GB/Z 29630-2013Static var compensators (SVC) - System design and application guidelines (English PDF)

Foreword

This guiding technical document was drafted in accordance with the rules given in GB/T 1.1-2009.

This guiding technical document was proposed by the China Electrical Equipment Industry Association.

This guiding technical document is under the jurisdiction of the National Technical Committee for Standardization of Power Electronics (SAC/TC 60).

The main drafting organizations of this guiding technical document are: Xi'an High Voltage Apparatus Research Institute Co., Ltd., China Southern Power Grid Electric Power Research Institute Co., Ltd., NR Electric Co., Ltd. (Nanjing), Rongxin Power Electronic Co., Ltd., Guodian Nanjing Automation Co., Ltd., Xi'an University of Technology, Xi'an XD Power Capacitor Co., Ltd., Southwest Electric Power Design Institute (Power Grid Branch), Xi'an Power Electronics Technology Research Institute, State Grid Electric Power Research Institute, Kunming Electrical Apparatus Research Institute, Xi'an XD High Voltage Electric Co., Ltd. and the Flexible Power Transmission Company of XJ Group Corporation.

The main drafters of this guiding technical document are: Sun Wei, Fu Chuang, Chen Chihan, Zhang Fanyong, Yang Xiaohui, Tian Enwen, Li Lu, Tong Xiangqian, Xin Jianwei, Wang Youlong, Yang Zhiyong, Zhang Hualiang, Yu Hongqi, Zhu Zhenfei, Liang Shuaiqi, Zhou Qiongfang, Zhao Yongtao, Hu Xuhui, Meng Chen and He Qinglian.

1 Scope

This guiding technical document specifies the design content required for a static var compensator (hereinafter SVC) to meet system operating requirements, and sets out basic requirements for SVC components, subsystems, layout, installation and related design content.

This guiding technical document applies to the design of thyristor-based SVCs in transmission and distribution systems.

This guiding technical document is prepared mainly for thyristor controlled reactor (TCR) type and thyristor switched capacitor (TSC) type SVCs; thyristor switched reactor (TSR) type SVCs may be designed with reference to it.

Every SVC project has its own particular features; this document should be applied according to the specific project conditions and requirements and supplemented where necessary.

2 Normative references

The following documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including all amendments) applies.

GB 311.1 Insulation co-ordination - Part 1: Definitions, principles and rules (GB 311.1-2012, IEC 60071-1:2006, MOD); GB/T 1094.6 Power transformers - Part 6: Reactors (GB/T 1094.6-2011, IEC 60076-6:2007, MOD); GB 1984 High-voltage alternating-current circuit-breakers (GB 1984-2003, IEC 62271-100:2001, MOD); GB 1985 High-voltage alternating-current disconnectors and earthing switches (GB 1985-2004, IEC 62271-102:2002, MOD); GB/T 6451 Specification and technical requirements for oil-immersed power transformers; GB/T 10228 Specification and technical requirements for dry-type power transformers.

GB/T 11024.1 Shunt capacitors for AC power systems having a rated voltage above 1 000 V - Part 1: General (GB/T 11024.1-2010, IEC 60871-1:2005, MOD); GB 11032 Metal-oxide surge arresters without gaps for AC systems (GB 11032-2010, IEC 60099-4:2006, MOD); GB/T 12325 Power quality - Deviation of supply voltage; GB/T 12326 Power quality - Voltage fluctuation and flicker; GB/T 14285 Technical code for relaying protection and security automatic equipment; GB/T 14549 Quality of electric energy supply - Harmonics in public supply network.

GB/T 14598.9 Measuring relays and protection equipment - Part 22-3: Electrical disturbance tests - Radiated electromagnetic field immunity (GB/T 14598.9-2010, IEC 60255-22-3:2007, IDT); GB/T 14598.10 Measuring relays and protection equipment - Part 22-4: Electrical disturbance tests - Electrical fast transient/burst immunity test (GB/T 14598.10-2012, IEC 60255-22-4:2008, IDT); GB/T 14598.13 Electrical relays - Part 22-1: Electrical disturbance tests for measuring relays and protection equipment - 1 MHz burst immunity tests (GB/T 14598.13-2008, IEC 60255-22-1:2007, MOD); GB/T 14598.14 Measuring relays and protection equipment - Part 22-2: Electrical disturbance tests - Electrostatic discharge tests (GB/T 14598.14-2010, IEC 60255-22-2:2008, IDT); GB/T 15166.4 High-voltage alternating-current fuses - Part 4: External fuses for shunt capacitors (GB/T 15166.4-2008, IEC 60549:1976, MOD).

GB/T 15291 Semiconductor devices - Part 6: Thyristors (GB/T 15291-1994, eqv IEC 60747-6:1983 and its Amendment 1:1991); GB/T 15543 Power quality - Three-phase voltage unbalance; GB/T 15945 Power quality - Frequency deviation for power system; GB/T 20298-2006 Functional performance characteristics of static var compensators (SVC); GB/T 20994 Shunt capacitors and AC filter capacitors for HVDC transmission systems; GB/T 20995 Power electronics for electrical transmission and distribution systems - Testing of thyristor valves for static VAR compensators (GB/T 20995-2007, IEC 61954:2003, MOD); GB/T 22075 Audible noise of HVDC converter stations.

