Section 2 insulation materials and properties mp4 l. Dec 3, 2012 basic insulation level bil is level designed to withstand surge voltages. Basic principles, standard insulation levels and test procedures. This is the insulation level that is designed to withstand surge voltages rather than only normal operating voltages.
Normally, 100 percent insulation level is used on a grounded system and is. The basic insulation level bil of equipment such as transformers, is defined as the. Capacitance charging current which starts out at a high level and drops after the insulation has been charged to full voltage. Total current in insulation testing has three components. Review of the basic insulation level for 400 kv oil. Significant if application is outdoors and high intensity indoors. Basic insulation level article about basic insulation. When lightning impulse over voltage appears in the system, it is discharged through surge protecting devices before the equipments of the system get damaged. It was assumed that lightning overvoltages would be introduced into the cgit system due to lightning strokes. Their use is recommended also for resonant grounded systems. A conductor is a substance which contains many mobile charged particles called charge carriers which are free to move about inside the material. The minimum level is known as the basic insulation level bil that must be that of all.
The bil or the basic impulse insulation level indicates the ability of the transformer to withstand these heavy surges. I read up about basic insulation levels and to my understanding is that the system from the table for 22 kv should be able to handle 125 kv surge. An insulation level defines various insulation thicknesses within a single voltage rating. Basic insulation level bil tested with lightning impulse 1. Study to determine the basic insulation level requirements. Insulation values above this level for the lines and equipment in the system must be so coordinated that specific protective devices operate satisfactorily below that minimum level. Cable insulation is designed to withstand the voltage stresses a cable will experience over its expected lifetime. For a given electrical equipment at a rated voltage of say 11kv, how is the basic insulation level bil determined 09022014 02. What is the basic insulation level of various electrical. Transformers operating at 2400 v and 4160 v are rated at 25 kv bil.
Scribd is the worlds largest social reading and publishing site. Home engineer reference and training manuals table 84. Lightning arresters are coordinated with standard electrical equipment insulation levels so that they will protect the insulation against lightning over voltages. Basic concept of equipment protection is insulation coordination. Each type of electrical equipment has a standard bil rating. Nema 9 insulation classes, maximum hot spot temperature, and typical materials are listed in fig. First edition 2003 second edition 2004 third edition 2005 fourth edition 2006 fifth edition 2007 sixth edition 2010 published by abb sace via baioni, 35 24123 bergamo italy. Basic insulation level table free download as word doc. Temporary over voltage tov an oscillatory phase toground or phase tophase over voltage, at a given location and of relatively long duration 1s to 10s, is undamped or only weakly damped tov level establishes the rating of surge arrestors. Common bil ratings are for different voltage systems are shown below.
The design of a transformer makes it capable of withstanding voltage surges to a certain level. With a little recordkeeping and common sense, however, you can get a good picture of the insulation condition from values that are only relative. Product safety considerations for insulation coordination of lowvoltage equipment scott aldous, compliance engineer. Why ac needs more insulation than dc for the same working voltage level. Introduction to basic insulation terms insulation outlook. Insulation withstand and clearances with exlim and pexlim surge. The insulation coordination standard and guide apply to threephase ac systems above 1 kv and are divided into two parts. Insulation coordination and surge arrester selection transport for. Daily allowable peak loads for normal life expectancy.
Basic insulation level article about basic insulation level. It specifies basic impulse insulation levels in terms of a withstand voltage for a specified test wave. The minimum level is known as the basic insulation level bil that must be that of all of the components of a system. This report of the joint committee on coordination of insulation of aiee, edison electric institute, and national electrical manufacturers association is the culmination of more than ten years study to establish basic insulation coordination. Iec tc 109 standards on insulation coordination for lowvoltage equipment. Insulation coordination for lightning transients based on. Hence, the insulation of such equipment must be designed to withstand a certain minimum voltage before the lightning impulse over voltage gets discharged. Statistical methods of insulation coordination at higher transmission voltages, the length of the insulator strings and the clearance in air do not increase linearly with voltage but approximately to v 1. Generally, the impulse insulation level is established at 15 to 25 % above the protective level voltage of protective devices. Hence, the insulation of such equipment must be designed to withstand a certain minimum v. Bil or basic insulation level definition table and calculation. General calculations excerpt from prysmians wire and.
