Operations

Operations-Training-SolutionsThe focus of O-T-S is the development and delivery of training programs for electric power system operations personnel.

Southwest 2011 OutageThe Dynamics of Disturbances class has been updated to include a detailed description of the 9/8/2011 Southwest outage.

NERC Practice Tests

Synchronizing and Synchronizing Equipment1. Synchronizing and Synchronizing Equipment1.1 Theory of SynchronizingWhen closing a circuit breaker between two energized parts of the power system, it is crucial to match voltages on both sides of the circuit breaker before closing. If this matching or "synchronizing" process is not done correctly, a power system disturbance will result and equipment (including generators) can be damaged. In order to synchronize properly, three different aspects of the voltage across the circuit breaker must be closely monitored. The three aspects of the voltage are called the synchronizing variables and are:1. The voltage magnitudes2. The frequency of the voltages3. The phase angle difference between the voltages1.1.1 Voltage Magnitude Synchronizing VariableIf the voltage magnitudes are not closely matched, a sudden rise in Mvar flow will appear across the circuit breaker as it is closed. For example, if a 345 kV circuit breaker were closed with a 20 kV difference in voltage across the open circuit breaker, a large Mvar flow would suddenly occur upon closing. The allowable voltage magnitude differences across the open circuit breaker are system specific. However, for general guidance, a difference of a few percent is unlikely to cause any serious problem.1.1.2 Frequency Synchronizing VariableIf the frequencies on either side of an open circuit breaker are not matched prior to closing, a sudden change in MW flow will appear across the circuit breaker as it is closed. The sudden MW flow change is in response to the initial frequency difference as the system seeks to establish a common frequency once the circuit breaker is closed. The allowable frequency difference is again system specific. However, a general guideline would be to have the frequencies within 0.1 Hz of each other prior to closing.1.1.3 Phase Angle Synchronizing VariableThe third synchronizing variable - and likely the most important of the three - is the voltage phase angle difference. If the phase difference between the voltages on either side of the open circuit breaker is not reduced to a small value, a large MW flow increase will suddenly occur once the circuit breaker is closed. The voltage phase angle difference is the difference between the zero crossings of the voltages on either side of the open circuit breaker. Ideally, the voltage phase angle should be as close to zero degrees as possible before closing the circuit breaker.1.2 Synchronizing ExamplesThe importance of synchronizing cannot be overstated. All system operators should understand the theory and practice of synchronizing. If two power systems are synchronized via an open circuit breaker, and the synchronizing process is not done correctly, generators can be severely damaged. Two scenarios for synchronizing follow to further describe the synchronizing process.1.2.1 Scenario #1: Synchronizing Two IslandsThe first scenario assumes that two islands are about to be connected together using the open circuit breaker as illustrated in Figure 1. The two islands, since they are independent electrical systems, will have different frequencies so all three of the synchronizing variables must be monitored to ensure they are within acceptable limits prior to closing the open circuit breaker.The system operators for the two islands will likely have to adjust generator MW output levels (or adjust island load magnitudes) in one or both islands to achieve the desired adjustment in frequencies and phase angles. Voltage control equipment (reactors, capacitors, etc.) may also be used as necessary to change voltage magnitudes to within acceptable levels.

Figure 1Synchronizing Two Islands1.2.2 Scenario #2: Establishing the Second TieOnce the first transmission line is closed interconnecting the two islands, the frequency will be the same in the two areas. Therefore, one of the three synchronizing variables (the frequency) is no longer a factor. However, as illustrated in Figure 2, the other two synchronizing variables must still be monitored. Generation and/or voltage control equipment may be to be utilized to ensure the phase angle and voltage magnitude differences are within acceptable limits prior to closing the second circuit breaker. This process should be easier than closing the first transmission line (Scenario #1) as frequency is no longer a factor. Figure 2Establishing the Second Transmission Tie1.3 Synchronizing Equipment1.3.1 SynchroscopeA synchroscope is a simple piece of equipment that is used to monitor the three synchronizing variables. A basic synchroscope (illustrated in Figure 3) inputs voltage waveforms from the two sides of the open circuit breaker. If the voltage waveforms are at the same frequency, the synchroscope does not rotate. If the voltage waveforms are at a different frequency, the synchroscope rotates in proportion to the frequency difference. The synchroscope needle always points to the voltage phase angle difference.A synchroscope is a manual device in that an operator must be watching the "scope" to ensure they close the circuit breaker at the correct time. The synchroscope is normally mounted above eye level on a "synch panel". The synch panel also contains two voltmeters so that the voltage magnitudes can be simultaneously compared.The synchroscope in Figure 3 reflects a slight voltage magnitude mismatch, and a stationary synchroscope with a phase angle of approximately 35. The fact that the synchroscope needle is not rotating indicates frequency is the same on either side of the circuit breaker.

