Shunt reactors with a saturable core could also be possible. Steps to draw the phasor diagram at capacitive load. Nonroutine maintenance schedule tests to prove the integrity of a voltage transformer is also given in annexure 1 maintenance schedules of voltage transformers and capacitor voltage transformers. The component of the applied voltage to the primary equal. In contrast, this research will place ferroresonance in capacitive voltage transformer cvt as the main focus. This oilfilled coupling capacitive voltage transformer will. The capacitive voltage transformer consists of one condenser unit and one electromagnetic measuring unit emu. They have a capacitive voltage divider but also have a dualwinding transformer to couple the divided voltage to the metering circuit. Analysis and applications of the capacitive transformer. The ferroresonance phenomenon in voltage transformers is analyzed in this section through several software simulation examples, using the software tool matlab. Capacitor voltage transformer cvt or ccvt construction. The two basic types of transformerless power supplies are resistive and capacitive. Difference between capacitive voltage transformer and.
Pdf identification of parameters for coupling capacitor voltage. Iran transformer research institute, tehran, iran abstract with changing the parameters of layer winding in transformers, capacitive characteristic coefficient of winding will be changed. The voltage regulation determines the ability of the transformer to provide the constant voltage for variable loads. They do not have losses from heat, noise and induction. Universal resistive capacitive reference voltage divider. Capacitive voltage transformers of type ecf are used in highvoltage switchgears from 72 to 550 kv. The voltage is applied to the divider over a lead with damping resistor at the beginning. Jan 19, 2017 capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. For example, if a 480 volt primary transformer with a 240 volt secondary is operated at 240 volts, the secondary voltage is reduced to 120 volts.
A calibration service for voltage transformers and high. It is demonstrated in this research that ferroresonance can also occur in cvt due to circuit breaker switching. One of the advantages the capacitive type has, in comparison to the inductive type, is the possibility to use capacitive voltage transformers as highfrequency coupling units towards the primary system over headlines a typical application would be to utilize the cvts for power line carrier plc highfrequency signal interface units. It also serves the purpose of power line carrier communication. A potential transformer is a conventional transformer having primary and secondary windings. Study on the measuring harmonics based on capacitor voltage. Transformers voltage and current transformer in one unit. Jun 01, 2015 for an ideal voltage transformer, the voltage produced in the secondary winding is an exact proportion to the primary voltage and are exactly in phase opposition. There are several capacitive elements in a transformer. Capacitive voltage transformers of type ecf are used in high voltage switchgears from 72 to 550 kv. Acalibrationservicefor voltagetransformersand highvoltagecapacitors williame.
That also means less loss,so that voltage increasing. In this article we are going to have details of the parameter which are mentioned on a nameplate of capacitive voltage transformer. Apr 11, 2020 a cvt, or capacitor voltage transformer, is a transformer circuit used in high voltage applications. Pdf selfcapacitance of highvoltage transformers luca. Voltage transformers and capacitor voltage transformers. All capacitive voltage transformers require some sort of ferroresonance damping circuit the capacitance in the voltage divider, in series with the inductance of the compensating reactor and the wound transformer inside the electromagnetic unit emu, constitutes a tuned resonance circuit. Examples of ferroresonance in a high voltage power system. The capacitive voltage transformer cvt is also called capacitive potential transformer. Identification of parameters for coupling capacitor voltage. What are the advantages of using a capacitor voltage. It is also used for power line communication between different substations.
The emu incorporates an inductive reactor, connected in series between the voltage divider and the high voltage end of the primary winding, to compensate for the shift in phase angle caused by the capacitive reactance of the cvd. Nameplate details of capacitive voltage transformer cvt. The capacitor voltage transformer is used as a means of delivering a filtered, low voltage signal to the protected relay portions of the attached electrical circuitry. Using transformer parasitics for resonant converters a. Cvt in electrical capacitive voltage transformer cvt.
This paper reports the digitaltime domain and frequency domain studies on a typical 2kv capacitor voltage transformer cvt model. As part of trenchs product scope, the company produces a diversified range of instrument transformers for transmission class instrument transformers include. There are two types of voltage transformers, magnetic voltage transformers vt and capacitive voltage transformers cvt. For the voltage measurement purposes, the behavior and. Nameplate details of capacitive voltage transformer cvt explained. The pv voltage instrument transformers are used in electric power grids with system voltage of up to 123 kv and frequency of 50 hz. This circuit is one of a category of circuits called a transformerless ac to dc powersupply or a cr dropper circuit. Clearly, the rc network can be made to act as an ideal transformer paralleled by a capacitance c at the primary side, with the resistive load r. Capacitive voltage transformer oa capacitor voltage transformer cvt or ccvt, is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for metering or operating a protective relay. Transformer supplied through a long transmission line or b. Primary line to ground connected voltage ratios are available from 525. The active part of the voltage transformer is located in the foot housing. Since, impulse voltage distribution ivd along a winding is depended on this coefficient, so analyzing this coefficient is important in transformers.
