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TRANSIENT STABILITY STUDIES (POWERTRS) Indonesia Clean Energy Development (ICED) project Indonesia Wind Sector Impact Assessment Presented by: Dr. Balaraman, Ph.D. Makassar, February 17 to 21, 2014

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Voltage stability Rotor angle stability Study period: 0-10 sec Mid-term/long-term stability Study period: seconds to several minutes (slow dynamics) Small signal stability Non-oscillatory Insufficient synchronizing torque Oscillatory Unstable control action Transient stability Large disturbance (First swing) Stability

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f, v, loading acceptable, load met, n-1 or n-2 contingency acceptable f, v, loading acceptable load met n-1 or n-2 contingency not satisfied f, v, loading not acceptable, load not met Power System Operating States

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DS: Distribution System G : Generator Control Hierarchy

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Power System Subsystem & Controls

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Power System Stability Ability of a power system to remain in synchronism Classification of transients : Electromagnetic and Electromechanical Stability classification Transient stability : Transmission line faults, sudden load change, loss of generation, line switching etc. Dynamic stability : Slow or gradual variations. Machine, governor - Turbine, Exciter modelling in detail. Steady state stability : Changes in operating condition. Simple model of generator.

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Transient Stability: First swing and Multiple Swings

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Assumptions : Synchronous speed current and voltage are considered. DC off set currents, harmonics are neglected. Symmetrical components approach. Generated voltage is independent of machine speed. Circuit parameters are constant at nominal system frequency. (Frequency variation of parameter neglected).

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Steady State Stability

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J : Moment of inertia of rotor masses (kg-mt 2 ) m : Angular displacement of rotor w.r.t. a stationary axis (mechanical radians) t : Time (seconds) T m : Mechanical or Shaft Torque ( N-m ) T e : Net electrical torque (N-m ) T a : Net accelerating torque (N-m) For generator, T m and T e are +ve. Mechanical Equation

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m : Angular displacement of the rotor in mechanical radians.

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Where M : Inertia constant = at synchronous speed in Joules-sec per mechanical radian.

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Constant is defined as the ratio of stored Kinetic Energy in Mega Joules at synchronous speed and machine rating in MVA

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At t = 0, breaker is opened. Initially Pe = 1 pu on machine rating Pm = 1pu and kept unchanged. In 2H seconds, the speed doubles.

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Inertia constant (H) is in the range for various types of machines. Hence H-constant is usually defined for machine.

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Relation between H constant and Moment of Inertia is given by:

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Example : S mach = 1333 MVA, WR 2 = lb – ft 2, N= 1800 RPM = pu (MJ/ MVA) On 100 MVA base : H = 1333 / 100 = (MJ / MVA)

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H = H 1 + H 2 P m = P m1 + P m2 P e = P e1 + P e2 G 1 and G 2 are called coherent machines. Inertia Constant

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MKS system

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British units Given

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MVA rating : 555 WR 2 : lb-ft 2 Example

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Non coherent machines Unit TypeH Constant Hydro Unit2 to 4 Thermal unit 2 pole – 3600 RPM2.5 to 6 4 pole – 1800 RPM4 to 10 Typical Values

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Relative swing (with reference to one machine) is more important, rather than absolute swing.

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Relative Plot ( i - ) Absolute Plot 11 oo 22 33 44 33 22 00 11 T in sec. Swing curves Relative swing (with reference to one machine) is more important, rather than absolute swing.

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I E’ = V t + (0 + jx d ’) I E’ VtVt jx d ’ I Ref. VtVt I E’ jx d ’ + - Classical model : (Type 1) Constant voltage behind transient reactance

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E 1 : Magnitude of voltage at bus1 E 2 : Magnitude of voltage at bus2 : 1 - 2 X s : Reactance jX s Power angle equation

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Machine Parameters Synchronous : Steady state, sustained. Transient : Slowly decaying Sub-transient : Rapidly decaying

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Typical values ParameterHydro (pu)Thermal (pu) xdxd xqxq xd’xd’ xq’xq’ xd”xd” xq”xq” T d0 ’ s s T q0 ’ s T d0 ” s s T q0 ” s s RaRa

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Stability Stable At s ; P m = P e ; net accelerating torque = 0. Let P e decrease slightly. increase (acceleration) comes back to original position. Stable region. Hence s is stable operating point.

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Unstable At u ; Pm = Pe ; Net accelerating torque = 0, Let P e decrease slightly. increases, (acceleration) P e further decreases. Chain reaction never comes back to normal value Hence u is unstable operating point.

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Infinite bus Generator connected to infinite bus. High inertia. H compared to other machines in the system. Frequency is constant. Low impedance. X d ’ is very small. E’ is constant and V t is fixed. Infinite fault level symbol.

