Mitsubishi Electric Power System Stabilizer

1 Mitsubishi Electric Power System Stabilizer (PSS). Power System Stabilizer (PSS). Step response PSS OFF PSS ON. Generator Power 0 1 2. Time (sec). Grid one line open PSS OFF PSS ON. Generator Power 0 1 2. Time (sec). HEAD OFFICE: TOKYO BUILDING, 2-7-3, MARUNOUCHI, CHIYODA-KU, TOKYO 100-8310, JAPAN. Improper use of the products can cause severe injury or death, and may result in damage to the products and other property. Please read the instruction manual before installing or using the products. New publication, effective Sep. 2010. G-171-0-C8641-A HQ-1009 Printed in Japan (MDOC) Specifications are subject to change without notice. Mitsubishi Power System Stabilizer (PSS). The Power System Stabilizer (PSS) is a device that measures improvements in System stability when added to a generator's automatic voltage regulator (AVR). Therefore, compared to System reconstruction or enhancement, it offers overwhelmingly superior cost performance.

2 With an abundant System line-up including analogue, digital and P/ / f input type models, Mitsubishi Electric is ready to respond to the diversified needs of its customers. Summary of Power Theory of PSS. System Stability Summary Generator Though generator output Power is output Power Generator output Power G decided by a turbine's mechanical torque, it can be changed by transiently changing the excitation value ( ). Fault (3-phase fault, several cycles open) A PSS detects the change in generator By changing the excitation A PSS detects the change in Power output Power , controls the excitation Excitation value value, generator output Excitation value generator output Power , controls Power can be changed the excitation value, and reduces value, and reduces the rapid Power transiently the rapid Power fluctuation fluctuation ( ). Unstable (less dynamic stability) ( ) ( ). Power Explanation of torque vector Block diagram Torque characteristics.

3 K1 (Damping torque). 1 0 K1+D.. Stable Constant Tm Ms S. Step out (less transient stability) excitation . D. 0 (Synchronizing torque). K1 : Synchronizing torque D : Damping torque M : Inertia Time Fault occurrence Fault cleared . K1+K1A. 1 0 K1+D.. Tm Ms S. AVR . D+DA. Resultant torque Transient Dynamic area 0. area K1A : Synchronizing torque by AVR. DA : Damping torque by AVR. K1A+DA (Unstable at D DA 0).. K1+K1A+K1P. Resultant torque 1 0. AVR Tm Ms S.. + . PSS D+DA+DP 0. K1P : Synchronizing torque by PSS. DP : Damping torque by PSS (Stable at D DA DP 0). 1 2. Mitsubishi Power System Stabilizer (PSS). Types of PSS. As previously mentioned, the PSS detects fluctuations in generator output Power and controls the excitation. The type of PSS is distinguished by its detection signal. The simplest and most typical type is the P input type unit; however, and f input type units have been introduced to improve the stability of the intra- System oscillation mode ( , long-term or interface mode) in view of the large increase in Power systems and Power re-routing in recent years.

4 Each of the features is outlined below. Vref PT. AVR. Local Mode Individual generator oscillates Single-frequency PSS, such as Power against the System P, or f P PSS CT P PSS. Frequency is approx. 1Hz P type PSS is more effective Oscillation EXC.. Vref PT. Inter-area The whole System oscillates as a result Single-frequency PSS, such as AVR. of long-distance, large-capacity Power (Long-cycle) Mode transmission P, or f PSS.. or f type PSS is more effective PSS. Power Oscillation Frequency is to EXC.. Vref PT. Complex Complex Power oscillation mode, AVR. Multi-input PSS is more effective Power such as local mode inter-area P type or P f type f PSS. f PSS. Oscillation mode EXC.. P signal Gain and phase compensation Limiter . Multi-input PSS AVR.. or Gain and phase f signal compensation 3 4. Mitsubishi Power System Stabilizer (PSS).. Hardware Speed Detection Configuration in Input Type The generator speed is detected by the input type PSS.

5 It is necessary for the PSS speed detector Analogue to be able to detect very small fluctuations with high accuracy. Mitsubishi Electric developed a highly The dimensions of the analogue PSS are 250 x 680 x 480mm (LxWxD). Each unit is equipped with the accurate, high-performance speed detector (16-bit resolution, accuracy) and a filter to eliminate following devices: torsional oscillation in the spinning component. Device Function Specification Power /Voltage Detects generator Power and Power converter: 0-1kW/0-30mV, response time: less than 10msec, converter voltage from PT, CT signal voltage converter: 0-150 VAC/0-5 VDC. Inductor Electromagnetic Speed detection card PSS main card Amplifier (Gain) [Kpss] Kpss= (typical range) pick-up (SPMT) Reset filter [Tr] Tr=1 20sec Lag [Tlag] Tlag= 1sec to PSS. Speed detection Torsional oscillation filters functions Limiter Setting range based on generator voltage Standard setting PSS auxiliary card Lead/Lag1 [Tlead1,Tlag1] Tlead 1= , Tlag 1= (SPST) Lead/Lag2 [Tlead2,Tlag2] Tlead 2= , Tlag 2= M s2+N s+W.

