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Design of a 3-phase FC-TCR Static Var Compensator for Power factor correction and Preventation of negative sequence current

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1 | P a g e
COURSE: EE 5374
COURSE TITLE: POWER SYSTEMS PROTECTIVE RELAYING
INSTRUCTER: DR.W.J.LEE
TERM: SPRING‐2015
NAME:...
2 | P a g e
Sr.No
INDEX
Subject Page No
1 Abstract 3
2 Introduction 4
3 Design Procedure 5
4 Algorithm 6-7
5 Results 9
6 S...
3 | P a g e
Abstract:
In a transmission system, only the positive sequence is usually selected to analyze a
load flow beca...
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Design of a 3-phase FC-TCR Static Var Compensator for Power factor correction and Preventation of negative sequence current

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The research has shown that SVC has been proved successful to prevent negative sequence current more over it also has capabilities for Power factor correction.
• Negative-sequence current causes some problems in generator systems. Though every generator is capable of withstanding a certain level of negative-sequence current, excess and/or persistent amounts of negative sequence current may cause rotor overheating and serious damage.
• Since its frequency quite matches the natural mechanical frequency of turbine blades and the zero sequence current is blocked by delta connected step-up transformer, the negative sequence current becomes the only reason for the super synchronous resonance of a generator due to an unbalanced system, especially in an isolated power system.
• SVC has the potential to overcome some adverse effects of the negative sequence current to the turbine generator systems

The research has shown that SVC has been proved successful to prevent negative sequence current more over it also has capabilities for Power factor correction.
• Negative-sequence current causes some problems in generator systems. Though every generator is capable of withstanding a certain level of negative-sequence current, excess and/or persistent amounts of negative sequence current may cause rotor overheating and serious damage.
• Since its frequency quite matches the natural mechanical frequency of turbine blades and the zero sequence current is blocked by delta connected step-up transformer, the negative sequence current becomes the only reason for the super synchronous resonance of a generator due to an unbalanced system, especially in an isolated power system.
• SVC has the potential to overcome some adverse effects of the negative sequence current to the turbine generator systems

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Design of a 3-phase FC-TCR Static Var Compensator for Power factor correction and Preventation of negative sequence current

