Integration of Variable Renewable Energy

Transcription

1 Integration of Variable Renewable Energy PRAMOD JAIN, Ph.D. Consultant, USAID Power the Future October 1, 2018 Almaty, Republic of Kazakhstan Venue: Almaty University of Power Engineering and Telecommunications (AUPET) 7/6/2018

2 Agenda Transient stability analysis Dynamic stability analysis 2

3 Power System Stability In general, it is the ability of power system to stay in synchronism following a fault Transient Stability Analysis: Study of behavior of grid when subjected to large disturbances Dynamic Stability Analysis: Study of behavior of grid when subjected to small disturbances Stricter definition of stability: Ability of power system to stay in synchronism without change of topology following a fault 10/2/2018 IWE 3

4 Transient Analysis 10/2/2018 IWE 4

5 Transient Analysis Disturbances occur constantly in a power system Power systems possess inertia to absorb the shock of a disturbance Generators have variety of control systems to respond to voltage and frequency changes Automated Voltage Regulation (AVR) and Governor Transient analysis provides an understanding of how inertia, AVR, governor and other components act in response to disturbance The results are used to determine critical clearing time of protection systems 10/2/2018 IWE 5

6 Scenarios for Transient Analysis Two additional conditions: Each scenario above is studied for two types of clearing of fault: Clearing (after 9 cycles, which is 180ms) and no clearing Partial Generation loss at different buses Generation loss of wind turbine High Wind High Load High Wind Low Load No Wind High Load No Wind Low Load X X X X X Partial load loss at buses X X X X Bus fault X X X X Transmission line fault X X X X X 10/2/2018 IWE 6

7 Result Variables Voltages Generator terminal, bus Frequency Bus Active Power Generator, Transmission line Reactive Power Generator, Transmission line Rotor angle Generator 10/2/2018 IWE 7

8 Control systems for stability analysis Inertial response. Covers milliseconds to a few seconds response of synchronous generators. Governor response. Part of the primary response with duration of 1/10 second to tens of seconds Automated Voltage Regulator (AVR) response. Ensures that the output voltage of the generator is close to the reference voltage. Power System Stabilizer (PSS) response. The primary function of electronic PSS is to damp rotor angle swings that have a frequency in the range 0.1 to 3 Hz. 8a

9 Process Setup study-cases in DPF Attach AVR, Governors and other control models of Gens Pick Variables to Track Define Events Related to Disturbances Iterate Until All Parameters are in Range Analyze Results Run Dynamic Stability Analysis Create Plots for Voltage, Frequency, Rotor Angle, Active Power 9

10 Examples of Power System Stability Study Recommendations Issues Frequency dip/rise that is outside the limit specified in the Grid Code due to lack of load following capacity to host the proposed WPPs or SPPs Potential Mitigating Measures This is likely to occur during transient events due to lower grid inertia. Lower grid inertia occurs because the percentage of conventional generators with inertia in the generation mix is too weak for the proposed WPPs or SPPs,. Possible solutions are: 1. Scheduling additional generators, if available, to increase inertia. For example, if 3 gas generators are dispatched at 90% capacity factor and the system inertia is low, then dispatching 4 generators at about 70% capacity factor would increase inertia. 2. Replacement of an existing lower inertia generator with a higher inertia generator. 3. Install fast responsive units to inject active and/or reactive power into the grid to arrest the rapid drop in frequency. 4. Require VRE to activate frequency response capacity in excess of standard grid parameters. 10

11 Examples of Power System Stability Study Recommendations Issues Instability due to instantaneous loss of WPP or SPP Potential Mitigating Measures Two cases: (i) sizes of all the WPPs and SPPs are less than the largest conventional generation, and (ii) size of one of the WPPs or SPPs is larger than the largest conventional generation in the grid. In the first case, instability may be caused because of low grid inertia and low headroom. If grid inertia is low then the rate of change of frequency is higher, which may lead to unacceptably lower frequency nadir causing instability. If there is insufficient headroom then the governor response (which is additional power provided by the generators) is limited, which leads to lower frequency nadir and slower recovery of frequency. The resolution may include: 1. Increase grid inertia, see solutions in item 1 of this table. 2. Dispatch generators with higher amount of headroom. In the second case, the solutions mentioned above should be tried first, and if that fails, then consider lowering the capacity of the largest proposed WPP or SPP. 11

12 Examples of Power System Stability Study Recommendations Issues Large rotor angle oscillations and loss of synchronicity Potential Mitigating Measures Large rotor angle oscillations can occur when the disturbance is too large, grid inertia is too low, or there are sections of the grid that are weak. If the disturbance caused by loss of WPP or SPP is too large, the solutions described earlier in this table may be considered. If inertia is too low, then the solutions are the same as those presented in item 1 of this table. If the grid is weak, then rotor angle oscillations will start with generators in the weakest part of the grid and then spread to all other generators. In this case, strengthening of the gridwould be the solution. 12

13 Examples of Power System Stability Study Recommendations Issues Undamped oscillations of frequency and voltage Potential Mitigating Measures This is likely to occur due to frequency stability issues, low grid inertia and control algorithm issues. If the oscillations are out-of-phase, see the next row. Otherwise, if the oscillations are primarily in phases, then increasing grid inertia or adding Power System Stabilizer (PSS) controls may resolve the issue. Out-of-phase oscillations of frequency This instability may be caused by a combination of governors that compete to find a stable solution. In this case tuning of parameters of one or more governors of the generators involved in the oscillations may remove the instability. 13

14 Photo: Trend.Az USAID Regional Program Power the Future Pramod Jain President, Innovative Wind Energy, Inc. Power the Future 6, Sar y Arka Ave, Office 1430 Astana, Kazakhstan DISCLAIMER This product is made possible by the support of the American People through the United States Agency for International Development (USAID). The contents of this presentation are the sole responsibility of Tetra Tech ES, Inc. and do not necessarily reflect the views of USAID or the United States Government. 10/2/