Magnetization System of Magnetically Controlled Shunt Reactors

Transcription

1 Magnetization System of Magnetically Controlled Shunt Reactors Leonid Kontorovych, Technical Director of ZTR PJSC, PH.D. in Engineering Sciences; Igor Shyrokov, head of the department of reactors control systems development Vladimir Vitrenko, senior electronic engineer for control systems This article describes the magnetization system of a Magnetically Controlled Shunt Reactor (MCSR), designed by Zaporozhtransformator PJSC. Zaporozhye, Ukraine. Magnetically controlled shunt reactors produced by Zaporozhtransformator PJSC have been operating for more than 10 years in Russia, Kazakhstan, Belarus and Lithuania grids and have proved their reliability and efficiency, over the period. The operation principle of such reactors is in the controllable changing of the saturation level of the semi-limbs of the electromagnetic part, by changing of the rectified current which flows through MCSR control winding. The changing of the saturation level of the semi-limbs causes change of the inductance of the MCSR power winding and consequently changing of the reactive power absorption from the grid. Structure of the magnetization system Block diagram of the MCSR magnetization system is shown on the figure 1. Basic components of the magnetization system are: 1. Transformer with semiconductor converter units (one or more) which consists of transformers and semiconductor converters. These units connected to the MCSR control winding and supplied from the substation auxiliary grid or from the MCSR compensation winding. Transformer with semiconductor converter units ensures flowing of the rectified current through MCSR control winding. Value of the rectified current switch determines the condition of the magnetic system of the reactor s electromagnetic part. 2. Automatic control system (ACS) which generates control commands of the semiconductors converters in accordance with determined algorithms. It can perform control in order to maintain determined voltage at the point of MCSR connection (regulation according to voltage) or in order to maintain determined reactive power absorbed by MCSR (regulation according to absorption current). 3. Direct current and voltage transducers, which ensures measurement of the output parameters of the semi-conductor converters. 1 MCSR magnetization system

2 Figure 1 Block diagram of the MCSR magnetization system Converter Units The main and reserve converter units ensure smooth regulation of the reactive power absorbed by MCSR, during main operation modes. It ensures, MCSR power changing from 5% to 100% and back during 0,7 seconds in commercialized by PJSC Zaporozhtransformator MCSRs with different voltages and power. MCSR power changing from 5% to 100% and back during 0,3 seconds is ensured in cases where additional forcing converter unit is used. Such response time is enough for most of the practical tasks. In case of requirements for response time decreasing MCSR magnetization device can be modernized, but this will lead to an increase in price. For example, a forcing converter with increased power can be used for decreasing of the response time in many cases. MCSR compensation winding feed main converter unit. Auxiliary grid of 10(6) kv substation feed reserve and forcing converter units. A reserve and forcing converter unit can perform initial magnetization of MCSR magnetic system (when reactor is switched-off). If necessary, initial magnetization can be realized from 0,4 kv grid with the help of a low-power converter unit. Three-phase matching transformers of the converter units with nominal power 1000 kva ensure decreasing of the MCSR compensation winding voltage and auxiliary grid substation voltage to 400 V for feeding of the main and reserve semi-conductor converters and voltage decreasing to 1100 V for feeding of the forcing semi-conductor converter. Magnetic system and windings of the matching transformers are located in oil filled tank with shut-off valves for oil drain and filling, oil sampling, conservator and gas relay connection. Bushings, terminal boxes, conservator with air breathers are placed on the tank cover. Following control and protection equipment are included in the transformers: conservator oil level indicator, manometric thermometer, gas relay and pressure relief safety valve. Transformer cooling is natured, oil. Overall dimensions (length x width x height) is 2210 mm 1430 mm 2300 mm. Mass is 3375 kg. 2 MCSR magnetization system