GB 50052 Code for design of electric power supply systems; GB 50059 Code for design of 35 kV - 110 kV substations; GB 50060 Code for design of 3 kV - 110 kV high voltage electrical installations; GB 50227-2008 Code for design of installation of shunt capacitors; GB/T 29629-2013 Water cooling equipment for static var compensators; Guide of the International Telegraph and Telephone Consultative Committee (CCITT).

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1 static var compensator (SVC): a shunt-connected static var compensator that maintains or controls certain parameters at its point of connection to the power grid (typically the bus voltage) by automatic adjustment of inductive or capacitive current. Note: an SVC generally comprises TCR, TSC, TSR, etc., and together with mechanically switched var compensation devices generally forms a static var compensation system. 3.2 thyristor controlled reactor (TCR): a shunt reactor controlled by thyristors, whose equivalent inductive reactance is varied continuously by controlling the conduction angle of the thyristors. 3.3 thyristor switched capacitor (TSC): a shunt capacitor switched by thyristors, connected or disconnected by turning the thyristors on or off. 3.4 thyristor switched reactor (TSR): a shunt reactor switched by thyristors, connected or disconnected by turning the thyristors on or off.

3.5 fixed capacitor (FC): a shunt device formed by a suitable combination of capacitors (sometimes also reactors). Note: it can usually also be designed as a filter. 3.6 thyristor level (TL): the basic unit of a thyristor valve, consisting of thyristors connected in parallel or anti-parallel, including auxiliary circuits (firing, protection, voltage grading, damping components, etc.) [adapted from GB/T 20995-2007, definition 3.1]. 3.7 thyristor valve (TV): the electrical and mechanical assembly of thyristor levels, complete with all connections, auxiliary components and mechanical structures, which can be connected in series with the reactor or capacitor of each phase of the SVC [GB/T 20995-2007, definition 3.5]. 3.8 valve base electronics (VBE): an electronic unit at earth potential forming the interface between the SVC control system and the thyristor valves [GB/T 20995-2007, definition 3.7]. 3.9 thyristor electronics (TE): electronic circuits at valve potential that perform control, protection and other functions; they receive control signals from the VBE and report thyristor status information back to the VBE.

3.10 control system: the collective term for the units that perform regulation, protection, control, firing and monitoring of the SVC. 3.11 valve blocking: the operation that prevents the thyristor valve from firing by suppressing the valve control pulses [adapted from GB/T 13498-2007, definition 7.17]. 3.12 angle: the description of a time interval in a sine wave by the corresponding angle; Figure 1 shows the angles commonly used (voltage u and current i waveforms of a thyristor-controlled reactor, with firing angle alpha, conduction angle sigma and extinction angle gamma). 3.13 trigger angle (alpha): the interval from the instant the thyristor begins to be subjected to forward voltage to the instant the thyristor begins to conduct (see Figure 1) [adapted from GB/T 13498-2007, definition 7.20]. 3.14 conduction angle (sigma): the interval during which the thyristor conducts; under normal conditions it is the difference between the extinction angle gamma and the trigger angle alpha (see Figure 1). 3.15 extinction angle (gamma): the interval from the instant the thyristor begins to be subjected to forward voltage to the instant the thyristor stops conducting (see Figure 1) [adapted from GB/T 13498-2007, definition 7.23]. 3.16 false firing: firing of the thyristor valve at an incorrect instant.

3.17 response time: the time taken, after a step control input signal, for the SVC output to reach 90 % of the required output value without overshoot occurring in the meantime (see Figure 2). Note: because the voltage variation range is small and a clear voltage curve is difficult to obtain, the response time can generally be illustrated by the reactive current curve. Figure 2 shows the definition of response time and settling time: control target, 90 % level, maximum overshoot and the plus/minus 5 % band following a step in the SVC control input (control target reference value). 3.18 settling time: the time taken, after a step control input signal, for the SVC output to come within plus/minus 5 % of the required output value (see Figure 2). 3.19 voltage-current characteristic: the relationship between the fundamental steady-state voltage and current of the SVC at the point of common coupling. 3.20 control range: the maximum range, from inductive to capacitive, of the reactive current or reactive power provided by the SVC at the point of connection.

3.21 lagging operation: the operating mode in which the SVC current lags its voltage, equivalent to a shunt reactor. 3.22 leading operation: the operating mode in which the SVC current leads its voltage, equivalent to a shunt capacitor. 3.23 reference voltage: the voltage on the SVC voltage-current characteristic at which the total reactive output is zero (the point at which the SVC neither generates nor absorbs reactive power); the reference voltage range is adjustable, generally 0.90 p.u. to 1.10 p.u. 3.24 slope level (SL): within the linear controllable range (capacitive and inductive) of the SVC voltage-current characteristic, the ratio of the per-unit voltage change to the per-unit current change, generally expressed as a percentage.

3.25 voltage break-over protection (VBO): an overvoltage protection of the thyristor; when the voltage reaches a set value the thyristor is fired into conduction, protecting it from voltage breakdown; generally implemented with a break-over diode (BOD) or equivalent circuit. 3.26 check point (CP): the point at which performance indices are measured, as stipulated in the contract between supplier and purchaser. 3.27 flicker improve ratio: the 95 % probability value of short-term flicker before the SVC is put into operation minus the 95 % probability value of short-term flicker after the SVC is put into operation, divided by the 95 % probability value before the SVC is put into operation, expressed as a percentage; the flicker improvement ratio should generally be not less than 50 %.

