Dynamic Performance Comparison of Synchronous Condenser and SVC Sercan Teleke, Tarik Abdulahovic, Torbjörn Thiringer, and Jan Svensson, Member, IEEE
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1606 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY 2008 Dynamic Performance Comparison of Synchronous Condenser and SVC Sercan Teleke, Tarik Abdulahovic, Torbjörn Thiringer, and Jan Svensson, Member, IEEE Abstract—In this paper, a comparison of the dynamic per- formance between a conventional synchronous condenser, a superconducting synchronous condenser, and a static var compen- sator (SVC) is made in a grid setup by simulating different cases that affect the performance of reactive power compensation. The results show that the SVC injects more reactive power and has a better dynamic performance during faults that cause a moderate or minor voltage drop on its terminals, such as single-phase to ground faults in weak grids. The synchronous condensers, on Fig. 1. Single-line diagram with a synchronous condenser connected to grid. the other hand, bring the voltage to the nominal value quicker and show a better dynamic performance for severe faults such as three phase to ground faults in stiff grids. The superconducting synchronous condenser injects up to 45% more reactive power The purpose of this paper is to compare the dynamic perfor- compared to the conventional synchronous condenser during a mance of a conventional synchronous condenser, a supercon- nearby three phase to ground fault. ducting synchronous condenser (SuperVAR)and an SVC during Index Terms—Static var compensator (SVC), superconducting various grid set ups and fault types. synchronous condenser, synchronous condenser. II. PRESENTATION OF REACTIVE I. INTRODUCTION POWER COMPENSATION DEVICES In this section, the synchronous condenser and the SVC are EACTIVE power compensation is defined as the reactive presented. R power management with the aim of improving the perfor- mance of ac power systems [1]. Reactive power compensation is A. Synchronous Condensers viewed from two aspects: load compensation and voltage sup- port. In load compensation, the objectives are to increase the Synchronous condensers have played a major role in voltage power factor, to balance the load and to eliminate current har- and reactive power control for more than 50 years [7]–[12]. monics from nonlinear industrial loads [2], [3]. Voltage support In this section, conventional and superconducting synchronous reduces voltage fluctuation at a given terminal of a transmis- condensers are described. 1) Conventional Synchronous Condenser: sion line [1] and improves the stability of the ac system by in- A synchronous creasing the maximum active power that can be transmitted. It condenser is a synchronous motor without any mechanical load also helps to maintain a substantially flat voltage profile at all [13]. Its field is controlled by a voltage regulator to generate or levels of power transmission, increases transmission efficiency, absorb reactive power to support a system’s voltage or to keep controls steady-state and temporary over-voltages [4], and helps the system power factor at a specified level. Synchronous con- to avoid catastrophic blackouts [5], [6]. densers installation and operation are identical to large electric As reactive power compensation is an effective way to im- machines. A single-line diagram with a synchronous condenser prove the electric power network, there is a need for controlled is shown in Fig. 1. 2) Superconducting Synchronous Condenser (SuperVAR): reactive power compensation which can be done either by syn- chronous condensers or static var compensators (SVCs), which Only the field winding of the synchronous condenser utilizes utilize power electronic devices. a high-temperature superconductor winding cooled with a cryocooler subsystem to about 35–40 K [14]. The cryocooler modules are placed in a stationary frame and helium gas is Manuscript received April 16, 2007; revised September 9, 2007. This work used to cool the rotor of the machine. The stator winding is was supported by ABB FACTS, Västerås, Sweden. Paper no. TPWRD-00216- 2007. a conventional copper winding. However, the winding is not S. Teleke is with the Department of Electrical and Computer Engi- placed in conventional iron core teeth, since the iron core neering, North Carolina State University, Raleigh, NC 27606 USA (e-mail: saturates due to the high magnetic field, typically 1.5–2.0 T, [email protected]). T. Abdulahovic and T. Thiringer are with the Department of Energy and En- imposed by the field winding. Only the stator yoke (back iron) vironment, Chalmers University of Technology, Göteborg SE-412 96, Sweden uses magnetic iron to provide magnetic shielding and to carry (e-mail: [email protected]; [email protected]). flux between adjacent poles. The absence of iron in most of J. Svensson is with ABB FACTS, Västerås SE-721 64, Sweden (e-mail: jan.r. [email