Pss´S

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PSS with Integral of Accelerating Power
Technical Description

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M. Delgado 2005-03-30 Christer Norling 2005-04-01 Doc. TechnicalDescription des. PSS with Integral of Accelerating Power
Resp. dept. Document number

Ref. des.

Lang.

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Sheet No. of sh.

1 8

HPE 5-001E
TEMPLATE: TECHN DOC PLANT DOC, A4 P EN, R7.DOT; FILENAME: PSS TYPE 2A; PRINTDATE: 05-04-01 14:34; SAVEDATE: 05-04-01 14:32

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PSS with Integral of Accelerating Power 1. General
Due to several restrictions: economical, technical,environmental etc. power system networks are operated near to their stability limit. For this reason many systems have experienced the necessity of improve stability in order to increase allowable power transfers. Local modes of power oscillations are related to individual generators at a power station oscillating together against a large power system (f= 0.7 to 2 Hz). Inter-unit modes of poweroscillations are related to machines from one power station swinging against a nearby power station machines (f= 1.5 to 3 Hz). Inter-area modes of oscillations (small signal angular instability) are related to the swinging of many machines in one part of the system against machines in other parts (f= 0.1 to 0.5 Hz). PSS introduces to damp power system swing mode oscillations in order to extend powertransfer limits. The control is based on terminal voltage and current measurements which are used to obtain a signal proportional to the integral of deviation of mechanical power from a combination of the deviation of electrical power and calculated deviation of angular frequency. To produce a signal proportional to the integral of accelerating power, the conditioned measured input signal ofelectrical power is then subtracted from the derived signal proportional to the mechanical power. The integral of accelerating power allows significantly higher gains, hence better performance by comparison with to single input stabilizer that measure only power (active power), frequency, or speed, providing a greater contribution to damping of rotor oscillations.

2. PSS type 2A Operating PrinciplesThe task of a PSS is to extend the angular stability limits of a power system by providing supplemental damping to the oscillation of synchronous machine rotors through the generator excitation. This damping is provided by a electric torque applied to the rotor that is in phase with the speed variation. Once the oscillations are damped, the thermal limit of the tie-lines in the system may then beapproached. This supplementary control is very beneficial during line outages and large power transfers. The mathematic equations that describe the movement of a rotating machine are based on the swing equation of the rotating inertia. The equation system is non-linear but, for small perturbations the response of machine can be modeled by linear differential equations. The accelerating torque is thedifference between the shaft torque and electromagnetic torque. The rotor speed is maintained constant, when there is balance between the mechanical and electrical torques. Any difference between the torques will cause the acceleration or deceleration of the machine.

d 2δ dω T acc = J dt 2 = T m − T e = J dt

[1]

Doc. kind Title

Technical Description PSS with Integral of AcceleratingPower

Project

Document number

Lang.

Rev. ind.

Sheet No. of sh.

2 8

HPE 5-001E
TEMPLATE: TECHN DOC PLANT DOC, A4 P EN, R7.DOT; FILENAME: PSS TYPE 2A; PRINTDATE: 05-04-01 14:34; SAVEDATE: 05-04-01 14:32

en

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Where: Tacc J Tm Te δ = Accelerating torque. = Moment of inertia J=2H*S/ω2, (S= Apparent power, H= Total (turbine + generator) inertia constant, ω= Angular speed...