Abstractalthough there is an abiding interest in the application of current transformers ct for relaying, few written rules exist for selecting ratings. C100 class for example, a c100 ct class means that the ct is capable of passing 20. Instrument transformers application guide abb group. Modeling the ct scanner spectra function of beam energy geometry focal spot to isocenter, fan angle beam collimation nominal or actual filtration bowtie filter typically proprietary other addl filtration also proprietary tube current modulation scheme. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as current transformer ct and lead. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8. Explain and interpret information found on transformer name plates. T fundamental period of the structure tl longperiod transition period, given in asce 710 figure 22, which is the transition period between the velocity and. Eq 5 this is the most important reference current for all ct performance calculations. It indicates 10% accuracy at 10 times rated secondary current at rated burden. Slightly more complicated is the effective factor, k scc. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors.
If a service has both cts and pts then the two values are multiplied together to give the billing multiplier. Appendix c tceq publication rg211 revised may 20 c. Ps is defined by knee point voltage of current transformer vk and excitation current ie at vk2. As illustrated in 1ec600441, the class x current transformer is needed. Thompson, and brad heilman, schweitzer engineering laboratories, inc. It also imposes a maximum value of rct ct secondary winding resistance.
Ct application guide ge grid solutions online store. Ct shorting terminal strips the illustration below shows the termination of a multi ratio ct on a special shorting terminal strip. The ct secondary resistance should be calculated according to tnb technical. Ct concentration x time ct is the concentration of chlorine in your water times the time the water is in contact with that chlorine. Ctbased monitoring is the most simple and costeffective solution for retrofitting systems.
Knee point voltage of current transformer electrical. Learn how to specify current transformers photo credit. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices. Map out all endtoend linked actions, processes and functions necessary for transforming inputs to outputs to identify and eliminate. Concentration of disinfectant x contact time x baffling factor 0. Of course additional requirements like type, frequency, isolation level, maximal short circuit current and environmental conditions should also be specified.
Calculation of the current transformer 1mrs 755481 accuracy limit factor 1. Selecting ansi class metering current transformers 142 h b0. This class specifies the minimum value of the knee point voltage vk of the ct. Abstractcurrent transformer ct saturation, while a fairly common occurrence in protection systems, is not often clearly. Class x current transformer is use in conjunction with high impedance circulating current differential protection relay, eg restricted earth fault relay.
If your available primary fault current drives the secondary ct current greater than 20 x 5a, then you would need to go to a higher class ct. These measurements are made for each ct scan protocol used, and the data are entered into the ct scanners computer. It is the ctdi vol multiplied by the length of the scan. Ct class definitions ge grid solutions online store. In more practical terms, it guarantees a 10% accuracy provided the voltage across. Please understand that the ct required here is class px or x. So in the above example, if you had a 6005 ratio ct, and your primary fault current was 18ka, the ct secondary current would be 150 a, which is 30 x the 5a secondary ct current rating. T0 to t1 however, the japanese papers submitted in support of fumigation treatments at 2009tppt.
Threephase ac current measurement using current transformer reference design the current flowing through a conductor can be detected using a resistive shunt, current transformer ct, hall effect sensor, and so forth. The auxiliary ct is installed as close as possible to the current transformers. How can you calculate in detail the va burden of current transformer used for restricted earth fault protection. Ct saturation in industrial applications analysis and application guidelines 8 of 34 get8501 10 20 30 40 50 60 70 80 5 10 15 20 25 30 35 fault current, ka peak secondary current, % of fault current 50. Instrument security factor or isf of current transformerinstrument security factor is the ratio of instrument limit primary current to the. Ct primary current rating should be equal to or greater than the maximum expected current for the associated breakers or transformers. Selecting a current transformer ct if the current ratio, burden and class are selected, the current transformer ct has been specified basically. Our systems support additional features such as automated robotic scanning, precision metrology, 4d scanning, and more. Class x current transformer free download as powerpoint presentation. The main purpose of a current transformer is to translate the primary current in a high voltage power system to single level that can be handled by delicate electromechanical or electronic device. Industrial ct 3d xray systems 2d dr xray north star. It is always possible to find an equivalence between a ct defined in class x and a 5p ct or in some cases even a 10p ct.
