CN101800415B - Longitudinal differential protection method of electric furnace transformer - Google Patents

Abstract

The invention relates to a longitudinal differential protection method of an electric furnace transformer. Adopted three-point big differential protection of high, medium and low-voltage sides not only can be used for effectively reflecting the fault of the electric furnace transformer and be accurately actuated but also ensures the number of current transformers is reduced to 9, which is accepted with pleasure and reduces investment funds, and meanwhile, a Rogowski coil current transformer is used as the low-pressure side current transformer, which solves the problem that the traditional electromagnetic type current transformer can not measure overlarge current, and the method enables the high, medium and low-voltage side current of the electric furnace transformer not need to be corrected in phases, and thereby, the operation is simplified.

Description

Longitudinal differential protection method of electric furnace transformer

Technical field

The invention belongs to electric power pool relaying protection field, relate to longitudinal differential protection method of electric furnace transformer.

Background technology

The furnace transformer that enterprise's (like various ore smelting works such as steel rolling mills) uses a kind of property and structure is frozen in the smelting of various mines; Mostly be Y/ Δ-11/ Δ-11 or Y-Y-12/ Δ-11 mode of connection; High side voltage is 35～220Kv; The low-pressure side output voltage is that directly power supply is to the electric arc type electric furnace about tens volts to 200 volts, and generation high temperature is smelted ore.High side voltage is taken from electric power system, and is basicly stable, and low-pressure side voltage can (about 50%) pressure regulation in broad range.

A kind of common iron core formula furnace transformer that is called is arranged in the furnace transformer, be characterized in the shared iron core of main transformer and voltage regulating transformer, so be called common iron core formula.The protective device of this furnace transformer all just adopts simple overcurrent protection both at home and abroad current; Protective value is poor; Overcurrent protection tripping phenomenon often appears in (most is short circuit or single-line to ground fault between casket) when the furnace transformer internal short circuit fault; The render electrical furnace transformer burns, and has a strong impact on the safety in production of smelting enterprise.

The longitudinal difference protection scheme of arc furnace transformer can adopt traditional branch side differential protection scheme; But this scheme needs 18 current transformers altogether; The user is reluctant to accept, and the high, medium and low voltage that adopts the present invention to propose is surveyed 3 big differential longitudinal difference protection schemes, can make current transformer quantity be reduced to 9; And protective value is variation not, and the low-pressure side Δ connects electric current and also need not carry out phasing.These 3 big differential longitudinal difference protection schemes can be reacted the single phase ground fault and the shorted-turn fault of furnace transformer effectively.

Summary of the invention

It is high to the purpose of this invention is to provide a kind of protective value, needs the little longitudinal differential protection method of electric furnace transformer of current transformer quantity.

For realizing above-mentioned purpose, longitudinal differential protection method of electric furnace transformer of the present invention adopts 3 big differential protections of high, medium and low voltage side, and step is following:

(1) inserts electromagnetic current transducer mutually respectively in the height of furnace transformer, each of medium voltage side; And insert the electronic current mutual inductor that adopts based on the Rogowski coil mutually respectively in each of the low-pressure side of this furnace transformer, and high, medium and low voltage side current transformer is Y and connects;

(2) calculate the differential current I of longitudinal difference protection by the measured value of the high, medium and low voltage side current transformer of furnace transformer _Op, stalling current I _Res, formula is following:

I in the formula _H, I _In, I _ΔBe respectively longitudinal difference protection high-pressure side, medium voltage side, low-pressure side current transformer homophase side primary side current;

(3) longitudinal difference protection is the ratio brake formula, the output of three phase composition OR-gates, and operation equation is:

I in the formula _Op.set=I _Opo+ S (I _Res-I _Reso), starting current I _Op0, keen current I _Res0, restraint coefficient S for the protection setting value;

(4) judge whether the size of differential current satisfies the requirement of braking equation; If the size of differential current satisfies the requirement of braking equation; Then transformer generating region internal fault is judged in protection, and the protection tripping operation is not if the size of differential current satisfies the requirement of differential equation; Then protection judges that transformer does not have troubles inside the sample space and takes place, and protection is failure to actuate.

Further, this method is applicable to Y/Y-12/ Δ-11 type furnace transformer.

Further, low-pressure side primary current I _ΔIntegration I for its secondary output voltage signal _Δ=K ∫ udt, in the formula, u is a Rogowski coil output voltage signal, and K is a proportionality coefficient, and it depends on the making parameter of Rogowski coil.

Further, get I in the said step (3) _Op0=0.4I _e, I _Res0=I _e, S=0.6, I _eBe the furnace transformer rated current.

Further, low-pressure side primary current I _ΔDo not carry out phasing.

Longitudinal differential protection method of electric furnace transformer of the present invention; Can not only react the fault of furnace transformer and accurately action effectively, and make current transformer quantity be reduced to 9, be used to take like a shot; The input funds have been reduced; Simultaneously, the low-pressure side current transformer uses Rogowski coil current instrument transformer, has solved the not problem of the big especially electric current of energy measurement of traditional electromagnetic current transducer; And method of the present invention makes the high, medium and low voltage side electric current of furnace transformer need not carry out phasing, has simplified computing.