Figure 3Synchroscope in a Synch Panel1.3.2 Synchro-Check RelaysA synchro-check or synch-check relay electrically determines if the difference in voltage magnitude, frequency and phase angle falls within allowable limits. The allowable limits will vary with the location on the power system. Typically, the further away from generation and load, the more phase angle difference can be tolerated. Synch-check relays typically do not provide indication of the voltage magnitude, frequency or phase angle. A synch-check relay decides internally whether its conditions for closing are satisfied. The synch-check relay will either allow or prevent closing depending on its settings. A typical synch-check relay may allow closing if the voltage angle across the breaker is less than 30.1.3.3 Application of Synchronizing EquipmentAt power plants, synchroscopes are routinely installed to permit manual closing of a circuit breaker. In addition, synch-check relays can be used to "supervise" the closing of the circuit breaker and prevent distracted or inexperienced operator from initiating a bad close.Modern power plants typically utilize automatic synchronizers. Automatic synchronizers send pulses to the generator exciter and governor to change the voltage and frequency of the unit. The synchronizer will automatically close the breaker when it is within an allowable window.Substations on the transmission system have traditionally had synchroscopes installed. However, few substations are now manned due to the availability of powerful SCADA systems. Because of this development, newer substations may or may not have a synch panel, depending on the transmission company procedures. Since most circuit breaker operations are done remotely, transmission companies often rely on synch-check relays to supervise closing of breakers.Figure 4 illustrates a possible synchronizing system for substation breakers. Note the use of a synch scope and a synch-check relay. Electrical contacts can be opened or closed to rearrange the synchronizing system as desired.

Figure 4Synchronizing System for a Substation Breaker

Operations-Training-SolutionsThe focus of O-T-S is the development and delivery of training programs for electric power system operations personnel.

Southwest 2011 OutageThe Dynamics of Disturbances class has been updated to include a detailed description of the 9/8/2011 Southwest outage.

NERC Practice Tests

Surge Impedance Loading (SIL)The surge impedance loading or SIL of a transmission line is the MW loading of a transmission line at which a natural reactive power balance occurs. The following brief article will explain the concept of SIL.Transmission lines produce reactive power (Mvar) due to their natural capacitance. The amount of Mvar produced is dependent on the transmission line's capacitive reactance (XC) and the voltage (kV) at which the line is energized. In equation form the Mvar produced is:

Transmission lines also utilize reactive power to support their magnetic fields. The magnetic field strength is dependent on the magnitude of the current flow in the line and the line's natural inductive reactance (XL). It follows then that the amount of Mvar used by a transmission line is a function of the current flow and inductive reactance. In equation form the Mvar used by a transmission line is:

A transmission line's surge impedance loading or SIL is simply the MW loading (at a unity power factor) at which the line's Mvar usage is equal to the line's Mvar production. In equation form we can state that the SIL occurs when:

If we take the square root of both sides of the above equation and then substitute in the formulas for XL (=2pfL) and XC (=1/2pfC) we arrive at:

The term in the above equation is by definition the "surge impedance. The theoretical significance of the surge impedance is that if a purely resistive load that is equal to the surge impedance were connected to the end of a transmission line with no resistance, a voltage surge introduced to the sending end of the line would be absorbed completely at the receiving end. The voltage at the receiving end would have the same magnitude as the sending end voltage and would have a phase angle that is lagging with respect to the sending end by an amount equal to the time required to travel across the line from sending to receiving end. The concept of a surge impedance is more readily applied to telecommunication systems than to power systems. However, we can extend the concept to the power transferred across a transmission line. The surge impedance loading or SIL (in MW) is equal to the voltage squared (in kV) divided by the surge impedance (in ohms). In equation form:

.Note in this formula that the SIL is dependent only on the kV the line is energized at and the line's surge impedance. The line length is not a factor in the SIL or surge impedance calculations. Therefore the SIL is not a measure of a transmission line's power transfer capability as it does not take into account the line's length nor does it consider the strength of the local power system. The value of the SIL to a system operator is realizing that when a line is loaded above its SIL it acts like a shunt reactor - absorbing Mvar from the system - and when a line is loaded below its SIL it acts like a shunt capacitor - supplying Mvar to the system.Figure 1 is a graphic illustration of the concept of SIL. This particular line has a SIL of 450 MW. Therefore is the line is loaded to 450 MW (with no Mvar) flow, the Mvar produced by the line will exactly balance the Mvar used by the line.

