The purpose of the project is to design and implement a load reduction and load recovery plan for the electricity system. Underfrequency load shedding is more popular compared to undervoltage due to its efficiency and robustness. Frequency-time curve for load recovery service (I st step) Loss of 12.5% generation without load shedding.
Problem Statement
An underfrequency load shedding scheme did exist to restore system generation load balance under severe generation loss contingencies. It stands to reason that if an effective and efficient load shedding system existed, sufficient load could have been removed when the BGlli feeder first tripped. Consequently, this project will be directed towards the development of an effective and capable load shedding system in electric power systems to prevent recurrence of similar incident.
Objectives and Scope of Study Objectives
The area and scope of this project has been carefully planned, so the project is feasible and can be completed within the allotted time frame. A project plan (methodology) and Gantt chart were developed to guide the progress of the project.
LITERATURE REVIEW
- Load shedding- Definition and purpose
- Load recovery
- Underfrequency Load Shedding
- Undervoltage load shedding
Error upon errors, e.g. automatic load shedding, must not ensure the simultaneous shutdown of two power supply units due to failure. Therefore, the total amount of load to be removed should not exceed the capacity of the largest power supply unit. The characteristics and locations of the loads to be removed are more important for voltage problems than for frequency problems.
METHODOLOGY
Procedure Identification
Breakdown of tasks for first semester
A planned underfrequency load shedding scheme is presented using Visual Basic 6.0 in a snap-and-do manner. A one-line diagram of the power system is displayed (as shown in Figure 3, page 33). At this moment, the corresponding circuit breakers in the one-line diagram change color, indicating that the circuit breakers have tripped.
Tools
LOAD SHEDDING AND RESTORATION
Why underfrequency?
- Limitations of undervoltage load shedding
- Strengths of underfrequency load shedding
- Load shedding
Due to its effectiveness and efficiency, underfrequency discharge is widely used in w or. This project will work towards developing an effective under frequency load shedding scheme and add necessary improvements to improve the existing schemes. When there is an overload or a loss in production, there is not enough mechanical power input to the system; the rotor slows down and supplies power to the system.
These regulators adjust the mechanical power input of the generating units to maintain normal frequency operation. For gradual load increases or sudden but mild overloads, the unit controllers will detect the change in speed and increase the generator power input. The additional load is handled by spinning in reverse, the unused capacity of all generators operating and synchronized with the system.
Such an arrangement is called an under-frequency load shedding scheme and is designed to maintain system integrity and minimize shutdowns. Because the amount of overload cannot be easily measured at the time of a disturbance, the load is shed block by block until the frequency stabilizes. If this load drop is not sufficient, the frequency will stabilize or even stabilize again, but at a slower rate.
This process will continue until the overload is relieved or all frequency relays operate.
Design considerations
- Definition of important parameters Inertia constant, H
- Maximum anticipated overload
- Number ofload shedding steps
- Size of the load shed at each step
- Frequency settings
The system should be studied with respect to the overload that would result from the unexpected loss of key generating units, transmission belts and buses. The load reduction factor, d must be taken into account as this will reduce the overload once the frequency has dropped. The higher-set relay will trip first, which stops the frequency decrease as long as the overload is half or less of the worst case value.
For more severe overloads, the frequency will continue to drop, albeit at a slower rate, until the second group of relays is activated to shed the other half of the expandable load. The number of load shedding steps can be increased practically without limit with a large number of steps, the system can shed load in small increments until the decrease stops. Most utilities use between two and five load shedding steps, with three being the most common.
When a study of the system configuration reveals that there is a relatively high probability of loss of certain generation units or transmission lines, load relief blocks should be sized accordingly. Each step must be evenly distributed throughout the system by dropping loads at different locations. The frequency at which the stage relieves the load depends on the normal operating frequency range of the system, the operating speed and accuracy of the frequency relays, and the number of stages of relief.
The frequency of the first step should be just below the normal operating frequency band of the system, which allows the relay tripping frequency to be varied.
Load recovery .1 Definition
- Important considerations
If there is a significant loss of generation in a concentrated area of the system, transmission lines to that area may be heavily stressed just to supply essential loads. If frequency relays are used for automatic recovery, as they sometimes are in unattended installations, they should have a frequency setting of the normal system frequency. The load should be restored in blocks of 1% to 2% of the system load and the restoration should be sequential with a time delay.
