TRV-appnotes.doc

Single line bus fed Transient Recovery Voltage (TRV) Studies.This example case is based on IEEE PES Special Publication “Modeling and Analysis of System Transients”, chapter 4: Modeling Guidelines for Switching Transients section 3.4 Single line bus fed transient recovery voltage (TRV). The aim is to find the transient recovery voltage (TRV) across a receiving end circuit breaker after clearing a fault.The single line view of the PSCAD model of this network is shown below. All system data comes from the above mentioned IEEE Special Publication 1.Fig. 1 Single line view of the networkA three phase to ground fault is applied to a simple system equivalent which represents a short line that is faulted at the remote end, with roughly 7 unfaulted long lines connected. TRV is measured across the breaker as shown. The TRV across the first pole to open of a circuit breaker against the appropriate TRV capability envelops is used to exam if the breaker can withstand the TRV stress. System Representation:The network equivalent is represented as a voltage source with 138kv magnitude and R/L of 51.57ohm / 7.04mH. The inductance value is obtained from the short circuit current of 30kA at the bus. The parallel resistance is the combined surge impedance of the 7 unfaulted lines, which are simplified as a reflectionless lumped capacitance of 10000pF. The 40km short line is represented as the frequency dependent phase domain model, and the chukar line conductor is used which has slightly higher surge impedance than the published line of 360ohms. In the studies of TRVs, it is important to proper represent the stray capacitances of the elements on the system. In general, only inductance and capacitance are needed; resistance can be neglected. Accurate information on the inductance of apparatus is given by the manufacturer. The effective value of capacitance is the lumped value at the terminals that is equivalent to the distributed capacitance of the apparatus in the frequency range of the recovery voltage. In many cases, there may not be an opportunity to measure the effective capacitance of the equipment to be used. In these cases, Table B.1 through Table B.9 of C37.011-2005 may be used for estimated values. In this example case, 600pF, which is typical for a small substation is represented at the station at the end of the line. TRV Capability Envelop Representation:For a 138 kV substation, the available fault current at the main bus is 30kA. The fault current at the short line end is about 3.7kA which is about 10-30% of short circuit level. According to IEEE C37.011-2005, two parameters TRV envelop T30 (if fault current is in 10 to 30% of short circuit level) or T10 (if fault current less than 10% of short circuit level) will be used. Parameter selection will be based on IEEE C37.04-2006 andC37.06-2004. Fig2 shows how the two parameters envelop are generated. For T30 envelop, Rate of Rise of 5kV/us and Peak Voltage of 243kV are used, while for T10 envelop, Rate of Rise of 7kV/us and Peak Voltage of 271kV are used.Fig.2 TRV envelop for T30 and T10Simulation Methodology: In order to find worst saturation of TRV, point on wave fault inception is applied by using Multiple Run component. A snapshot is taken at 0.99s when the system reaches steady-state. Twenty-one numbers of point on wave fault are applied in one cycle at 1s to 1.016667s with 0.000833s increment. The last run of 22nd run repeats the worst TRV. At each simulation, the fault lasts 3 cycles (0.05s), and is then cleared by the corresponding breaker. The TRV waveforms of the first open-pole contact are plotted against the rated breaker TRV capability envelope. First the Multiple Run component is disabled and the snapshot is taken by run the simulation over 1second. Then enable the Multiple Run component, change the duration of simulation run to 0.15s to speed up the simulation and run the simulation from snapshot. Fig. 3 shows how to find the first open pole by finding the first “1” breaker state from phase A, B and C breaker state. Fig. 3 also show how to use Multiple Run component to generate different fault time “timef” and then breaker clearing time “timeb”. These two signals will be used to control the Timed Fault Logic and Timed Breaker Logic blocks in the system shown in Fig. 1. Maximum TRV will be recorded as “Etrv” for each run. The output file TRV.out will summarize the run results.Fig.3 Multiple run fault time generationSimulation Results: The Multiple run output file Fig.4 TRV.out shows the worst TRV will happen at #19 run, in which fault is applied at 1.014994s and the first pole to open is phase C when current cross zero at 1.065051s, which can be found from zoomed fault current waveform. The worst TRV is 230.65999KV. This run is repeated at last run of #22.Fig. 5 shows the TRV waveform against T30 envelop. Etrv is the measured TRV across the breaker, Vs is the system voltage, envT30 and envT302 are the T30 TRV envelop, If is the fault current. Fig. 6 shows the zoomed waveform of Fig. 5 around first pole open. From the result, we can see the worst TRV doesnt exceed the breaker TRV capability. Time reaches to maximum magnitude is 275us and the rate of rise of recovery voltage RRRV = 230.66kV / 275us = 0.839 kV/us.Fig.4 Multiple run outputFig. 5 the TRV waveform against T30 envelop and fault currentFig. 6 the zoomed waveform of Fig. 5 around Reference: 1. IEEE PES Special Publication TP-133-0 “Modeling and Analysis of System Transients Using Digital Program ”2. C37.04-2006 “IEEE Standard for Rating Structure for AC High-Voltage Circuit