Figure 1Surge Impedance Loading of a Transmission Loading.

Power Plant InfromationFriday, 10 January 2014Circuit Breaker Logic Circuit in Power plantCircuit Breaker Logic Circuit in Power Plant

Circuit breakers are geographically distributed in the power plant to control the power supply to busses or loads in power plant. So the circuit breakers need to be controlled from different locations in addition to the circuit breaker board. The circuit breaker should also operate for different protection according to their application. These requirements are full filled using control logic (Relay logic or PLC) for the circuit breaker which will initiate close or open signals to the circuit breaker. Circuit breaker is latching device i.e. if it is in a closed position it will be in that position until unless the open signal is applied to it. So the breaker consists of one closed coil and trip coil. A required current flow is needed through the close coil to close the circuit breaker and cause the breaker to latch the breaker. Once the breaker is closed the closing coil is de-energized by stopping the current flow. To trip (open) the circuit breaker, a flow of current is required through the trip coil. The plunger operated by the trip coil releases the latch and rapidly opens the breaker. Once the breaker is open, the trip coil is de-energized.

The logic circuit controls the flow of current to the closed coil and trip coil according to the logic conditions. Thus the logic has two paths 1) closed circuit path and 2) trip (open) circuit path.

Closed Circuit path

This path controls the flow of current to the closed coil according to the logic switches placed in the path. The figure shows the closed circuit path for energizing the 52 C close coil. The path consists of the following parts

Fuse part

A separate fuse is provided in closed path to ensure that if the fuse in closed circuit blows the breaker still has the tripping supply to open the breaker.

Breaker closing logic part

This contains the actual logic from the remote or local close of the circuit breaker. When the Push button from local or remote logic close is activated then it allows the current to flow through closing auxiliary relay (52 X). The auxiliary relay energizes main close coil 52 C. The reason for placing auxiliary relay is that for energizing the 52 C coil, it requires large current which the control circuit cannot tolerate.

Circuit Breaker closing mechanism

By energizing the 52C coil it activates the breaker closing mechanism. Once the breaker closes the Lb contact which is mechanically with the circuit breaker closing mechanism opens the contacts and supply to 52 X auxiliary relay to de-energize the 52C coil. This is to ensure that the absence of 52C close coil supply during tripping of circuit breaker.

Tripping circuit path

The tripping circuit path is separately fused with isolation from the closing circuit to ensure the reliability of tripping circuit. The tripping circuit has also three parts as same as closed circuit.

When the breaker is closed the LB contact in tripping circuit closed which is in series with trip logic circuit. In tripping logic in-addition to opening logic from remote and local, it also consists of protection logic. The protection logic activates the contact for the specified protections like over current, earth fault depending on the application. Once the any of the contact closes then the current flow will energizes the 52 T coil same as the closing coil. The tripping energizing operates the plunger and opens the circuit breaker rapidly. Posted byRaju Sat03:11Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest1 comment:1.

noddy dane25 March 2014 at 02:24Valuable information and excellent design you got here! for more details something like visit circuit breaker types get more informations.ReplyDeleteAdd commentLoad more...Older PostHomeSubscribe to:Post Comments (Atom)Popular Posts Generator synchronization procedures in the power plant What is synchronization and effects of poor synchronization in power plant Hydraulic Governor Functions and Limitations Circuit Breaker Logic Circuit in Power plant Types of Excitation Systems of Generator Ecitation System of Generator and Tasks of excitation system Load Frequency control in Thermal power plants RANKINE Cycle of a Power Plant Generator Transformer in power plant Types of Nuclear Power Plant

Blog Archive 2014(3) January(3) Circuit Breaker Logic Circuit in Power plant Generator Transformer in power plant REHEAT CYCLE of Power Plant 2013(22) September(2) August(20)

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Power Plant InfromationSunday, 11 August 2013What is synchronization and effects of poor synchronization in power plant

Synchronization of Turbo Alternator or an AC generator is the process of connecting the generator with grid power supply which is an interconnection of large pool of generators and power consumption loads. Simply the grid is parallel operation of some number generators with same frequency. So to connect the Generator in power plant in this pool of parallel running generators, The incoming generator parameters like frequency, phase angle and voltage should be matching with the existing grid frequency.

Before going detail description first let us understand what is the need of synchronization of generator. Generator is connected with the prime mover which provides the rotating magnetic field and hence this rotating magnetic field will induces the voltage in the stationary part. The frequency and phase angle of the voltage signal is controlled by the prime mover speed and magnitude of the voltage signal is controlled by the generator excitation.

