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Э Н Е Р Г Е Т И Ч Е С К И Е К О М П Л Е К С Ы E N E R G E T I C C O M P L E X E S
УДК 621.316.925.1
АЛГОРИТМ БЛОКИРОВКИ ТОКОВЫХ ЗАЩИТ ПРИ БРОСКЕ ТОКА НАМАГНИЧИВАНИЯ
Докт. техн. наук, проф. РОМАНЮК Ф. А.1, магистр техн. наук ЛОМАНМ. С.2
1 Белорусский национальный технический университет, 2ОАО «Белэлектромонтажналадка»
E-mail: faromanuk@bntu.by
BLOCKING ALGORITHM FOR CURRENT PROTECTION DURING INRUSH MAGNETIZATION CURRENT
ROMANIUK F. A.1, LOMAN M. S.2)
1 Belarusian National Technical University, 2 JSC ■ "Belelektromontazhnaladka "
Представлен алгоритм блокировки токовых защит при броске тока намагничивания, реализуемый на основе оценки отношения тока прямой последовательности второй гармоники к току обратной последовательности первой гармоники.
Ключевые слова: бросок тока намагничивания, токовая защита.
Ил. 5. Библиогр.: 3 назв.
The paper presents blocking algorithm for current protection during inrush process. The algorithm is based on the evaluation of the ratio of the positive sequence second harmonic current to the negative sequence first harmonic current.
Keywords: inrush current, current protection.
Fig. 5. Ref.: 3 titles.
An important task for transformer current protection development is ensuring protection blocking at the inrush of magnetization current (IMC). IMC occurs at switching on of a no-load transformer, in cycles of automatic reclosing and automatic load transfer, at voltage recovery after external fault clearing. IMC can reach tenfold value in relation to rated current of transformer [1]. In all phases IMC is various in value, harmonious structure, form and decays rather slowly. Under the IMC influence all stages of current protections can operate falsely. The probability of false operations increases with increasing of sensitivity and operating speed of the protection stage.
IMC is an asymmetrical mode. As a rule, in two phases currents have unipolar character, as well maximum in value and contain an aperiodic component, main frequency harmonic and the highest harmonics. The third phase current is less,
practically doesn't contain an aperiodic component and is characterized with the significant presence of the highest harmonics. During IMC process all phase currents contain the first and second harmonics irrespectively of conditions of IMC emergence.
In symmetrical three-phase systems the first harmonics with the frequency f= 50 Hz in phase currents iA, iB, iC form positive sequence system [1]:
1A\h -1 ej — 1M\he ■0 . ;
1B\h — 1M\he 2 T J T
1C\h -1 e — 1M\he 2t 3 ?
and second harmonics with frequency 2f= 2 • 50 = = 100 Hz - negative sequence system:
Наука итехника, № 3, 2014
IA2h — IM 2he j 2-0 —
IB2h — IM 2he 2-2л -j
2-2л j -3-
IC 2h — IM 2he
M 2h>
,2л
- I e 3 ■
— ÂM2he ■
2л
- I в ] 2Л
— 1M 2h e ,
where h, IB1h, Iclh - vectors of first harmonic
currents of phases A, B, C correspondingly; h;
Imh, IC2h - vectors of second harmonic currents
of phases A, B, C correspondingly; IMlh, IM2h -amplitudes of first and second harmonics currents correspondingly.
In asymmetrical fault and asymmetrical loading modes current components of the positive and the negative sequences occur with the frequency of 50 Hz generally.
In IMC modes the first harmonic of phase currents includes a component of the negative sequence I\h-mg considerably, the second harmonic of phase currents includes a component of the positive sequence I2h-pos considerably. On the basis of the evaluation of the ratio I2h-pos/I1h-neg the blocking unit from IMC for the three phases current protection is constructed (Fig. 1).
The blocking unit includes the frequency filter 1 of the first current harmonic, the frequency
filter 2 of the second current harmonic, filters 3 and 5 of the positive sequence current, the filter 4 of the negative sequence current, the element 6, which forbids current protection blocking, the element 7 of the negative sequence current occurrence control, the element 8 of calculation and control of blocking parameter at IMC, the element 9 logical "And", the element 10 "Ban".
The filter 1 allocates 50 Hz components iA1h, iB1h, iC1h from phase currents iA, iB, iC and the filter 2 allocates 100 Hz components iA2h, iB2h, iC2h. The filter 3 forms positive sequence current I1h-pos of the first harmonic and the filter 4 - negative sequence current I1h-neg of the first harmonic. The filter 5 forms positive sequence current I2h-pos on the basis of the second harmonic currents iA2h, iB2h, iC2h. The element 6 compares current value I1h-pos with setting Iwfcmax. The element 7 counts I1h-neg/I1h-pos ratio and then compares it with setting Kneg. The element 8 counts I2h-pos/I1h-neg ratio and then compares it with setting Kbm. The element 9 allows blocking of the current protections when negative sequence of the first harmonic current has high level. The element 9 forms an output signal at simultaneous performance of conditions on the element 7 and the element 8. The element 10 forbids blocking of current protections by the signal created in the element 6.
Fig. 1. The logical scheme of blocking unit from IMC for current protection
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итехника, № 3, 2014 53
Энергетические комплексы
Signals at the outlets of filters 2 and 5 have a low level caused by an error of measurements in normal and overload modes, during self-start of engines and symmetric faults not being accompanied with current transformers (CT) saturation. Signals at the filter 1 outlets are proportional to phase currents and I1h-neg current at the filter 4 outlet is close to zero. Thus I2h-pos/I1h-neg value can exceed value Kblk that lead to signal formation at the element 8 outlet. In considered symmetric modes the positive sequence current of the first harmonic I1hpos has a significant value and the negative sequence current of the first harmonic I1h-neg has low value, thus I1h-neg/I1h-pos relation less than the coefficient Kneg and the signal at the element 7 outlet isn't formed then the element 9 "And" doesn't allow blocking of the current protection.
