Difference between switching converter type compensators and variable impedance type compensators

Difference between switching converter type compensators and variable impedance type compensators | Difference between SSSC and TSSC

Sr. No.	Switching converter type compensators(SSSC)	Variable impedance type compensators (TSSC)
1.	The SSSC is capable of internally generating a controllable compensating voltage over an identical capacitive and inductive range independently of the magnitude of the line current.	The compensating voltage of the TSSC over a given control range is proportional to the line current.
2.	The SSSC has the inherent ability to interface with an external dc power supply to provide compensation for the resistance by the injection of real power, as well as for the line reactance by the injection of reactive power, for the purpose of keeping the effective XIR ratio high, independently of the degree of series compensation.	The TSSC can not exchange real power (except for circuit losses) with the transmission line and can only provide reactive compensation.
3.	The SSSC with an energy storage (or sink) increases the effectiveness of power oscillation damping by modulating the series reactive compensation to increase and decrease the transmitted power, and by concurrently injecting an alternating virtual positive and negative real impedance to absorb and supply real power from the line in sympathy with the prevalent machine swings.	The variable impedance type compensator can damp power oscillation only by modulated reactive compensation affecting the transmitted power.
4.	The SSSC use GTO thyristors. These devices presently have lower voltage and current ratings, and considerably lower short-term surge current rating. They are suitable for short-term bypass operation only if the anticipated line fault current is relatively low. Therefore, they may need external fast protection during severe line faults by an auxiliary conventional thyristor bypass switch, or a MOV arrestor type voltage limiter, or by some other means of suitable speed.	The TSSC employs conventional thyristors (with no internal turnoff capability). These thyristors are the most rugged power semiconductors, available with the highest current and voltage ratings, and they also have the highest surge current capability. Forshort-term, they are suitable to provide bypass operation to protect the associated capacitors during line faults.
5.	The SSSC requires a coupling transformer, rated for 0.5 p.u. of the total series var compensating range, and a dc storage potential and operated at a relatively low voltage (typically below 20 kv). Thus, this installation needs only relatively low voltage insulation for the cooling system and a control interface.	The TSSC is coupled directly to the transmission line and therefore is installed on a high voltage platform. The cooling system and control are located on the ground with high voltage insulation requirements and control interface.