Capacitive voltage transformers of type ecf are used in high voltage switchgears from 72 to 550 kv. The capacitive voltage transformer cvt is also called capacitive potential transformer. Voltage potential transformers inductive and capacitive types, current transformers and combined instrument transformers voltage and current capacitor voltage transformers convert. Since, impulse voltage distribution ivd along a winding is depended on this coefficient, so analyzing this coefficient is important in 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. 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. Pullman, w a usa abstract capacitive voltage transformers cvts are common in highvoltage transmission line applications.
What are the advantages of using a capacitor voltage. 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. They transform high voltage into standardised values for meters, measuring and protection devices. Distance relays and capacitive voltage transformers balancing speed and transient overreach page 2 of 22 1. Selfcapacitance of highvoltage transformers article in ieee transactions on power electronics 225. There are two types of voltage transformers, magnetic voltage transformers vt and capacitive voltage transformers cvt. Pdf investigation of transient performance of capacitor. Study on the measuring harmonics based on capacitor voltage. Capacitive voltage transformers pfiffner instrument transformers. Among kinds of voltage transformer, cvt which is the common short form for. 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. These types of transformers are used in the same manner, however, they are.
In capacitor voltage transformers capacitors are used as voltage divider. 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. The type of the cvt is always a singlepole one, thus the connection is between phase and earth. Coupling capacitor voltage transformers ccvts are commonly used devices to supply ac potential to protective relays, particularly transmission line relays. 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. Capacitor voltage transformer induced ferroresonancecauses.
The value of the voltage transformers magnetizing reactance varies as a. 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. 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. Phasor diagram of the transformer on capacitive load. Shunt reactors with a saturable core could also be possible. It also provides electrical isolation same as potential 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. 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. 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. Capacitor voltage transformer cpb 72 pdf english pdf drawing. Transformer on load condition phasor diagram on various.
If the transformer was originally rated 10 kva, the reduced rating would be 5 kva, or in direct proportion to the applied voltage. Cvt the fundamental frequency voltage signal retains the. Characterisation of the capacitive voltage transformers. Pdf dynamic compensation of capacitive voltage transformers. Capacitive voltage transformers cvts have been widely used within transmission power systems for applications ranging from highvoltage to ultra highvoltage. Instruments beside the universal resistive capacitive voltage divider the instruments for reference measuring systems can be delivered as well, e. I cannot find the right words to express the admiration and sincere gratitude towards dr. This oilfilled coupling capacitive voltage transformer will. The transformer on capacitive load leading power factor load is shown below in the phasor diagram. Apr 11, 2020 a cvt, or capacitor voltage transformer, is a transformer circuit used in high voltage applications. Capacitive voltage transformers cvt for hv measurements. 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. Self capacitance of high voltage transformers article in ieee transactions on power electronics 225.
A calibration service for voltage transformers and highvoltage. The coupling capacitance is primarily made up of the capacitance of the system dielectric between the phase conductor and ground. Primary line to ground connected voltage ratios are available from 525. The capacitive voltage transformer stepdown the high voltage input signals and provide the low voltage signals which can easily measure through the measuring instrument. Transformerless power supplies provide a lowcost alternative to transformer based and switcherbased power supplies. If the constant voltage transformer is subjected to a line voltage frequency change the output voltage will vary, as shown in figure 115. It is demonstrated in this research that ferroresonance can also occur in cvt due to circuit breaker switching. The pv voltage instrument transformers are used in electric power grids with system voltage of up to 123 kv and frequency of 50 hz. They have a capacitive voltage divider but also have a dualwinding transformer to couple the divided voltage to the metering circuit. Apr 29, 2018 cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values. Capacitor voltage transformer in hindi cvt concept duration. 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.
Ll 50 transmission relaying voltage transformer failure. The two basic types of transformerless power supplies are resistive and capacitive. Voltage transformer connected to an isolated neutral system 14 papers 10, 5. Pdf this paper presents the digital algorithm for online dynamic compensation of the secondary voltage of a capacitive voltage transformer cvt. They enable transmission of high frequency signals through the high voltage hv lines. This paper reports the digitaltime domain and frequency domain studies on a typical 2kv capacitor voltage transformer cvt model. Iran transformer research institute, tehran, iran abstract with changing the parameters of layer winding in transformers, capacitive characteristic coefficient of winding will be changed. Capacitive voltage transformer is mainly used for measurement of voltage and for protection purpose. Jan 19, 2017 capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. Pdf identification of parameters for coupling capacitor voltage. What is the difference between the inductive voltage. Capacitive voltage transformer 1 linkedin slideshare. Capacitive voltage transformer model dfk up to 800 kv, model ddb up to 170 kv.
It is shown that the leakage inductance can be regulated in the range. Transformers made from capacitors are almost 100% efficient. It is also used for power line communication between different substations. Capacitor voltage transformers are used for measurement of ultra high voltages in a transmission line. As such, the need for accurate and reliable voltage. 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. The ddb123 outdoor coupling capacitive voltage transformer is rated for use on 115,000 volt systems with 550kv bil. Capacitive voltage transformers of type ecf are used in highvoltage switchgears from 72 to 550 kv. 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. That also means less loss,so that voltage increasing. Nameplate details of capacitive voltage transformer cvt.
