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 Post subject: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 12:53 pm 
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Hello,
I am from Saudi Arabia so my English is not that good ! :?

I am working in operation. Our network is 13.8kv from main feeders in grid station up to 13.8k/400:230 v transformers. It consists of
1- main breakers at grid stations
2- 13.8 kV 3 C 300 mm2 aluminum cables
3- Oil & SF6 Ring Main Units (RMU's)
4- delta star 13.8 k/400:230 volts transformers

We are responsible for switching, energizing ,denergizing, continouty test, phase rotation, meger etc...

The short circuit current for main breakers and RMU's is 10kA for 3 sec.

What is the proper PPE we should use? 2 or 4

Thank you for help


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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 1:53 pm 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 676
Location: Rutland, VT
Hasan wrote:
Hello,
I am from Saudi Arabia so my English is not that good ! :?

I am working in operation. Our network is 13.8kv from main feeders in grid station up to 13.8k/400:230 v transformers. It consists of
1- main breakers at grid stations
2- 13.8 kV 3 C 300 mm2 aluminum cables
3- Oil & SF6 Ring Main Units (RMU's)
4- delta star 13.8 k/400:230 volts transformers

We are responsible for switching, energizing ,denergizing, continouty test, phase rotation, meger etc...

The short circuit current for main breakers and RMU's is 10kA for 3 sec.

What is the proper PPE we should use? 2 or 4

Thank you for help


Hello and Welcome to the Forum.

From your description, it seems like this is in a substation type installation. This type of installation would fall under OSHA rules here in the states. OSHA contains a table that specifically states what analysis method should be used. OSHA also does not utilize PPE Categories rather incident energy and states that an employer must protect the employee.

So if it is open air type installation, the one item I see that causes me to pause is that the fault current duration is 3 seconds which is an extremely long duration. I would question that time.

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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 3:45 pm 
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Joined: Mon Mar 14, 2016 12:27 pm
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Thank you for your reply.

We are working in distirbution and
It is written that Breaker can withstand 10kA for 3 sec. So it is not the time to interupt the arc flash. I will check this point and post it here.

Thanks


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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 4:34 pm 
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Location: Rutland, VT
Thank you, that is what I thought. What you need is the fault current (3ph & SLG) and clearing time for each

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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 6:45 pm 
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Location: North Carolina
Withstand ratings are totally inappropriate for calculating incident energy and arc flash hazards. Although it is a generally accepted practice to overestimate fault current for sizing purposes, this will result in greatly under rated incident energy.

Arc energy is equal to Varc*Iarc*time. Iarc is the same as bolted fault current at 13.8 kV but will be much less than this at 400/230 V. Varc is not really related to system voltage V. The important thing here though is that circuit breakers and fuses have a time-current curve where the fault time increases at a rate that is much faster than the decrease in current. So as current decreases when you are in an inverse-time relationship, arcing energy increases.

So although it is acceptable to overestimate for withstand rating purposes, this is very wrong and will result in underprotecting workers. It is important to estimate fault current very accurately such as using the IEC comprehensive method.

Second and partly for the same reason (transformers add a lot of impedance), the incident energy on the secondary (load) side of a transformer is frequently much larger than on the primary side. Thus as system voltage decreases for the same amount of power, the arcing energy increases.

How much does it increase? For many systems the incident energy is well over 40 cal/cm^2 on the secondary side of a transformer bigger than 1500 kVA for a 400/230 V system. At 13.8 kV to reach over 40 cal/cm^2 it would typically have to be well over 20 MVA.

These are all general statements of trends that occur but should give you some idea of why no one can give you a general table with any degree of accuracy. Arc flash has to be determined on a case-by-case basis.


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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 8:16 pm 
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I could be completely wrong, but since he is discussing s Ring Bus, it seems to me the grid station mentioned is actually a step-UP to 400/230 kV. 230/400kV Wye is commonly used in Europe and some other nations.


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 Post subject: Re: PPE required for 13.8 kV network
PostPosted: Mon Mar 14, 2016 9:45 pm 
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Thank you for your comments. I will try to give you an idea about our electric system.
Generation (fuel, steam and gas at 13.8kV then step up transformer up to 380kV or 230kV)
> Transmission 380 or 230 kv transmission lines and near the loads we have BSP's (Bulk supply points) and Grid stations contain step down transformers from transmission voltages to > > >distribution voltages (33 or 13.8 kV) and then 500,1000 or 1500 KVA transformers (33 or 13.8kv / 400:230 or 220:127 v)
Frequency is 60 Hz smiller to USA.


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