CN114362101A - Excitation variable differential protection method for double-core asymmetric phase-shifting transformer - Google Patents
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Abstract
The application discloses an excitation variable differential protection method for a twin-core asymmetric phase-shifting transformer based on a turn ratio intelligent following principle, which comprises the following steps: the method comprises the following steps of secondary current phase correction, equipment parameter input, tap joint real-time gear acquisition, intelligent turn ratio following calculation, intelligent secondary current real-time balance coefficient following calculation, real-time secondary current amplitude compensation, excitation variable differential protection differential current and brake current calculation, and identification of coordinate positions of the differential current and the brake current in a proportional action area or a brake area. The invention can provide a set of perfect differential protection configuration scheme according to the complex and compact primary structure, frequently-changed gears and CT actual installation of the dual-core asymmetric phase-shifting transformer, and provides a feasible technical method for engineering differential protection application of the dual-core asymmetric phase-shifting transformer.
Description
Technical Field
The invention relates to the field of transformer differential protection, in particular to an excitation variable differential protection method for a double-core asymmetric phase-shifting transformer.
Background
A Transformer (Transformer) is a device that changes an alternating-current voltage by using the principle of electromagnetic induction, and main components are a primary coil, a secondary coil, and an iron core (magnetic core). The main functions are as follows: voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), and the like.
The double-core phase-shifting transformer consists of two parts, namely a series transformer and an excitation transformer, wherein the neutral point of the double-core phase-shifting transformer is grounded, and the excitation part is not directly connected with a system. The adjustment characteristics are classified into a symmetrical type or an asymmetrical type. The symmetrical type can change the phase difference at two sides of the phase-shifting transformer, and the asymmetrical type can simultaneously change the phase difference and the voltage amplitude of the phase-shifting transformer. By utilizing the characteristics, in the power grid loop closing operation process, the phase-shifting transformer can enable the voltages and phases at two sides of the loop closing operation switch to be approximately the same, so that very small impact and even no impact switching-on are realized, and further, uninterrupted power supply of the load is realized.
The differential protection configuration of the phase-shifting transformer is closely related to the primary structure of the phase-shifting transformer, and the series transformer and the excitation transformer are arranged in the same box body, so that the structure is complex. Compared with the conventional transformer, the installation position and the number of the CTs are limited by the one-time compact structure of the phase-shifting transformer, and influence is brought to the engineering configuration and realization of differential protection. Especially for the excitation transformer of the phase-shifting transformer, the turn ratio of the primary side and the secondary side is not fixed in the working process, a conventional fixed coefficient cannot be provided for differential flow calculation, and a new differential protection implementation method needs to be designed.
Disclosure of Invention
The application provides an excitation variable differential protection method for a double-core asymmetric phase-shifting transformer, which aims to solve the problems that the differential protection configuration of the phase-shifting transformer is closely related to a primary structure of the phase-shifting transformer, a series transformer and an excitation transformer are arranged in the same box body, the structure is complex, the turn ratio of a primary side and a secondary side is not fixed in the working process, and a conventional fixed coefficient cannot be provided for differential current calculation, and comprises the following steps:
collecting secondary current data as current excitation quantity of differential protection, performing phase correction on secondary current of star-shaped or angle-shaped wiring according to the collected secondary current data, and calculating corrected secondary current data;
acquiring equipment parameter data and tap real-time gear data of a device, and carrying out turn ratio intelligent following calculation according to the acquired data to obtain balance coefficients Kpn and Kpm of each secondary current;
calculating differential current and brake current of the excitation transformer differential protection according to the corrected secondary current data obtained by calculation and balance coefficients Kpn and Kpm of each secondary current, and if the coordinates of the differential current and the brake current are in a differential proportional action area and other locking conditions do not exist, performing differential protection action;
the phase correction is: changing the star connection into an angular connection or changing the angular connection into the star connection;
the excitation variable differential protection method of the double-core asymmetric phase-shifting transformer is adapted to the double-core asymmetric phase-shifting transformer, and the double-core asymmetric phase-shifting transformer is provided with: a series transformer primary system side current CT1, a series transformer primary load side current CT2, an excitation transformer primary side current CT3, an excitation transformer secondary side phase modulation winding N current CT4, a series transformer secondary side winding and an excitation transformer secondary side voltage regulating winding M.
