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nirdesh soni
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Location: bilaspur cg
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Why Use 245kv for 220kv SF6 Circuit Breaker?

04/20/2011 4:44 AM

hear i put my question about sf6 Circuit breaker. In the 220kv swich yard Why we are using 245kv rated voltage SF6 CB .
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A.A.Khi
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#1

Re: why we use 245kv for 220kv SF6 circuit breaker?

04/20/2011 5:05 AM

While the nominal voltage is 220 Kv the allowed voltage deviation is 10 % plus - minus , in other words increase of system voltage to 242 Kv from the power supply Co. cannot be objected.

In consideration of the over voltage condition (242 kv) you have to select 245Kv rated equipment in the yard.

Please also note that besides SF6 this conditions is equally applicable to conventional grid equipment.
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nirdesh soni
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#2
In reply to #1

Re: why we use 245kv for 220kv SF6 circuit breaker?

04/20/2011 5:20 AM

Ok sir, but voltage shall be drop not plus , because of voltage drop .

please clareify sir
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TonyS
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#3

Re: why we use 245kv for 220kv SF6 circuit breaker?

04/20/2011 5:36 AM

220KV is the nominal value, it will vary due to demand on the system.

The last system I worked on you could 2nd guess when the transformer OLTC would kick in depending on the loading at the time of day.

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electricalexpert65
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#4

Re: why we use 245kv for 220kv SF6 circuit breaker?

04/20/2011 6:49 AM

There are something called Nominal System Voltage (NSV) & Highest System Voltage (HSV) . The NSV is 220 kV and for an NSV of 220kV is 245 kV as per Standards. This is to cater to the fluctuations in the system voltage, particularly on the plus side. If the breaker is exactly rated for 220kV, then during a overvolatge condition it would fail. That's why any switchgear will have both NSV & HSV Ratings.
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hien.nguyenquoc
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#5
In reply to #4

Re: why we use 245kv for 220kv SF6 circuit breaker?

04/20/2011 11:10 AM

EE65 made a GA for the question. More over, according to the information below for any switchgear, between 170 and 245kV, there is no other option.

Switchgear's Standardized rated Voltages: 3.6; 7.2; 12; 17.5; 24; 36; 52; 72.5; 100; 123; 145; 170; 245; 300; 362; 420; 550; 800 kV

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Anonymous Poster #1
#6

Re: Why Use 245kv for 220kv SF6 Circuit Breaker?

04/21/2011 6:58 AM

Yes, you must use the standard voltage levels avilable. However, I have used higher voltage ratings to obtain the fault current design characteristics required at that site.
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hien.nguyenquoc
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#7
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Re: Why Use 245kv for 220kv SF6 Circuit Breaker?

04/21/2011 9:56 AM

As you have stated, your nominal voltage is 220kV and you chose 245kV switchgear and I saw it. What I I don't understand here is how you will obtain the fault current by selecting the higher voltage of switchgear since the switchgear suppliers suggests that they designs switchgear with two level of voltage just to meet the transient voltage.

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electricalexpert65
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#8
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Re: Why Use 245kv for 220kv SF6 Circuit Breaker?

04/26/2011 9:00 AM

I am afraid that you are a veebit incorrect. NSV & HSV has nothing to do with transient overvoltages. HSV is to cater to POWER FREQUENCY over voltage conditions due to system fluctuations and it could be persisting for a longer duration too.

Moreover, any switchgear, apart from NSV & HSV is also specified with Power Frequency Withstand Voltage Rating and Impulse Voltage Withstand Rating. Combined, this HSV, PFOV & IOV are known as the Basic Insulation Level or BIL of the switchgear. For example, for a switchgear used in a 220kV (RMS) system, the HSV is 245kV (RMS), the power frequency withstand voltage is 460kV (RMS) and the Impulse Withstand Volatge is 1050kV (Peak). It is generally specified in the name plate as: BIL: 245/460/1050kV.
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hien.nguyenquoc
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#9
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Re: Why Use 245kv for 220kv SF6 Circuit Breaker?

05/09/2011 12:27 AM

electricalexpert65:

"I am afraid that you are a veebit incorrect. NSV & HSV has nothing to do with transient overvoltages." Could you please refer to the #4 reply?

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Users who posted comments:

A.A.Khi (1); Anonymous Poster (1); electricalexpert65 (2); hien.nguyenquoc (3); nirdesh soni (1); TonyS (1)

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