  1. 1. 1 | P a g e COURSE: EE 5374 COURSE TITLE: POWER SYSTEMS PROTECTIVE RELAYING INSTRUCTER: DR.W.J.LEE TERM: SPRING‐2015 NAME: HARDIK PARIKH STUDENT ID: 1001090431 SUBJECT: PROJECT-2 Project Title: DESIGN A THREE-PHASE INDIVIDUAL CONTROLLED FIXED CAPACITOR-THYRISTOR CONTROLLED REACTOR (FC-TCR) STATIC VAR COMPENSATOR (SVC) TO PERFORM POWER FACTOR CORRECTION AND PREVENT NEGATIVE SEQUENCE CURRENT
  2. 2. 2 | P a g e Sr.No INDEX Subject Page No 1 Abstract 3 2 Introduction 4 3 Design Procedure 5 4 Algorithm 6-7 5 Results 9 6 Source code 10-11 7 Conclusion 12 8 Learning Outcome 12 9 Reference 12
  3. 3. 3 | P a g e Abstract: In a transmission system, only the positive sequence is usually selected to analyze a load flow because the power system is assumed to be balanced. In practice, however, a completely balanced power system is almost impossible to be obtained, so the zero and negative sequences should exist in the power system. Since a Δ- Yground connected step-up transformer can block the zero sequence current on the primary side, the current entering a generator just consists of positive and negative sequence parts. Beside this negative sequence current produced by the system heats the windings to possibly damage the generator, it may also cause a mechanical resonant problem on the generator. When a system is unbalanced, the frequency of negative sequence current will be converted into a mechanical vibration frequency through the rotor shaft. This will create small chronicle damage over the time and results in mechanical failure of the turbine. As a result we are required adjust the setting of the I2 relay to limit the negative sequence current going into the generator or to implement methods which prevent I2 from entering back to generator. The research has shown that SVC has been proved successful to prevent negative sequence current more over it also has capabilities for Power factor correction. • Negative-sequence current causes some problems in generator systems. Though every generator is capable of withstanding a certain level of negative-sequence current, excess and/or persistent amounts of negative sequence current may cause rotor overheating and serious damage. • Since its frequency quite matches the natural mechanical frequency of turbine blades and the zero sequence current is blocked by delta connected step-up transformer, the negative sequence current becomes the only reason for the super synchronous resonance of a generator due to an unbalanced system, especially in an isolated power system. • SVC has the potential to overcome some adverse effects of the negative sequence current to the turbine generator systems
  4. 4. 4 | P a g e FC-TCR SVC can change the real and reactive power flow and force the output o f the generator become balanced even though the load is unbalanced. Besides, a correct and simplified mathematical model which is selected among several compensating methods would be built up. This model would be easily implemented in a control program and reduce negative sequence current to the expected value. Introduction: To analyze the effects to the whole system when using SVC to reduce the negative sequence current entering a generator, a three-phase transmission load flow program has been developed. The connection of an SVC, however, is delta to avoid producing zero sequence problems; an appropriate delta connected load model for a load flow program needs to be developed because the load o r shunt reactive elements used to be in grounded wye. The function of an SVC to reduce the negative sequence current entering a generator. Before presenting the special application of a static var compensator system, the principle of a fixed-capacitor Thyristor Controlled Reactor (FC-TCR) as shown in Fig. 1, is briefly discussed. The adding of the Fixed-Capacitor is to make this SVC also have the capability of supplying reactive power. The basic elements of the thyristor controlled reactor, as shown in the right half of Fig. 1, consist of a fixed reactor with inductance L, and a bidirectional thyristor valve which conducts on alternate half- cycles. The current flowing through the thyristors can be adjusted from zero to maximum by controlling the delay angle a. Fig 1. Basic Elements of a FC-TCR Circuit
  5. 5. 5 | P a g e The fundamental of the negative sequence current reduction on the generator with SVC is to lead the I Design procedure: 2 current into the SVC instead of the generator. Beside generating reactive power; the adjustment o f the firing delay angle o f the SVC can obtain the unbalanced susceptance to balance the equivalent load impedance, which connection is delta. The following will compare several different approaches to reduce generator I2 current with an SVC. Fig 2. A power system with compensator Theoretically, a complete compensation can be obtained and the negative sequence current can be compensated by an SVC. The Equation can be divided into real and imaginary parts and will have three variables and two equations. An additional constraint has to be added to obtain a Unique solution. From the practical point of view, the following constraint is selected.
  6. 6. 6 | P a g e Case-I: Algorithm:
  7. 7. 7 | P a g e Case-II:
