Analysis and applications of the capacitive transformer. Capacitive voltage transformers cvt for hv measurements. Pullman, w a usa abstract capacitive voltage transformers cvts are. Transformer on load condition phasor diagram on various. 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. Help with a toroidal transformer voltage readings all. Apr 29, 2018 cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values. Practical techniques to avoid instability due to capacitive loading. Capacitive voltage transformers of type ecf are used in high voltage switchgears from 72 to 550 kv. Pullman, w a usa abstract capacitive voltage transformers cvts are common in highvoltage transmission line applications. Capacitor voltage transformer isolates the measuring instruments, meter, relays, protections, etc. Get access to premium hvmvlv technical articles, electrical engineering guides, research studies and much more. The high voltage insulation is implemented in oilpaper technology. Cvt is rated for high voltage levels above 100 kv, while pts arent designed for such large values.
What is the difference between the inductive voltage. 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. Capacitive voltage transformers cvts are common in highvoltage transmission line applications. 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. 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. Capacitive voltage transformers and line arresters. Transformers made from capacitors are almost 100% efficient. May 14, 2017 for the love of physics walter lewin may 16, 2011 duration. Jan 19, 2017 capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. 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 of type ecf are used in highvoltage switchgears from 72 to 550 kv.
In contrast, this research will place ferroresonance in capacitive voltage transformer cvt as the main focus. These remote relay operations resulted in outages to five transmission lines and the substation where the ccvt failed. In its most basic form, the device consists of three parts. The abb group of companies operate in around 100 countries. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. Capacitive voltage transformer model dfk up to 800 kv, model ddb up to 170 kv. Practical considerations transformers transformers. 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. 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. As the cvt is connected between the line and earth, therefore phase voltage 4001.
Capacitive voltage transformers cvt electrical concepts. 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. This type of transformer is categorized on the basis of a number of turns in the primary and secondary windings and the induced emf. Rather than use a transformer 230 v to 110 volt i thought of using capacitive voltage divider. 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. 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. Steps to draw the phasor diagram at capacitive load. Capacitive voltage transformers cvts are common in high voltage transmission line applications. Available from 25 kv to 800 kv for measurement, protection and control. 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.
Hv outdoor capacitor voltage transformers robust design. 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. Coupling capacitors are only used for coupling high frequency communication. Not shown a re the means for adjusting the magnitude and phase angle of the seconda ry voltage. Induces emf e 1 and e 2 lags the flux by 90 degrees. Capacitive voltage transformers cvts are used on higher voltage levels, starting from 66 kv and upwards. Investigation of transient performance of capacitor. The capacitive voltage transformer stepdown the high voltage input signals and provide the low voltage signals which can easily measure through the measuring instrument.
Capacitive voltage transformers electrical performance and. 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. 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. 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 scope of transformer types starts with generator transformers and ends with distribution transformers. They enable transmission of high frequency signals through the high voltage hv lines. How does the protection engineer know what type of cvt is used. Hv outdoor capacitor voltage transformers robust design and.
It is variable because the core is free to move between the windings. 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. Phasor diagram of the transformer on capacitive load. Practical techniques to avoid instability due to capacitive. The type of the cvt is always a singlepole one, thus the connection is between phase and earth. These same applications require fast, yet secure protection. Ll 50 transmission relaying voltage transformer failure. It also serves the purpose of power line carrier communication. Investigation of transient performance of capacitor voltage. Power engineers is one of the leading constant voltage transformer and. Lesson learned transmission relaying voltage transformer failure 2 august 10, 2011 cleared by the operation of remote backup relay elements. Investigation of transient performance of capacitor voltage transformer cvt journal the institution of engineers, malaysia vol.
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. Help with a toroidal transformer voltage readings all about. Bee basic electric engineering is common to first year branches of ug engineering expect bt. 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. What are the advantages of using a capacitor voltage. The engineering verification proves that uhv cvt has good performance and. According to the contamination classes of common standards, different creepage distances can be selected. The capacitive voltage transformer cvt is also called capacitive potential transformer. Capacitive voltage transformers cvt for hv measurements eep. As evident from the name itself, the inductive volt. For over a century, utilities around the world have relied on ge to deliver.
Figure 1 capacitive voltage transformers principal construction. The capacitive voltage transformer consists of one condenser unit and one electromagnetic measuring unit emu. The cvt instruction manual contains this recommendation. Autotransformer a type of transformer in which the secondary coil is part of the primary coil. Capacitive voltage transformers isolate the measuring instruments, meters, relays, protections, etc. Fundamental in engineering mathematics and physics course objectives. 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. Capacitive voltage transformers and line arresters electric. Apr 29, 2018 a capacitive voltage transformer works on capacitor voltage divider principle. Often the secondary voltage is adjustable via a movable tap. 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.
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. A capacitive voltage transformer works on capacitor voltage divider principle. The active part of the voltage transformer is located in the foot housing. 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. The various types of transformer shown in the figure above are explained in detail below. Distance relays and capacitive voltage transformers balancing speed and transient overreach page 4 of 22 r 1536 resistance. 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.
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. Difference between capacitive voltage transformer and. Educational tutorial on electrical engineering 126 by g k agrawal. Th e transformer was successfully energised to the 230 kv line voltage of the utility supply. For the love of physics walter lewin may 16, 2011 duration. Leakage inductance tends to worsen a transformers voltage regulation secondary voltage sags more for a given amount of load current. Capacitor voltage transformer cvt or ccvt construction. Capacitive voltage transformers electrical performance and effective diagnostic measures. Capacitive transformer this is a forgotten technology, invented over 100 years ago, and seriously needed today. The higher the voltage level is, the more pricecompetitive the capacitive type becomes. It is demonstrated in this research that ferroresonance can also occur in cvt due to circuit breaker switching. Inductive voltage transformers bill west electrical 5 mar 20 09. The component of the applied voltage to the primary equal.
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. In general, part of the designers task is to keep capacitance to a minimum. The transformer on capacitive load leading power factor load is shown below in the phasor diagram. This lists the bus, by number, whose voltage or connected equipment controls this switched shunt. 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. This displays the bus number and the bus name with the bus voltage in kv in their respective columns. They transmit voltages to standardised, equivalent values for meters, measuring and protective devices. They do not have losses from heat, noise and induction.
Digital relays and capacitive voltage transformers. Transformers which are directly connected to the generator of the power station are called generator transformers. Characterisation of the capacitive voltage transformers. Figure 6 shows the measurement for phase l1, which shows partial discharge. In the latter case, the device is known as a coupling capacitor voltage transformer ccvt, and when the transformer primary winding. I should have to install three 115 kv capacitive voltage transformers inside my substation on line side of 115 kv disconnect switch. Capacitive voltage transformer 1 linkedin slideshare. A capacitor voltage transformer cvt or ccvt, is a transformer used in power systems to step. Hv outdoor capacitor voltage transformers and coupling. Types of transformer different types of transformer.
Ac instrumentation transducers ac metering circuits. Partial discharge activity was detected at the cable termination at the transformer, by the utility company, and it was measured, using hfct sensors. The emu is an inductive intermediate voltage transformer which is housed in the foot case of the transformer. There are two types of voltage transformers, magnetic voltage transformers vt and capacitive voltage transformers cvt. Cvt transients revisited college of continuing and professional. As a result, research conducted in this area is limited and the awareness on ferroresonance is relatively low amongst the utility engineers.
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