Discuss About The Earth Fault Relay Explained Elaborately?

Berserker Substation and Its Component Design

Question:

Discuss About The Earth Fault Relay Explained Elaborately?

The substation’s main purpose is to obtain power from the high voltage source that is from the power stations. In this scenario, the Berserker Substation is focussed.

This report will highlight the equipment, design associated and also the redundancy and the protection relay will be showcased.

The Berserker Substation is constructed along with the equipment incorporated keeping in mind the following advantages it can provide-

• The primary objective of the substation is to acquire the power which flows at a high voltage from the stations where power is generated [2].
• Gas Insulated Switchgear (GIS) technology reduces substation accommodation to seventy per cent.
• Switchgear which involves the circuit breakers and these circuit breakers are responsible for intervening the short-circuit current generated from the power stations.
• Surge arresters to safeguard the switchgear from over voltages happened due to lighting thus regulates the normal current flow [1].
• Substation automation to protect, secure and control the electrical components.
• The construction work must be comparatively simpler and cheaper and must be flexible for an extension if required.

The Berserker Substation along with its component design has been highlighted in this report (Refer to Appendix A). The major function of the substation is to acquire the power which flows at a high voltage from the stations where power is generated [3]. Synchronous condensers are installed within the substations to enhance the power factor and giving facilities to administer and monitor different parts of the power system.

The substations can be elaborated according to the service prerequisites and design features. The service pre requisites include converting substations, transformer substations and switching substations.

Transformer substations: These transformer substations are responsible for converting power from one voltage level to other. They can be further elaborated into distribution substations, step-up substations, secondary substations and primary grid sub stations [6]. The step-up substations generate about 11kV and that needs to be stepped up to the primary transmission voltage level of 220kV. The primary business stations are situated at the transmission lines' end and the primary voltage here drops down to secondary voltages of 66kV. The distribution sub stations are situated immediately to the consumer localities to distribute the power of 400V, three phases or single phase to the users.

Switching substations: The switching substations generally switch the workings of power lines without converting the voltage. Various connections are generated in between the transmission lines.

Converting substation: The converting substation is responsible for transforming AC to DC or vice versa [4].

Isolator- When the current supply is interrupted, the isolator either makes connections or disconnects the circuit; the isolator is basically used to break the charging current of the transmission line.

Lightning arrester- This component is used to protect the entire substation from the lighting fallout.

CT Metering- This equipment basically measures and keep track of the current usage at the time when the secondary terminal [7].

Step down transformer- this device is used to convert the range of voltage current from high to low.

Types of Substations and Their Functions

Capacitor Bank- This device is generally used to enhance the power factor of the transmission line; it basically involves the series connection of the capacitor or else the parallel connection of the capacitor.

Circuit Breaker- It basically restricts the excess flow of current.

The substation requires proper earthing as it ensures that no potential threats occur in the substation, so while designing a substation three voltage must be kept in mind, they are- mesh voltage, touch voltage and step voltage [2].

There are four varieties that guarantee the securities of current supply –

1. No modification is required for the maintenance of the substation
2. Little modification is required to relocate the load to the alternate circuit.

1. Loss of substation as a whole due to lack of maintenance.
2. Various Layouts

There are various layouts for the substations, one is single busbar, and the other one is mesh substation, one and a half circuit breaker layout.

To diminish the power interruption, power grids are rapidly increasing day by day retrofitting substation system [1]. The retrofitting applications can be executed by the following two structures- centralised system architecture and decentralised system architecture.

Decentralised management architecture mainly involves system redundancy and this redundancy can be achieved by multiple computer systems, where each computer system executes only one operating system and one application at a time. That means only one application and one operating system can be deployed in the physical server at a time.

Centralised management architecture involves the deployment of multiple operating systems and multiple applications on a single physical structure. Here the server provides the virtualisation facility, here multiple operating system and multiple applications can be executed, so applications need not be isolated, also there is no chance of compatibility issue [4]. Secondly, the life of the legacy software applications can be prolonged or extended by Centralised management architecture.

The legacy power substation is upgraded with IEDs and then those IEDs are integrated with the substation. The task is not simple and can only be accomplished by effective management-system redundancy [6]. Retrofitting of the power substations can be achieved by the method.

Protection relays are responsible to detect the abnormal behaviours within the system, to check the faults within the system and directs more than one circuit breaker to explore and separate the faulty equipment and systems.

Circuit breakers fail relay is responsible to connect electric equipment and circuits in an efficient way. They are opened or closed based on the command, they are basically opened to suspend or clear any fault within and they have been designed in such a way that it can make a minimal impact on the power system [3].

