Abb oem instrument transformer reference guide april 2014. Current transformers or cts are instrument transformers that convert a generally high primary current i p to a ktimes lower secondary current i s that can be connected to standard measuring or protection devices. On a multitap current transformer ct, once the selected. If the secondary circuit is closed, a current will flow through the. It may be used with insulated or uninsulated conductors, and mounts to substation structures or pedestals in. Np proportion of total number of current transformer turns in use vel current transformer lol accuracy class voltage for example, if the 4005 ampere tap of a 6005 multiratio current transformer is used, np 400600 0. Marker 6 multiratio current transformers shall be installed to allow for future. To assure the safe and reliable operation, the neutral of the current transformer. The typical multi ratio unit will have a schematic showing the number of turns between each tap. The iron core inside the transformer is magnetized.
Standard burdens for current transformers with 5 a secondary windings. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Nonstandard taps also available l optional aluminum ground shield design to provide bushing flashover protection l permanent stainless steel or aluminumnameplate, with pertinent information, mounted on the transformer l conforms to ieee standard c57. Krated transformers 64 open core and coil 65 industrial control type eo transformers 66 type t and multitap transformers 67 type tf transformers 67 instrument, 600 volt class voltage and current transformers 68 torroidal current transformers 69 shorting terminal blocks 610 multiratio current transformers 611 rectangular window. The grounding of current transformers is important to both safety and the proper operation of the protective relays. Standard current transformer multiratio taps 214 burden standards 214 5 kv 36 kv indoor voltage transformers primary current class abb type geiti equivalent abb product bulletin page 2400 to 4800 5 kv indoor viy60 ptw3160 and ptw3260 1vap429511db 148149 2400 to 72007200 8. A multiratio ct is voltage rated using the maximum turns ratio. Multi ratio current transformer wiring diagram sample. Multi ratio current transformers engineering stack exchange. This standard is intended for use as a basis for performance and interchangeability of equipment covered, and to assist in the proper selection of such equipment.
Ct is a very dependable and accurate device for the most part except when in goes in to saturation. Each current transformer is tested for all the routine test parameters as per ieeeansi c57. Table 8current transformer ratings, multiratio type. Marker 7 motor control center bus shall be sized based on the full load amps of connected load, and for future additional loading. If the secondary circuit is closed, a current will flow through the secondary circuit in proportion to the ct ratio. Current transformer tape wound ct manufacturer from udaipur. Current transformer standard burden characteristics 60 hz and 5 ampere secondary burden. E96461 600 volts, indoor 10 kv bil, 25 thru 400 hz mechanical rating. Current transformer basics and the current transformer. The purpose of a current transformer ct is to produce an exact replica of the primary current waveform with its magnitude reduced in proportion to the turns ratio.
Current ratings a secondary taps current ratings a secondary taps. I have little information about the type of ct i am using. Bct which are installed on 600 volt, and higher electrical systems. Typically, these will have five taps and the ratio can be changed within a predetermined range by using different combinations of these taps. It is possible to get other multi ratio ratings with different taps as the need requires. Below is a list of all current transformers available through flexcore, however, not all models are instock. 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. This standard covers certain electrical, dimensional, and mechanical characteristics, and takes into consideration certain safety features of current and. Taps on transformers 225 kva and larger may vary in 35% steps to obtain best design.
Back to the basics current testing valence electrical. Faq current transformers ct electromagnetic industries llp. Interconnecting cable paths could be shown approximately, where certain receptacles or fixtures have to get on a typical circuit. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding. Multi ratio current transformer ct scottf electrical 11 sep 07 09. If this current transformer has a 10l200 rating, vel 200. Current transformer saturation voltage disturbance. Many substation cts include a multiratio secondary, therefore the mct1605 has the ability to plot and simultaneously display up to 10 ct saturation curves. Manufacturer of current transformer tape wound ct, nexgen ring type ct, standard multi ratio current transformer and resin cast ring type current transformer offered by nexgen technology, udaipur, rajasthan.
Taps shall be two 2 steps above and two 2 steps below nominal voltage in 2. It produces a current in its secondary which is proportional to the current in its primary. As part of itis product scope, the company produces a diversified range of bushing current transformers. Accuracy, polarity, dielectric and turnsratio tests are standard for every current transformer. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Ieee standard requirements for instrument transformers. Current ratio turn ratio secondary taps 600 ampere multiratio 50 to 5 10 to 1 x2x3 100 to 5 20 to 1 x1x2. If this same transformer had a primary voltage of 4160 v instead, there would be 208 primary turns and 2. Bushing current transformersbushing current transformers. Marker 6 multi ratio current transformers shall be installed to allow for future additional loading. Relay connected to ct tap which provides the desired ratio. Current transformers, along with voltage or potential transformers, are instrument transformers.
