PROTECTION SCHEMES FOR HYBRID POWER SYSTEMS

PROTECTION SCHEMES FOR HYBRID POWER SYSTEMSSanjay Vinayak H.K.Roll No : 451st Sem F sectionComputer Science Engineering

Introduction to Hybrid Power Systems Hybrid power systems are designed for the generation of electrical power. They are generally independent of large centralized electric grids and are used in remote areas.

Hybrid systems by definition contain a number of power generation devices such as wind turbines, photovoltaic, micro-hydro and/or fossil fuel generators connected to a power grid

2 Wind Power systemsWind power systems are power systems used to convert mechanical energy of wind to electrical energy. They consist of wind turbines connected to a power grid using transformers as shown

Diagram of a Wind Diesel Hybrid power system

PRINCIPLE OF WORKING OF A GENERATORPrinciple: An generator works on the principle of Faradays law of Electromagnetic Induction . It is stated as follows:The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit.

STRUCTURE OF A WIND TURBINE

FOUNDATION

TOWER

3. NACELLE WITH DRIVE TRAIN

ROTOR BLADES

ROTOR 6. ELECTRONIC EQUIPMENT

Need For Protection SystemsThe modern society has come to depend heavily upon continuous and reliable availability of electricity and a high quality of electricity too. Computer and telecommunication networks, railway networks, banking and post office networks etc. cannot function without electricity.No power system can be designed to never fail, in other words faults are always present in a power system. Protection systems are designed to prevent faults and mitigate the consequences of the faults.

TO PREVENT THIS FROM HAPPENING Power System Protection

Power system protectionis a branch of electricalpower engineeringthat deals with the protection of electrical power systems fromfaultsthrough the isolation of faulted parts from the rest of theelectrical network. The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of the network as possible still in operation Some essential qualities of protection are: Reliability Selectivity Fastness Discrimination TRANSMISSION PROTECTION

Shunt Faults or Short Circuits- The path of the load current is cut short because of breakdown of insulation. There are two types of shunt faults namely:Phase Faults-Faults involving two or more phase conductors, with or without groundGround Faults- Involve only one of the phase of conductors and groundTYPES OF FAULTS:An electric arc, or arc discharge, is an electrical breakdown of a gas that produces an on going plasma discharge, resulting from a current through normally nonconductive media such as air.

ARCING TAKING PLACE IN A TRANSFORMER9Series Faults- Series faults are nothing but a break in the path of current.

Some examples of abnormal operating conditions are starting currents of motors, inrush currents of transformers and stable power swings.

The resistance of an arc according to the Warrington model is given by

PROTECTION COMPONENTS

FuseThe fuse allows the normal current to flow but melts itself out, thus breaking the circuit, when the current exceeds a certain magnitude for a certain amount of time. It combines the functions of sensing, comparing, and interrupting the current into one. It steps down the current to such levels that it can be easily handled by the relay current coil. It isolates the relay circuitry from the high voltage of the EHV system. Current Transformers

Voltage or Potential Transformers

The voltage transformer steps down the high voltage of the line to a level safe enough for the relaying system (pressure coil of relay) and personnel to handle. A PT primary is connected in parallel at the point where a measurement is desired. RELAYS

Relay is a protective device which senses the faulty conditionsin a power system line and initiates the operation of circuit breaker to isolate the faulty part from the rest of the healthy power system

Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.MICROPROCESSOR RELAY CLASSIFICATION

Thermal relays, of the bimetallic type, work on the principle of strain generated due to unequal linear expansion of two different metals as a result of heat generated by the passage of the fault current. The change in length of a metal on heating is given by L=L0T An "overcurrent relay" is a type of protective relay which operates when the load current exceeds a preset value. The plug setting multiplier is given by

16 CIRCUIT BREAKERSA circuit breaker is a manually or automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow

Some Types of circuit breakersGenerator Protection Mechanical ProtectionsFailure of Prime-moverFailure of FieldOver-currentOver-speedOver-voltage

Electrical ProtectionsUnbalanced LoadingStator Winding Faults

Protection Against Unbalanced Loading

Unbalanced loading arises from fault to earth or faults between phases on the circuits external to the alternator.

Unbalanced current may burn the mechanical fixing of the rotor core or damage the field winding.Stator Winding FaultsFault between phase and ground

Fault between phases

Inter-turn faults involving turns of same phase winding

Differential Protection

Fault between phase and ground

Fault between phases. Inter-turn faults involving turns of same phase windingInter Turn Fault ProtectionWhen a short circuit develops between adjacent turns in one of the armature windings, unbalanced current flows in two winding.This unbalanced current flows through the relay to operate the circuit breaker

23CONCLUSIONA protection scheme in a power system is designed to continuously monitor the power system to ensure maximum continuity of electrical supply with minimum damage to life, equipment, and property. CTs and PTs are the 'eyes' and the 'ears' of the protection system while the protective relays and the circuit breakers are the 'brain' and the 'brawn' of the system. Each of these components is important in its own right. All of them have to work in tandem with each other to mitigate the effects of faults. Failure of any one of these components is treated as failure of the protective system. The job of the protection engineer is to devise such schemes where closest possible match between the fault characteristics and the tripping characteristics is obtained. The design has to ensure that relays will detect undesirable conditions and then trip to disconnect the area affected, but remain restrained at all other times. BIBLIOGRAPHYFundamentals of Power System Protection by Y.G. Paithankar and S.R.BhidePower System Protection and Switchgear by Badri RamWikipediaSchweitzer Engineering Lab Research papersGoogle Image Searchhttp://www.ceere.orghttp://hyperphysics.phy-astr.gsu.eduTHANK YOU