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Example : H = 3.2, Z = 10% on own rating, X d 1 = 25%, tap = 1, R a = 0.0 and neglect R. Establish the initial condition. Perform the transient stability without disturbance. Open the transformer as outage & do the study. How long the breaker can be kept open before closing, without losing synchronism.

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Load Modeling

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Vary the tap. Switch on the capacitor. Determine the response (charge) in load. Compute the parameters. P = P 0 (C P + C I. V + C Z. V 2 ) ( 1+K f. f) P varies with time, voltage and frequency. P 0 varies with time - can be constant at a given time of a day. C P, C I, C Z & K f are constants. V & f are known at any time instant. P is known from measurements. Solve the non linear problem over a set of measurements.

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Let the load be 10,000 MW. i.e. P 0 = 10,000 Let for 1 Hz change in frequency, let the load change be 700 MW. What it implies : –Initial load 10,000 MW. –Loss of generation 700 MW –Increase in load 700 MW –Frequency 49 Hz.

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Load model Parameters

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Loads

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Reactive Power Control Synchronous generators Overhead lines / Under ground cables Transformers Loads Compensating devices

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Control devices Sources /Sinks --- Shunt capacitor, Shunt inductor (Reactor), Synchronous condenser, and SVC. Line reactance compensation --- Series capacitor Transformer -----OLTC, boosters

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Speed governor systems:

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Types of Control: Primary Control : Governor action Secondary Control : AGC, load frequency control (For selected generators) Under Frequency operation : Vibratory stress on the long low pressure turbine blades Degradation in the performance of plant auxiliaries say, induction motor

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Limitations Only maximum spinning reserve can be achieved Turbine pickup delay Boiler slow dynamics Speed governor delay

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Other measures : * Fast valving * Steam by-passing Load shedding

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Modules in a program Data reading Initialization –Steady state load flow –Control block parameter AVR, Gov., Machine, Motor, PSS, HVDC, SVC. Disturbance model Control block modeling Machine modeling Load flow solution Protective relay modeling Special functions –Cyclic load –Arc furnace –Re-closure Results Output –Report –Graph

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Typical swing curve :

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Integration step size : Typical value : 0.01 seconds, Range : to 0.02 seconds Typical swing curve :

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AVR : Type 1

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AVR : Type 2

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AVR TYPE – 5

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Steam Turbine Governing System K 1 : 0.05P max : 1.0 T 1 : 0.1P min : 0.0 T 2 : 0.03P up : 0.1 T 3 : 0.4P dn : -1.0

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Turbine Model

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Hydro Governor

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Hydro Turbine

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Transient Stability Enhancement Philosophy Minimize the disturbance influence by minimizing the fault severity and duration. Increase the restoring synchronizing forces. Reduce accelerating torque.

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Transient Stability Enhancement Methods : 1.High speed fault clearing. 2.Reduction of transmission system reactance. 3.Regulated shunt compensation. 4.Dynamic Braking. 5.Reactor switching. 6.Independent pole operation of circuit breaker. 7.Single pole switching 8.Fast valving. 9.Generator tripping. 10.Controlled system separation and load shedding. 11.High speed excitation systems. 12.HVDC transmission link control.

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Major references used in the development of Transient Stability Studies Module 1.Dommel, N. Sato “Fast Transient Stability Solutions”, IEEE Transactions on Power Apparatus and Systems, 1972, PP W. Dommel, “Digital computer solution of electromagnetic transients in single and multiphase networks”, IEEE Transactions on Power Apparatus and Systems, April 1969, Vol. PAS-88, PP IEEE Committee Report, “Dynamic Models for Steam and Hydro Turbines in Power System Studies”, IEEE PES Winter Meeting, New York, Jan./Feb (Paper T ). 4.IEEE Committee Report, “Proposed Excitation System Definitions for Synchronous Machines”, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-88, No. 8, August IEEE Committee Report, “Computer representation of excitation systems”, IEEE Transactions Power on Apparatus and Systems, June 1968, Vol. PAS-87, PP

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For further information please contact: Office Address of ICED-USAID (Indonesia Clean Energy Development – United States Agency for International Development) ICED-USAID Jakarta Office: Tifa Building, 5th Floor, Jl. Kuningan Barat No. 26 Jakarta 12710; Phone/Facsimile: / ICED-USAID Medan Office: Jl. Tengku Daud No. 7A Medan 20152; Phone/Facsimile: / Contact Person: Pramod Jain, Ph.D. President, Innovative Wind Energy, Inc , Dr.K.Balaraman Ph.D CGM, PRDC 61

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