protected]). the magnetic circuits in these machines results in a very low Digital Object Identifier 10.1109/TPWRD.2007.916109 synchronous reactance (typically 0.3–0.5 p.u.). More details of 0885-8977/$25.00 © 2008 IEEE Authorized licensed use limited to: UNIVERSIDADE DO PORTO. Downloaded on March 10,2010 at 11:57:01 EST from IEEE Xplore. Restrictions apply. TELEKE et al.: DYNAMIC PERFORMANCE COMPARISON OF SYNCHRONOUS CONDENSER AND SVC 1607 Fig. 2. Single-line diagram of the SVC used in the simulations. Fig. 3. Single-line diagram of the used grid setup. the SuperVAR, including performance features, design config- urations, and maintenance challenges can be found in [15]. with 0.9 power factor; 10 kV with inertia constant of 2 s. These units are connected to a 36 kV substation via 25 MVA trans- B. Static VAR Compensator (SVC) formers (10% leakage reactance, 36/10 kV). Moreover, a resis- Maintenance requirements of conventional synchronous con- tive and an inductive load of 16 MW and 12 Mvar are also con- densers rose interest in the development of static VAR systems nected to the substation via a 25 MVA transformer (10%, 36/10 [16]. Several papers have studied modeling [17]–[20] and the kV). A capacitor bank of 8 Mvar is connected to each 10 kV application of SVCs [16], [21], [22]. A typical SVC, composed load bus in order to keep the 10 kV bus within 95% to 100% of thyristor-switched capacitors (TSCs) and thyristor-controlled of nominal voltage during full load operation. The short-circuit reactors (TCRs), together with filters, is shown in Fig. 2. The ratio (SCR), which is the ratio between the short-circuit power filters (FCs) are used to remove low-frequency harmonics pro- measured at the 36-kV bus and the load total apparent power, is duced by the TCR and to produce reactive power. With proper 3.9 which represents a medium strong system. coordination of the capacitor switching and reactor control, the Four 8 MVA synchronous condensers or one 32 Mvar SVC reactive power output can be varied continuously between the are/is connected to the 36 kV bus via a 32 MVA transformer capacitive and inductive ratings of the equipment. (10%, 13.8/36 kV), to provide reactive power compensation, es- The compensator operates to regulate the voltage of the trans- pecially in case of faults occurring in the network that transfers mission system at a selected terminal. However, the maximum the power from the generator to the factory. The network con- obtainable capacitive current decreases linearly with the system sists of two 200 km lines with an X/R ratio of 15 where the fault voltage since the SVC becomes a fixed capacitor when the max- occurs in one of the lines, which will cause the breakers to open imum capacitive output is reached. Therefore, the conventional after a 250 ms delay, and accordingly to disconnect the faulted thyristor-controlled SVC rapidly deteriorates its voltage support line and connect it back 500 ms after the fault is cleared. capability with the decrease of system voltage. In the 36 kV substation, there is a 70 MVA step down trans- former (10%, 130/36 kV) that adapts the voltage level to the factory. Finally, the 130 kV source is an infinite bus. III. SETUP OF PERFORMANCE STUDY A. Setup of Compensators IV. SIMULATION RESULTS FROM THE STUDY For comparison of the SuperVAR [15], the conventional syn- To compare the synchronous condensers with the SVC, the chronous condenser and the SVC, a grid setup using PSCAD is parameters of the grid have been altered. The configuration made, where the parameters are given in the Appendix. The con- without any reactive power compensation is denoted by WOC. ventional synchronous condenser and the SuperVAR are using The cases with conventional synchronous condensers and the type DC2A exciter and the type ST1A exciter, respectively. SuperVARs connected to the 36 kV bus are denoted by CON The 32 Mvar SVC consists of two TSC banks where each bank and SCO, respectively. Finally, the configuration with the SVC has 35.8% of the rated power, two 3rd and 5th harmonic filters connected to the 36 kV bus is denoted by SVC. where each carries 10.2% of the rated power and two 7th and 11th harmonic filters where each carry 4% of the rated power. A. Different Fault Types For reactive power consumption, one TCR with the size of 38% In this section, single-phase-to-ground, two-phase-to-ground, of the rated power is employed. In the connection of the SVC and three-phase-to-ground faults are simulated and analyzed. to the network, a 10% coupling transformer with the size 1) Single Phase to Ground Fault: To determine the perfor- of rated reactive power is used, where the high voltage side was mance of the different compensators, a single phase to ground connected with Y grounded. fault in the middle of one of the two lines is applied. The re- sulting positive-sequence voltage, reactive power injection and B. Grid Setup the speed of the induction machines are displayed in Figs.