WHAT IS FIRST POLE TO CLEAR FACTOR IN EHV CLASS CIRCUIT BREAKER | LinkedIn

http://www.linkedin.com/groups/WHAT-IS-FIRST-POLE-CLEAR-1801744.S.201767110[12-06-2013 17:37:21]

Alex Tich

Mohammad

Ahmad

Bojan

Alex Tich

Bojan

Edward

ali

Bojan

Ahmad

13 comments

WHAT IS FIRST POLE TO CLEAR FACTOR IN EHV CLASS CIRCUITBREAKER5 months ago

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sanjeev P., Arul G. like this

5 months ago

Alex Tich M. • This normally refers to Circuit breakers which aremechanically linked (Ganged) to one operating mechanism, it can neverhappened that all poles will open at the same time no matter how manyadjustments you make.

5 months ago

Mohammad I. • When CB operates, each of the three poles clear attheir respective current zeros. While one pole clears first, the other twopoles continue to carry current. This gives rise to a temporary over-voltage across the open contacts of the pole that clears first. Now, theratio of this over-voltage and nominal system voltage is the first pole toclear factor, as I understand.

It can be mathematically shown that this factor can be up to 1.5 for aCB at EHV level. This means that this over-voltage could be up to1.5PU.

5 months ago

Ahmad A. • First Pole to Clear Factor is defined as the ratio between: 1- The voltage on the terminal of the first pole of the circuit breaker toclear the three phase fault, which is normally the most highest andsever voltage. And 2- The Voltage on the terminal of the circuit breaker after clearing thefault, which is normally less than the first pole. Selection of this factor is mainly dependent on the system neutralearthing, if solidly earthed (grounded) or not. As well known, faults onthe un-earthed system generates higher voltages then the earthedsystem, so: We select a circuit breaker for un- earthed/ resistance earthed systemwith a factor of 1.5, while for solidly earthed system we select a circuitbreaker with factor of 1.3. In very special uses we select Circuit breaker with factor of 1.0.

4 months ago

Bojan V. • Just to add: 1,5 first pole to clear factor is valid forungrounded three phase short-circuit, neutral point is earthed. Or whenthree phase short circuit is grounded, and neutral point isolated. So,when first pole break current, we have occurs described by mr. Ahmadand mr Mohammad. After first pole shut down electric arc(finally breakcurrent), there is two-phase short-circuit through other two poles, andcurrents in these poles are in opposition. That means that their valuescomes to zero point at the same point and also arcs in both poles areextinguished in the same time with factor 1,0. This is my point of view, ifit is wrong I am accepting objections :)

4 months ago

Alex Tich M. • I think this question should be answered by people whoare in manufacturing and tell us what they mean. If it refers to whatpeople are talking about then all breakers should have the same firstpole to clear factor. Remember the phases have an angle of 120degrees between them.

4 months ago

Bojan V. • I work in manufacturing of circuit breakers :) During the twophase short circuit, symetry is lost and angle is not 120 degreesbetween phases.

4 months ago

Edward G. • It is Ratio between Voltage appearing across Faulty phasebefore interrupting faulty current to Voltage appearing across all threephase after fault has been cleared. It is designed as 1.3 for Solidly grounded system and 1.5 forUngrounded system.

4 months ago

ali S. • The first-pole-to-clear-factor (kpp) is depending on the earthingsystem of the network. The first-pole-to-clear-factor is used forcalculating the transient recovery voltage for three-phase faults. In general the following cases apply: - kpp = 1.3 corresponds to three-phase faults in systems with anearthed neutral. - kpp = 1.5 corresponds to three-phase faults in isolated systems orresonant earthed systems. - kpp = 1.0 corresponds to special cases, e.g. two-phase railwaysystems. A special case is when there is a three-phase fault without involvingearth in a system with earthed neutral. This case corresponds to kpp =1.5. This special case is however not normally considered in thestandards.

4 months ago

Bojan V. • I made one mistake in upper comments. After first pole breakcurrent: - with first pole to clear factor 1,5(in isolated systems), other two polesbreak current in the same time with factor 0,87 - with first pole to clear factor 1,3(grounded systems), second pole breakwith factor 1,27, and third with 1,0. In this case, other two poles dontbreak in the same time... Apologize!

4 months ago

Ahmad A. • Great help guys

WHAT IS FIRST POLE TO CLEAR FACTOR IN EHV CLASS CIRCUIT BREAKER | LinkedIn

http://www.linkedin.com/groups/WHAT-IS-FIRST-POLE-CLEAR-1801744.S.201767110[12-06-2013 17:37:21]

guilhem

Bojan

Franco

3 months ago

guilhem B. • It has to be mention that cb with a kpp of 1,5 does notcover a cb with a design with kpp1,3.! Even though the TRV transient recovery voltage across the circuitbreaker terminal is higher with a kpp 1,5 (phase to ground peak voltage* kpp * kat (amplitude factors), the arcing window of a kpp with a 1,5have a shorter arcing window ! See IEC 62271-100 drawing part. Kpp is important but also arcing window !!!

3 months ago

Bojan V. • I think that in practice nothing would happened if you installbreaker with kpp=1,5 in effectively ground system(kpp=1,3). Of course,standard IEC 62271-100 request separate testings with longer arcingtimes for kpp=1,3, but my opinion is that it is requested to equalize peakof recovery voltage and produced heat energy during the arcing.Something similar is obvious during short-circuit switch type tests, whereT10 test-duty has higher peak recovery voltage and rate of rise thenT100s (100% of rated short-circuit current). Please, I would like to hearyour opinions about this matter. Regards...

Franco L. • What Guilhem wrote above (hello Guilhem) is correct. Wemay add that according to IEC 62271-100 a circuit breaker can betested to cover both the Kpp conditions, giving the TRV parameters forkpp=1.5 (higher peak than 1.3) and verifying the arcing time as perkpp=1.3 (longer arcing window than 1.5) in one test.