4 SVC installation site

4.1 Environmental conditions. The following climatic and environmental conditions of the SVC installation site shall be provided; an SVC operating under these conditions shall achieve its rated design level for all performance indices: a) altitude (m); b) average annual precipitation (mm); c) maximum monthly precipitation (mm); d) average annual ambient temperature (deg C); e) maximum ambient temperature (deg C); f) minimum ambient temperature (deg C); g) average annual relative humidity (%); h) maximum relative humidity (%); i) ice coating thickness (mm); j) maximum ground snow depth (mm); k) maximum frost thickness (mm); l) frozen soil depth (m); m) average annual wind speed (m/s); n) maximum annual wind speed (m/s); o) seismic intensity (degree); p) average annual thunderstorm days (d/a); q) pollution class; r) solar radiation intensity (W/cm2); s) soil resistivity (ohm-m).

4.2 System conditions. System conditions include: a) nominal voltage at the SVC connection point and its variation range; b) grid frequency and its variation range; c) grid harmonic impedance; d) overvoltage protection levels, including lightning impulse and switching impulse protection levels; e) substation earthing method; f) main connection and equipment parameters of the supply system, supply mode, capacity of supply equipment, and associated reactive compensation devices and their parameters; g) background power quality parameters at the check point, including voltage variation range (curve), harmonic voltages, harmonic currents, voltage fluctuation and flicker, three-phase voltage unbalance, etc.; h) short-circuit level at the point of common coupling or check point, including three-phase and single-phase short-circuit currents (or short-circuit capacity) under maximum and minimum operating modes; i) relevant protection settings and fault clearing times.

4.3 Load conditions. Load conditions include: a) contracted power demand; b) load capacity and nature, including harmonic generation, voltage fluctuation and flicker values, range of variation of active and reactive power or curves of their variation with time, power factor, maximum negative-sequence current, etc.; c) load operating conditions.

4.4 Other conditions. Other conditions include: a) SVC footprint area; b) external conditions required by the cooling equipment; c) existing related installations and equipment (including earthing, lightning protection, etc.); d) layout arrangement (outdoor or indoor, single-level or two-level layout, cable or overhead connections, etc.); e) monitoring mode (local and/or remote); f) power supply conditions at the site of use; g) noise level.

5 Main functions

The functional characteristics of an SVC according to its application are as follows.

The functional characteristics of an SVC in a transmission system generally include: phase and voltage regulation under normal conditions (i.e. reactive power control and voltage deviation regulation) and voltage support under fault conditions; suppression of power-frequency overvoltage and reduction of voltage fluctuation; improvement of system stability, increase of transmission power and reduction of transmission losses; suppression of harmonic currents; other supplementary functions (damping of system power oscillations, suppression of subsynchronous oscillations, etc.).

The functional characteristics of an SVC in a distribution system or at an industrial user generally include: suppression of voltage fluctuation and flicker; correction of three-phase load unbalance; suppression of harmonic currents and reduction of harmonic voltage distortion; improvement of power factor.

6 Types and connection arrangements

The main SVC types are the thyristor controlled reactor (TCR) type, the thyristor switched capacitor (TSC) type and the thyristor switched reactor (TSR) type; these may be used alone or in combination as required.

A TCR (TSR) branch may be provided with its own circuit breaker or may share one circuit breaker with all or some of the fixed capacitor branches.

The TCR reactor of each phase is generally split into two identical upper and lower halves, one connected on each side of the thyristor valve of that phase, and the three phases as a whole are delta-connected (Figure 3, TCR connection diagram). The TSC thyristor valve is generally placed between the capacitor and the reactor, with delta connection (Figure 4, TSC connection diagram).

For fixed capacitors, depending on the SVC capacity and number of branches, a technical and economic comparison determines whether one circuit breaker serves one branch or several branches. General rules for fixed capacitor branch connections: a) the fixed capacitors are mainly of four types: single-tuned, double-tuned, C-type and high-pass filters (Figure 5 shows the four arrangements with their L, C, R elements); b) fixed capacitor branches should use star connection with the neutral point not earthed; c) where each phase or arm of a fixed capacitor branch capacitor bank consists of several capacitors in series-parallel combination, the capacitors shall be connected first in parallel and then in series; d) where the filter reactor or series reactor is installed on the supply side, its current rating shall meet dynamic and thermal withstand requirements.

7 Main parameters and performance

The basic characteristics of an SVC are determined by its steady-state voltage-current characteristic, as shown in Figure 6. In Figure 6, a-b-c is the linear operating region (ab capacitive region, bc inductive region); cd is the inductive overload region (thyristor conduction angle held at maximum); when I exceeds Imax the TCR is taken out of operation by protection action. The control range extends between the capacitive limit (leading) and the inductive limit (lagging).