3 Block diagram of the semiconductor converter of the converter unit is shown on figure 2. Basic converter functional elements are controlled rectifier, coupling cabinet and voltage suppressor. Figure 2 Block diagram of the semiconductor converter Controlled rectifier (figure 3) consists of three-phase controlled thyristor bridge (six thyristor cells), shunting gate (2 thyristor cells), pick-off diode (one diode cell) and three current transformers. Figure 3 Block diagram of the controlled rectifier 3 MCSR magnetization system

4 Each thyristor cell consists of: low frequency power pill thyristor; impulse node, which forms thyristor control impulses in accordance with recommendation of thyristor producer; damping RC circuit; shunt resistor; protective circuit ensures thyristor switch on, at applied direct over voltages and voltage limitation on it, till safe level at applied reverse over voltages; saturating choke for limitation of the anode current rise speed at thyristor activation. Diode cell consist of: low frequency power pill diode; damping RC circuit; shunt resistor; protective circuit ensures overvoltage limitation on the diode till safe level; The rated rectified current of the controlled rectifier is 2000 A. The maximum rectified voltage at no load mode of the main and reserve unit is 540 V; the maximum rectified voltage at no load mode of the converter unit is 1485 V. Power semiconductor devices of the controlled rectifier (thyristors, diodes) are placed on doubleended all-metal coolers. The controlled rectifier is placed in oil filled tank with shut-off valves for oil drain and filling, oil sampling, conservator and gas relay connection. Bushings, terminal boxes, conservator with air breathers are placed on the tank cover. Following control and protection equipment are included in the transformers: conservator, oil level indicator, manometric thermometer, gas relay and pressure relief safety valve. Cooling of the controlled rectifier is natured, oil. Coupling cabinet of the semiconductor converter (figure 4) is intended for: receiving of the control commands from the automatic control system; forming of the control signals by rectifier thyristors; acquisition and transfer of the converter condition data (temperature of oil upper level in rectifier tank, currents in input converter busses) into automatic control system; organization of the fast-acting thyristor protection during fault at converter output. The information exchange between coupling cabinet of the semiconductor converter and remote automatic control system is carried out through fiber-optic connection lines (command and information lines). Such an approach allows increasing noise immunity and the reliability of MCSR magnetization system. A coupling cabinet is placed on the external tank wall of the semiconductor converter. The coupling cabinet is equipped with a climate control system. Nonlinear voltage suppressors intended for protection of the semiconductor converter from MCSR control winding commutation over voltages are placed on the semiconductor converter tank cover. Overall dimensions of the semiconductor converter (length x width x height) is 2680 mm 1430 mm 2300 mm. Mass is 2500 kg. 4 MCSR magnetization system

5 Design of the converter unit consists of semiconductor converter and matching transformer, fixed on the metallic frame and connected by the system of busses (figure 5). Overall dimensions of the converter unit (length x width x height) is 3145 mm 2680 mm 2450 mm. Mass is 6300 kg. Figure 4 Coupling cabinet of the semiconductor Automatic Control System 5 MCSR magnetization system Figure 5 Converter unit at the substation Automatic control system (ACS) is intended for forming of the control commands of the semiconductor converter of converter units, depending on determined operation mode and condition signals of MCSR and substation equipment. ACS ensures the following MCSR operation modes: initial magnetization; automatic maintenance of the determined voltage in the point MCSR connection (voltage control); automatic maintenance of the determined reactive power absorbed by MCSR (absorption current control); forcing MCSR power increasing;

6 forcing MCSR power decreasing; manual control of absorbed by MCSR current; no-load mode. ACS consists of: signal normalization device; control and indication units; regulation and control device; contact signals formers; communication equipment; power supply equipment. Signal normalization device is intended for conversion of substation voltage measurement transformers (rated actual value is 100 V), MCSR current measurement transformers (rated actual value is 1 A or 5 A), direct current transducer (rated value is ± 400 ma) and direct voltage transducer (rated value is ± 50 ma) input analogue signals into voltage in ±10 V range. It is also used for conversion of substation equipment (switchers and protection devices state) input contact signals into logical potential signals. Control and indication units are intended for ACS operation control and also for displaying of MCSR equipment state information. Control and indication units consist of operator panel realized on panel PC basis with sensor data input and command formers (switchers) START/STOP and LOCAL/REMOTE. Operator panel consist s of CONTROL screen which has groups of virtual control and indication units (figure 6) and STATE screen which has virtual indication units (figure 7). Figure 6 CONTROL screen 6 MCSR magnetization system