Signals at the filters 2 and 5 outlets have low level caused by an error of measurements, signals at the filter 1 outlets are proportional to phase currents, the signal at the filter 4 outlet has significant value during asymmetrical faults not being accompanied with CT saturation. Thus I2h-p0JIih-neg value doesn't exceed value Kblk and the signal for the current protection blocking isn't formed.
The frequency filter 2 allocates 100 Hz current components, at the filter 5 outlet there is the positive sequence current of the second harmonic I2h-pos during symmetric and asymmetrical faults which are accompanied with CT saturation. At deep CT saturation I2h-pos/I1h-neg value can exceed value Kbk that lead to signal formation at the element 8 outlet. CT saturation is caused by high fault's currents, thus value of current I1h-pos exceeds setting Ibkmax and the element 6 forms the signal which forbids signal formation for current protection blocking.
Significant values of second harmonic appear in currents iA, iB, ic in modes which being accompanied with inrush magnetization current. Signals
which are proportional to the first harmonic in currents iA, iB, ic appear at the filter 1 outlets. First harmonic current components of the positive and the negative sequences appear at the filters 3 and 4 outlets respectively. I1h-neg/I1h-pos ratio is more than the coefficient Kneg and the signal which allows current protection blocking is formed at the element 7 outlet. Signals which is proportional to the second harmonic in currents iA, iB, ic appear at the filters 2 and 5 outlets. The numerical value of the blocking parameter I2h-pos/I1h-neg exceeds setting Kblk and signal occurs at the element 8 inlet. Current I1h-pos can reach value equal to several rated currents of power transformer but doesn't exceed Ibik.max setting and the element 6 doesn't form a signal at the outlet. Existence of signals at the element 9 "And" inlets leads to forming the signal at the element 10 first inlet. As the signal at the element 10 second inlet is absent so the element 10 forms the signal for the current protection blocking.
Parameters of the offered criterion were calculated on the data basis obtained by the experience of switching on of the no-load transformer 110/10 kV with power 6.3 MY-A. Oscillograms of the IMC process are presented in Fig. 2-4. IMC in a phase A has periodic character, in phases B and c - aperiodic character.
In Fig. 5 values of the offered criterion and a classical restraining method from IMC [2] which based on the presence of the second harmonic in phase currents are shown. The frequency filters 1 and 2 are implemented on the basis of Goertzel's digital algorithm [3]. The offered criterion for IMC determination on the basis of the evaluation of the I2h-pos/I1h-neg ratio provides the current protection blocking in three phases and has higher sensitivity to IMC compared to blocking which based on presence of the second harmonic into the phase currents (Fig. 5).
iA, A 100
50
-50
-100
-150
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
t, ms
Fig. 2. IMC in phase A after switching on of no-load transformer 6.3 MV-A
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0
iA, A 100 50 0
-50 -100 -150
.пПЛЛ nfflhr НШ nhhm
¡III ||UI VII Urn tWfr HVffV1 mWl ffYTf kWYY IflfVYYl fmnr rVYTT IfDYW IWifi
P
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
t, ms
Fig. 3. IMC in phase B after switching on of no-load transformer 6.3 MV-A
iA, A 100 50 0
-50 -100 -150
ЩШОШМиииш
ни
LUU
ALU
ид
LUU.
Цщцщцц
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
t, ms
Fig. 4. IMC in phase C after switching on of no-load transformer 6.3 MV-A
200 % 150 100 50 ^-Ih-pc л 1 A A Jv M rtf 41
h h-neg IC2h IClh v*. '"J V 0 Л 1 » j цЛ* л/ ■ It V .'.ÎtÎÏ
IA2h IAlh ЛГ*1 Л чА VA. i, ^ И* » V ViJ w + u
Г" I IB1h ..... ....
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
t, ms
Fig. 5. Values of blocking parameters at IMC mode
C O N C L U S I O N S
The paper presents blocking algorithm for current protection during inrush process. The algorithm is based on the evaluation of the ratio of the positive sequence second harmonic current to the negative sequence first harmonic current.
The offered algorithm provides higher reliability due to simultaneous blocking of three phases of the current protection and also higher sensitivity due to use of the positive sequence current of the second harmonic in comparison with classical blocking which based on presence of the second harmonic into the phase currents and executed separately for three phases.
The offered algorithm needs to be tested in wide range of the IMC modes and at symmetric
and asymmetrical faults including faults accompanied with CT saturation.
R E F E R E N C E S
1. Evdokimov, F. E. (1971) Theoretical Bases Electricians. Moscow: Vysshaya Shkola, 437-439.
2. Kashtenni, B., & Sevov, L. (2009) Advanced Algorithm of Tuning From Magnetization Current Inrush. Relei-shchik [Releyshchik], 1, 31-41.
3. Romaniuk, F. A., & Loman, M. S. (2012) Formation of Orthogonal Component Controlled Values in Microprocessor Protection Reducing Transformer. Izvestiia Vysshikh Uchebnykh Zavedenii i Energeticheskikh Ob 'edinenii - Energeti-ka [Proceedings of the Higher Education Institutions and Power Engineering Associations - Power Engineering], 4, 5-9.
Поступила 19.12.2013
Наука итехника, № 3, 2014
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