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Phase modifier is normally installed in the case of
Short transmission lines
Medium length lines
Long length lines
For all length lines
Long length lines
A phase modifier, typically a synchronous condenser (synchronous motor operating at no load with over-excited field), is installed to control the voltage profile of long transmission lines. By varying the excitation, it can supply or absorb reactive power to compensate for the voltage drops caused by line impedance during varying load conditions.
A phase modifier, typically a synchronous condenser (synchronous motor operating at no load with over-excited field), is installed to control the voltage profile of long transmission lines. By varying the excitation, it can supply or absorb reactive power to compensate for the voltage drops caused by line impedance during varying load conditions.
Q=VsтАЛVrтАЛXsin(╬┤)тАЛ тАФ Relationship between reactive power flow and power angle
Vr(load)тАЛ=VrтАЛ(noтИТload)тИТI(R+jX) тАФ Voltage drop principle necessitating compensation
In long transmission lines, Ferranti effect and large line charging currents affect voltage regulation. The synchronous condenser acts as a variable reactive power source: over-excited operation generates reactive power to boost voltage, while under-excited operation absorbs reactive power to reduce voltage. This keeps the receiving end voltage constant regardless of the loading state.
Synchronous condensers provide continuously variable reactive power.
Used extensively in EHV/UHV long transmission lines to improve stability.
Helps in maintaining the voltage profile within statutory limits.
More flexible than static shunt capacitors or inductors.
Stepless control of reactive power
Improves transient stability
Self-starting and robust
High maintenance cost due to rotating parts
High capital investment
Higher losses compared to static compensators (SVC)
Grid substations for voltage regulation
Industrial plants for power factor correction
High voltage DC (HVDC) converter stations
In short lines, the impedance is low, making reactive power compensation less effective/necessary.
Medium lines use shunt compensation but usually static devices.
Long lines (typically > 200 km) require active voltage control via phase modifiers or FACTS devices.
C is correct тАФ Phase modifiers are utilized in long transmission lines to regulate voltage by supplying or absorbing reactive power based on line loading conditions.
Always remember: Shunt capacitors are for load power factor improvement, while Synchronous condensers are primarily for voltage regulation of long lines.