7 Figure 7 STATE screen A Regulation and control device is used for hardware and software realization of ACS operation algorithms. It is realized on real time industrial controller base, programmable logic and inputoutput modules of analogue and discrete signals. The following four groups of functions are ensured in the regulation and control device: 1. Formation of the logical potential signals of MCSR readiness for connection to the grid, ACS fault and ACS protection actuation. Signals are taken out into contact signals formers. The regulation and control device ensures, also, local and remote MCSR control. Selection is performed with the help of LOCAL/REMOTE command former. The operator inputs data into ACS with the help of the Control screen in local control mode (values of control settings and identifiers of MCSR operation mode). Data is inputted into ACS from the substation control system in remote control mode. 2. Formation of the control commands for ensuring of each convertor unit operation in controlled, diode, shunt or block mode. Commands are outputted through RS-485 interface into ACS commutation equipment through reserved lines. Time for command output is determined in reference to synchronizing voltage (from substation measurement voltage transformers) taking into account calculated thyristor delay angle of converters in accordance with ACS algorithm. 3. Determination and processing of emergency modes signals. absence of the synchronizing voltage; heating of the semiconductor converter (actuation of the first step of the converter thermometer); overheating of the semiconductor converter (actuation of the second step of the converter thermometer); overload of the semiconductor converter (root-mean-square value of the converter phase currents exceeds acceptable value which is regulated in % from the rated value); 7 MCSR magnetization system

8 protection of the semiconductor converter (root-mean-square value of the converter phase currents exceeds acceptable value which is regulated in % from the rated value); current overloading of the MCSR power winding; current overloading of the MCSR control winding; absence of the confirmation for the successful ACS command pass to the converter unit; protection actuation signal from the substation relay protection system. 4. Determination and processing of ACS stop mode signals Selection is performed with the help of START/STOP command former. Semiconductor convertors control commands which block thyristor control impulses formed in the stop mode. Contact signals formers are intended for the conversion of the potential logic readiness, failure and protection actuation signals into the contact signals, transferred to the substation systems. ACS communication equipment includes Ethernet switch and optical media converters. Ethernet switch is intended for organization of the local network between ACS panel PC, regulation and ACS control panel, coupling cabinets of the semiconductor convertors. Network is intended for regular data exchange between ACS panel PC and ACS regulation and control device and also for the remote connection of the technology equipment to the coupling cabinets of the semiconductor converters for installing and debugging of the software. Optical media converters are intended for the organization of the duplicate fiber optic command lines and data lines between ACS and coupling cabinets of the semiconductor converters. ACS power supply equipment includes voltage control relay of the power supply and secondary power supply source of the ACS equipment. ACS power supply is carried out from AC grid with voltage ( ) V and frequency (48 52) Hz. Possibility of the automatic switching to the power supply from DC grid with voltage ( ) V is provided in case of AC grid voltage deviation exceeds acceptable limits. Power supply voltage control relay is intended for the measurement of the AC grid voltage and automatic switching of the AC to the DC grid power supply. ACS power consumption is no more than 300 W. ACS Design ACS design consists of two-sided service electromechanical cabinet with transparent front door (figure 8) and electrical apparatuses which are located inside of the cabinet. ACS overall dimensions (length x width x height) is 600 mm 800 mm 2200 mm. Mass is 2500 kg. ACS overall dimensions can be changed in accordance with client requirements. MCSR magnetization system software MCSR magnetization system software includes: ACS software; main converter unit software; reserve converter unit software; 8 MCSR magnetization system