  8. 8. 8 | P a g e Available Data: 1. i. The internal voltage of the generator is balanced. 2. ii. The zero sequence current is blocked by using the Δ‐ Y grounded step up transformer. 3. iii. The magnitude of the phase A voltage is maintained at 1.0pu. 4. iv. The source impedance of the generator is j0.1 pu. 5. v. For simplicity, assume that the SVC is connected at the terminal of the generator. 6. vi. To avoid the appearances of zero sequence current, the SVC is Δ connected. 7. vii. The loads are Pa + jQa, Pb+jQb and Pc+jQc. Procedure: 1. We are provided the phase powers Sa, Sb, Sc. where Sa = Pa + jQa ; Sb = Pb + j Qb; Sc = Pc + jQc 2. The generator terminal voltage is set at 1.0 pu. 3. We calculate phase currents entering the generator using Ia = (Sa/Va)’ similarly for Ib and Ic and also consider the phase shifts. 4. From these phase currents we calculate the sequence currents I0, I1, I2. 5. Our aim is to reduce the I2 (negative sequence current) as close to zero as possible. 6. The FC-TCR will generate reactive power Qab, Qbc, Qca and its susceptances are calculated by dividing the reactive powers by V2 7. Once reactive power from FC-TCR is calculated the total power entering the generator is calculated using formulas in method 3 of the reference dissertation. i.e. generator terminal voltage. 8. Then the phase and sequence currents are calculated.
  9. 9. 9 | P a g e Results: Description Case-I Without PF Correction B -1.4989e-006ab B 1.9535e-007bc B 1.3036e-006ca I2 -8.7711e-007 -7.2809e-006isystem I2 -8.7893e-007 -7.2808e-006isvc I2 1.8287e-009 -6.1762e-011inet Case-II Description With PF Correction PF = 0.8 PF = 1 B -1.4989e-006ab 0.0999 B 1.9535e-007bc 0.1002 B 1.3036e-006ca 0.0999 K 5.5511e-017 0.3000 I2 -8.7711e-007 -7.2809e-006isystem -8.7711e-007 -7.2809e-006i I2 -8.7893e-007 -7.2808e-006isvc -9.8327e-004 -8.7025e-006i I2 1.8287e-009 -6.1762e-011inet 9.8239e-004 +1.4217e-006i PF New 0.8 1.0
  10. 10. 10 | P a g e Source Code: %% CASE:1- Without power factor correction % Load data as provided Pa= 0.4; Qa= 0.3; Sa= Pa+Qa*i; Pb= 0.4; Qb= 0.3; Sb= Pb+Qb*i; Pc= 0.4; Qc= 0.3; Sc= Pc+Qc*i; % Terminal Voltage at Transformer primary VA= 1; VB= -0.5-0.866i; VC= -0.5+0.866i; % Terminal Voltage at Transformer secondary Va= VA*(0.866025+0.5i); Vb= VB*(0.866025+0.5i); Vc= VC*(0.866025+0.5i); a= -0.5+0.866i; % Phase current, Transformer secondary side Ia= conj(Sa/Va); Ib= conj(Sb/Vb); Ic= conj(Sc/Vc); % Phase current, Transformer Primary side IA = Ia*(0.866025-0.5i); IB = Ib*(0.866025-0.5i); IC = Ic*(0.866025-0.5i); %Sequence current in system Iseq = (1/3) * [1 a a^2; 1 a^2 a; 1 1 1]*[IA; IB; IC]; % Iseq = [Iseq(1); Iseq(2); 0]; % As delta configuration will eliminate zero serquence current. I2= [real(Iseq(2)); imag(Iseq(2)); 0]; A= [1.5 -2.99 1.5; 2.598 -0.0001 -2.598; 1 1 1]; I2netbefore= Iseq(2) B= inv(A)*I2; Bab=B(1) Bbc=B(2) Bca=B(3) A= [1 a^2 a]; V= [VA-VB 0 VA-VC; VB-VA VB-VC 0; 0 VC-VB VC-VA]; I2SVC= A*V*B I2netafter = Iseq(2)-I2SVC
  11. 11. 11 | P a g e %% CASE:2- With power factor correction % Load data as provided Pa= 0.4; Qa= 0.3; Sa= Pa+Qa*i; Pb= 0.4; Qb= 0.3; Sb= Pb+Qb*i; Pc= 0.4; Qc= 0.3; Sc= Pc+Qc*i; % Terminal Voltage at Transformer primary VA= 1; VB= -0.5-0.866i; VC= -0.5+0.866i; % Terminal Voltage at Transformer secondary Va= VA*(0.866025+0.5i); Vb= VB*(0.866025+0.5i); Vc= VC*(0.866025+0.5i); a= -0.5+0.866i; % Phase current, Transformer secondary side Ia= conj(Sa/Va) Ib= conj(Sb/Vb) Ic= conj(Sc/Vc) % Phase current, Transformer Primary side IA = Ia*(0.866025-0.5i); IB = Ib*(0.866025-0.5i); IC = Ic*(0.866025-0.5i); S1= VA*conj(IA); P1= real(S1); Q1= imag(S1); % Phi1= atan(Q1/P1); % PF1= cos(phi1); P2=P1; PF2= 0.8; PF= 1; % As provided Q2= P2*tan(acos(pf2)) Q3= Q1-Q2; K= Q3/VA^2 % Q2new= Q3+Q2avg pfnew= P2/(sqrt(P2^2+Q3^2)) %Sequence current in system Iseq = (1/3) * [1 a a^2; 1 a^2 a; 1 1 1]*[IA; IB; IC]; % Iseq = [Iseq(1); Iseq(2); 0] % As delta configuration will eliminate zero serquence current.
  12. 12. 12 | P a g e I2= [real(Iseq(2)); imag(Iseq(2)); K]; A= [1.5 -2.99 1.5; 2.598 -0.0001 -2.598; 1 1 1]; B= inv(A)*I2 Bab=B(1) Bbc=B(2) Bca=B(3) A= [1 a^2 a]; V= [VA-VB 0 VA-VC; VB-VA VB-VC 0; 0 VC-VB VC-VA]; I2SVC= A*V*B I2net = Iseq(2)-I2SVC Conclusion: In both the cases it is observed that the net negative sequence flowing in the system is reduced with introduction of SVC. It is observed that the SVC based FCTCR reduce the negative sequence current with variable switching of Thyristor. It is also important that SVC also supplies reactive power in case of power factor improvement. In this project we have learnt about operation of FC-TCR based Static VAR Compensator and how to implement SVC for negative sequence current reduction and power factor improvement. The approach followed is quite unique and novel method which can be widely implemented to overcome the consequences of negative sequence current in modern power system. Learning outcome: 1) Thesis: The prevention of super synchronous resonance problem on the turbine system of generator with staticvar compensator References: By Jen-hung chen 2) Negative sequence current reduction for generator turbine protection Wei-jen lee, Tze-yee ho, member, Jih-phong liu, Yuin-hong liu, IEEE member

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