preparing the earthing design calculation for a substation

 preparing the earthing design calculation for a substation

Solution: To determine the right calculation, we conducted the soil investigation test by SEC approved testing company and determined the soil electrical resistivity.

According to SEC Technical specification TES-P-119.10 and guidelines given in IEEE standard 80-2000 specifications, the required system fault current was 40kA. I was required to use the soft, drawn bare copper conductor.

After inputting all the data, the soil resistivity came as 34.36 Ohm-m. The next step was to determine the size of the copper conductor and the number of electrodes. By using Eq.40 IEEE80, I decided that the cross-sectional required was 142.06sqmm, the therefore standard size of the conductor selected of 240sqmm with a diameter of 17.20mm. I determined touch voltage (tolerable) by using Eq.32 IEEE80, which came as 477.86V.

I had to calculate the actual touch voltage for a safe grid design, which came as 468V. I did some paper calculations to find a way to bring resistance to less than 1 Ω. By using a spacing of 4.5m ground resistance was calculated by using Eq.52 IEEE80, which came as 0.1956Ω <1 Ω as per specifications requirements.

Since the actual touch potential is less than tolerable potential, and since the grid resistance is less than 1 Ω, the ground design is safe. I prepared drawings and all designs according to the project’s specifications.

Outcome: I submitted earthing design calculations to the client, and they approved it without any comment. My manager was satisfied with this approval, and we successfully designed the earth mat layout based on calculations.

1.2 Situation: I was required to change the indoor lighting system design for the substation from the client.

Solution: The client was not satisfied with the initial design and lighting fixtures used in that design; I was required from the company to redesign the system with acceptable lighting fixtures as per Saudi electric company requirements.

I checked and calculated the required lux level in different rooms and halls by using the software Dialux.

I calculate and visualize the lighting fixture locations and to attain the required lux in the room. I recommended Saudi Lighting company lighting fixtures, which were readily available at a reasonable price and simple in installation.

After I finalized the fixtures type, I designed the pushbuttons and switches location as coordination with architectural drawings. I reviewed the design with the client, and after getting initial approval, I coordinated with civil and mechanical to have a well-coordinated installation method and route the conduits, location of junction boxes. There should not be any conflict with fire alarm conduits, civil opening, or HVAC ducts.

It was taken into consideration that no conduit shall be filled up more than 40%, cable was chosen as per IEC60228 standards, and the maximum load was kept at 120%.

Outcome: The client finally approved the design and material used as he found this according to specifications. The installation of lighting fixtures was correctly done without any conflict, as all disciplines were coordinated well. I calculated actual lux by a lux meter and found is in line with the requirements. A quality inspector from the client was also satisfied with the work done. We designed a lighting panel schedule and lighting panel design based on the same lighting system design.

1.3 Situation: I was advised to check and study the installation details of 13.8kV switchgear and medium voltage cable terminations in the substation because the cable had been burnt two times as well transformers were tripped.

Solution: Initially, I did a study and found a problem in the installation of a switchgear cable compartment. It was very small so that gland earthing was very near to cable termination; it can make spark and can cause short circuits later. To avoid that, I recommended to extend the box and keep minimum vertical spacing with 700mm height as per SEC standards 32-SDMS-18. I requested a switchgear manufacturer to provide the extension boxes of the same switchgear material to extend the cable compartment. I found a similar type of issue inside the medium voltage cable compartment. It was not possible to extend the box here, so I recommended to cut some length of bus bar so that cable will go up and gland earthing will be away from cable termination. As per the transformer manufacturer, there was no harm in cutting the bus bar to a certain length. I discussed the same with the client engineer from the cable department, and he agreed. So, we implemented this solution for the substation we had a fault and as well as other new substations to eliminate this risk.

Outcome: The client engineer and our company department head were happy and satisfied with the proposed solution. They appreciated me as the issue was resolved. No tripping or any problem happened after that till date.

1.4 Situation: I was responsible for studying and designing the auxiliary power layout design, SLD, and calculations for the 132kV substation.

Solution: To prepare a design for auxiliary power, I studied the complete substation requirement for indoor and outdoor outlets for different equipment, their required power, and amperes ratings. Once I finished and calculated accumulative power requirements, I designed an adequate SLD to show the power connections from Main AC Distribution, which was connected with an auxiliary transformer with the required capacity of the main circuit breaker to sub-distribution boards. Moreover, I calculated the voltage drop across the bus bar as well as cable sizing calculations from the sub-distribution board to the main equipment outlets. I recommended adding disconnect switches between the SUB DB main breaker and equipment breaker for safety purposes. I found some discrepancies in panel manufacturing design refers to my calculations; the main ACDB breaker was lower than the actual requirements. As per my calculation, the full load current (A) was 1085A, while the recommended breaker was of 1000A capacity. Therefore, I immediately advised to change it to standard ratings of 1250A as per IEC 60947-2, also urged to change to copper bus bar from aluminum bus bar to improve the conductance. I recommended adding under voltage and under frequency relay for safe operation as well as REF615 IEC61850 relay for overcurrent and earth fault protection. I designed SLD as per my calculations using ETAP software and reviewed it with the client for approval.