The main characteristics of an SVC are described by the following parameters and performance: a) rated voltage Un (kV): the nominal voltage at the SVC connection point (bus); b) rated capacity Qn (Mvar): the maximum thyristor-controlled fundamental reactive power the SVC can output under rated conditions; c) dynamic regulation range (Mvar): the adjustable reactive range achieved by thyristor control, i.e. the maximum range of variation of SVC reactive power at rated voltage; d) reference voltage Uref (p.u.): the voltage at point b in Figure 6; Uref should normally be adjustable, Uref = 0.9 p.u. to 1.1 p.u.; e) slope (%): the slope of segment ac in Figure 6, generally adjustable within 0.5 % to 10 %; f) response time (ms): generally provided by the supplier, and obtainable by dedicated system studies or measurement.

g) overload capability: the overload multiple and duration the SVC can achieve; h) rated inductive reactive power QLS: the maximum inductive reactive power the SVC can output in continuous operation under rated conditions; i) rated capacitive reactive power QCS: the maximum capacitive reactive power the SVC can output in continuous operation under rated conditions; j) rated capacity of the TCR QTCR: the maximum inductive reactive power the TCR branch can output in continuous operation under rated conditions; k) rated capacity of the fixed capacitor QFC: the fundamental capacitive reactive power output by the fixed capacitor when operating under rated conditions.

8 System design

8.1 Design objectives. The basic objective of SVC system design is to determine rationally, under the specified design conditions and functional requirements, the SVC main connection scheme and basic parameters, so as to ensure safe and reliable SVC operation and achieve the expected compensation performance.

8.2 Design content. The design mainly includes: a) confirmation of system conditions and functions; b) confirmation of external conditions at the SVC site; c) selection of SVC basic parameters and main connection; d) verification of performance indices (see 8.3); e) verification of safe operation of SVC components (see 8.3); f) verification of system harmonic resonance (see 8.3); g) calculation of switching overvoltages and determination of the protection method, protective component configuration and parameters (see 8.3); h) parameters and procurement specifications of the main SVC components; i) relay protection configuration and determination of protection settings (see 8.3); j) determination of SVC control strategy (see 8.3); k) determination of communication protocols and interfaces; l) SVC installation layout scheme and related drawings (see 8.4); m) availability and reliability (see 8.5); n) evaluation of losses (see 8.6); o) noise (see 8.7).

8.3 System studies. 8.3.1 Study content. System studies generally include, but are not limited to, studies of dynamic performance, harmonics, negative sequence, voltage fluctuation and flicker, and overvoltages; the specific study content may be determined according to the actual project. 8.3.2 Dynamic performance. The performance of SVC control during system disturbances (e.g. major faults and load rejection) should be studied from the standpoint of transient and dynamic stability: a) voltage support, stability performance and response characteristics of the SVC during system faults and switching operations; b) SVC protection and protection coordination; c) if required, verification of the supplementary control functions needed for the SVC to damp system power oscillations and suppress subsynchronous oscillations after a system disturbance; d) interaction between SVC control and other nearby control systems, including HVDC control, generator control and other flexible AC transmission system (FACTS) device controls.

8.3.3 Harmonic, negative-sequence, voltage fluctuation and flicker performance. This includes: a) verification, through harmonic load-flow studies, that the SVC harmonic filter design is reasonable; the study shall evaluate harmonic levels at the SVC check point and/or point of common coupling, and the study report should include: 1) maximum and minimum reactive power and harmonic current output of the SVC under specified system operating conditions (including maximum and minimum system voltage levels); 2) harmonic suppression effect; 3) non-characteristic harmonics generated under system voltage unbalance and firing angle unbalance; 4) possible harmonic resonance overvoltages; 5) checking of safety margins of filter components; b) evaluation of the effect on the power system of negative-sequence current produced by the load and of the improvement achieved with the SVC; c) evaluation of bus voltage fluctuation and flicker caused by load reactive power impacts (see Annex A) and of the improvement achieved with the SVC. Otherwise refer to the requirements of GB/T 12326, GB/T 12325, GB/T 14549, GB/T 15543 and GB/T 15945.

8.3.4 Overvoltage. Studies of overvoltages (including lightning and switching overvoltages) are used to determine the overvoltage protection method, equipment insulation levels, surge arrester parameters, etc. The study covers: a) power-frequency, lightning and switching overvoltages; b) bus faults (single-phase-to-earth, phase-to-phase and three-phase short circuits); c) overvoltages caused by switch restrikes (single-phase or two-phase); d) thyristor valve faults (including possible false turn-on).

8.4 Equipment layout. The SVC equipment layout requirements are: a) in principle, SVC equipment layout and installation design shall ensure safety, facilitate ventilation and heat dissipation, and ease operational inspection and maintenance; general requirements may refer to GB 50052, GB 50059, GB 50060 and GB 50227-2008; b) thyristor valves and their cooling equipment should be arranged indoors; c) monitoring and protection devices should not be placed in the valve hall, but should be close to the valve groups to shorten signal transmission distances; d) phase-controlled reactors should be arranged outdoors phase-segregated, or may be arranged indoors; otherwise see 8.3 of GB 50227-2008; e) phase-controlled reactors should not affect other substation equipment, particularly secondary circuits and devices.

8.4 (continued) f) the influence of reactors on external equipment refers to CCITT Guide Volume 6, Chapter 6; g) filter reactors are arranged on the same principle as d), but to reduce footprint three-phase stacked installation may also be used; h) shunt capacitor banks should be arranged outdoors, but in special areas with severe cold, humid heat or sandstorms and in special environments with pollution, flammability or explosion hazard they should be arranged indoors; otherwise see 8.23 of GB 50227-2008; i) installation of external protective fuses for capacitors: see GB/T 15166.4; j) depending on small-animal activity in the surroundings, the SVC may be provided with anti-intrusion sealing, fences, mesh barriers and similar facilities.