9 forcing converter unit software. Figure 8 ACS external view ACS software is intended for: organization of the human-machine interface; manual data input with the help of the sensor panel; data output to the screen in the graphic format; data input from MCSR equipment and substation systems; data transfer to the substation systems; hardware-in-the-loop realization of the MCSR operation algorithms; determination of the emergency operation modes; forming of the converter units thyristor control commands; reserve switching control of the command and informational lines; reserve switching control of the converter units. Converter units software is intended for: receiving of the commands for control of the semiconductor converter unit thyristors; forming of the signals for control of the semiconductor converter unit thyristors; receiving of the semiconductor convertor sensors signals; data forming for the semiconductor convertor condition; realization of the fast-acting protection of the semiconductor converter. Operation of the MCSR magnetization system Magnetization system switches MCSR into initial magnetization mode before MCSR connection to the grid. At the same time, ACS forms and transfer commands of switch into controllable mode and thyristor activation with angle corresponded to the initial magnetization current flowing in the 9 MCSR magnetization system

10 MCSR control winding into reserve or forcing converter unit. Rest converter units are switched into block mode. MCSR magnetization system forms and transfer s MCSR readiness signal for connection to the grid into substation systems after the achievement of the necessary level of the initial magnetization current which is controlled by the DC transducer. Magnetization system switches MCSR into the mode defined by an operator in advance, after MCSR connection. At the same time, ACS switches semiconductor converter of the main converter unit into the controllable mode. In automatic mode thyristors delay angle of the semiconductor converters is calculated in accordance with control law. In the manual mode it is determined by the operator. In forcing power increasing/decreasing mode ACS forms commands which switches forcing converter unit into controllable mode with fixed thyristors delay angle. ACS switches semiconductor converter of the main converter unit into controllable mode after forcing power increasing/decreasing. ACS switches semiconductor convertor of the reserve converter unit into controllable mode in case of failure modes related with failures in the main converter unit (overheating, exceeding of the consumption current on phases, actuation of the fast-acting protection). ACS switches convertor units into shunt mode in case of failure modes related with exceeding of the acceptable limits of the measured values (absence of the synchronizing voltage, overloading of the MCSR power or control winding current). MCSR magnetization system test results Off-line routine and type tests of MCSR magnetization system and also special combined tests of MCSR magnetization system with MCSR electromagnetic parts were carried out on PJSC Zaporozhtransformator test fields. Scope of the converter units routine tests: checking of the working drawings for compliance with the requirements; tank leakage test; checking of the insulation resistance against tank; testing of insulation with applied voltage. Scope of the converter units type tests: control of control impulses form; checking of the operation at rated voltage; checking of the operation at rated current; temperature rise tests (combined with checking of operation at rated current). Scope of the ACS routine tests: checking of the working drawings for compliance with the requirements; checking of operation of measuring lines; checking of operation of control lines; checking of insulation resistance of electrically separated circuits. 10 MCSR magnetization system

11 Scope of the ACS type tests: checking of system s algorithms and software. Besides, ACS electromagnetic compatibility tests were conducted in the special independent accredited metrological laboratory. All above mentioned tests confirmed compliance of the MCSR magnetization system equipment parameters with specified values. For example, figures 9, 10, 11 and 12 show some measurement results of these tests for MCSR 100 MVAr 220 kv. Figure 9 Oscillogram of the semiconductor convertor phasing. Control impulse of the thyristor coincides on phase with voltage crossing С А through 0 from + to Figure 10 Regulating characteristic of the semiconductor convertor Ud = f(alpha) on output of the ACS signal normalization device without cosine correction 11 MCSR magnetization system

12 Figure 11 Current of MCSR control winding in rated power consumption mode Figure 12 Voltage of MCSR control winding in rated power consumption mode Copyright 2014 Zaporozhtransformator PJSC. The document, or parts thereof, should not be copied, adapted, redistributed, or otherwise used without the prior written permission of Zaporozhtransformator PJSC. 12 MCSR magnetization system