Preferably, the secondary current data includes: the secondary current of the excitation transformer primary side current CT3 and the secondary current of the excitation transformer secondary side phase modulation winding N current CT 4.
Preferably, the device parameters include: the phase modulation winding N, the voltage regulation winding M tap intermediate gear and the corresponding turn ratio; the turn percentage of each gear of the phase modulation winding N and the voltage regulating winding M; the nameplate capacity and the rated voltage of the transformer; the transformation ratio of the primary side current CT3 of the excitation transformer and the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer are obtained.
Preferably, the current tap position is: the current gear of the phase modulation winding N tap and the current gear of the voltage regulating winding M tap.
Preferably, the calculation formula of the real-time balance coefficient Kpn of the secondary current of the secondary side phase modulation winding N current CT4 of the excitation transformer is as follows:
Kpn＝Pn*(1+Rn*(Dn-On))*K4/K3
in the formula: pn is the turn ratio corresponding to the middle gear of the phase modulation winding N tap; rn is the turn percentage of each gear of the phase modulation winding N; dn current gear of said phase modulated N winding tap; on the phase modulation winding N tap middle gear; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
Preferably, the calculation formula of the real-time balance coefficient Kpm of the secondary current after the M-angle connection of the excitation transformer secondary side voltage regulating winding is as follows:
Kpm＝Pm*(1+Rm*(Dm-Om))*K4/K3
in the formula: pm is the turn ratio corresponding to the middle gear of the M tap of the voltage regulating winding; rm is the turn percentage of each gear of the voltage regulating winding M; the current gear of a winding tap of the Dm voltage regulating winding M; om the M tap intermediate gear of the voltage regulating winding; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
Preferably, the excitation transformer primary-side current CT3 secondary current is used as a reference side for calculating a balance coefficient, and the excitation transformer primary-side current CT3 secondary current balance coefficient is 1.
Preferably, the differential current and the braking current are calculated by the following equations:
in the formula:
the primary side current CT3 of the excitation transformer is the secondary current of each phase after phase correction;
each phase of secondary current after phase correction is carried out on the excitation transformer secondary side phase modulation winding N current CT 4;
each phase secondary current after the excitation voltage-changing winding is connected in an M-angle mode, namely each phase secondary current flowing through the exciting transformer secondary side phase-changing winding N current CT 4; i isdzIs the differential current; i iszdIs the braking current.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the embodiments of the invention and, together with the description, serve to explain the principles of the embodiments of the invention. It is obvious that the drawings in the following description are only some of the embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a typical engineering layout of a dual-core asymmetric phase-shifting transformer CT to which the present invention is applied;
fig. 2 is a flow chart of an excitation variable differential protection method of a twin-core asymmetric phase-shifting transformer according to the present invention.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, apparatus, steps, and so forth. In other instances, well-known techniques have not been shown or described in detail to avoid obscuring aspects of embodiments of the invention.
Further, the drawings are merely schematic illustrations of embodiments of the present invention, in which the same reference numerals denote the same or similar parts, and thus, repeated descriptions thereof will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in the form of software, or in a plurality of hardware modules or integrated circuits, or in different networks and/or processor means and/or microcontroller means.
Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in fig. 1, fig. 1 is a typical engineering configuration diagram of a dual-core asymmetric phase-shifting transformer CT suitable for the present invention, due to the structural limitation of the phase-shifting transformer, only "current CT1 on the primary system side of the series transformer, current CT2 on the primary load side of the series transformer, current CT3 on the primary side of the excitation transformer, and current CT4 on the secondary side of the excitation transformer" can be configured, and loops at two ends of the secondary side winding of the series transformer and the secondary side voltage regulating winding M of the excitation transformer are all installed in a box and cannot be installed with a CT, and the differential protection engineering implementation scheme of the dual-core asymmetric phase-shifting transformer must be implemented based on the CT configuration.
As shown in figure 1, the current of the secondary side winding of the series transformer is connected to the current of the secondary side phase modulation winding N of the excitation transformer after angular connection, and the angular connection mode is Y/Y/delta-9 type. Based on the ampere-turn balance relation, a series longitudinal variation protection which is fixed to be Y/Y/delta-9 in a wiring mode and mainly used for protecting phase-to-phase faults, grounding faults and winding turn-to-turn faults of a phase-shifting transformer outgoing line and a series transformer can be formed by a series transformer primary system side current CT1, a series transformer primary load side current CT2 and an excitation transformer secondary side phase modulation winding N current CT 4. The method for correcting the phase of the Y-side current of the primary system side current CT1 and the primary load side current CT2 of the series transformer is adopted, and the Y-side current correction formula is as follows
In the formula:
is the secondary current of CT on the Y side;
the corrected phase currents for the Y side.