8.5 Availability and reliability. Refer to Annex E of GB/T 20298-2006.

8.6 Evaluation of losses. 8.6.1 Loss calculation. Within the designed operating range of the SVC, total losses are calculated separately at different operating points. The loss calculation does not include losses of switchgear, busbars, cables, clamps and connectors, and neglects losses related to harmonic currents; these parts shall however be considered when determining parameters of resistors, cooling equipment, etc. The estimated or guaranteed total SVC loss is obtained from items a) to f): a) thyristor valve loss Pvalve: see Annex B; b) loss of the SVC dedicated step-down transformer: data from the manufacturer or test laboratory; c) reactor loss Preac, calculated by formula (1): Preac = 3 x Rreac x I^2, where Rreac is the DC resistance of the reactor, available from the reactor test report, and I is the r.m.s. reactor current; d) capacitor bank loss Pcap, calculated by formula (2): Pcap = Qcap x tan(delta), where Qcap is the capacitor capacity and tan(delta) is the capacitor dielectric loss tangent, available from test reports, taking the average tan(delta) of all capacitors; e) resistor loss Pres, calculated by formula (3): Pres = 3 x Rres x I^2, where Rres is the resistor resistance and I the r.m.s. resistor current; f) power consumed by SVC auxiliary systems, including pumps, fans, heating systems and control and protection systems.

8.6.2 Loss evaluation. Assuming an ambient temperature of 20 deg C and a bus voltage of 1.0 p.u., with the SVC rated operating range from inductive QLS to capacitive QCS, TCR rated capacity QTCR and fixed capacitor rated capacity QFC, the losses at the following operating points are used to evaluate total SVC loss: a) SVC 100 % inductive output QLS (TCR branch at full capacity, fixed capacitor branch at full capacity, net inductive output), total loss P1 (kW) for 10 % (t1) of annual operating time; when QLS = 0, this loss item, apart from the operating time, is recommended to be treated as in c); b) SVC 100 % capacitive output QCS (TCR branch at zero output with only no-load losses, fixed capacitor branch at full capacity), total loss P2 (kW) for 10 % (t2) of annual operating time; c) SVC zero output (TCR branch output exactly equal to filter branch capacity), total loss P3 (kW) for 20 % (t3) of annual operating time.

d) SVC 50 % inductive output QLS (after the TCR capacity offsets the filter branch capacity, the SVC can still output 50 % inductive reactive power), total loss P4 (kW) for 15 % (t4) of annual operating time; when QLS is zero, this loss item, apart from the operating time, is recommended to be treated as in c); e) SVC 50 % capacitive output QCS (TCR capacity offsets half the filter branch capacity, SVC outputs 50 % capacitive reactive power), total loss P5 (kW) for 45 % (t5) of annual operating time. At each operating point the losses of all SVC working or connected parts specified in 8.6.1 shall be calculated, whether or not they carry current. The sum of the above losses is the evaluated loss: Sum P (kW) = P1 x t1 + P2 x t2 + P3 x t3 + P4 x t4 + P5 x t5, with t1 + t2 + t3 + t4 + t5 = 1. The total loss should not exceed 1 % of the SVC rated output capacity.

8.7 Noise. Reactors, capacitors, thyristor valves and other equipment in the SVC produce noise; the audible noise level shall be kept within the limits required by the relevant standards (see GB/T 22075).

9 Basic requirements for SVC components and subsystems

9.1 Thyristor valves. Basic requirements include: a) thyristor valves shall be designed according to system operating conditions and performance requirements, including the necessary protections and accessories, to ensure safe and reliable operation; b) the valve structure shall allow the user close-range inspection of thyristors, routine maintenance, fault handling and component replacement; c) a thyristor valve consists of a number of series-connected thyristor levels, including all necessary heat sinks, voltage grading and protection circuits, firing and power-extraction circuits, and control and monitoring signal channel components; d) thyristors shall be designed for the maximum overvoltage and overcurrent caused by system faults and switching; e) valve design shall allow an appropriate margin for non-uniform voltage distribution among thyristors; the minimum redundancy of series thyristor levels in each single-phase valve group is 1; f) SVC design shall consider prevention of false firing (any thyristor in the valve firing at a wrong instant, or firing without a firing command); g) in TCR and TSR, two independent firing systems, normal firing and forced firing, shall be provided; h) TSC valves shall not be fired when overvoltage occurs, and blocking and interlocking measures shall be taken to avoid false firing; i) basic technical requirements for thyristors: see GB/T 15291; j) testing of thyristor valves: see GB/T 20995.

9.2 Cooling equipment for thyristor valves. See GB/T 29629-2013. 9.3 Phase-controlled reactors. Basic requirements include: a) TCR phase-controlled reactors should be single-phase dry-type air-core reactors; b) the rated reactor capacity shall be determined according to the SVC dynamic reactive compensation capacity, taking into account the thyristor valve conduction angle, harmonic currents flowing and overload capability; c) reactance tolerance: the deviation of the total reactance of each phase shall not exceed plus/minus 3 %, and the deviation between each phase reactance and the average of the three phases shall not exceed plus/minus 2 %; d) rated insulation level shall comply with GB 311.1; reactors installed in severe cold, high altitude or humid tropical areas and in polluted, flammable or explosive environments shall meet corresponding special requirements. Otherwise see GB/T 1094.6; special requirements are agreed between supplier and purchaser.

9.4 Capacitor banks. Refer to the relevant requirements of GB/T 11024.1 and GB/T 20994. 9.5 Filter (series) reactors. Dry-type air-core reactors should be used. Otherwise see GB/T 1094.6; special requirements are agreed between supplier and purchaser.