Description of drawings

Fig. 1 is two broken line sketch mapes of operation equation of the present invention;

Fig. 2 is a longitudinal difference protection internal high pressure winding single-line to ground fault electric current flow graph;

Fig. 3 is the outside single-line to ground fault electric current of a longitudinal difference protection scope flow graph;

The outside d4 point of longitudinal difference protection scope single-line to ground fault current distributing figure when Fig. 4 is the DLn combined floodgate.

Embodiment

Longitudinal differential protection method of electric furnace transformer of the present invention adopts 3 big differential protections of high, medium and low voltage side, and step is following:

(1) inserts electromagnetic current transducer mutually respectively in the height of furnace transformer, each of medium voltage side; And insert the electronic current mutual inductor that adopts based on the Rogowski coil mutually respectively in each of the low-pressure side of this furnace transformer, and high, medium and low voltage side current transformer is Y and connects;

(2) calculate the differential current I of longitudinal difference protection by the measured value of the high, medium and low voltage side current transformer of furnace transformer _Op, stalling current I _Res, formula is following:

I in the formula _H, I _In, I _ΔBe respectively longitudinal difference protection high-pressure side, medium voltage side, low-pressure side current transformer homophase side primary side current;

(3) longitudinal difference protection is the ratio brake formula, the output of three phase composition OR-gates, and operation equation is:

I in the formula _Op.set=I _Opo+ S (I _Res-I _Reso), starting current I _Op0, keen current I _Res0, restraint coefficient S for the protection setting value, get I _Op0=0.4I _e, I _Res0=I _e, S=0.6, I _eBe the furnace transformer rated current, can obtain two broken line characteristic curves of differential current longitudinal difference protection, as shown in Figure 1;

(4) judge whether the size of differential current satisfies the requirement of braking equation, if the size of differential current satisfies the requirement of braking equation, promptly differential current is positioned at braking district, the characteristic top of two broken lines; Then transformer generating region internal fault is judged in protection; The protection tripping operation, if the size of differential current does not satisfy the requirement of differential equation, promptly differential current is positioned at two broken line characteristic curves below; Then protection judges that transformer does not have troubles inside the sample space and takes place, and protection is failure to actuate.

As shown in Figure 2, establish the d point the inner A phase of high pressure winding single-line to ground fault, short circuit current take place

Flow through the part number of turn W of high pressure winding ₁(W ₁Be the number of turn between earth point and the winding overhang), magnetic potential

At the low-pressure side stream of inducting Among the figure

Not can medium voltage side induced current (because high pressure winding B, C mutually in no current, pining down in mesolow side b, the c phase winding and do not admitting of electric current, thus medium voltage side a mutually in also no current).

By TA _HPositive ends flow into, For on the occasion of;

By TA _LThe negative polarity end flow into,

Be negative value.

With

Be the passing through property short circuit current that amplitude does not wait, inevitable I _{The a Δ}＜I _AH(desired value).

Vertical difference A phase: $\left\{\begin{array}{c}{I}_{\mathrm{OP}\·A}=|{\stackrel{\·}{I}}_{A\·H}+(-{\stackrel{\·}{I}}_{\mathrm{A\Δ}})|=I_{A\·H}-I_{\mathrm{A\Δ}}\\ I_{\mathrm{Res}\·A}=\frac{|{\stackrel{\·}{I}}_{A\·H}-(-{\stackrel{\·}{I}}_{\mathrm{A\Δ}})|}{2}=\frac{I_{A\·H}+I_{\mathrm{A\Δ}}}{2}\end{array}\right.$

I _{The a Δ}＜I _AH, if I _OpGreatly, I _ResLittle, I then _Op.setLittle, I _Res＞I _Op.set, the protection action; Certainly also maybe I _Res＜I _Op.set, the protection tripping either way maybe.

Normal magnetic potential I in service before the ground short circuit _AHW _H=I _{The a Δ}W _L, W _H, W _LBe the number of turn of every phase high-low pressure winding,

N _{By (just)}No-load voltage ratio during for normal operation between the transformer high and low pressure side.Behind the ground short circuit, magnetic potential I _AHW ₁=I _{The a Δ}W _L,

N _{By (weak point)}No-load voltage ratio for transformer behind the ground short circuit.I _{The a Δ}=I _AHN _{By (weak point)}High pressure winding earth point position change, W ₁Change, along with the change of earth point position has changed the no-load voltage ratio of transformer, W ₁＜W _H, N _{By (weak point)}＜N _{By (just)}, no-load voltage ratio is little after the short circuit, I _{The a Δ}Reduce, and coefficient of balance does not become, then unsymmetrical current increases, I _OpIncrease, make the protection action.

Ground short circuit point is the closer to the end of transformer high-voltage side, W ₁More little, N _{By (weak point)}More little, I _{The a Δ}More little, I _Ap=I _AH-I _{The a Δ}Big more, the protection action sensitivity is high more.When at transformer high-voltage winding terminal minister (in the protection range) single-line to ground fault, W ₁=0, I _{The a Δ}=0, I _Op=I _AH, the protection action sensitivity is the highest.Otherwise ground short circuit point is during the closer to transformer neutral point, W ₁Big more, N _{By (weak point)}Big more, I _{The a Δ}Big more, I _Op=I _AH-I _{The a Δ}More little, the low more and tripping of protection sensitivity.

