in electric power system，ferroresonance occurs frequently. during ferroresonance, there will be overvoltage, which is a serious threat to the safety of the system. ferroresonance overvoltage can occur in any system between 3kv. to 220kv.. especially in network of 35kv. and below, nearly all inner overvoltages are caused by ferroresonance. overvoltage caused by ferroresonance lasts long and may long exist. in the sub-frequency resonance, the voltage is usually not high, but the current of pt is large. this can make pt explode easily for its overheating. during the fundamental and harmonic resonance, the current is usually not large, but the overvoltage is very high, which often destroys the insulation of equipments and causes serious accidents.
series scm-controlling harmonic elimination device is a new intelligent power harmonic elimination device. the way to use it is simple and convenient. it doesn’t need any maintenance. the device can eliminate ferroresonance of all frequencies rapidly with high accuracy. meanwhile, it can print relative information or send it through communication interface to the monitoring system of a higher level according to users’ demand, which applies to unattended stations.
2 functions and features
ø it’s applicable to a variety of voltage levels in distribution network.
ø it can monitor up to four stages of generatrix.
ø it can eliminate ferroresonance with the characteristic frequency of trisection frequency, dichotomy frequency, power frequency and tripling frequency rapidly.
ø it’s able to distinguish among external overvoltage ferroresonance and single-phase ground.
ø it adopts high-powered, non-contacted harmonic elimination elements to make ferroresonance elimination rapid and reliable.
ø it provides a set of passive alarm node.
ø it can show fault reports when fault occurs (type, time, voltage and frequency of the fault).
ø the matching mini-printer can print the fault reports in time.
ø it can configure communication interfaces to send relative information to monitoring system of a higher level.
ø it can save the latest ten pieces of fault information and the data is not lost after power lost.
ø it has the function of watch dog to prevent system crashing.
ø it has complete function of self checking.
ø its man-machine interface makes operations simple. full chinese menus display abundant intuitionistic information.
ø it has the function of auto-production after the thyristor is punctured.
3 technical parameters
3.1 environmental requirements
ø used indoor, so ventilation should be good.
ø ambient temperature: -10℃ ～ 55℃
ø relative humidity: less than 90%, with no condensation on the surface.
ø atmosphere pressure: 80 ～ 110kpa 。
ø altitude: < 2000m 。
ø in surrounding medium, there’s no conductive dust or conducting metal and no corrosive gases or mold to cause damage to insulations.
3.2 technical parameters
ø working power：ac/dc110v-220v（please note any special requirements when ordering），power waste≤20w。
ø alarm node capacity：ac250v，5a；dc30v，5a。
ø communication interface：rs232/485（alternatively. please note either when ordering）, baud rate: 1200～9600bps。
ø communication protocol：three kinds of communication protocols have been built in: cm90、cdt、modbus.
3.2 selection guide
ø design serial no.: 1—small chassis. device of this series does not have printing function. 2—common chassis. device of this series have matching printing function. see page 10 of this manual for contour dimension and installation dimension of chassis of the two types.
ø quantity of generatrix to monitor: four sections: maximum of four sections. 1—one section，2—two sections, 3—three sections, 4—four sections.
ø communication interface: t—rs232，f—rs485. device without this suffix does not have communicating function.
ø printing function：d means the device has printing function. device without this suffix does not have printing function.
4 operating principle
there are great amount of iron-core inductors in power system, such as transformers, voltage transformer, arc extinguishing and parallel compensation reactor. most of them are nonlinear elements. together with the capacitance of system, they make up many complex oscillator circuits, which can stimulate a long-lasting ferroresonance overvoltage. the high overvoltage and the large overcurrent during ferroresonance can easily cause damage to the insulation of equipment and endanger the safety of operators under serious circumstances.
hdkx-196 series scm-controlling harmonic elimination device monitors the voltage and frequency of pt opening triangle point at voltage transformer in real time. when ferroresonance occurs, the device will start non-contact harmonic elimination elements to make great damping so as to eliminate ferroresonance.