9.6 Circuit breakers. Basic requirements include: a) the main SVC circuit breaker shall be capable of switching the maximum output current and short-circuit current of all connected reactive compensation equipment; b) circuit breakers for fixed capacitors shall be capable of breaking capacitive current without restrike, and of withstanding the combined effect of closing inrush current, power-frequency short-circuit current and high-frequency capacitor discharge current; c) where branch rated current, short-circuit breaking capacity, rate of rise of recovery voltage, etc. cannot be met, a circuit breaker of higher voltage class may be used, and if necessary small parallel capacitors may be added to meet the rate of rise of recovery voltage. Otherwise see GB 1984; special requirements are agreed between supplier and purchaser.

9.7 Disconnectors and earthing switches. Basic requirements include: a) disconnectors and earthing switches shall be selected according to voltage class, maximum steady-state current and fault transient current; b) disconnectors and earthing switches are provided to ensure a visible isolating gap between main SVC components under maintenance and energized (or possibly energized) parts of the system; earthing switches shall also be provided as appropriate for capacitor discharge or maintenance safety. Otherwise see GB 1985; special requirements are agreed between supplier and purchaser.

9.8 Surge arresters. Basic requirements include: a) SVC surge arresters limit switching overvoltages and shall be gapless metal-oxide arresters; b) the arrester rated voltage shall be based on the upper limit of normal operating line voltage and the power-frequency voltage rise caused by a single-phase earth fault, with a certain margin; c) the energy absorption capability of arresters shall be checked in design to ensure safe operation; for arresters protecting filters, the checking condition for energy capability is a switching restrike overvoltage of the circuit breaker when a single-phase earth fault occurs on the supply side. Otherwise see GB 11032; where RC absorbers are required in special cases, this is agreed between supplier and purchaser.

9.9 Dedicated transformer (if required). Basic requirements include: a) if the SVC is connected to the grid through a transformer, the transformer insulation level shall be consistent with that of the grid at the connection point; b) the transformer shall be able to deliver 100 % reactive current, and its core flux density shall be designed lower than that of general-purpose transformers; c) the transformer shall withstand normal harmonic currents. Otherwise see GB/T 6451 or GB/T 10228; special requirements are agreed between supplier and purchaser.

9.10 Control system. Basic requirements include: a) the control system shall achieve the control objectives required in Clause 5; b) the design of the valves and their control system shall avoid crosstalk on a pair of anti-parallel thyristors; c) if TSC switching control is included, in order to obtain smooth regulation of SVC output the supplier shall describe in detail the control method for coordinating TCR operation with TSC switching in and out; d) it shall provide calculation, automatic regulation, monitoring, protection, communication, sequence control, event recording and other functions; e) it shall exchange information and operating commands with the site control and higher-level control (or dispatch centre) through communication interfaces.

9.11 Protection system. The basic requirement is to satisfy safe and reliable SVC operation and to meet the requirements of reliability, selectivity, sensitivity and speed; protection settings and time delays shall be coordinated with upstream protection to prevent overreaching trips. Generally: a) filter banks and shunt capacitor banks should be provided with: overvoltage, undervoltage, instantaneous overcurrent (quick-break), overcurrent, differential voltage or differential current unbalance, capacitor bank internal fault, underfrequency (filter branch), and interlocking trip to avoid harmonic amplification due to abnormal SVC operating modes; b) reactor banks should be provided with: overvoltage, undervoltage, quick-break, overcurrent and overload protection; c) the control system itself should be provided with protection against: UPS fault (if used), abnormal input signals, power supply fault, hardware fault and subsystem fault; d) valve assemblies should be provided with protection for: BOD operation, pulse loss, thyristor fault, firing/detection channel fault and frequent operation of backup firing.

e) thyristor controlled reactors (TCR) should be provided with: overvoltage, undervoltage, TCR branch quick-break, TCR branch overcurrent and TCR branch overload protection; f) cooling equipment protection: the cooling equipment shall be designed to keep thyristors and auxiliary components within the permissible temperature range during operation; it shall have an independent monitoring unit that detects and uploads operating parameters and abnormal states to the host computer; where one or more abnormal operating modes of the cooling equipment may seriously endanger the valves, the TCR branch shall be taken out of service to protect the main equipment; the cooling equipment shall monitor its own operating status and the cooling medium. Otherwise see GB/T 14285.

9.12 Fault recording system. Basic requirements include: a) recorded analogue quantities shall include at least the TCR branch and fixed capacitor branch currents, the bus voltage at the SVC connection point, and the regulated target voltage or current; b) recorded binary quantities shall include at least the SVC circuit breakers, disconnectors, main transformer main circuit breaker (SVC connection side) and fault recording trigger signals issued by the controller. Otherwise refer to GB/T 20298-2006.

9.13 Metering and monitoring system. Local or remote monitoring shall include at least: a) main system interface; b) SVC in-operation indication; c) SVC shutdown indication; d) SVC total reactive power and three-phase currents; e) reactive power of TCR/fixed capacitor branches; f) TCR branch three-phase phase currents, three-phase line currents and three-phase firing angles; g) transformer high/low voltage side voltages; h) reference voltage setting; i) reactive power setting; j) power factor setting; k) slope setting; l) current of each filter branch; m) status and event list of main SVC equipment.

