System Protection Schemes in Eastern Denmark Joana Rasmussen COWI A/S, Energy Department
System Protection Schemes in Eastern Denmark 1.Advanced system protection schemes are investigated and perspectives are discussed 2.Synchronized phasor measurements are utilized in Eastern Denmark for disturbance monitoring 3.A new concept for power system protection against voltage instability is developed for Eastern Denmark.
Fundamentals of System Protection Schemes System Protection Schemes aim to counteract power system instability and preserve the system capability. Input: Detect abnormal system conditions Output: Determine control action Disturbance Electrical variables Direct detection Power system Input Decision process Action
Perspectives of System Protection Schemes in Denmark Improved utilization of the transmission system: Increase the transfer capacity by operating the power system closer to its operational limits Restrain the investments in grid reinforcement and operate the system in the most efficient and economical manner Increased power system security: Avoid extreme disturbances and counteract system instability. Phasor measurements in power system control: Phasor Measurement Units (PMUs) give more precise information about the actual state of the power system than the existing SCADA. The combination of SCADA and PMU measurements can be used for more accurate system monitoring and utilized in different control concepts, where time synchronization of the recordings and angle information are considered crucial.
Wide-area monitoring and control Phasor Measurement Units based on GPS clocks enable real-time monitoring of synchronized phasor measurements. WAMS consists of several PMUs that communicate with a control center. GPS PMU ASV400 PMU HVE400 GPS Data concentrator Data analysis System monitoring (database archive) System control System protection GPS PMU RAD132 PMU HVE132 GPS
Synchronized phasor measurements A phasor is a vector representations of an AC signal. By synchronizing the sampling processes for different remote signals-it is possible to put the phasors in the same diagram. The most promising feature is to utilize PMUs as angle comparators. A A φ φ U = A sin (2 π 50 t + φ) = A e jφ
Phasor Measurement Unit The Phasor Measurement Unit utilizes the GPS clock to provide timing signal to synchronize sampling of the measured input signal. Phasor values are computed with regards to the global reference GPS Modem Analog. input: U,I Filter A/D converter Micro processor
Transmission system of Eastern DK North: Strong system Middle Middle-strong system South Weak system
Why system protection schemes? The major part of wind turbines are connected to a weak part of the transmission system. The weak system has limited reactive power control capability due to the large distance to the main power plants. The power system of Eastern Denmark is prone to voltage (and transient) stability problems related to the increasing amount of wind generation. Voltage stability and thermal capacity constraints related to large wind farms call for dedicated system protection schemes, dynamic compensation of reactive power and enhanced monitoring of the power system
Concept of system protection against voltage instability
Benefits of SPS in Eastern Denmark 1. It is feasible to design a simple, robust and inexpensive SPS in order to counteract voltage instability in the weak transmission system ( large distance to power plants and limited reactive power control capability). 2. The SPS detects violation of V.S. limits and critical impact of wind power and line outages in the Radsted corridor using reactive and active power flow (phase angle) and low voltage indicators. 3. Emergency control in case of impeding voltage instability is seen in wind power reduction and improved local reactive power control (SVC and generator units).
Dynamic impact of wind farms in Eastern Denmark Voltage at RAD132 with/without control 160 120 V (kv) 80 40 0 0 1 2 3 4 Time (s) V_RAD' V_RADgenerel' V_RADstvmav' 'V_RADswshn' V_RAD_SVCmax' The best voltage recovery at Radsted after busbar fault is observed when SVC and wind turbine rejection is applied.
Phasor Measurements in Eastern DK 1. PMU implementation in Eastern Denmark 2. Event identification Case 1: Wind power rejection Case 2: Power oscillation monitoring 3. Benefits of phasor measurements Disturbance monitoring Warning for impeding instability Enhanced state estimation
180 Wind power rejection Production at Nysted wind farm 08.jan05 AngleRAD-HVE132 08jan05 14 160 Prds-rad (MW) 140 120 100 80 60 40 20 0 AngRAD-HVE(deg) 12 10 8 6 4-20 13:0013:0513:1013:1513:2013:25 13:3013:3513:4013:4513:5013:55 14:00 Time (h) 2 13:0013:0513:1013:1513:2013:25 13:3013:3513:4013:4513:5013:55 14:00 Time (h) PMU analysis, Nysted 08/03/2005
Wind power rejection 139 Voltage at RAD132 08.January 2005 13:00-14:00h 40 Reactive power ORH-RAD 08jan.05 138 35 137 30 Voltage (kv) 136 135 134 133 132 131 Qorh-rad (MVAr) 25 20 15 10 5 130 13:0013:0513:1013:1513:2013:25 13:3013:3513:4013:4513:5013:55 14:00 Time 0 13:00 13:05 13:10 13:15 13:20 13:25 13:30 13:35 13:40 13:45 13:50 13:55 14:00 Time (h) PMU analysis, Nysted 08/03/2005
PMU monitoring of Nordic oscillation modes Oscillation mode of approx. 0.7 Hz: Eastern Denmark against Sweden Oscillation mode of approx. 0.4 Hz: Denmark& Norway against Finland Nordic oscillation modes are identified from synchronized phasors of angles and power flows.
Power oscillation monitoring Phase angle SAN-ASV (deg) 3 2,5 Measured phase angle difference between SAN & ASV Phase angle (deg) 1 0,5 measured angle 2 0 1,5 1-0,5 simulated angle 0,5-1 0 0-0,5 50 100 150 200 250 300 350 400-1 -1,5-2 Time (s) -1,5-2 320 330 340 350 360 370 380 390 400 410 420 Time (s) The relative phase angle can be used to detect power oscillations in the early stage.
Power oscillation monitoring P (MW) 200 195 190 185 180 175 170 165 160 155 150 Measured active power in 132 kv tieline 0 50 100 150 200 250 300 350 400 Time (s) Active power (MW) 180 175 170 165 160 155 measured power simulated power 320 330 340 350 360 370 380 390 400 410 420 Time (s) The time-domain simulations are verified by phasor measurements.
Improved monitoring by phasor measurements Synchronized phasor measurements can be used as an efficient tool both in disturbance analysis and in on-line warning of abnormal changes in phase angles, frequency etc. in due time. The case with wind power rejection underlines the close relation between voltages, power flows and phase angles over a wide area. The phase angle information is a supplement to traditional voltage and power flow measurements in a transmission system. Nordic power oscillation modes have been identified from synchronized phasor recordings of angles and power flows. The PMU recordings are successfully applied in verification of the power system simulations.