To understand the phenomenon let us correlate the entire operation with the person wants to catch a running travel bus. Consider the travel bus is grid power supply and the person is incoming generator. Now if the person wants to get in to the bus then he should equally or little faster than the bus same the generator tries connect to the grid should run equally or little faster than the grid. Here the speed is measured with the frequency because speed is proportional to the frequency( 50 Hz, 60 Hz). The person is now running with the same speed of the bus but the bus door is one end of the bus and he is at another end of the bus so he needs to match with the door to get in to the bus. Like the same if the generator is running at the same frequency of grid it cannot be synchronized until unless the phase of the two voltages matches.

Effects of poor synchronization: Prime mover damages if the speed and rotor angle is not matches with grid voltage frequency and phase angle due to rapid acceleration or deceleration. Let us suppose generator has to connected to the grid frequency of 60 Hz. But the breaker has closed with poor synchronization at the generator frequency of 58Hz (i.e for two pole generator speed is 3480 out of 3600 rated), now once the breaker closes the generator is connected in the pool of parallel generators which forces the incoming generator to rotate at the same grid frequency. Due to this sudden acceleration of the rotor from 3480 to 3600 rpm and a sudden break at 3600 rpm damages the rotor mass. Same way in the reverse when the generator is running higher frequency than the grid frequency. A large currents may suddenly flow through the Generator windings and Generator transformer windings due to poor synchronizations which damages the windings. There will be power and voltage oscillations because of this sudden acceleration and deceleration of the rotor. It may leads to activation of the generator protective relays which causes the major interruption so the process should be started once again after clearing the protection. Posted byRaju Sat03:28Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest1 comment:1.

Deepraj Singh16 February 2014 at 01:42thankyou very much, i like your way of explanation.DeeprajReplyDeleteAdd commentLoad more...Newer PostOlder PostHomeSubscribe to:Post Comments (Atom)Popular Posts Generator synchronization procedures in the power plant What is synchronization and effects of poor synchronization in power plant Hydraulic Governor Functions and Limitations Circuit Breaker Logic Circuit in Power plant Types of Excitation Systems of Generator Ecitation System of Generator and Tasks of excitation system Load Frequency control in Thermal power plants RANKINE Cycle of a Power Plant Generator Transformer in power plant Types of Nuclear Power Plant

Blog Archive 2014(3) January(3) 2013(22) September(2) August(20) In-Phase Auto Bus Transfer Mode Fast Auto Bus Transfer Mode Bus Trasfer and Types of Bus Transfer Hydraulic Governor Functions and Limitations Types of Excitation Systems of Generator Ecitation System of Generator and Tasks of excitat... Types of Nuclear Power Plant What are Thermal Nuclear Reactors and Fast Nuclear... What is a Nuclear Energy and Nuclear Chain Reactio... Class I System in the Nuclear power plant RANKINE Cycle of a Power Plant Classfication of power plants or list of power pla... Effects of Grid Frequency distrubances on Nuclear ... Generator synchronization procedures in the power ... What is synchronization and effects of poor synchr... Electrical power system of nuclear power plant Thermal Power Plant Operation or Thermal Power Pla... Causes of Changes in Power Grid Frequency Load Frequency control in Thermal power plants Load frequency control in nuclear power plant

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Anonymous PosterGenerator Circuit Breaker 02/27/2009 7:06 AM

for one of our project we are using generator circuit breaker (GCB) instead of station transformer. GCB is inbetween Gen. Trf and Generator. So power (generator trf) trfr is back charged and feeds the Unit aux. tr at starting. Once the load picksup, GCB is opened and generator feed the UAT.At this stage, whether power flow will be in back to the genertor?what is the recative implication on genertor with this procedure?

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Bottom of FormInterested in this topic? By joining CR4 you can "subscribe" tothis discussion and receive notification when new comments are added. Join CR4, The Engineer's Place for News and Discussion!V.Ambarani.Associate

Join Date: Nov 2007Location: IndiaPosts: 41Good Answers: 3#1Re: generator transformer (power transformer) 02/27/2009 8:38 AM

Dear Sir,Please note that in this case GCB is being used as synchronisation breaker to synchronise external power source (say Switchyard bus) and the generator connected to bus through GSU-Generator step of up transformer.Hence GCB will be closed during synchronisation and not opened as stated.Further synchronisation will take place when unit-Generator is connected to external source.Till that time UAT will be fed from external source.Once synchronisation takesplace external source and generator get locked and Generatorwill feed UAT. No back power will flow.The reactive power willbe as per generator excitation control.V.Ambarani=====================================================================__________________Best Regards

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