Figure 1 capacitive voltage transformers principal construction. It is demonstrated in this research that ferroresonance can also occur in cvt due to circuit breaker switching. The cvt instruction manual contains this recommendation. A capacitor voltage transformer cvt, or capacitance coupled voltage transformer ccvt is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. Capacitive voltage transformers cvt electrical concepts. Help with a toroidal transformer voltage readings all about. Transformer on load condition phasor diagram on various. Capacitive voltage transformers electrical performance and. May 14, 2017 for the love of physics walter lewin may 16, 2011 duration. Steps to draw the phasor diagram at capacitive load. They transmit voltages to standardised, equivalent values for meters, measuring and protective devices. Capacitive voltage transformers of type ecf are used in high voltage switchgears from 72 to 550 kv. Fundamental in engineering mathematics and physics course objectives.
Cvt capacitor voltage transformer hv high voltage mv medium voltage ehv extra high voltage uhv ultra high voltage emtprv electro magnetic transient programrestructure version ieee institute of electrical and electronics engineers oc over current ov over voltage pu per unit kv kilo volts ka kiloamperes hz hertz ms millisecond. Capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. Apr 29, 2018 a capacitive voltage transformer works on capacitor voltage divider principle. The transformer on capacitive load leading power factor load is shown below in the phasor diagram. In contrast, this research will place ferroresonance in capacitive voltage transformer cvt as the main focus. Capacitive voltage transformer 1 linkedin slideshare. This type of transformer is categorized on the basis of a number of turns in the primary and secondary windings and the induced emf.
Capacitive voltage transformers and coupling capacitors oilpaper insulation model ddn model ddb they enable transmission of high frequency signals through the high voltage hv lines. Capacitive voltage transformer model dfk up to 800 kv, model ddb up to 170 kv. There should be isolation between the input ground and the output voltage thats one important function of a mains transformer so any voltage you read is likely just due to capacitive coupling between the primary and secondary of the transformer. It is variable because the core is free to move between the windings. These remote relay operations resulted in outages to five transmission lines and the substation where the ccvt failed. Hv outdoor capacitor voltage transformers robust design. Also, i am informed that i have to install three line arresters on the same line side of 115 kv ds, because cvts are provided on the line side, not substation side of disconnect switch. 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.
They transform high voltage into standardised values for meters, measuring and protection devices. For better understanding, assume a simple circuit of cvt which is connected between a line of 400 kv and earth. Adi has published a lot of information on dealing with capacitive loading and other stability issues in books, such as the amplifier seminar series, in earlier issues of analog dialogue, and in some design tools. Inductive voltage transformers bill west electrical 5 mar 20 09. Analysis and applications of the capacitive transformer. 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.
The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. They enable transmission of high frequency signals through the high voltage hv lines. They do not have losses from heat, noise and induction. Educational tutorial on electrical engineering 126 by g k agrawal. Capacitive voltage transformers cvts are common in high voltage transmission line applications. Transient overreach concerns and solutions for distance relaying daqing hou and jeff roberts schweitzer engineering laboratories, inc.
Rather than use a transformer 230 v to 110 volt i thought of using capacitive voltage divider. Capacitor voltage transformer isolates the measuring instruments, meter, relays, protections, etc. Practical techniques to avoid instability due to capacitive loading. 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. 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. What is the difference between the inductive voltage. The abb group of companies operate in around 100 countries. Full voltage reduced voltage binarycoded decimal usually refers to the 84 code where four bits are used to bcd represent decimal digits 0 through 9.
Induces emf e 1 and e 2 lags the flux by 90 degrees. Get access to premium hvmvlv technical articles, electrical engineering guides, research studies and much more. This displays the bus number and the bus name with the bus voltage in kv in their respective columns. Capacitive voltage transformers cvt for hv measurements eep. The emu is an inductive intermediate voltage transformer which is housed in the foot case of the transformer. Characterisation of the capacitive voltage transformers.
The scope of transformer types starts with generator transformers and ends with distribution transformers. This paper covers the fundamental inductorcapacitor pair for ferroresonance initiation and the modes of ferroresonance, followed by ferroresonance in capacitive voltage transformer cvt, constituting its impact, initiation, and suppression techniques. Current transformers, inductive voltage transformers, capacitive voltage transformers, combined currentvoltage transformers and station service voltage transformers are designed to transform high current and high voltage levels down to low current and low voltage outputs in a known and accurate proportion specified by the. Capacitive voltage transformers cvt for hv measurements. Available from 25 kv to 800 kv for measurement, protection and control. Investigation of transient performance of capacitor voltage. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. As evident from the name itself, the inductive volt. Practical considerations transformers transformers. What are the advantages of using a capacitor voltage. Magnetic saturation of a transformer core may be caused by excessive primary voltage, operation at too low of a frequency, andor by the presence of a dc current in any of the windings. Capacitive voltage transformers and line arresters. Partial discharge activity was detected at the cable termination at the transformer, by the utility company, and it was measured, using hfct sensors.