The voltage regulation determines the ability of the transformer to provide the constant voltage for variable loads. 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. In general, part of the designers task is to keep capacitance to a minimum. The high voltage insulation is implemented in oilpaper technology. In this article we are going to have details of the parameter which are mentioned on a nameplate of capacitive voltage transformer. Induces emf e 1 and e 2 lags the flux by 90 degrees. The voltage regulation is defined as the change in the magnitude of receiving and sending voltage of the transformer.
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 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. Acalibrationservicefor voltagetransformersand highvoltagecapacitors williame. What is the function of a capacitor voltage transformer. Steps to draw the phasor diagram at capacitive load.
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. The active part of the voltage transformer is located in the foot housing. Capacitor voltage transformer cvt or ccvt construction. Transformer connected to a deenergized transmission line running in parallel with one or more energized lines 6 papers 16, 17, 7. Lesson learned transmission relaying voltage transformer failure 2 august 10, 2011 cleared by the operation of remote backup relay elements. Transformer less capacitive bleed power conversion or st an1476. 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. Selfcapacitance of highvoltage transformers request pdf. Capacitance occurs winding to winding, turn to turn, windings to core and stray capacitances between terminals and case. Instrument transformers high voltage 31 capacitive voltage transformers isolate the measuring instruments, meter, relays, protections, etc. The capacitive voltage transformer consists of one condenser unit and one electromagnetic measuring unit emu. Capacitive voltage transformers exist and are used by utilities for high voltage greater than 66 kv metering.
In the latter case, the device is known as a coupling capacitor voltage transformer ccvt, and when the transformer primary winding. 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. There are several capacitive elements in a transformer. As part of trenchs product scope, the company produces a diversified range of instrument transformers for transmission class instrument transformers include. How electrical capacitive voltage transformer cvt works explained in the video. Capability for handling a short circuit is an inherent feature of a constant voltage transformer.
They transmit voltages to standar dised, equivalent values for. Capacitor voltage transformers shall be hermetically sealed to eliminate breathing and to prevent ingress of air and moisture into the capacitor stack and into the tank of capacitor voltage transformer. Capacitive voltage transformers isolate the measuring instruments, meters, relays, protections, etc. These remote relay operations resulted in outages to five transmission lines and the substation where the ccvt failed. This voltage transformer contains a high voltage coil, secondary windings and a core encapsulated in hermetic housing filled with pcbfree transformer oil. 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. A potential transformer is a conventional transformer having primary and secondary windings. 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. For over a century, utilities around the world have relied on ge to deliver. Pdf a method to obtain the coupling capacitor voltage transformer ccvt model parameters from frequency response curves is presented. Nameplate details of capacitive voltage transformer cvt explained. Difference between capacitive voltage transformer and.
The low voltage stresses within the capacitor elements ensure a safe and reliable product. Capacitor voltage transformer cpb is designed for revenue metering and protection in high voltage networks. Analysis and applications of the capacitive transformer. May 14, 2017 for the love of physics walter lewin may 16, 2011 duration. Voltage transformers and capacitor voltage transformers. Transient overreach concerns and solutions for distance relaying daqing hou and jeff roberts schweitzer engineering laboratories, inc. On rare occasions winding capacitance is increased to reduce ringing in switching transformers. This application note will discuss both with a focus on the following.
Figure 6 shows the saturation curve of the voltage transformer model developed. Capacitive voltage transformers isolate the measuring instruments, meter, relays, protec tions, etc. 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. 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. Hv outdoor capacitor voltage transformers and coupling. Capacitor voltage transformers convert transmission class voltages, 72. Pdf selfcapacitance of highvoltage transformers luca. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. Capacitive transformer this is a forgotten technology, invented over 100 years ago, and seriously needed today. Capacitor voltage transformers international trench. Universal resistive capacitive reference voltage divider.
As such, the need for accurate and reliable voltage transformation is essential. In its most basic form, the device consists of three parts. Identification of parameters for coupling capacitor voltage. Cvt in electrical capacitive voltage transformer cvt. Using transformer parasitics for resonant converters a. 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. The component of the applied voltage to the primary equal. Diagnostic testing and monitoring of power transformers. Figure 1 capacitive voltage transformers principal construction. Transformers voltage and current transformer in one unit. In contrast, this research will place ferroresonance in capacitive voltage transformer cvt as the main focus. The regulation of a constant voltage transformer can be designed to be better than a few percent.
The transient studies are conducted using alternative transient program atpemtp. The ferroresonance phenomenon in voltage transformers is analyzed in this section through several software simulation examples, using the software tool matlab. Digital relays and capacitive voltage transformers. They do not have losses from heat, noise and induction. For the voltage measurement purposes, the behavior and. This circuit is one of a category of circuits called a transformerless ac to dc powersupply or a cr dropper circuit.
The voltage is applied to the divider over a lead with damping resistor at the beginning. A calibration service for voltage transformers and high. 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. The ks8695x, ks8695ppx, ks8993, ks8993mf, and ks8995maxa all have voltage drive 10baset transmitter circuitry. Capacitive voltage transformers cvts are used on higher voltage levels, starting from 72. Mar 11, 20 i dont feel like getting into the nitty gritty of it but phase shifting increases voltages in ac circuits.
Examples of ferroresonance in a high voltage power system. As soon as total capacitance load is no more able fully compensate the increasing inductance load, voltage starts decreasing. Transformer supplied through a long transmission line or b. Capacitive voltage transformers cvt for hv measurements eep. They transmit voltages to standardised, equivalent values for meters, measuring and protective devices. Voltage transformers type eof are used in high voltage networks within the 24245 kv range. A software model has been developed based on test data obtained on a real voltage transformer.
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