VARIABLE FREQUENCY RESONANT TEST SYSTEM

Transcription

1 VARIABLE FREQUENCY RESONANT TEST SYSTEM 400kV,1200kVA Tank Type Reactor for Outdoor Cable Test Field 650kV, 5850kVA, Cylinder Type Reactors for Onsite Testing of GIS and Cable PHENIX Variable Frequency Test Systems are the system of choice for onsite testing. The systems comply with IEC60060, and IEEE Standard 4. The capability to perform Partial discharge measurements compliant with IEC60270 qualifies VRTS systems as the most practical choice for onsite testing. PHENIX supplies three types of VRTS systems, grounded steel tank types, cylindrical module types and SF6 insulated system for direct flanging to gas insulated bus. EXPERIENCE QUALITY RELIABILITY

2 VARIABLE FREQUENCY AC AND DIAGNOSTIC TESTING PHENIX Technologies developed the first variable frequency resonant test system (VRTS) in The first VRTS was designed to perform diagnostic testing, partial discharge, on large generators. With the advent of advanced low cost power electronics and digital signal processing, Phenix has reintroduced the variable frequency resonant test system as the system of choice for onsite testing. The low weight to kva ratio, easy setup and the capability to perform diagnostic testing such as partial discharge and tan d measurements qualifies the VRTS systems as the most practical onsite test system. Application VRTS systems are generally used where a lightweight transportable unit is a requirement. The primary applications of a VRTS system are cable, generator, motor and GIS testing. Test objects, which are capacitive in nature, may also be tested. Systems for test objects with very large capacitances (non mobile units), as sometimes required for factory or laboratory testing are also available. Theory of Operation A variable frequency resonant test system like a variable inductance resonant test system takes advantage of resonance theory. To achieve resonance the capacitive reactance (test object) has to the equal the inductive reactance (high voltage reactor). In conventional resonance test systems this is achieved by varying the inductance. In variable frequency resonance system the reactor is non-variable therefore the frequency of the circuit is adjusted until resonance is achieved. This adjustment of the resonant circuit is commonly referred to as tuning. Once resonance has been achieved only the real losses ( I 2 R losses in the high voltage reactor and losses in the test object) have to be supplied by the mains. The output voltage and the power drawn from the mains is a function of the Q or quality factor of the circuit. The Q of the test specimen and the Q of the high voltage reactor determine the Q of the test system (Q System ). The Q load is defined as ratio of the reactive power of the load over the real losses of the load (Q load = kvar load / kw load). Table 8.1 shows typical quality factors for different kind of loads. Table 8.1 Q Values of Different Loads TEST OBJECT tan d Typical Load Q GIS (SF6 Insulated) <1* XLPE Cable 2 5*10-4 ~1000 EPR Cable 3 5*10-3 ~150 PILC Cable 1.5 3*10-3 ~200 Oil Insulated Capacitors 5 10*10-3 ~100 Motors / Generators.1 ~10 Cable Water Termination.1 ~10 The Q Reactor is defined as the ratio of the reactive power over the real losses in the reactor (Q Reactor = kvar reactor / kw reactor). Therefore Q System can be defined as Qreactor Qsystem = Qreactor 1 + Qload Based on the previous equation for Q System, it is obvious that the Q Reactor can have large influence on the input power (mains) requirements. Phenix reactors are designed with this fact in mind; the high quality grain orientated laminated core steel and the use of optimum wire sizing insures low loss reactors. Phenix reactors usually have a quality factor in excess of 90. On larger high power reactors quality factors in the excess of 200 can be achieved. VRTS System Components A VRTS systems consist of five major components: Controls, Power Supply, Exciter Transformer, High Voltage Reactor and High Voltage divider. Some of these components such as the controls and power supply can be combined into single cabinet, which may be more practical for onsite applications.