They transmit voltages to standar dised, equivalent values for. What is the difference between the inductive voltage. The data can be displayed and analyzed a er the test, or transferred to pc through usb disk and produce a word or pdf. The ks8695x, ks8695ppx, ks8993, ks8993mf, and ks8995maxa all have voltage drive 10baset transmitter circuitry. Pullman, w a usa abstract capacitive voltage transformers cvts are common in high voltage transmission line applications. Another form of capacitor voltage transformer is one that is either attached to or run in sequence with something called a capacitance coupled voltage transformer, or ccvt. The regulation of a constant voltage transformer can be designed to be better than a few percent. For over a century, utilities around the world have relied on ge to deliver. The transformer on capacitive load leading power factor load is shown below in the phasor diagram. The value of the voltage transformers magnetizing reactance varies as a. Characterisation of the capacitive voltage transformers. Figure 1 capacitive voltage transformers principal construction. The type of the cvt is always a singlepole one, thus the connection is between phase and earth.
The low voltage stresses within the capacitor elements ensure a safe and reliable product. It also provides electrical isolation same as potential transformers. If the constant voltage transformer is subjected to a line voltage frequency change the output voltage will vary, as shown in figure 115. Capacitive voltage transformers cvts are used on higher voltage levels, starting from 72.
Capacitance occurs winding to winding, turn to turn, windings to core and stray capacitances between terminals and case. As such, the need for accurate and reliable voltage. Instruments beside the universal resistive capacitive voltage divider the instruments for reference measuring systems can be delivered as well, e. On rare occasions winding capacitance is increased to reduce ringing in switching transformers. If you want to get a real understanding, looking at pulsating dc voltage multipliers and add a phase style phase converters used to mimic 3 phase power where only 2 phase is available. Capacitive voltage transformer is mainly used for measurement of voltage and for protection purpose. Distance relays and capacitive voltage transformers balancing speed and transient overreach page 2 of 22 1. Model dfk introduction capacitive voltage transformer model dfk up to 800 kv, model ddb up to 170 kv. Hv outdoor capacitor voltage transformers robust design and. If the transformer was originally rated 10 kva, the reduced rating would be 5 kva, or in direct proportion to the applied voltage. Capacitive voltage transformers pfiffner instrument transformers. Cvts offer the advantage that the voltage divider capacitor, being itself relatively smaller and lighter, configuration makes the transformers iron core much smaller in size, and hence more economical, versus what it would be if a pure magnetic transformer would be used. Pdf dynamic compensation of capacitive voltage transformers. Potential transformer is inductive step down transformer used for measurement of voltage and protection where as cvt is capacitive voltage transformer consisting of stack of series connected capacitor the voltage across the capacitor is used to measure the voltage.
Figure 6 shows the saturation curve of the voltage transformer model developed. I cannot find the right words to express the admiration and sincere gratitude towards dr. In the latter case, the device is known as a coupling capacitor voltage transformer ccvt, and when the transformer primary winding. Self capacitance of high voltage transformers article in ieee transactions on power electronics 225. May 14, 2017 for the love of physics walter lewin may 16, 2011 duration. Nevertheless, the ferroresonance phenomenon also depends on many other factors and conditions, such as residual fluxes in the transformer core, type of transformer winding connection, capacitance. A method of realtime calibrating the voltage signal from the capacitive tap on an abb current transformer using unipowers up2210rabb capacitive tap module has produced accurate results of unbalance, harmonics and transients with no limitation in bandwidth. Cvt the fundamental frequency voltage signal retains the. They transform high voltage into standardised values for meters, measuring and protection devices. Among kinds of voltage transformer, cvt which is the common short form for. Introduction capacitive voltage transformers cvts are the predominant source of the voltage signals for distance relays in high voltage hv and extra high voltage ehv sy stems.
As such, the need for accurate and reliable voltage transformation is essential. Capacitor voltage transformer induced ferroresonancecauses. Induces emf e 1 and e 2 lags the flux by 90 degrees. Hv outdoor capacitor voltage transformers and coupling. The voltage regulation is defined as the change in the magnitude of receiving and sending voltage of the transformer. This application note will discuss both with a focus on the following. The capacitive voltage transformer stepdown the high voltage input signals and provide the low voltage signals which can easily measure through the measuring instrument. The coupling capacitance is primarily made up of the capacitance of the system dielectric between the phase conductor and ground. Voltage potential transformers inductive and capacitive types, current transformers and combined instrument transformers voltage and current capacitor voltage transformers convert.
Kolar, senior member, ieee abstractparasitic capacitances of conventional transformers can be used as resonant elements in resonant dcdc converters in order to reduce the overall system size. Capacitor voltage transformer in hindi cvt concept duration. The most common cases are singlephase power transformers and voltage transformers energized through a series capacitance, and threephase distribution transformers subject to singlepole switching or interrup tion. Capacitive voltage transformer model dfk up to 800 kv, model ddb up to 170 kv. Instrument transformers high voltage 31 capacitive voltage transformers isolate the measuring instruments, meter, relays, protections, etc. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. Because capacitance load compensate part of inductance load comes from transformer. Capacitive transformer this is a forgotten technology, invented over 100 years ago, and seriously needed today.
