Comparison between Shunt compensation and Synchronous phase modifier

⚡ Shunt Compensation

Shunt compensation is a method of controlling system voltage by connecting shunt capacitors or shunt reactors directly to the transmission network.

• Shunt Capacitors → supply reactive power (kVAR) to the system, thereby raising voltage during light load or under-voltage conditions.

• Shunt Reactors → absorb reactive power, thereby reducing voltage during no-load or light-load conditions when the voltage tends to rise.

🔑 Engineering perspective:

• Simple, static, and reliable solution.

• Provides step-by-step voltage regulation since capacitor banks can be switched in or out.

• Widely used in transmission and distribution systems due to low cost and negligible maintenance.

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⚡ Synchronous Phase Modifier (Synchronous Condenser)

A synchronous phase modifier (also known as a synchronous condenser) is essentially a synchronous motor running without mechanical load.

• When under-excited, it draws reactive power → acts like an inductor.

• When over-excited, it supplies reactive power → acts like a capacitor.

🔑 Engineering perspective:

• Provides smooth and continuous voltage control, unlike stepwise switching.

• Can improve short-circuit power and system inertia, but consumes active power for operation.

• Requires a proper starting method (pony motor, damper winding, or static frequency converter) to reach synchronous speed.

• Being a rotating machine, it demands higher maintenance and has a much higher capital and operating cost compared to shunt devices.

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👉 In practice:

• Shunt compensation is the most common choice in modern grids.

• Synchronous phase modifiers were historically used in large transmission networks before the development of Static VAR Compensators (SVCs) and STATCOMs, which are now preferred for dynamic voltage control.

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Shunt Compensation vs. Synchronous Phase Modifier

Sr. No.	Shunt Compensation	Synchronous Phase Modifier
1	Separate shunt capacitor and reactor are required for voltage control	A single synchronous motor works as an inductor (under-excited) or capacitor (over-excited) for voltage control
2	Step-by-step voltage regulation is possible	Smooth continuous voltage regulation is possible
3	No starting methods required	Requires starting methods to achieve synchronism
4	Consumes reactive power only	Consumes active power in addition to reactive adjustment
5	Improves transient stability	Reduces transient stability
6	Requires very little maintenance	Requires more maintenance due to rotating machinery
7	Very low cost	Much higher cost
8	Most practical solution for voltage control	Rarely used in practice due to disadvantages

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