A current transformer is just the opposite and is unloaded with the secondary terminals shortcircuited. Electrical, dimensional, and mechanical characteristics are covered, taking into consideration certain safety features, for current and inductively coupled voltage transformers of types generally used in the measurement of electricity and the control of equipment associated with. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Cts are required because standard current measuring devices are not configured to measure highcurrent levels. Instrument transformers scale the large values of voltage or current to small. Rectangular window current transformers single ratio. Schneider electric instrument transformers steven engineering. Current transformers, or cts, are transformers used to step down the current level of highpower transmission systems to measure or monitor the current levels. When current flows through the primary winding, the following actions occur. Jun 29, 2016 ieee standard requirements for instrument transformers abstract. The circuit connection shall be made as shown figure 4.
Williams, firstenergy corporation ariana hargrave, matthew watkins, and vinod k. To determine the tap location to be used, divide the primary current with the secondary current. Mechanical rating shall be equal to shorttime current carrying capability of the circuit interrupters. The classification of protection current transformers follows the following. The family of curves below describe the excitation characteristics for the 6005 multi ratio bushing current transformer shown on the previous sheet. The foremost interface device between the power system and the protective relaying is the ubiquitous current transformer. When the circuit burden gets too large, the ct secondary voltage. General purpose standard transformers are intended for power, heating, and lighting applications.
The above is the standard ansi multi ratios with their respective taps. To check pricing and availability for a specific current transformer model, give us a call at 614 8896152 or use our quote request form. This means that for this particular transformer, tap increments cannot be any smaller than 4. A multi ratio ct is just that, its a ct that has multiple secondary taps.
There are four typical types of current transformers. For example, the potential transformer mentioned above having a rating of 480. Bushing current transformersbushing current transformers 600v. Multi ratio current transformers typically have 8 to 10 primary values multiratio current transformers are multitap units.
Another common variation is the split core or take apart current transformer. Cts are required because standard current measuring devices are not configured to measu. Instrument transformer basic technical information and. The primary and secondary windings are galvanically separated and can be on a different potential level.
The most common ct secondary full load current is 5 amps which matches the standard 5 amp full scale current. Stonger even, when the secondary terminals of a ct are open, there is no secondary flux to oppose the primary flux and the core goes to positive saturation on the positive current sine and to negative saturation on the negative current sine. Whether utilizing a standard ei core or a toroidal core, current transformers generally employ a single turn primary winding and a multi turn secondary winding. There are several classes of accuracy for instrument transformers defined by the ieee, csa, iec, and ansi standards. Turns ratio tests optional test this test is to ensure the turns ratio of ct at all taps. Mct1605 multitap automatic current transformer saturation, ratio and polarity test set n one button automated test. The hfa outdoor rated stationpost current transformer is a windowtype suitable for use on line voltages up to 36kv 200kv bil. In most instrument transformer applications where the ct is being used for measurement of amperage magnitude only, the ct will work regardless of direction of current flow through the ct. These products are obsolete and can no longer be ordered. 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.
Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Current transformer shall be sized based on motor full load amps, so. Abstractmicroprocessorbased transformer differential relays offer fast and dependable. For multi ratio ct, using a lower tap reduces the effective accuracy and increases the chance of saturation. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating. Beyond the nameplate selecting transformer compensation. It allows all types of single and multiratio current transformers to be tested onsite in power system. Aug 14, 2018 the purpose of a current transformer ct is to produce an exact replica of the primary current waveform with its magnitude reduced in proportion to the turns ratio. The magnetized iron core induces a voltage in the secondary coils.
The turns ratio is approximately equal to the voltage. Your companys standards and work practices will differ from some. Current transformer ct performance can be estimated using one of the following methods. Automated testing of multitap cts without the need for. The turns ratio and winding connections of a transformer make it so that the current entering the transformer is not the same as the current leaving the transformer, even under normal conditions.
With multitap cts, as long as there is a loadburden on the chosen ratio terminals of the unit, potentially hazardous voltages will not build up at the terminals. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. This is a plot of the ct secondary current against secondary voltage. You can also use our live chat tool to speak directly with a sales representative. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding wound type. The information in this table is for reference only. This will give you the number of turns you need for that given primary current. With multi tap cts, as long as there is a loadburden on the chosen ratio terminals of the unit, potentially hazardous voltages will not build up at the terminals. The transformation ratio k of a current transformer is the number. Current transformer instrument transformer division also, it is important to specify correct burden in context of instrument security factor i. Outdoor stationpost current transformer electrical products.
However, typically the h1 faces source and h2 faces load. Types scr and scrd indoor current transformers instrument transformers product features. While the latter configuration would not be used today, one may be required to make this calculation on an existing system. The concept of current differential protection is simple, but it is made more complicated when the zone of protection includes a transformer. The assembly shall be installed on vibrationabsorbing pads. I encountered a problem in measuring electrical energy using a multi ratio current transformer ct. The standard current transformer secondary winding is rated at 5a as per ansi standards. A multi ratio ct is voltage rated using the maximum turns ratio. Bushingtype current transformers bct instrument transformers, inc. Ratio the ct ratio is the ratio of primary current input to secondary current output at full load.
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