9.14 Electromagnetic compatibility. Radiated electromagnetic field immunity tests shall meet GB/T 14598.9, electrical fast transient immunity tests shall meet GB/T 14598.10, 1 MHz burst immunity tests shall meet GB/T 14598.13, and electrostatic discharge immunity tests shall meet GB/T 14598.14.

9.15 Auxiliary equipment. Current transformers used for unbalance protection of high-voltage capacitor banks shall meet the following: insulation level selected according to grid voltage at the connection point; rated primary current not less than the maximum steady-state unbalance current; able to withstand short-circuit current and high-frequency discharge current under fault conditions, and if necessary a gapless zinc-oxide arrester may be installed between neutral and earth; accuracy class may be determined according to relay protection requirements. Voltage transformers used for unbalance protection of high-voltage capacitor banks shall meet the following: insulation level selected according to grid voltage at the connection point; rated primary voltage not lower than the capacitor bank rated voltage; when the primary winding serves as the capacitor discharge circuit, it shall meet the discharge capacity requirement; accuracy class may be determined according to voltage protection requirements.

Post insulators and wall bushings for high voltage shall be selected and checked according to voltage class, creepage distance, leakage current, mechanical load and other technical conditions. The auxiliary power supply shall include all power supplies necessary for SVC operation, such as step-down transformers, AC distribution panels, batteries, battery chargers and UPS; the supply shall meet the needs of all pumps, fans, control systems, air-conditioning systems, lighting equipment, etc.

10 Other requirements

10.1 Installation. Refer to GB/T 20994 and GB/T 1094.6.

10.2 Fire protection and ventilation. In accordance with GB 50227-2008 and GB 50060. Air inlets and outlets of each SVC room shall have facilities to prevent the entry of rain, snow and small animals. In areas with heavy wind-blown sand, air inlets and outlets should be fitted with filters. In severely cold areas, air inlets and outlets should have cold protection measures.

10.3 SVC project description and scope of supply. See Annex C.

10.4 Technical documentation and training. See Annex D.

Annex A (informative) Flicker improvement ratio

The flicker suppression effect of the SVC should generally meet the provisions of GB 12326. In engineering practice, the flicker improvement ratio is usually used to evaluate the flicker suppression effect of an SVC.

The flicker improvement ratio K can be defined by formula (A.1): K = |(Psto - Pst) / Psto| x 100 %, where Pst is the 95 % probability value of short-term flicker after the SVC is put into operation and Psto is the 95 % probability value of short-term flicker before the SVC is put into operation.

The flicker improvement ratio should generally be not less than 50 %.

Annex B (normative) Loss calculation method for thyristor valves

B.1 General. In theory the losses of an individual thyristor are measurable and the total valve loss could be derived from measured data. In practice, however, it is difficult to measure losses by electrical or calorimetric methods. The following calculation method is therefore used for loss evaluation.

B.2 Total loss. The total loss Pvalve is composed as in formula (B.1): Pvalve = Pcvalve + PTsw + Pvd + Psn, where Pvalve is the total loss of the thyristor valve; Pcvalve the on-state (conduction) loss of the thyristor valve; PTsw the total thyristor switching loss, PTsw = PTswon + PTswoff; Pvd the voltage grading circuit loss; Psn the snubber (absorption) circuit loss.

B.3 On-state loss. For each different thyristor firing angle, the average on-state thyristor current shall be estimated by formula (B.2): ITAV = ITCR x (sqrt(2)/pi) x [sin(pi - alpha) - (pi - alpha) cos(pi - alpha)], where ITAV is the average on-state thyristor current, ITCR the r.m.s. fundamental current with the TCR thyristor valve in full conduction, and alpha the TCR firing angle (pi/2 to pi radians). The r.m.s. thyristor current is calculated by formula (B.3): ITrms = ITCR x sqrt({(pi - alpha) x [1 + 2 x cos^2(pi - alpha)] - 1.5 x sin[2 x (pi - alpha)]} / pi). The on-state loss of the thyristor valve Pcvalve is calculated by formula (B.4): Pcvalve = 3 x 2 x [n x (UTO x ITAV + rT x ITrms^2) + Rbusbar x ITrms^2], where n is the number of series thyristors in the valve, UTO the thyristor threshold voltage, rT the thyristor slope resistance, and Rbusbar the DC resistance of the circuit between valve terminals excluding the thyristors.

B.4 Turn-on spreading loss of thyristors. For TCR valves, the turn-on loss PTswon is calculated by formula (B.5). Assuming a typical loss per firing pulse of 0.2 J (varying with the thyristor, generally with some differences): PTswon = 3 x 2 x n x 0.2 x f, where f is the system fundamental frequency. For TSR and TSC valves, the switching loss is calculated by formula (B.6): PTsw = 0.03 x Pcvalve.

B.5 Turn-off loss of thyristors. For TCR valves, the turn-off loss PTswoff is calculated by formula (B.7): PTswoff = 3 x 2 x Qr x f x sqrt(2) x U1 x sin(alpha), where Qr is the thyristor recovery charge (see Figure B.1), f the grid fundamental frequency and U1 the r.m.s. fundamental valve voltage. Figure B.1 (charge stored in the thyristor) shows the thyristor current falling with di/dt = recovery voltage / L through zero to the peak reverse recovery current Irr at instant t0 and then decaying; the shaded area is the stored charge Qr = Q1 + Q2, where L is the circuit inductance, Q1 the accumulated carrier charge before t0 and Q2 the accumulated carrier charge from t0 until the valve is fully turned off.