The capacitive voltage transformer cvt is also called capacitive potential transformer. Lesson learned transmission relaying voltage transformer failure 2 august 10, 2011 cleared by the operation of remote backup relay elements. 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 active part of the voltage transformer is located in the foot housing. Jan 19, 2017 capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. Capacitive transformer this is a forgotten technology, invented over 100 years ago, and seriously needed today. Not shown a re the means for adjusting the magnitude and phase angle of the seconda ry voltage. Power engineers is one of the leading constant voltage transformer and. 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. Digital relays and capacitive voltage transformers. These same applications require fast, yet secure protection.
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. Capacitive voltage transformers and line arresters electric. Hv outdoor capacitor voltage transformers robust design and. Ac instrumentation transducers ac metering circuits. On rare occasions winding capacitance is increased to reduce ringing in switching transformers. As the cvt is connected between the line and earth, therefore phase voltage 4001. 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 magnetic voltage transformers are most economical for voltages up to about 145 kv and the capacitive voltage transformers for voltages higher than 145 kv. Leakage inductance tends to worsen a transformers voltage regulation secondary voltage sags more for a given amount of load current. It also serves the purpose of power line carrier communication. The high voltage insulation is implemented in oilpaper technology.
A highgrade composite or porcelain insulator can be used as insulator. Distance relays and capacitive voltage transformers balancing speed and transient overreach page 4 of 22 r 1536 resistance. Transformers made from capacitors are almost 100% efficient. I have quite a few voltage adapters that function only on 110 volt. How does the protection engineer know what type of cvt is used. Pullman, w a usa abstract capacitive voltage transformers cvts are common in highvoltage transmission line applications. Practical techniques to avoid instability due to capacitive. According to the contamination classes of common standards, different creepage distances can be selected. Capacitive voltage transformers electrical performance and effective diagnostic measures. Cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values. 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. The engineering verification proves that uhv cvt has good performance and. Voltage transformers type eof are used in high voltage networks within the 24245 kv range.
Oct 03, 2017 there should be isolation between the input ground and the output voltage thats one important function of a mains transformer so any voltage you read is likely just due to capacitive coupling between the primary and secondary of the transformer which the high impedacne of the meter can read. Difference between capacitive voltage transformer and. Hv outdoor capacitor voltage transformers and coupling. Capacitor voltage transformer cvt or ccvt construction. Investigation of transient performance of capacitor. As a result, research conducted in this area is limited and the awareness on ferroresonance is relatively low amongst the utility engineers. Cvt transients revisited college of continuing and professional. Ll 50 transmission relaying voltage transformer failure. Current transformers, inductive voltage transformers, capacitive voltage transformers, combined current voltage transformers and station service voltage transformers are designed to transform high current and high voltage levels down to low current and low voltage outputs in a known and accurate proportion specified by the.
Th e transformer was successfully energised to the 230 kv line voltage of the utility supply. A capacitive voltage transformer works on capacitor voltage divider principle. There are two types of voltage transformers, magnetic voltage transformers vt and capacitive voltage transformers cvt. Apr 29, 2018 cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values. I should have to install three 115 kv capacitive voltage transformers inside my substation on line side of 115 kv disconnect switch. The type of the cvt is always a singlepole one, thus the connection is between phase and earth. Coupling capacitors are only used for coupling highfrequency communication signals and they are equivalent to the capacitive part of cvt. Design of an equipotential shielding kv capacitor voltage. Investigation of transient performance of capacitor voltage transformer cvt journal the institution of engineers, malaysia vol. Often the secondary voltage is adjustable via a movable tap. The component of the applied voltage to the primary equal.
This lists the bus, by number, whose voltage or connected equipment controls this switched shunt. 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. Autotransformer a type of transformer in which the secondary coil is part of the primary coil. A capacitor voltage transformer cvt or ccvt, is a transformer used in power systems to step. Help with a toroidal transformer voltage readings all. Transformers which are directly connected to the generator of the power station are called generator transformers. For the love of physics walter lewin may 16, 2011 duration. Capacitive voltage transformers of type ecf are used in highvoltage switchgears from 72 to 550 kv. The capacitive voltage transformer consists of one condenser unit and one electromagnetic measuring unit emu. Types of transformer different types of transformer. In its most basic form, the device consists of three parts.
Figure 6 shows the measurement for phase l1, which shows partial discharge. Capacitive voltage transformers cvts are common in highvoltage transmission line applications. The higher the voltage level is, the more pricecompetitive the capacitive type becomes. For over a century, utilities around the world have relied on ge to deliver. In general, part of the designers task is to keep capacitance to a minimum. In the latter case, the device is known as a coupling capacitor voltage transformer ccvt, and when the transformer primary winding. Capacitive voltage transformers isolate the measuring instruments, meters, relays, protections, etc. Coupling capacitors are only used for coupling high frequency communication. Pullman, w a usa abstract capacitive voltage transformers cvts are. The various types of transformer shown in the figure above are explained in detail below. Bee basic electric engineering is common to first year branches of ug engineering expect bt.
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