Pdf a method to obtain the coupling capacitor voltage transformer ccvt model parameters from frequency response curves is presented. Transformer connected to a deenergized transmission line running in parallel with one or more energized lines 6 papers 16, 17, 7. Apr 29, 2018 cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values. This voltage transformer contains a high voltage coil, secondary windings and a core encapsulated in hermetic housing filled with pcbfree transformer oil. The ddb123 outdoor coupling capacitive voltage transformer is rated for use on 115,000 volt systems with 550kv bil. Another equivalent network may be drawn as indicated by fig. As soon as total capacitance load is no more able fully compensate the increasing inductance load, voltage starts decreasing. But in actual pts this is not so because of the presence of voltage drops in primary and secondary resistance and also due the power factor of the burden on secondary. The capacitor voltage transformer cvt or capacitor coupled voltage transformer ccvt is a switchgear device used to convert high transmission class voltage into easily measurable values, which are used for metering, protection, and control of high voltage systems.
The transient studies are conducted using alternative transient program atpemtp. Pullman, w a usa abstract capacitive voltage transformers cvts are common in highvoltage transmission line applications. It is shown that the leakage inductance can be regulated in the range. How electrical capacitive voltage transformer cvt works explained in the video. These remote relay operations resulted in outages to five transmission lines and the substation where the ccvt failed. A software model has been developed based on test data obtained on a real voltage transformer. Mar 11, 20 i dont feel like getting into the nitty gritty of it but phase shifting increases voltages in ac circuits.
Transformer less capacitive bleed power conversion or st an1476. Capacitive voltage transformers cvts have been widely used within transmission power systems for applications ranging from highvoltage to ultra highvoltage. A calibration service for voltage transformers and highvoltage. Lesson learned transmission relaying voltage transformer failure 2 august 10, 2011 cleared by the operation of remote backup relay elements. They enable transmission of high frequency signals through the high voltage hv lines. They transmit voltages to standardised, equivalent values for meters, measuring and protective devices. A capacitor voltage transformer cvt or ccvt, is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for metering or operating a protective relay. Selfcapacitance of highvoltage transformers request pdf. Voltage transformer connected to an isolated neutral system 14 papers 10, 5. In its most basic form, the device consists of three parts. In general, part of the designers task is to keep capacitance to a minimum. Capacitor voltage transformer cpb is designed for revenue metering and protection in high voltage networks.
These types of transformers are used in the same manner, however, they are. Capacitor voltage transformer cpb 72 pdf english pdf drawing. Transient overreach concerns and solutions for distance relaying daqing hou and jeff roberts schweitzer engineering laboratories, inc. Voltage transformers type eof are used in high voltage networks within the 24245 kv range. Pdf investigation of transient performance of capacitor. Diagnostic testing and monitoring of power transformers. Capacitive instrument transformers resistive capacitive voltage reducers portfolio for ais and gis application several thousands of trenchs instrument transformers have been successfully operating for many decades all over the world and under every environmental condition.
Capability for handling a short circuit is an inherent feature of a constant voltage transformer. Phasor diagram of the transformer on capacitive load. In capacitor voltage transformers capacitors are used as voltage divider. Capacitive voltage transformers cvt for hv measurements. Transformerless power supplies provide a lowcost alternative to transformer based and switcherbased power supplies. Capacitive voltage transformers cvt for hv measurements eep. The magnetic voltage transformers are most economical for voltages up to about 145 kv and the capacitive voltage transformers for voltages higher than 145 kv. Transformers made from capacitors are almost 100% efficient. Capacitive voltage transformers isolate the measuring instruments, meters, relays, protections, etc. Capacitive voltage transformers isolate the measuring instruments, meter, relays, protec tions, etc. Ultraprecise test set for dissipationpower factor and capacitance measurements on high voltage assets with an external source and reference capacitor lightweight test set for fast and reliable moisture content determination of oilpaper insulated power transformers.
Transformer on load condition phasor diagram on various. According to figure 1, the voltage of any point in capacitive network of the winding in the time of the strike of impulse voltage u with assuming the grounded transformer winding is deduced from equation 1 4. Capacitor voltage transformers international trench. The abb group of companies operate in around 100 countries. What is the function of a capacitor voltage transformer. Capacitive voltage transformers exist and are used by utilities for high voltage greater than 66 kv metering. Capacitive voltage transformer 1 linkedin slideshare. The shape of transmitted voltage suggests a capacitive coupling of the highfrequencies during the front of applied voltage, from the output of capacitive divider, through the interturns capacities of medium voltages choke l0 and the capacity between the primary and secondary windings of output transformer. Digital relays and capacitive voltage transformers.
Capacitor voltage transformers convert transmission class voltages, 72. Coupling capacitor voltage transformers ccvts are commonly used devices to supply ac potential to protective relays, particularly transmission line relays. Ll 50 transmission relaying voltage transformer failure. The high voltage insulation is implemented in oilpaper technology. Capacitor voltage transformers are used for measurement of ultra high voltages in a transmission line.