3 VRTS CONTROLS The VRTS controls are designed to provide control, metering and monitoring of the VRTS system and the test object. The VRTS controls are based on Phenix C style series. C series controls were first introduced in 1994, and since then have established a track record of reliability unmatched in the industry. Having been consistently upgraded and refined since their introduction nevertheless the core components of C controls have stayed the same. The core components consist of a rugged graphical display (HMI) and a programmable logic controller (PLC). The HMI and PLC are based on industrial grade microprocessors. A typical VRTS system is equipped with an operator station (Controls) and two additional PLCs. The PLCs are distributed; one PLC is located in the exciter transformer and one in the power supply section. The PLCs communicate via an RS485 network, which is implemented with multimode fiber optic modems and cable. The controls are designed to be ergonomically efficient and user friendly. The HMI displays all relevant information in an organized manner. Many objects are prioritized so that the operator can recognize critical or abnormal situations immediately. A VRTS system is easy to use regardless whether it operates in an automated mode or in operator controlled manual mode. VARIABLE FREQUENCY VARIABLE VOLTAGE POWER SUPPLY The VRTS power supply converts the mains voltage, usually consistent of a three phase service into the single phase output square wave. An imbedded microprocessor closely controls and monitors the power supply. Generally speaking the power supply can be divided into to three sections. The first section consists of silicon controlled rectifiers (SCRs). The SCRs rectify the three phase AC mains into DC and is responsible for charging the DC bus capacitors. By controlling the bus voltage, the SCRs also control the output voltage of the VRTS system. The second section consists of an insulated gate bipolar transistor (IGBT) inverter section. The IGBT section inverts the DC bus voltage into a weighted AC square wave. The weighted AC square wave is switched at 30 and 150 degrees of each half wave to approximate a sine wave a close as possible. See figure 8.2 for further details. OUTPUT (kv) ###.# EXCITER ##.## kv FREQUENCY ###.## HZ RATE RESONANCE MESSAGE AREA OUT RATE SPECIMEN(A) ##.## TEST VOLTAGE> ###.# KV OVER VOLTAGE> ###.# KV MANUAL CONTROL MODE [F2] AMTR DWELL> 0###: 0#. 0# PARALLEL 50KV 20A TAP [F3] MODE 1. Output Kilovoltmeter 2. Output Voltage Bar Graph. 3. Resonance Meter 4. Exciter Voltmeter 5. Frequency Meter 6. Frequency Rate of Change 7. Rate of Exciter Output Voltage Change.. 8. Specimen / Exciter Current 9. Manual / Automatic Testing Modes. 10. Series / Parallel modes. 11. Press [F5] to enter the Menu Screen. 12. Display of present output tap selection. See # Display of present output mode selection. 14. Display of present over-voltage setting. 15. Display of present test voltage setting. 16. Display of present Dwell Time setting 17. Dwell timer 18. Output Currentmeter 19. Message Area [F1] RESET [F4] TAP [F5] MENU A very stable frequency and voltage control is necessary to keep the VRTS system in resonance. Phenix power supplies feature a 16 bit frequency control with results in a resolution of approximately 5.4mHz and have a 14 bit voltage control with a stability of better than 0.1%. The frequency range of the power supplies is a maximum of 10 to 360Hz. Phenix recommends the frequency ranges detailed in table 8.2 for various applications. High voltage reactors equipped with a steel core are usually designed with a minimum frequency at which full output power can be achieved. In order to protect the reactors from overload, the power supply is factory set never to go below the reactor minimum frequency. An adjustable width TTL level gating signal centered on the IGBT firing pulse is a standard feature on Phenix power supplies. This signal is designed to be used to gate partial discharge detectors.