The objective of this work was to check the impact of switching surges on the choice of bil and to re. The megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. Overvoltages and insulation coordination in mv and hv. The basic impulse level bil is the maximum impulse voltage that electrical equipment can withstand without damage. Basic insulation level definitionwhen lightning impulse over voltage appears in the system, it is discharged through surge protecting devices before the equipments of the system gets damaged. Reinforced isolation in data couplers analog devices. This approach compares overvoltage stress with insulation strength. Basic insulation level definitionwhen lightning impulse over voltage appears in the system, it is discharged through surge protecting devices. The feasibility of a 0 kv basic insulation level bil with respect to lightning surges was assessed for an hvdc compressed gas insulated transmission line. Its value is doubled by the fact that it concerns high voltage networks. Insulation coordination in power system electrical4u. The two most common levels are 100 percent and 3 percent.
Protective earthing is also considered a single level of protection. Having a strong knowledge of the terminology in the insulation industry is the foundation upon which a more complex understanding is built. Transformers with a rating of 600 volts and below are designed to have a bil of 10 kv. The application and selection of lightning arresters. Airinsulated mediumvoltage secondary distribution switchgear sbcw panel is ideal for all applications where is required the lsc2a service continuity together with a withdrawable circuit breaker for a fast circuit breaker replacing, in case of maintenance or fault. Square dschneider electrics low voltage dry type distribution transformers utilize an insulation with a 10kv bil. Flame spread and smoke developed ratings are of vital importance. The insulation capability of an item of electrical equipment to withstand specified voltage surges explanation of basic insulation level.
Basic insulation level how is basic insulation level. Consult the cable manufacturer for insulation thicknesses. Ieee guide for the application of insulation coordination. Materials are often classified as electrical conductors or electrical insulators based on their resistivity. Product safety considerations for insulation coordination. Bil or basic insulation level definition table and. What is the meaning of the basic insulation level bil. Breakdown voltage is a characteristic of an insulator that defines the maximum voltage difference that can be applied across the material before the insulator conducts. Basic insulation level for a 22 kv system electrical.
The rated insulation level is the value of the impulse withstand voltage and the value of the power. Applies to low voltage transformers by square dschneider electric resolution. The mechanism by which overvoltages within the cable can exceed the protective level of the arresters at the cable terminals is outlined. Bil or basic impulse insulation level is the dielectric. The complete guide to electrical insulation testing.
Standard basic impulse insulation levels ieee journals. Types of insulation cellular insulation insulation composed of small, individual cells separated. Jul 25, 2018 generally, the impulse insulation level is established at 15 to 25 % above the protective level voltage of protective devices. General calculations excerpt from prysmians wire and cable. Jun 05, 2017 the design of a transformer makes it capable of withstanding voltage surges to a certain level. Standard insulation levels relative to bil table 2. Basic insulation insulation applied to live parts to provide basic protection. The minimum level is known as the basic insulation level bil that must be that of all of the components of a. Board of industry leaders consumer electronics association bil. The basic insulation withstand data for the substation is.
Electrical installation handbook protection, control and. Why ac needs more insulation than dc at same voltage level. For instance, all transformers rated 600 v and below have a bil rating of 10 kv. For a cable or wire, it is the maximum impulse voltage that the wire or cable is designed to withstand without damage. What is the transformer bil basic insulation level. In solid insulating materials, this usually citation needed creates a weakened path within the material by creating permanent molecular or physical changes by the sudden. May 15, 2018 basic insulation level definitionwhen lightning impulse over voltage appears in the system, it is discharged through surge protecting devices before the equipments of the system gets damaged.
Product safety considerations for insulation coordination of. Basic insulation level of a transformer is also called its lightningimpulse withstand voltage level. Instrument transformer basic technical information and. Overvoltages and insulation coordination in mv and hv studiecd. Review of the basic insulation level for 400 kv oilfilled cable. Bil is defined as basic insulation level iec somewhat frequently. Comparison of ieee and iec standards for calculations of insulation. What is the basic insulation level bil power engineering. Cables in this category may be applied in situations where the clearing time requirements of the 100 percent level category cannot be met, and yet there is adequate assurance that the.
The insulation capability of an item of electrical equipment to withstand specified voltage surges explanation of. At this voltage level, the procedure for calculations refer to. The associated insulation levels shall be provided regardless of whether tests are or can be performed. Which means that the arrestor bracket must have a bil lower than that in order to absorb the surge. The basic impulse level bil of the transformer insulation is specified according to the voltage rating transformer and to the. Impulse test is a dielectric test which consists of the application of a high frequency steep wave front voltage between windings and between windings and ground. Insulation level requirements for a prototype 1200 kv cgit. Insulation levels in electrical equipment are characterized by the withstand voltages used during the impulse test. Reinforced insulation in data isolators is designed and qualified to provide the protection of double insulation systems while providing the data transmission performance available with a single isolation barrier. Switching and temporary overvoltages tov this paper. Insulation coordination electrical and computer engineering.
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