1 System Protection Schemes in Eastern Denmark Joana Rasmussen COWI A/S, Energy Department
2 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.
3 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
4 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.
5 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
6 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
7 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
8 Transmission system of Eastern DK North: Strong system Middle Middle-strong system South Weak system
9 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
10 Concept of system protection against voltage instability
11 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).
12 Dynamic impact of wind farms in Eastern Denmark Voltage at RAD132 with/without control V (kv) 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.
13 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
14 180 Wind power rejection Production at Nysted wind farm 08.jan05 AngleRAD-HVE132 08jan Prds-rad (MW) AngRAD-HVE(deg) :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
15 Wind power rejection 139 Voltage at RAD January :00-14:00h 40 Reactive power ORH-RAD 08jan Voltage (kv) Qorh-rad (MVAr) :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
16 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.
17 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, , ,5-2 Time (s) -1, Time (s) The relative phase angle can be used to detect power oscillations in the early stage.
18 Power oscillation monitoring P (MW) Measured active power in 132 kv tieline Time (s) Active power (MW) measured power simulated power Time (s) The time-domain simulations are verified by phasor measurements.
19 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.