The new generation of TKRM series static VAR compensators is designed to improve power quality of industrial networks with a voltage of 6.3 and 10.5 kV, which feed high-current thyristor electric drives in rolling mills machines and shafts, arc furnaces and ore-thermal furnaces, as well as other loads with abruptly variable VAR consumption.
Thyristor-controlled VAR compensators are manufactured in accordance with technical specifications TU U 27.1-13626132-005: 2015.
By using SVC you can achieve the following:
- improve power quality by reducing the network voltage fluctuations amplitude as compared to the rated value and by improving the harmonic composition of current and voltage;
- reduce current loads of power system elements, and in that way reduce losses therein, and as a result reduce the bill for active energy;
- balance in phases of the network consumed active and reactive power in case of abruptly variable and unbalanced loads;
- reduce losses in electric motors, transformers, cables; increase service life of insulation and electrical equipment by reducing higher harmonics in the mains;
- reduce payment for consumed and generated reactive power almost to zero and eliminate possible surcharges on power rates for VAR consumption above contractual values through automatic VAR compensation;
- increase reliability and energy efficiency of power supply by reducing the full-load current;
- provide a voltage regulation mode (as per separate request by the customer), which is relevant for “weak” mains.
The cost of the product is optimal, as SVCs and harmonic filters are designed individually for each specific case of their application. This can ensure the best possible results for higher harmonics filtering and power factor correction, and excludes surcharge payment for power margin (in case of selecting from a standard range of products).
The average payback period of the compensator is less than 2 years.
Each product is being checked in computer simulation with parameters of a specific application (in the standard power supply scheme and typical modes of equipment’s operation), in order to identify possible resonant and emergency events.
Concept of operation
Non-linear electric users (for example, thyristor converters, electric arc furnaces and induction furnaces) in the course of their operation comprise sources of harmonic distortion in power circuit.
The higher harmonics affect electrical equipment performance, in particular:
- cause additional losses in electrical machines, transformers and circuits;
- make it difficult to compensate power factor;
- shorten the service life of insulation for electrical machines and equipment;
- worsen the performance of automation, telecontrol and communication devices;
- result in measuring errors for electricity-measuring instruments.
SVC Functional Diagram
Power factor compensation principle
These problems can be resolved by static VAR compensators (SVC) in case of abruptly variable loads or by harmonic filters (HF) in case of VAR alteration in a small range. SVC consists of a semiconductor voltage regulator (SVR), compensating reactors and harmonic filters.
Harmonic filters ensure:
- reduce the total harmonic distortion (THD) by approximation of voltage waveform to a sinusoidal waveform;
- compensate VAR to a set level.
SVC allows to maintain a given level of VAR (or power factor) when it varies over a wide range (from 0 to 100%). The time for disturbance compensation is up to 10 ms.
The compensator with the structural-functional diagram as shown on Image 1 uses indirect compensation scheme. VAR regulation and stabilization in distribution network input is made via power circuit in a semiconductor voltage regulator (SVR) cabinet, and a capacitor unit serves as a reactive power source. Together with filter reactors it constitutes a filter circuit tuned to A1..An high-order harmonics.
SVR external appearance
Inductance of filter reactor and capacitor bank form a series RLC circuit, which, when parallel-connected with the load, minimizes a specific high-order harmonic in the power system voltage.
SVR and compensating reactors L1..L3 form three circuits of delta connected compensating reactor and a pair of parallel-opposite thyristors, which are parallel connected to the load and power filters.
The compensator ensures balanced value of VAR consumed in the power system, as well as balancing adjustment in phases of the network for consumed active and reactive powers in case of abruptly variable and unbalanced loads. At the same time the following signals are sent to the control system input: voltage signals, circuit currents and loads from secondary windings of voltage transformers (TU) and current transformers (TA).
External appearance of SVR with top cable entry
Therefore, var flows only happen between VAR consumers and SVC. The VAR is neither consumed nor generated from the circuit, respectively the counter does not register it. Interchange in the network is only done by active power. This is shown in Image 2, where the red line displays the total power.
Control system
SVR administration, protection and alarm system, auto-adjustment are exercised by a microprocessor control system (CS). The CS is installed in a separate control cabinet. Printed wire boards of control system are easy to replace and set up.
CS is consistent for the entire range of high-voltage converters and contains:
- built-in diagnostics system and recording of accident track;
- full-featured protection system;
- high-speed two-wire interfaces for communication with top-level equipment, including equipment by other suppliers.
CS allows to implement any object orientation according to the Customer’s request.
If there is a breakdown of a single thyristor on one side, the control system generates a warning signal, but the converter remains in operation. The breakdown of a second thyristor on the same side causes an emergency shutdown with corresponding emergency message sent on the console terminal.
External appearance of compensating reactor
Configuration
The main components of SVC are:
- semiconductor voltage regulator;
- compensating reactors;
- high-order harmonic filter consisting of a filter reactor and a capacitor unit.
SVR depending on its power is made either in the form of a single or several cabinets combined in a section. In terms of design, SVR is executed as double-sided cabinet, with IP-21 level protection.
The control panel is installed on the front door of the unit and the control cabinet. It contains a LCD display and a keypad consisting of seven sealed buttons. User interface is implemented as a menu on the LCD display.
In order to ensure safety for maintenance staff during operations with the cabinet door, SVRs are equipped with electromagnetic locks and limit switches which disconnect the power voltage when the door is opened.
External appearance of harmonic filter
The power section of SVR consists of the following components:
- series of anti-parallel connected thyristors;
- thyristor management cells;
- damping RC-circuits;
- cooling fans.
Compensating reactors provide for the designs as follows:
- air compensating reactor;
- iron-core reactor.
The designs for filter reactors include a single-phase and three-phase designs. Capacitor units of power filters are executed as frames with parallel-connected and protected by fuses capacitors installed therein.
The scope of delivery
The scope of delivery includes the following::
- power cabinet;
- control system (unit in a power cabinet or a separate cabinet);
- compensating reactor;
- harmonic filters consisting of a filter reactor and a capacitor unit;
- a set of spare parts, tools and accessories as per the List of Spare Parts for the appropriate type of a capacitor;
- a set of accompanying documents according to the List of Operating Documents.
Completion
SVC is completed with power equipment produced by the following manufacturers:
- thyristors ABB (Switzerland) or Dynex (England);
- high-voltage capacitors ZEZ SILKO s.r.o (Czech Republic);
- reactors Eltiz (Ukraine)
Projects:
• Novokramatorsky Mashinostroitelny Zavod, complete delivery of SVC, 6kV, 13MVAR, comprised of:
– the 3rd harmonic filter with a power of 9MVar;
– the 5th harmonic filter with a power of 7.2MVar;
– semiconductor power stabilizer with a rated current of 700A;
– RKOS type compensating reactors with divided winding.
• ZAPORIZHSTAL, supply of two semiconductor power stabilizers 1000A, 6kV;
• ZAPORIZHSTAL, modernization of SVC, control cabinet replacement;
• Dneprospetsstal, supply of SVC control cabinet;
• Mittal Steel, supply of SVC control cabinet.