Qr is defined by formula (B.8): Qr = k1 x (dIT/dt)^0.6, where k1 is a thyristor type parameter representing the relationship, at the corresponding operating junction temperature, between the thyristor recovery charge and diT/dt at turn-off, obtainable by testing; dIT/dt is the rate of rise of current at zero crossing at thyristor turn-off, in A/us (amperes per microsecond). In the above formulae for total loss, the coefficient related to thyristor losses is 1 - kQ; kQ relates to the damping resistance of the overvoltage absorption circuit and represents the sharing ratio of the recovery charge, formula (B.9): kQ = Q1 / (Q1 + Q2).

B.6 Voltage grading circuit loss. The voltage grading circuit loss Pvd depends on the voltage applied across the thyristor valve. Depending on the firing angle, this voltage is calculated by formula (B.10): U1alpha = U1 x sqrt((2/pi){alpha - pi/2 - [1/2 x sin(2 alpha)]}), where U1 is the r.m.s. fundamental voltage of the thyristor valve and U1alpha the r.m.s. thyristor blocking voltage. The loss is calculated by formula (B.11): Pvd = 3 x U1alpha^2 / (Rvd x n), where Rvd is the grading resistance (per level).

B.7 Overvoltage absorption circuit loss. For TCR, the overvoltage absorption (snubber) circuit loss Psn can be calculated by formula (B.12): Psn = 3 x f x (Csn / n) x (sqrt(2) x U1 x sin(alpha))^2 x 2.0, where Csn is the snubber circuit capacitance (per level).

Annex C (informative) SVC project description and scope of supply

C.1 SVC project description. For a given specific SVC project, the following shall be described: a) installation location (substation name); b) SVC voltage class (kV); c) SVC rated capacity (Mvar), including capacitive and inductive reactive capacity; d) purpose of the SVC; e) equipment plan layout drawing at the SVC installation site; f) SVC electrical single-line diagram; g) electrical equipment connection diagrams after SVC installation, including circuits, earthing, control and protection, site services, etc.; for turnkey projects, other drawings such as fences, site underground information and civil engineering data shall also be provided; h) if the SVC project is expected to be extended in future, the design and layout shall take this into account and a proposed planning layout shall be given.

C.2 Scope of supply and project schedule. C.2.1 Scope of supply. The equipment, materials and services provided by the SVC project supplier shall include at least: a) SVC thyristor valves and their cooling equipment; b) high-voltage AC equipment (if supplied by the supplier, to be stated in the contract), including: 1) dedicated transformer; 2) circuit breakers; 3) disconnectors; 4) voltage transformers; 5) current transformers; 6) surge arresters; 7) earthing transformer; 8) switchgear; c) reactors, capacitors and filters; d) SVC site service facilities; e) SVC control, protection, alarm and monitoring systems; f) special maintenance equipment and tools; g) training plan for operation and maintenance personnel (see Annex D); h) spare parts; i) testing and commissioning services; j) technical documentation, including operating manuals (see Annex D). For turnkey projects the supply shall also include: SVC project ancillary facilities, including distribution rooms, guard rails, drainage and inspection walkways; SVC buildings, including the earthing system; foundations and structures of ground-connected equipment, including earthing and connection to the earthing grid.

C.2.2 Equipment, materials and services to be provided by the user. These include: a) the SVC installation site shall be ready within the agreed time; b) water supply at the site; c) temporary site power supply shall be ready within the agreed time; d) permanent power supply at the SVC site of use shall be ready within the agreed time; e) list of existing installations and equipment at the site and their condition.

C.2.3 Project schedule. Both parties to the SVC project shall agree on the various stages of the project according to the following requirements (but not limited to them): a) project completion date; b) within the time agreed by both parties, provision of a detailed project schedule, including start and end times of each part of the project, the times at which user-provided services are in place, the times at which the supplier provides drawings, and the specific timing of each activity; c) arrangements for design liaison and review.

Annex D (informative) Technical documentation and training

D.1 Technical documentation. The user may list the technical documents required and agree with the supplier on the documents finally to be provided. The following typical documents are submitted by the SVC supplier and shall be stated in the contract: a) technical report; b) equipment description; c) quality guarantee; d) equipment test reports; e) single-phase circuit diagram; f) three-phase circuit diagram for construction; g) control component drawings; h) plan layout and sectional drawings; i) civil works drawings; j) installation and construction drawings; k) operating manual; l) equipment maintenance and overhaul manual; m) software and operating system manual. If a mathematical model of the SVC is required for system simulation, its documentation shall also be submitted here.

D.2 Training. The supplier shall provide relevant training materials and give technical training to the user's operation and maintenance personnel at a designated location. The training materials should generally include: a) SVC principles and functions, including specific performance indices; b) valve electrical principles, valve structure and valve testing; c) main control room, operator interface, channels, etc.; d) settings and their principles; e) simulation testing of the control system; f) control and protection principles and their testing; g) use of fault recording software; h) valve channels, test equipment and test procedures; i) thyristor replacement procedures; j) main control room operator interface tests and replacement procedures; k) valve base electronics tests and replacement procedures; l) cooling equipment and its maintenance; m) cooling control system and its maintenance; n) introduction to other specialized equipment; o) operating manual; p) operation and maintenance manual.