6 Filter : 4 steps Deadband, absolute Setting range 0-1pu based on generator output K s2+D s+W. Standard setting PSS protection card Low- Power detection Setting range 0-1pu based on generator output (SPPT) Standard setting Generator over-and under-voltage Setting range based on generator voltage detection Standard setting over voltage: , under-voltage: Design of Fault detection Detects PSS output that is over a set value/time Setting range pick up: based on generator voltagetimer: 0-30sec PSS Parameters Standard setting , 10sec PSS ON/OFF switching circuit Automatic lock (OFF) and automatic reset (ON) by low Power detection, Generator over- and under-voltage detection An appropriate parameter design is very important in order for a PSS to operate effectively. In general, these Automatic lock (OFF) and manual reset (ON) by fault detection parameters are set with the single machine infinite bus model; however, on request, analysis using a multi- System model is also available.

7 Deadband Gain Reset filter Lead/Lag(1) Lead/Lag(2) Lead/Lag(3) Lag Limiter Transfer Tr s 1+Tlead1 s 1+Tlead2 s 1+Tlead3 s 1. Kpss 1+Tlag3 s 1+Tlag s function 1+Tr s 1+Tlag1 s 1+Tlag2 s Site Remarks) If Lead/Lag (3) is necessary, two PSS auxiliary cards (SPST) are used. Commissioning test of PSS. Digital During site examination, to confirm the effectiveness of the PSS, Power fluctuations are generated when the The functions of the digital PSS are realized through the software. Generally, computations are performed PSS is in use and when it is not in use, and damping measurements are compared. As a common method for in the same CPU as the digital AVR. The basic functions are the same as for analogue. Minor differences generating Power fluctuations, a generator voltage transient response test, is applied. In order to quantify the are as follows: effectiveness of the PSS, the damping torque is calculated from the test results.

8 Generally, in the case of (1) Fault detection: for analogue, excessive PSS output is detected. However, in the case of the digital unit, applying a local mode, the PSS is judged to be sufficiently effective if the damping torque is tenfold higher as a a fault occurring in individual parts ( , reset filter) is not realistic. Therefore, rather than basing fault result of using the PSS. detection on computation results, a self-diagnostics function is built into the hardware and software to detect faults. (2) Lag: analogue units have a lag circuit at the final stage that suppresses the noise signal. Generally, this is not incorporated in digital units since noise suppression is carried out at the point of input-signal P1. Calculation of P2. detection. damping torque : D = 2M P2. n T P1. Deadband Gain Reset filter Lead/Lag(1) Lead/Lag(2) Lead/Lag(3) Limiter Transfer Tr s 1+Tlead1 s 1+Tlead2 s 1+Tlead3 s function Kpss 1+Tr s 1+Tlag1 s 1+Tlag2 s 1+Tlag3 s T.

9 M : inertia 5 6. Integral of Accelerating Power Type PSS. ( Power System Stabilizer ). Step respnse of voltage reference AVR without PSS. Power AVR with PSS. time (sec). Power System fault (1 line open after 3 phases grounding). AVR without PSS. Power AVR with PSS. time (sec). Mitsubishi Integral of Accelerating Power Type PSS ( Power System Stabilizer ). A Power System Stabilizer (PSS), which is installed in the Automatic Voltage Regulator of a Generator, can improve Power System stability. The PSS has excellent cost performance compared to other Power System modifications or additions. Mitsubishi "Integral of Accelerating Power Type PSS" conforms to Type PSS2A in "IEEE Std. ". Integral of Accelerating Transfer Function Power Type PSS of PSS. The relation of change among mechanical Power , electrical Power , accelerating Power and rotor speed can be illustrated as from the swing equation where the integral of accelerating Power is equal to rotor speed.

10 STw1 sTw2 1 (1+sT8) N. Ks1. 1+sTw1 1+sTw2 1+sT6 (1+sT9)M. Mechanical Power (option). Ks3. Accelerating Power 1. Rotor Speed sTw3 sTw4 Ks2. Ms Pe Electrical Power 1+sTw3 1+sTw4 1+sT7. M=2H:Inertia constant Limiter VSTMAX. Thus, Integral of mechanical Power is derived as the following equation from measured electrical 1+sT1 1+sT3 1+sT10 1. To AVR. Power and rotor speed (or frequency). Pmdt = Pedt +M 1+sT2 1+sT4 1+sT11 1+sT12. VSTMIN. The resultant block diagram of sensing input signal can be illustrated as Thus, the input signal of "Integral of Accelerating Power Type PSS" is equivalent to rotor speed. Vg 1 Pmdt 1 : Added to PSS2A model M 2 : If generator voltage is continuosly kept higher than 105% or lower than 95% of rated voltage, generator F(s) Equivalent rotor voltage is automatically reduced within 95 to 105% by changing limit value after time delay. speed signal 1. Ms 1. Pedt M. Where, F(s) is transfer function of the filter for attenuating the torsional oscillation.