Protection grading studies are simulated activities that examine the health of power system components under a variety of stress conditions. The simulations reveal responses of the real power system.
Should a fault occur in the power grid, the strategy is to detach part of the system where the fault occurs so that the rest of the system can continue to work stably and reliably.
The protective system is composed of the following components:
- Current and Voltage Transformers: These devices decrease the high voltage to lower levels.
- Protective Relays: They relays first detect a fault and put a trip into place to divert any high voltage to protect the equipment.
- Circuit Breakers: These are used to isolate parts of the system.
- Batteries: These supply power during an outage.
Although the protective systems are made of different parts, the focus of the studies are the protective relays, which need to be checked for dependability, selectivity, and speed of reaction.
Requirements of Protection Grading Studies
Protective grading studies require specific data to detail the components of the power grid, according to Electrical Engineering Portal. These needed include:
- Single-line diagram of the power system involved, showing the type and rating of the protection devices and their associated current transformers.
- The impedances in ohms, per cent or per unit, of all power transformers, rotating machine and feeder circuits.
- The maximum and minimum values of short circuit currents that are expected to flow through each protection device.
- The maximum load current through protection devices.
- The starting current requirements of motors and the starting and locked rotor/stalling times of induction motors.
- The transformer inrush, thermal withstand, and damage characteristics.
- Decrement curves showing the rate of decay of the fault current supplied by the generators.
- Performance curves of the current transformers.
Once all of these details have been gathered, then the protection grading studies can take place.
Relays: The Vital Facet in Protection Grading Studies
Of all the components in your system, relays play the most important role. Relay co-ordination follows two basic and logical rules:
- Relays with the same characteristics need to be used in series.
- Relays that are the longest distance from the source must have settings that are equal to or less than relays in line closer to the source.
Relays can be coordinated by time, overcurrent or a combination of time and overcurrent with the aim that the setup will isolate only the section of the grid where the fault occurs while the rest of the grid operates normally.
- With time as the determining factor, it is necessary that the breaker with the fault opens first. The disadvantage of this system is that if the fault is close to the source, then the fault level is the highest.
- With current as the discriminating factor, there is an impedance value difference between the source and the fault. However, the impedance value must be discernable between the two circuit breakers. If the impedance is minimal, then a fault would not be detected.
- However, discrimination by both time and current can overcome the disadvantage of the previous two methods. In this method, time of operation is inversely related to the current level with the result that the weaknesses of the other two systems are overcome. Time grading is when the relay closest to the fault trips before any other relay.
Further technical procedures analyze more characteristics for relays, ring mains, and earth fault protection in protection grading studies. Each process details the different situations for any fault in the electrical grid to isolate the problem so that sections of the grid will continue to operate safely and efficiently.
Why are Protection Grading Studies Necessary?
Protection grading studies are a critical component of maintaining your power grid system. With this analysis, you will be able to determine problem areas before the issue shuts down your entire system. Also, you will have strategies and safeguards to put into place if an interruption occurs.
Running protection grading studies are a preventative measure and worthwhile investment that will save your company losses in revenue, time and reputation. It will also protect your workers from electrical hazards. Business interruptions will be non-existent or kept to a minimum.
Locating a qualified firm for Protection Grading Studies
Several vital factors define an expert firm to meet your needs to protect the health of your power grid.
- Depth and quality of experience in performing protection grading studies
- Ability to document the results of the process
- Proximity to your location
- State-of-the-art inspection and test equipment
- Adherence to government regulations
- An impressive list of partners
- Glowing customer reviews
- Case studies for previewing
A thorough investigation of expert firms will illuminate the most suitable firm to perform protection and maintenance services for your situation. If you are looking for a company that can conduct protection grading studies for your power system, Present Group can help you.
Send us a message today to find out the scope of our services.