Safety and Reliability of Electrical Distribution Systems of Existing Plants!!

Introduction

We performed the Power System Analysis for one of our clients who has been a leading intermediates company in the Indian chemical industry since 1970.

The client wanted to maintain the protection device’s proper coordination and ensure the system’s reliability to avoid any kind of unnecessary tripping. Also, the client didn’t have the required input documents/data to perform the required analysis.

They approached Elegrow Technology to provide a solution to mitigate the risk and provide proper device coordination.

System Overview

• The plant’s main incomer has been connected to the main 66kV Line incomer to SF6 Circuit Breaker.
• Further Output sections are connected to the Primary winding of two 66kV, 12.5 MVA, ONAN Distribution Transformers for stepping down from 66kV to 11kV.
• The output of the power transformers is further connected to seven power transformers (i.e., 2.5MVA, 3MVA) for stepping down from 11kV to 0.433kV.
• The output of the seven power transformers is in turn connected to the Power Control Centre (PCC). PCC Panel are incomers of various Feeders.
• The Output of the PCC Panel is further connected to the Different Motor Control Centres (MCC), Power Distribution Boards (PDB), and Main Lighting Distribution Boards (MLDB). There is a total of 7 no’s of PCC, 80+ no’s of MCC, 20+ no’s of MLDB, and 20+ no’s of PDB.
• The facility relies on several electrical distribution feeders, each with its own set of protective relays and circuit breakers, to supply power to the various equipment and processes.

Our Observations

• As all the data was not available. So We took the Data collection in our scope. The data has been collected by our team from the plant site and the analysis has been done in ETAP software using the Star – Protection coordination module as per standard IEEE 242-2001.
• From the data, we analysed that there is an improper time-current curve and coordination between protection devices, due to which when a fault occurs, the upstream circuit breaker trips instead of the downstream circuit breaker.

Methodology

• Firstly the single-line diagram has been prepared in ETAP software and the analysis was then carried out further.
• There is a total of 7 no.’s of PCC i.e., PCC-1A, PCC-1B, PCC-2, PCC-3, PCC-4, PCC-6, PCC-7.
• Let us take an example to understand the issue and method in detail,

Figure:1 ETAP Single Line Diagram of PCC-1A

• In Figure 1 the dotted line represents the following protection device

1. PCC-1A O/G 7F1 Feeder: 800A ACB
2. PCC-1A I/C Feeder: 5000A ACB
3. SS-1_Tr-1_Relay-1 (i.e., S/S-1 TR-1 ICOG Feeder): 800A VCB
4. SS-1_Tr-1_Relay-2 (i.e., 66kV S/S-1 O/G Feeder): 1250A VCB

• The coordination between the downstream circuit breaker (i.e., PCC-1A O/G 7F1 Feeder: 800A ACB is Siemens 3WT with ETU37WT trip circuit) & upstream circuit breaker (i.e., PCC-1A I/C Feeder: 5000A ACB, Make: Siemens, Model: WL III 5000H with ETU45B trip circuit) is not in proper sequence.
• In PCC-1A all O/G feeders downstream circuit breakers have the same Make: Siemens, Model: 3WT with ETU37WT, in which the long-time delay is fixed to 10s@6xIr and the instantaneous trip setting is fixed to 20xIn and if we change the long-time delay and instantaneous trip setting of the upstream circuit breaker to align with downstream circuit breaker then the ARC Flash incident energy and Coordination issue increases further.
• So therefore, the upstream circuit breaker needs to change from 5000A ACB, Make: Siemens, Model: WL III 5000H with ETU45B trip circuit to 5000A ACB, Make: Schneider, Model: MTZ3 50H1 with Micrologic 6.0X trip circuit as required for proper coordination. The trip settings have been done as per the load connected to PCC-1A.
• Besides that, there is a coordination issue in both the HT downstream relay (i.e., SS-1_Tr-1_Relay-1: 800A VCB, Relay Make: Siemens, Model: DNL 7SR) and HT upstream relay (i.e., SS-1_Tr-1_Relay-2: 1250A VCB, Relay Make: Siemens, Model: DNL 7SR). The trip setting of both the HT relays has been changed from the existing settings as per the full load current of the TR-1 HT side.

 Solution

• All outgoing circuit breakers of PCC-1A,1B, 3,4 are around 70-90 no’s make: Siemens 3WT with ETU37WT trip circuit, their long-time delay is fixed, and the instantaneous trip setting is fixed to 20xIn, which are required to replace but due to the cost constraints we have suggested the following 3 options.
• Instead of replacing the 70-90 no’s of PCC outgoing circuit breaker the incomer circuit breaker of PCC-1A,1B,3,4 can be replaced from Siemens make to Schneider make.
• Instead of replacing the 70-90 nos of PCC outgoing circuit breaker the incomer circuit breaker of PCC-1A,1B,3,4 can be replaced with a numerical relay.
• All outgoing circuit breakers of PCC-1A,1B, 3,4 around 70-90no’s of make: Siemens 3WT with ETU37WT trip circuit, their long-time delay is fixed, and the instantaneous trip setting is fixed to 20xIn. Due to this, there is a coordination issue with the upstream breaker and for proper coordination, they can be replaced with Siemens 3WL with ETU45B.

Value Addition by Elegrow Technology

• Digitization of overall electrical Single Line Diagram and Plant Load Calculation ( which were not available before starting the analysis)
• Technical Data Management And Accessibility across the organization (Provided all data in one place)
• Improved Electrical Protection Device Co-Ordination with minimum investment (Multiple time Expansion happened, Client was not aware that fault Level of the System Increases and due to that device Co-Ordination was missed)
• Improved Safety and Reliability with Arc flash Study and Proper Co-Ordination

Conclusion

With the help of recommendations and implementing proper protection coordination the equipment damage can be minimized, and system stability and reliability can be increased while ensuring the safety of personnel.

Now the client is discussing the recommendations with their management and will go ahead with the implementation of the solution once approved. Elegrow Technology will surely help them to implement the solution with the help of timely guidance and review.

A well-coordinated relay system is critical in preventing cascading failures, reducing downtime, and minimizing repair and maintenance costs. Therefore, it is vital to maintain a robust and reliable power grid.

Proper data management and standard compliance help organization increase safety, reliability and energy accessibility along with business profitability.