Ground Fault Protection - engineering site - Schneider Electric

More documents

Recommendations

Info

Study 1: management of neutral currentsTo simplify the reasoning process, this study is conducted on the basis of thefollowing diagram:b normal operation Nb load U1 generating neutral currents (harmonic and/or unbalance), i.e. phaselU1 = ∑ → I ph, neutral lU = INb no load U2, i.e. phase lU2 = 0, neutral lU2 = 0b no faults on U1/U2, i.e. ∑ → I ph + → I N = 0.DB117262Diagram 33b - U1 Neutral currentb From the remarks formulated above (see paragraph 4.2.1.), the following can bededuced:→ →v I→ = I N1 + I N2v primary current in GFP1: → I 1 = → I N1 + ∑ → I ph = - → I N2v secondary current of GFP1: i1 = - iN2.b Likewise, the measurement currents of GFP2 and GFP3:v secondary current of GFP2 : i2 = iN2v secondary current of GFP3 : i3 = - iN2.b With respect to secondary measurements, iA, iB and iC allow management of thefollowing GFPs:v iA = i1 - i3 → iA = 0v iB = - i1 - i2 → iB = 0v iC = i2 + i3 → iC = 0.b Conclusion: no (false) detection of faults: criterion a1 is properly verified.Study 2: management of fault currentsDB117263 activated. activated. gives rhe fault value.Diagram 33c - simplified fault on U1: no neutral current (∑ I → ph = 0, IN = 0)32
Same operating principle as for study 1, but:b normal operation Nb load U1 generating neutral currents (harmonic and/or unbalance), i.e. phaselU1 = ∑ → I ph, neutral lU1 = INb no load U2, i.e. phase lU2 = 0, neutral lU2 = 0b faults on U1 ( → I f), i.e ∑ → I ph + → I N + → I f = Ø.b Using study 1 and the remarks formulated above (see paragraph 4.2.1.),the following can be deduced:→ →v I→ f = I f1 + I f2v primary current in GFP1: → I 1 = - → I N2 + → I - → I f2 = - → I N2 + → I f1v secondary current of GFP1: i1 = - iN2 + if1.Likewise, the measurement currents of GFP2 and GFP3:vvbsecondary current of GFP2: i2 = iN2 + if2secondary current of GFP3: i3 = - iN2 - if2.i.e. at iA, iB and iC level: iA = if, iB = - if and ic = Ø.b Conclusion: exact detection and measurement of the fault on study 1: noindication on study 2. Criteria b 1 and b 2 are verified.Remarks: Both studies show us that it is extremely important to respect the primaryand secondary positioning of the measurement toroids.Extensively used in the USA, this technique offers many advantages:b it only implements standard RS GFPsb it can be used for complex systems with more than 2 sources: in this case couplingmust also be standardisedb it can be used to determine the part of the diagram that is faulty when the couplingcircuit-breaker is closed.On the other hand, it does not eliminate the neutral circulating currents in thestructures. It can only be used if the risk of harmonic currents in the neutral is small.4.2.2.2. Neutral breakingIn fact, the encountered problem is mainly due to the fact that there are 2 possiblepaths for fault current return and/or neutral current.In normal operationCoupling using a 4P switchgear allows the neutral path to be broken. Themultisource system with several earthings is then equivalent to 2 single-sourcesystems. This technique perfectly satisfies implementation criteria, including thea 2 criterion, because the TN-S system is completely conserved.In R1 and R2 operationIf this system is to be used in all case figures, three 4P devices must be used.DB117301Diagram 34This technique is used to correctly and simply manage multisource diagrams withseveral earthings, i.e.:b GFP1 and GFP2, RS or SGR standardsb GFP3 (on coupling), RS standard not necessary, but enables management in R1(or R2) operation of the fault on load U1 or U2.Moreover, there are no more neutral currents flowing in the structures.33
Page 1: Low voltage expert guidesGround Fau
Page 5 and 6: The role of “Ground FaultProtecti
Page 8 and 9: 1.2.1.2. Protection using an RCDRCD
Page 10 and 11: 1.2.2.2. Protection using GFP devic
Page 14 and 15: In shortDiscrimination between grou
Page 16 and 17: 2.2.3. ZSI logical discriminationZS
Page 18 and 19: In shortProtection using GFP device
Page 20 and 21: GFP implementationIn shortCorrect i
Page 22 and 23: In short3.2. Operating precautionsT
Page 24 and 25: In short3.3. Applications3.3.1. Met
Page 26 and 27: Study of MultisourceSystemsIn short
Page 28 and 29: 4.1.1.2. Study 2 / diagram 2Seeing
Page 30: In R1 (or R2) replacement operation
Page 33: In event of a fault on the loads 1,
Page 37 and 38: 5.2.2. Multisource / single-ground
Page 39 and 40: Installation and implementationof G
Page 41 and 42: DB117297External transformer (CT) f
Page 43 and 44: External transformer (CT) forresidu
Page 45 and 46: Ground fault protectionwith Compact
Page 48 and 49: Implementation in the installationD
Page 50 and 51: Study of discrimination betweenGFPT
Page 52: Study of ZSI discriminationDB117336
Page 56: 0Schneider Electric Industries SAS8

Ground Fault Protection - engineering site - Schneider Electric

Create successful ePaper yourself

Delete template?

Save as template?