Eee projects on generator reverse power protection — Simulation & Power Modeling

Abstract — Eee projects on generator reverse power protection

Eee Projects On Generator Reverse Power Protection: Power Electronics, MATLAB/Simulink & Circuit Modeling Integrated Analysis: MATLAB/Simulink · MOSFET/IGBT Gate Drivers · SPWM/SVPWM · THD Spectrum · ~9704 Words Chapter 1: Power Electronics Overview, System Specifications & Topology Modeling Ijraset Journal For Research in Applied Science and Engineering Technology Generators are one of the most important parts of the power system. Faults at the generator lead to severe failures and fatal accidents. Hence, generators’ protection is a major concern, especially from faults – voltage and current fluctuations, short circuit faults, frequency variations, over-fluxing, flow of reverse power, etc. In this project, a protection scheme is presented for power flow in opposite direction that is flow of power from grid to the generator, due to which the generator starts consuming and acts as a load. Modelling tools are important to have a basic idea of power system. These tools aid an engineer to modify the system under all circumstances. This paper contains the simulation and modelling of digital reverse power relay in MATLAB/ Simulink®. The libraries in MATLAB offer Power System Analysis Toolbox which are simulation based, for power system engineering projects.

Analytical & State-Space Control Methodology

I. INTRODUCTION In power systems, for detection of synchronous generator's motoring action, reverse power relays are used. When the field winding is connected electrically with the system of excitation but the prime mover failure occurs. Thus, the machine behaves like a synchronous motor, connected with enormous power system. In such conditions, the rotors behave like the active load on that machine. Motoring action eats power to rotate the prime mover and severe damage is caused to the prime mover. It is a dangerous condition since there is an objectionable rise in temperature, especially for steam turbines. Therefore, these must be detected immediately and the GCB should be tripped. Electromechanical relays are replaced with digital relays which are highly accurate and have high-speed operations. Fast operation of relay is a must, especially for faults which may result in system shutdown. Some additional perks of digital relays are - multiple variable settings, highly sensitive, control for a wide range and compact size. II. OPERATING PRINCIPLE OF REVERSE POWER RELAY Directional relays that is used to check the power flowing from generator (operating in parallel with another generator/utility) and take proper actions accordingly. Under certain conditions, the direction of power changes from the bus bar towards the generator. This generally happens when prime mover is unsuccessful. The grid-extracted active power is relatively small compared with the generator rating. To obtain the reverse power relay modelling, it has been organized into sections, namely - directional element, delay element and hold block. III. PRIME MOVER FAILURE FAULT OR REVERSE POWER FAULT A generator is incorporated with prime mover and is connected with the grid, yielding power. When the failure of the synchronized prime mover occurs, the condition is known as motoring. Here, the generator pulls power from the bus, operates like a motor and drives the prime mover. In a synchronized condition, frequency of all the generators is same. Any dip in frequency of one alternator causes the other sources of power to feed power into the alternator. This power flow in the opposite direction is called reverse power flow or motoring action of alternator. Another incident of reverse power occurs during synchronization. When the frequency of bus bar, which is also the machine synchronization frequency, is slightly greater than machine frequency and the breaker is OFF, power flows from the bus bar to the machine. Hence, during synchronization, the machine frequency is kept little more than that of the bus bar. This allows the machine to take load the moment the breaker closes. A reverse power relay can be used but it must have a time delay setting to ensure correct trip in case of short time fluctuations, phase swings and disturbed synchronization. Hence, when a power reversal issue occurs, the first thing is to decouple the corresponding alternator from live line with the help of the breaker. If it is stuck, then whole bus needs to be shut down. IV. REVERSE POWER RELAY Reverse Power Relays (RPR) are used to sense motoring operation of synchronous alternators. The RPR is a protective directional relay that restricts power to flow in the opposite direction. It is used in installations where a generator functions in parallel with other generator or the utility in order to prevent power to flow again into the first generator when it fails the output. The relay checks power from the generator and in case of output falling below a specific value, it immediately decouples the coil of the generator to avoid power from entering the stator coil. The generator output fails because of the prime mover issues, speed controller problems, turbine that runs the generator, or varied frequencies during synchronization. The RPR senses power flow in reverse direction and separates the generator to reduce damage up to a great extent. V. MATLAB/SIMULINK® MODELLING A. Directional Element For directional element, a low voltage signal from PT and current signal from CT are converted in perfect square waves with values +1 to -1. This means, ‘switch’ and ‘switch1’ output in the form of square wave and not touching zero. Later, these waves are multiplied to yield ‘1’ as an output during the overlapping and ‘-1’ during the non-overlapping interval. That is switch 2 output is: ? 1 for overlapping = normal condition ? -1 for non-overlapping = abnormal condition Then the product is integrated from ‘L’ to ‘-L’. To keep the integral always less than '0' under normal circumstances of load flow, the higher integrator limit is set at ‘0’ value. However, the output of integrator tends to drop till it touches a threshold value ‘L’, under power flow reversal scenarios. That is, more the overlapping condition, more the value of integral that is positive ('0' here) indicating healthy condition. And if the overlapping condition is a short span, the value of negative integral will be lower. When the threshold value ‘-L’ is crossed, trip signal travels from relay to breaker. This is why, L is 0.01, but values can be set depending upon how severe is the reverse power.

Simulink Waveforms & Power Quality Findings

B. Delay Element The job of the delay section is to avoid the relay from passing any false trip signals to the breaker during temporary faults or transients. The directional element output is fed to delay element decision block with output ‘0’ when normal and output '1' when abnormal conditions occur. This output is then integrated and the value of the integral is compared to the threshold level ‘T’, whose value is set equal to the delay time desired. When, Healthy conditions – integral value < T - delay element output is ‘1’. Under steady conditions, the integrator input is ‘0’. Therefore, the integrator value is ‘0’ always (< T), and so the delay element output is 1. Unhealthy condition - the integral value > T, delay element output is ‘0’. The integrator input is ‘1’ and ‘T’ seconds later, faulty condition is indicated through obtained integral value. Transients or a temporary fault - for < ‘T’ seconds, the integrator value is back to ‘0’ with the help of relational operator after fault clearing. C.

Scope & Practical Applications

• High-efficiency DC-DC converters and isolated resonant topologies (LLC / DAB)
• Sinusoidal and Space Vector PWM inverters for grid integration & industrial motor drives
• MOSFET / IGBT gate driver optimization with active Miller-clamp shoot-through protection
• Power quality conditioning with Total Harmonic Distortion (THD) strictly compliant with IEEE 519
• Complete Simscape .SLX model files, parameter calculation scripts, and IEEE dissertation reports