After the initial system recovery to the normal system frequency, there should be a delay of 30 seconds to several minutes, which is done automatically by a timer or manually by a timer or manually by a supervisory control. The first load block can then be restored; the frequency will decrease and return to the normal system frequency. The frequency will reset to the normal system frequency and the third block will expire and close again.
When restoring cold loads, it is necessary to temporarily disable the instantaneous overcurrent fault protection to prevent the initial current generation from tripping the supply again.
CASE STUDY ON PETRONAS PENAPISAN MELAKA
- Introduction to Cogeneration Plant Power generation
- Design strategy
- Design and calculations
- Load shedding priorities
- Load restoration service
To ensure that the generators are not shut down before the load shedding system takes effect, the maximum generation loss designed by the scheme is 50% or 48 MW at the system peak. The reserve I This leaves some margin for the system to recover after the final phase of load shedding.
Underfrequency load shedding can be performed based on frequency or rate of frequency decrease. For a small system like the power generation plant, this type of load shedding scheme tends to be unstable and unreliable. Those units which are mandatory to ensure the safe operation of the plant are not included in the load shedding scheme.
In this load shedding design, five load categories are defined namely non-essential, essential, crucial, very crucial and mandatory. Finally, the most critical units that could not be closed in the load shedding system fall into the mandatory category. In verifying the designed load shedding scheme, a stability study is first performed to see the system frequency decay when generation is lost, without any load shedding.
This data is then used in the stability study program to calculate the system frequency versus time curve with the proposed load shedding. In this section, the dynamic simulation results of the first two steps of the designed load shedding scheme are presented. The dynamic simulation results have shown that the designed load shedding scheme is feasible as it can prevent system collapse due to generation loss and restore normal frequency after load shedding.
CONCLUSION AND RECOMENDATIONS
Project work is followed by performing dynamic simulations on the designed system using ERACS Power Analysis Software fulfilling the third project objective which is to verify load shedding design via dynamic simulations. The main objective is to measure the performance of the proposed scheme with due consideration of power plant and network protection/control and system voltages. Transient lability studies are run and it is clear that the system frequency drops when generation is lost without any load shedding.
Immediately after switching on load shedding, the system frequency stops decaying and the normal frequency is restored. This result applies to four case studies, which lose 12.5% and 25% of generation with and without load shedding. The validity of the proposed relay scheme and settings is confirmed as sufficient load is shed quickly enough to prevent system collapse during generation loss.
The process of designing the load shedding scheme has not only taught the author the basics of project development and improvement, but also given the understanding of the importance and importance of load shedding schemes in power systems. Given that the duration of the project is only about 38 weeks, there is certainly a lot of room for improvement. Software that is able to simulate load shedding based on frequency settings allows users to see the actual time a frequency level is reached and manipulate other settings accordingly to increase the effectiveness of the load shedding scheme . iii) Develop the wired prototype of the project using PIC16F84 microcontroller.
This wired prototype can present the load shedding scheme more effectively and makes it more interesting and understandable. iv) Other recommendations include in-depth research on slow coherence theory and improving the adaptive feature, designing the restoration procedure to complete self-healing, and applying the algorithm to a large system scale.
APPENDICES
National Grid
CONNECTIVITY FOR FEBRUARY, 2003
I APMC I
Submission of Progress Report Drafting of simple load shedding scheme Preparation and compilation of interim report. 8 Project Dissertation Submission daft 9 Project Dissertation Final Changes 10 Preparation for Oral Presentation 11 Project Dissertation Submission.
Detail load shedding calculations
11P: Retarding power in unit kV connected A. itrip = trip + tbreaker + trele. tbr·eaker : Breaker opening time. tbreaker = 1 OOms for Merin Gerin Fluarc FG breaker 2) tral: Relay internal pickup time. Therefore, in 0.260 sec after the fault is detected, 12.5% of the load is disconnected from the system and the system frequency in that case is 48.82 Hz. Thus, in 0.173 sec after removing 25% of the total load, an additional 12.5% of the load is disconnected from the system, making the total load removed equal to 37.5%.