The following illustrates the method to size a class x current transformer. Knee point voltage of current transformer ps class. Before understanding knee point voltage of current transformer and current transformer ps class we should recall the terms instrument security factor of ct and accuracy limit factor instrument security factor or isf of current transformer. Calculation of the current transformer accuracy limit factor. The dlp can be used to calculate a rough estimate of the effective dose. When the objective is to detect very small defect in weld, it is a common practice. A ct rated at say 5p20 will stay linear to approximately 20 times its nominal current. C ratio error can be determined by calculation from the. Current transformer ps classbefore understanding knee point voltage of current transformer and current transformer ps class we should recall the terms instrument security factor of ct and accuracy limit factor. From the burden the rated impedance can be calculated and consequently the.
Maximum secondary current should not exceed 20 times the rated current 100a for 5a rated ct for ansi class c ct. Current transformers are the very important aspect of. Cts are categorized as protection ct, special protection ct and measuring ct. Formula sheet for all wastewater operator exams revised 8. A practical guide to ct saturation ariana hargrave, michael j. It must also be defined in the future standard iec 600441 under the name of class px. They are customized transformers therefore it is necessary to specify the individual characteristics of the current transformers such as the turns ratio, rated primary and secondary current, voltage knee point, the read more class x current. We also know much about cts and meters because of blondels theorem. Current transformers,voltage transformers and instrument. Calculating ct values problems and possible solutions.
The x indicates that they do not belong to any standardized class. Instrument transformer basic technical information and. Turns ratio tests optional test this test is to ensure the turns ratio of ct at all taps. The primary current of minimum of 25% rated primary current to be injected on primary side of ct with secondaries shorted and the secondary current can be measured and recorded for all cores limits. Eq 4 the saturation voltage from the ct excitation curve is 15 v, therefore the maximum current delivered by this ct to this burden without distortion is. Scope this document describes the calculation of the actual accuracy limit factor f a for protectiontype p current transformers ct. As a reminder, the 5 in the 5p20 would be the ct accuracy class and the p signifies a protection class ct. A current transformer ct is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree ct accuracy class or current transformer class. Class x is a class defined by british standard bs 3938.
They are defined by their ratio, power and accuracy class. How do you calculate an effective dose for ct given the. Value is defined by customer in terms of specific products and services identify the value stream. Class x cts are current transformers which are used for special applications. Current transformer saturation voltage disturbance. First, the calculation of the actual burden of the ct, including connection wires and protection relay impedance, is presented. Selecting cts to optimize relay performance gabriel benmouyal, ireq jeff roberts and stanley e. The performance of a class c ct based on standard excitation curve. Review questions for class iii wastewater treatment plant operators examination please circle your answers and show all calculations.
As illustrated in iec600441, the class x current transformer is needed. The burden of ct when used for protection purpose is quite high when compared with metering class ct, which means that voltage drop across the burden will be high. To use ct to demonstrate that you have sufficient water treatment, you need to do the following three things. Instrument security factor is the ratio of instrument limit primary current to the rated primary current. The metering class ct is specified with accuracy rating for each standard burden for which it is rated. Also please show the calculations for knee point vtg, stabilizing resistor, magnetising current. Protection ct class entries forum industry support. Accuracy class, asymmetrical current, ct burden, ct saturation, dc offset and xr ratio. This reduces the ct burden by reducing the length of the ct secondary current conductors. Class x current transformer class x current transformer is use in conjunction with high impedance circulating current differential protection relay, eg restricted earlh fault relay. Their performance is defined in terms of a kneepoint voltage kpv, the magnetizing current imag at the knee point voltage or 12 or 14 the kneepoint voltage, and the resistance of the ct secondary winding corrected to.
If a ct is rated as a turns ratio, then it likely does not contain a burden resistor. Protection class ct is normally specified as ps protection special. The circuit connection shall be made as shown figure 4. Class x corresponds to a better metering accuracy than classes 5p and even more so 10p see figure 3. Current transformer accuracy is specified by the standards ieee std c57. How can you calculate in detail the va burden of current. The calculator below can be used to determine the desired burden resistor value. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. Classification of industrial xray films as per astm e1815 class i.
1440 340 333 1359 990 955 1324 827 423 1462 147 1476 1325 183 1291 1334 775 1126 1027 1102 974 1251 1600 1368 261 942 1350 1106 336 954 1033 1261 140