Among Fig. 3, if high pressure winding isolated neutral when furnace transformer normally moves is normal in service at the outside (d among the figure of protection range ₁Point) A phase single-line to ground fault, short circuit current I take place _AHThough very big, it is the TA through longitudinal difference protection not _H, TA flows through _HThe three-phase current of primary side Electric current for furnace transformer three phase windings of flowing through; The zero-sequence component of this electric current is zero (isolated neutral), and its zero-sequence current of sensing medium voltage side, low-pressure side all is zero, and the differential current of 3 big differential protections is its unsymmetrical current Iunb; Less than its set point, protection is failure to actuate.

Among Fig. 4, DL _NLongitudinal difference protection outside transmission line d in furnace transformer high-pressure side in the making process ₄Point A point single-line to ground fault, TA flows through _HThe three-phase current of primary side

Be the electric current of furnace transformer three phase windings of flowing through, this electric current only contains zero-sequence current

No positive sequence does not have negative sequence component yet, and it is from TA _HThe negative polarity end flow into, so be negative value, promptly

The three-phase current of medium voltage side is sensed in the path of medium voltage side non-zero-sequence current circulation therefore

Sense the three-phase current of low-pressure side

Only contain zero-sequence current, no positive sequence does not have negative sequence component yet yet, and it is from TA _LPositive terminal flow into, on the occasion of; TA again _LWith TA _HVariation relation do

By

So

The IOP of longitudinal difference protection, Ires three-phase are identical, like fault phase A phase:

Be zero in theory, real is unsymmetrical current Iunb,

The Iop of B, C phase longitudinal difference protection, Ires distinguish identical with Iop.A, Ires.A.It is thus clear that if follow the outside single-line to ground fault of longitudinal difference protection, the longitudinal difference protection three-phase all is failure to actuate reliably in the DLn making process, being defined as of zero-sequence current distribution coefficient in the formula: ${\mathrm{\λ}}_{\mathrm{OM}}=\frac{Z_{\mathrm{NKO}}}{Z_{\mathrm{NKO}}+Z_{\mathrm{NKO}}},$ ${\mathrm{\λ}}_{\mathrm{ON}}=\frac{Z_{\mathrm{MKO}}}{Z_{\mathrm{MKO}}+Z_{\mathrm{NKO}}},$

0＜λ _OM＜1，0＜λ _ON＜1，λ _OM+λ _ON＝1；

Z _MKO---the zero sequence impedance between single-line to ground fault point K and the M side;

Z _NKO---the zero sequence impedance between single-line to ground fault point K and the N side.

Claims (5)

1. a longitudinal differential protection method of electric furnace transformer is characterized in that, adopts 3 big differential protections of high, medium and low voltage side, and step is following:

(1) inserts electromagnetic current transducer mutually respectively in the height of furnace transformer, each of medium voltage side; And insert the electronic current mutual inductor that adopts based on the Rogowski coil mutually respectively in each of the low-pressure side of this furnace transformer, and high, medium and low voltage side current transformer is Y and connects;

(2) calculate the differential current I of longitudinal difference protection by the measured value of the high, medium and low voltage side current transformer of furnace transformer _Op, stalling current I _Res, formula is following:

I in the formula _H, I _In, I _ΔBe respectively longitudinal difference protection high-pressure side, medium voltage side, low-pressure side current transformer homophase side primary side current;

(3) longitudinal difference protection is the ratio brake formula, the output of three phase composition OR-gates, and operation equation is:

I in the formula _Op.set=I _Op0+ S (I _Res-I _Reso), starting current I _Op0, keen current I _Res0, restraint coefficient S for the protection setting value;

(4) judge whether the size of differential current satisfies the requirement of braking equation; If the size of differential current satisfies the requirement of braking equation; Then transformer generating region internal fault is judged in protection, and the protection tripping operation is not if the size of differential current satisfies the requirement of differential equation; Then protection judges that transformer does not have troubles inside the sample space and takes place, and protection is failure to actuate.

2. longitudinal differential protection method of electric furnace transformer according to claim 1 is characterized in that: be used for Y/Y-12/ Δ-11 type furnace transformer.

3. longitudinal differential protection method of electric furnace transformer according to claim 2 is characterized in that: low-pressure side primary current I _ΔIntegration I for its secondary output voltage signal _Δ=K ∫ udt, in the formula, u is a Rogowski coil output voltage signal, and K is a proportionality coefficient, and it depends on the making parameter of Rogowski coil.

4. longitudinal differential protection method of electric furnace transformer according to claim 3 is characterized in that: said step is got I in (3) _Op0=0.4I _e, I _Res0=I _e, S=0.6, I _eBe the furnace transformer rated current.

5. longitudinal differential protection method of electric furnace transformer according to claim 3 is characterized in that: low-pressure side primary current I _ΔDo not carry out phasing.

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