4 Table 8.2Frequency Ranges Application Recommended Frequency Range GIS Testing Hz Standard Cable Testing Hz Extended Cable Testing Hz Long Cable Testing Hz VARIABLE FREQUENCY EXCITER TRANSFORMER The excitation transformer steps up the power supply voltage from low voltage level to the excitation output voltage. Generally the exciter is of an oil insulated two winding design equipped with two electro static shields. The shields are installed between the primary low voltage winding and the secondary high voltage winding. The use of the shields helps to reduce noise coupling from the power supply. The exciter windings are built into a grounded steel tank with overpressure and over temperature protection. Most exciters are equipped with multiple taps that are matched to the possible configurations of the reactor. The switching between the taps is accomplished via a standard manual tap switch. On larger systems the tap switch may be motorized; tap switches may be motorized upon request. When used with a grounded steel tank type reactor it is possible to operate the system in Series or Parallel resonance mode. With tank type systems it is sometimes possible to wind the exciter windings directly on the reactor core and achieve additional weight savings. This limits the system to be used in parallel mode only, but can offer significant weight savings. HIGH VOLTAGE VARIABLE FREQUENCY REACTORS Phenix offers three choices of reactor designs. Oil insulated reactors equipped with a grounded steel tank, oil insulated reactors equipped with a fiber glass cylinder and SF6 insulated reactors built in a pressurized tank. GROUNDED STEEL TANK TYPE REACTORS One of the features of the tank type reactors is possibility to run the VRTS system in series or parallel resonance. Tank type reactors can also be easily equipped with tap switches, which can greatly extend the testing capability. In case where continuous duty is required the tank may be equipped with radiators. The limitation of tank type reactors is very high voltage levels. Since tank type reactors are usually equipped with oil to air bushings; ratings above 400kV become impractical due to bushing size. Systems that feature oil to SF6 bushings are available for higher voltages. Tank type reactors may also be designed for outdoor all weather use, for use in outdoor cable test fields for example. CYLINDER TYPE REACTORS Cylinder type reactors are characterized by the fiberglass cylinder, which encloses the reactor coils. One of the main features of cylinder type reactors is the capability to stack multiple reactors. With the capability of connecting multiple reactors in series very high voltages can be achieved without the limitations imposed by bushings. Cylinder type reactors may also be designed for continuous use, but may require forced oil cooling. Cylinder type reactors may operate in series resonance mode only. There two types of cylinder type reactors Phenix manufactures; the first type uses a laminated steel core and is limited to the minimum design frequency. As the second type is a reactors design that consists of a disc type reactor without a steel core. This design offers the advantage of very small size, with a short duty cycle. Disc Type Reactor units are primarily used for short term withstand testing. SF6 INSULATED REACTORS The primary application for SF6 insulated reactors is GIS testing. The capability of the VRTS to directly flange to the GIS bus eliminates the need for an air busing. Since the connections are directly made the system more sensitive partial discharge measurements can be made onsite. One of the limitations of an SF6 design is the reduced duty cycle. SF6 VRTS systems are usually equipped with a coupling capacitors and a multiflange housing mounted on a steel frame designed for lifting and transportation.

5 HIGH VOLTAGE DIVIDER Phenix high voltage dividers are constructed out oilinsulated capacitors. The capacitors are designed to operate for a frequency range of Hz. During operation the capacitors are partial discharge free and are insulated with PCB free oil. VRTS system that is designed for onsite testing may feature quick disconnects for rapid breakdown onsite. METERING All meter calibration is traceable to NIST (National Standards Institute of America). All VRTS are delivered with a Calibration certificate and a test report with all calibration data. Reactor Voltmeter (Output) Type: Peak / v2 calibrated to RMS Uncertainty: ±(0.8 of reading + 0.2% of Range) Reactor Currentmeter (Output) Type: RMS Uncertainty: ±(0.8 of reading + 0.2% of Range) Exciter Voltmeter Type: Peak / v2 calibrated to RMS Uncertainty: ±2% of Full Scale Frequency Indicator Range: Hz Resolution: 0.01 Hz PARTIAL DISCHARGE SPECIFICATIONS All Partial discharge measurements are made according to IEC60270:2000, with gating of the IGBT pulses. The standard partial discharge specification at rated operating voltage is <10 pc, unless otherwise specified. Systems with lower partial discharge specifications are available upon request. WINDOWS SOFTWARE OPTION All Phenix VRTS system can be supplied with the optional VRTS-WIN software. This software was developed by Phenix with the user in mind. The software allows generation and storage of test recipes. The VRTS-WIN software allows real time monitoring and data acquisition. The bulit in data base allows recall of previous test results for comparison. The built in test report generation feature allows the creation of customized test reports. MOBILE CONTROL ROOM OPTION As an optional feature Phenix can offer a climate controlled containerized control room. The control is equipped with at least one window and has fully finished walls and floors. Mobile control rooms usually contain the power supply and controls. Since these control room are fully insulated they can be used in virtually any climate. TRUCK / VAN MOUNTING OPTION As an optional feature Phenix can mount smaller units in small trucks or vans. This feature is especially useful for unit used for onsite diagnostics of medium voltage cables. These units come completely equipped from Phenix and are guaranteed to withstand the rigors to of frequent movement. TRACTOR TRAILER MOUNTING OPTION As an optional feature Phenix can permanently mount large systems on tractor trailers. This reduce setup time since the unit does not have to be unloaded and can be directly run of the trailer. All tractor trailers are air ride equipped YOUR LOCAL REPRESENTATIVE IS Phenix Technologies Inc. 116 Industrial Drive Accident, MD USA Phone: {+1} (301) FAX: {+1} info@phenixtech.com