Among high-voltage reactive power compensation equipment, the traditional static var compensator (SVC) and the existing mainstream static var generator (SVG) are two types of equipment with significantly different technical paths. The core differences are reflected in multiple dimensions such as working principles, performance indicators, and applicable scenarios. The following is a detailed comparison of the main differences between the two from key dimensions:
Ⅰ. Working principle
SVC (Static Var Compensator)
Based on the principle of "impedance adjustment", reactive power compensation is achieved through a combination of **capacitors and inductors**. The core components include:
1. Thyristor-controlled reactor (TCR): By adjusting the conduction angle of the thyristor, the equivalent impedance of the reactor is changed to output inductive reactive power;
3. Fixed capacitor (FC) + filter: Cooperate with TCR/TSC to expand the compensation range and suppress harmonics.
The essence is to indirectly adjust the reactive power by changing the equivalent capacitive reactance/inductive reactance of the system.
Based on the principle of "current source", it directly generates reactive current with the same frequency and phase as the system through **power electronic converter** (such as IGBT module). The core is to invert the DC side voltage (supported by capacitors or DC power supply) into AC, and realize the "active injection" of capacitive/inductive reactive power by controlling the amplitude and phase of the output current.
The essence is to directly output reactive current without relying on the impedance characteristics of capacitors/inductors.
Ⅱ. Comparison of core performance indicators
Indicators
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SVC
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SVG
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Response time
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Slow (20-50 milliseconds). Limited by the thyristor switching speed, and the energy conversion time of capacitors/inductors needs to be considered.
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Extremely fast (5-20 milliseconds). Based on the high-frequency switching characteristics of IGBT, reactive changes (such as impact loads) can be quickly tracked.
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Compensation range
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The capacitive/inductive reactive adjustment range is narrow, and most of them are "step adjustment" (such as TSC switching is discrete).
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Full range continuously adjustable (from rated inductance to rated capacitance), compensation accuracy can reach ±1% rated value.
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Harmonic characteristics
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It will generate harmonics (such as TCR generates 3rd and 5th harmonics when half-conducting), and additional filters are required, which increases cost and volume.
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There are no inherent harmonics, and the "active filtering" function can be realized through the control algorithm (suppressing the original harmonics of the system).
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Voltage support capability
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As the system voltage decreases, the compensation capability decreases (due to dependence on the impedance characteristics of capacitors/inductors, Q=U²/Z).
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When the voltage decreases, the rated reactive current can still be output (I is constant), and the voltage support capability is stronger (especially suitable for weak power grids).
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Loss
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High (3%-5%). Mainly from the conduction loss of reactors and thyristors, and the loss accounts for a higher proportion when light load is used.
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Low (1%-3%). Mainly from IGBT switching loss, efficiency changes more smoothly with load.
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Floor area
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Large. Need to accommodate a large number of capacitors, inductors, filters, and need to consider heat dissipation and safety distance.
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Small (only 1/3-1/5 of SVC). The core is a power electronic module with a compact structure, suitable for space-constrained scenarios.
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III. Reliability and maintenance
SVC:
Simple structure, mature technology of core devices (thyristors, capacitors, inductors), high reliability; but there are mechanical switching components (partial design), and the filter needs regular maintenance (such as replacing capacitors), which requires a large amount of maintenance.
Depending on power electronic devices (IGBT) and complex control algorithms, it was limited by device reliability issues in the early days, but now that IGBT technology is mature, its reliability is close to SVC; modular design (such as multi-bridge parallel connection) can achieve redundancy, single point failure does not affect the overall operation, and maintenance is more convenient (just replace the module).
IV. Applicable Scenarios
SVC:
Suitable for scenarios where **load changes slowly and the response speed is not required**, such as:
- Traditional industries (such as stable loads in chemical and metallurgical industries);
- Steady-state voltage control of transmission lines;
- Cost-sensitive occasions with low requirements for harmonic suppression.
SVG:
Suitable for scenarios where **load fluctuates rapidly and compensation accuracy is required**, such as:
- New energy grid connection (fluctuating reactive power compensation for wind power and photovoltaic power);
- Impact loads (arc furnaces, rolling mills, high-speed rail traction stations);
- Urban distribution networks (load-intensive, space-limited, harmonic control must be taken into account);
- Weak power grids (such as power grids in remote areas, which require strong voltage support).
SVC is a traditional technology of "passive impedance adjustment", with the advantages of simple structure and low cost (small and medium capacity scenarios); SVG is a new technology of "active current generation", which has comprehensive advantages in response speed, compensation accuracy, harmonic control, spatial adaptability, etc., and is especially suitable for the complex and changeable reactive power requirements in modern power systems. As the cost of power electronic devices decreases, SVG has gradually replaced SVC and become the mainstream choice for high-voltage reactive power compensation.