Importance of Proper Earthing in Substations

Multifunction relay is combined with the primary control system by configuring few input and output points to work in between the controller and relay. This relay helps in real time monitoring of the power system and detects the faults within the Power system. The faults are detected basically on the monitoring of the system and monitoring involves the couple channel monitoring, monitoring of speed, monitoring of light curtain and extension of the relay to enhance the number of output contacts.

Neutral earth fault relay is responsible to detect the ground faults and it immediately interrupts the circuit based on the detection of ground faults. Thus the substation’s ground faults can be minimised [5].

Sensitive Earth fault relay also checks the earth fault or the ground fault within. It is basically used in the substation when the earth fault is set to significantly low value.

Capacitor Bank consists of the three element s- unit fuse, element fuse and bank protection and this is also used to detect and mitigate the internal and external faults.

Bus Differential relay in the substation is basically implemented to detect any faults on the busbar. It takes a huge lot of time to detect the fault and this bus-bar protection involves Kirchoff's current law [5].

Transformer Oil and Winding Trip relay are used to identify the temperature instantaneous temperature of the oil and windings, this can also detect the maximal rise of temperature of both oil and windings. These temperature indicators help to regulate the temperature of the substation.

Overcurrent Relay provides the earth fault protection. The Earth-fault Relay is utilised to secure the feeder opposing the faults which are correlated with the ground. The earth faults range from single line to ground whereas the double line ranges from double line to ground faults [8]. Here the single line to ground faults has been shown in the following diagram for the requirements of setting and coordination. The maximum financial current for the a-g fault can be provided by-

Accordingly, it can be inferred that there can be notable variety in the earth fault current values. They can be even beneath the load current because of large impedance to ground. Consequently, to give protection, earth fault relays utilize zero sequence current across phase current for fault recognition [8]. The zero sequence segments are missing in load current or phase faults.

                                                         Fig 2: Simple Radial Distribution System

                                                                               (Source: [8]

                                                               Fig 3: Phase and Earth Fault Relay Configuration

                                                                                             (Source: [8])

                                                                          Fig 4: Earth Fault Relay Coordination

                                                                                        (Source: [8])

Relay R₁ is responsible for giving protection to the earth fault at secondary side of 2.5MVA, 11/3.3kV transformer; R₂ is responsible for giving protection at bus B. There are 2 CTs, one CT that is 200:5, is linked to instantaneous relay while the other one 500:5 is linked to inverse current relay.

Conclusion

It can be concluded from the above discourse that the redundancy is beneficial for restricting power interruption and regulates normal flow of current whereas the protection relay is beneficial for securing the feeder and reducing the fault. The Earth-fault protection along with relay coordination for the earth-fault relay has been detailed.

References

[1] Zeynal, Hossein, Mostafa Eidiani, and Dariush Yazdanpanah. "Intelligent substation automation systems for robust operation of smart grids." In Innovative Smart Grid Technologies-Asia (ISGT Asia), 2014 IEEE, pp. 786-790. IEEE, 2014.

[2] Mainali, Krishna, Awneesh Tripathi, Sachin Madhusoodhanan, Arun Kadavelugu, Dhaval Patel, Samir Hazra, Kamalesh Hatua, and Subhashish Bhattacharya. "A Transformerless Intelligent Power Substation: A three-phase SST enabled by a 15-kV SiC IGBT." IEEE Power Electronics Magazine 2, no. 3 2015: 31-43.

[3] Hao, W. A. N. G., Y. A. O. Jian, Xuan-ni LIN, and S. U. I. Hong. "Research of the Redundancy Technologies in the Communication Network for Distribution Automation." DEStech Transactions on Computer Science and Engineeringwcne 2016.

[4] Ge, Xiongzi, Yi Liu, Chengtao Lu, Jim Diehl, David HC Du, Liang Zhang, and Jian Chen. "VNRE: Flexible and Efficient Acceleration for Network Redundancy Elimination." In Parallel and Distributed Processing Symposium, 2016 IEEE International, pp. 83-92. IEEE, 2016.

[5] Saleh, Khaled A., Ali Hooshyar, and Ehab F. El-Saadany. "Hybrid passive-overcurrent relay for detection of faults in low-voltage DC grids." IEEE Transactions on Smart Grid 8, no. 3 2017: 1129-1138.

[6] Stojanovi?, Zoran N., and Milenko B. Djuri?. "An accounting for directional earth-fault relay with no voltage inputs." Electric Power Systems Research 96 2013: 144-149.

[7] Davarpanah, Mahdi, Majid Sanaye-Pasand, and Reza Iravani. "Performance management of the transformer restricted earth fault relay." IEEE Transactions on Power Delivery 28, no. 1 2013: 467-474.

[8] NPTEL: Electrical Engineering - Power System Protection, Nptel.ac.in, 2017. [Online]. Available: https://nptel.ac.in/courses/108101039/17. [Accessed: 12- Sep- 2017].