/325 kV). NOTE The two items f) and g) may be combined into one marking (e.g. 72,5/140/325 kV). All information shall be marked in an indelible manner on the voltage transformer itself or on a rating plate securely attached to the transformer. In addition, the following information should be marked whenever space is available: h) rated voltage factor and corresponding rated time; i) class of insulation if different from Class A; NOTE If several classes of insulating material are used, the one which limits the temperature rise of the windings should be indicated. j) on transformers with more than one secondary winding, the use of each winding and its corresponding terminals. 1.2 Terminal markings 1.2.1 General rules These markings are applicable to single-phase voltage transformers and also to sets of single- phase voltage transformers assembled as one unit and connected as a three-phase voltage transformer or to a three-phase voltage transformer having a common core for the three phases. 1.2.2 Terminal identifiers Markings shall be in accordance with Figures 6 to 15 as appropriate. Capital letters A, B, C and N denote the primary-winding terminals and the lower-case letters a, b, cand n denote the corresponding secondary-winding terminals. The letters A, B and C denote fully insulated terminals and the letter N denotes a terminal intended to be earthed and the insulation of which is less than that of the other terminal(s). Letters da and dn denote the terminals of windings intended to supply a residual voltage.

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50BF breaker failure current detector: Breaker failure protection (BFP) is a backup protection for the power system that is needed when a power circuit breaker fails to clear a fault when called upon to do so by a protective relay. The BFP scheme acts to isolate the fault from the protected power system by removing from service power circuit elements located electrically adjacent to the failed power circuit breaker. In general, backup relay protection has been used on power systems for many years. Typically, all parts of the protection system including the relays, voltage and current transformers, circuit breakers, and control power source are vulnerable to failure. All of these components are needed to work properly to effectively clear a fault. To improve protection system reliability, components such as protective relays, power sources, and instrument transformers are often duplicated. Duplicate systems are designed to operate independently to ensure complete protection system functionality during failures. Because it is usually too costly to duplicate the breaker, breaker failure schemes are specifically employed to provide backup protection in the event that a circuit breaker fails to operate properly during fault clearing. Primary protection of the power system from performance failures of the power circuit breaker other than fault clearing failures is sometimes added to breaker failure schemes. These include failure to operate, either tripping or closing, manual or automatic. Where applied, this protection typically exists as an addition to, and as a part of, the same overall scheme as the breaker failure backup protection. The choice and successful application of any BFP scheme depends upon factors such as the local breaker arrangement and also the relative criticality of protected power circuit elements. There is a delicate balance between the risk of damage to unprotected equipment versus the impact of removing adjacent power circuit elements when the scheme operates. This guide reviews generally accepted breaker failure schemes used on utility transmission and generation systems. Many of the characteristics of these schemes also apply to the use of breaker failure on utility distribution systems. Schemes are carefully examined so that advantages as well as disadvantages can be compared. Application examples and testing practices are also included. The guide is written for engineers who have a working knowledge of power system protection but require a better understanding of breaker failure applications. It can also be used as an evaluation tool when comparing alternative breaker failure options. IEEEC37.119.2016