The Differences Between Three-Phase Reactors and Synchronous Transformers

1. Fundamental Definitions and Structural Design

A three-phase reactor, also known as a three-phase inductor, is a passive electrical component consisting of three inductive coils (one per phase) arranged for three-phase AC systems. It can operate with or without a ferromagnetic core. When a core is present, it is typically laminated to reduce eddy current losses. The absence of a core (hollow reactors) is common in high-frequency applications, where minimizing core losses is critical.

In contrast, a synchronous transformer is a specialized transformer designed to provide synchronized voltage signals for power electronic devices like thyristors. Structurally, it resembles a conventional transformer with primary and secondary windings wound around a laminated iron core. The core ensures efficient magnetic coupling between windings, enabling precise voltage transformation and phase synchronization.

2. Operational Principles

Three-Phase Reactors

Reactors leverage the principle of electromagnetic induction to oppose changes in current flow. When AC current passes through the coils, a magnetic field is generated, inducing an electromotive force (EMF) that resists current variations. This property makes reactors ideal for:

• Current Limitation: Restricting short-circuit currents to protect circuit breakers and other equipment.

• Harmonic Suppression: Filtering harmonic currents when paired with capacitors in harmonic mitigation systems.

• Voltage Stabilization: Dampening voltage fluctuations in long transmission lines.

Synchronous Transformers

Synchronous transformers operate on the same electromagnetic induction principle as conventional transformers but with a specific focus on maintaining phase synchronization. They step down high-voltage grid signals to low-voltage levels suitable for control circuits while preserving phase relationships. This synchronization ensures thyristors and other power devices trigger at precise moments, enabling accurate control of power flow in applications like HVDC transmission and motor drives.

3. Key Functional Differences

Aspect	Three-Phase Reactor	Synchronous Transformer
Primary Function	Limits current, improves power factor, suppresses harmonics, stabilizes voltage.	Provides synchronized voltage signals, isolates control circuits, adjusts voltage ratios.
Electrical Behavior	Inductive impedance dominates; dissipates reactive power.	Transforms voltage and power; maintains phase alignment.
Energy Conversion	Does not convert energy; only modifies current/voltage waveforms.	Converts electrical energy between voltage levels while preserving frequency.

4. Application Scenarios

Three-Phase Reactors

• Power Systems:

• Short-circuit current limitation in substations.

• Power factor correction in industrial plants.

• Harmonic filtering in nonlinear load environments (e.g., variable frequency drives).

• Renewable Energy:

• Smoothing DC link currents in wind turbine converters.

• Stabilizing grid connections for solar inverters.

Synchronous Transformers

• Power Electronics:

• Triggering thyristors in AC-DC converters (e.g., rectifiers).

• Providing phase-locked signals for grid-tied inverters.

• Motor Control:

• Synchronizing speed control in high-precision servo systems.

• Measurement and Protection:

• Isolating and conditioning voltage signals for relays and meters.

5. Design Parameters and Performance

Three-Phase Reactors

• Key Parameters:

• Inductance (L): Determines current-limiting capability and harmonic attenuation.

• Rated Current: Maximum continuous current without overheating.

• Voltage Rating: Must match system voltage to avoid insulation breakdown.

• Performance:

• Low losses in coreless designs but higher volume.

• Core-based reactors offer higher inductance but are prone to saturation at high currents.

Synchronous Transformers

• Key Parameters:

• Turns Ratio: Defines input-output voltage relationship.

• Frequency Response: Ensures accurate phase synchronization across the operating frequency range.

• Isolation Rating: Protects control circuits from high-voltage transients.

• Performance:

• High precision in phase retention (<1° error typical).

• Low magnetizing current to minimize power consumption.

6. Complementary Roles in Power Systems

While reactors and transformers serve distinct purposes, they often work together in complex systems. For example:

• In a thyristor-controlled reactor (TCR) used for reactive power compensation, a synchronous transformer provides the trigger signal, while the reactor adjusts the inductive reactance to stabilize voltage.

• In harmonic filter banks, reactors and capacitors form resonant circuits to trap specific harmonics, with transformers isolating the filter from the grid.

Conclusion

Three-phase reactors and synchronous transformers are indispensable in modern power systems, each addressing unique challenges. Reactors excel in current limitation, harmonic mitigation, and voltage stabilization, while synchronous transformers ensure precise control and synchronization in power electronics. Understanding their differences is crucial for optimizing system efficiency, reliability, and safety. For advanced solutions in power electronics and circuit protection, explore YFW’s range of diodes, MOSFETs, and thyristors at www.yfwdiode.com, designed to integrate seamlessly with these critical components