Outcome: The client design engineer approved the design without any comment or further clarification. Therefore, we gave the final copy to the manufacturer to proceed with manufacturing. Later on, we installed all the equipment successfully. The inspection engineer was satisfied with the calculation and used material.

1.5 Situation: I conducted a study for the lightning protection and shielding system for 132/33/13.8kV level substation.

Solution: To attain the project specifications and meet the Saudi Electricity company standards, as per TES-P-119.07, NFPA 780, the 0.1 percent exposure of substation to direct stroke is valid design criteria. That would practically eliminate the possibility of direct strokes to the substation. I studied and checked by doing hand calculations on how I can achieve standard exposure. I checked the length and width of different buildings, including 13.8kV SWGR, 33kV SWGR, 132kV GIS hall and control buildings along with the equipment installed on the roof and advised to install strike termination devices on parapet walls as well as top of HVAC package units at a distance of 4.5m between adjacent terminals. I also suggested installing multi-point termination devices on building corners to cover the whole area.

I checked the height of the power transformer, a capacitor bank, and the surge arrestor area. It came around 7m, 8m, and 8m, respectively. I advised using a 15m lightning mast with a 3.05m air terminal rod at the top to cover the entire area as per SEC standards. As per the calculation, we designed the layout for shielding showing actual protection with the help of SESShield and found that design and calculations were up to the SEC and NFPA standards.

After a discussion with the client electrical consultant and taking formal approval, I prepared the bill of quantities by considering the number of multi and single air terminals, copper tape, clamps, size of shielding cable, and the number of connections and forwarded to procurement team to consider it.

Outcome: Consultant approved all the calculations and layouts I built. All the material purchase was in line with SEC standards and installations were successfully done and inspected by the client.

1.6 Situation: During all my projects, I was required to follow the safety at the site, implement job safety procedures.

Solution: In all the substation construction, maintenance, and protection modification projects, I was involved in safety implementation and risk assessment. From the beginning, I was very strict regarding personal safety at the site as without the following safety, work can’t be done safely. I had always been very much involved with all the team members wearing PPE’s (Personal protective equipment) such as safety shoes, helmets, gloves, safety harness at the height and safety glasses for welding work. These items provide basic safety.

I was required to provide electricity to an un-energized substation; I calculated the power capacity of different electric tools and equipment needed for the completion of works. I installed a temporary generator higher than the total required capacity so that all jobs shall be done parallel without any tripping. I instructed to barricade the complete area around the generator to avoid any hazard.

I instructed to install safety signs inside and outside of the building to let workers know about the safety procedure and also instructed to conduct a safety toll box meeting every morning.

I used to make the risk assessment for every work before it starts. It was required to eliminate the risk to a minimum, and I always instruct to follow the alternate method of work, which will have the lowest risk.

Outcome: I completed all of my projects without any significant accidents successfully. No major accident or injury happened as there was strict safety implemented during the installation of civil, mechanical, and electrical works and erection of equipment. I always consider the SEC 5 star safety standard and regulations.

1.7 Situation: In the Wadi Dawasir project, the client required a fully operational automatic pump system for water drainage from the sump pits and transformer pits and water transfer pumps.

Solution: Our main concern to design a pump system was to select the type of pumps as per standards and requirements and their connection with the substation automation system to control the operation of pumps and monitor at the control center.

Firstly, I checked the required dynamic head from the plumbing calculation. I opt for Grandfus water transfer and submersible pumps as per the requirements based on the dynamic head, which was already in the approved list of the client.

I added RTU in the design of the SAS system to connect the pumps to control the sequence and duration of work.

I also connected float switches at a different level of tanks and pits to monitor the water level by assigning different numbering to float switches.

Outcome: The client approved the design and installation satisfactorily as an alternative working mode of pumps increase the pump life cycle.

1.8 Situation: I was required to handle the protection modification project for 132kV circuits with Saudi Electric Company and handover the project at the time.

Solution: I conduct a complete study of the scope of work, all major and minor requirements, and identify all related items. I submitted the required clarifications to the client to have a clear idea about the combined scope between our project and another company project.

Since it was a modification project for an existing system, I requested all the related existing drawings and data from the client to start our detailed design. I prepared a schedule of based design, detailed design, and the materials required as per the job order. I analyzed all related data and discussed the existing equipment, which we can utilize to reduce the cost and time.

I prepared a complete tender package based on all requirements. Requirements like Materials in hands, materials required, work to be done, and the projects timeline and sent to some subcontractors to bid on it. I reviewed each proposal, asked for prequalification documents, previous same type of work experience, catalogues and data sheets of materials along with the warranty and maintenance duration certificates.

After finalizing the best quality bid with low cost, I met with the supplier, discussed in-depth project details, and asked for the project timeline schedule. I organized a meeting between our client and subcontractor for client satisfaction. We set up the timeline and introduced some penalties in case of scope or HSE violation, under quality material usage or timeline violation. We agreed to prepare a change order in case of additional scope.

Outcome: we completed the project successfully and energized all the circuits in the given time without any damage or safety issue.