Based on kirchhoff's law, primary winding differential protection consisting of a current CT1 on the primary system side of the series transformer, a current CT2 on the primary load side of the series transformer and a current CT3 on the primary side of the excitation transformer can be adopted, and the primary winding differential protection is mainly used for improving the sensitivity of ground faults of a lead and a primary winding part in the installation range of the CT. The winding differential protection is not affected by the magnetizing inrush current, but does not protect the winding turn-to-turn fault.
As shown in fig. 1, in addition to the above-mentioned tandem differential protection and phase-shift primary winding differential protection of the series transformer, the phase-shift transformer should also be equipped with an ampere-turn balance-based split-phase differential protection of the excitation transformer, which is composed of an excitation transformer primary side current CT3, an excitation transformer secondary side phase-modulated winding N current CT4, and an excitation transformer secondary side voltage-modulated winding M current, and is mainly used for protecting the phase-to-phase fault, the ground fault, and the winding turn-to-turn fault of the excitation transformer.
As shown in figure 1, the secondary side voltage regulating winding M current of the excitation transformer is connected to the secondary side phase regulating winding N current of the excitation transformer after angular connection, and the angular connection mode is Y/Y/delta-9 type. Based on the ampere-turn balance relation, excitation longitudinal differential protection which is fixed to be Y/Y/delta-9 in a wiring mode and mainly used for protecting phase-to-phase faults, grounding faults and winding turn-to-turn faults of the excitation transformer can be formed by adopting a' excitation transformer primary side current CT3, an excitation transformer secondary side phase modulation winding N current CT4 (phase modulation winding N star-shaped wiring current) and an excitation transformer secondary side phase modulation winding N current CT4 (current after M-angle wiring of a voltage regulating winding). The method adopts a mode of carrying out phase correction on Y-side currents of a primary side current CT3 of the excitation transformer and a secondary side phase modulation winding N current CT4 (phase modulation winding N star-shaped wiring current) of the excitation transformer, and the Y-side current correction formula is as follows:
in the formula:
is the secondary current of CT on the Y side;
the corrected phase currents for the Y side.
The turn ratio of the primary side winding and the secondary side winding of the conventional transformer is fixed and unchanged. The engineering technical difficulty faced by the excitation longitudinal variation protection of the phase-shifting transformer is as follows: in order to realize respective voltage and phase regulating functions, a secondary side voltage regulating winding M and a secondary side phase regulating winding N of the excitation transformer are regulated in a dynamic bidirectional and full-range mode, so that the turn ratio of a primary side and a secondary side in the working process of the excitation transformer is not fixed, and a conventional fixed coefficient cannot be provided for differential flow calculation.
Aiming at the difficulty in the implementation of the longitudinal differential protection engineering of the excitation transformer, the invention provides the excitation variable differential protection method of the double-core asymmetric phase-shifting transformer based on the intelligent turn ratio following principle.
As shown in fig. 2, fig. 2 is a flowchart of an excitation transformer differential protection method of a two-core asymmetric phase-shifting transformer according to the present application. In this embodiment, the excitation transformer differential protection for the dual-core asymmetric phase-shifting transformer includes the following steps:
the method comprises the following steps: and collecting secondary current data as current excitation quantity of differential protection, performing phase correction on the secondary current of the star-shaped wiring according to the collected secondary current data, and calculating the corrected secondary current data.
Further, in this embodiment, the phase correction is: the star connection is changed into an angle connection, or the angle connection is changed into a star connection.
Further, in this embodiment, the secondary current data includes: the secondary current of the excitation transformer primary side current CT3 and the secondary current of the excitation transformer secondary side phase modulation winding N current CT 4.
In the application of transformer differential protection, in order to simplify field wiring, the CT of each side of the transformer adopts a star-shaped wiring mode, the polarity ends of the CT point to the same direction (such as a bus side), and the secondary current of the CT of each side is directly connected into protection. At this time, for the transformer with the Y/Δ -11 connection mode, a phase difference of 30 ° occurs between the secondary currents on both sides, and the protection device needs to correct the phase through a software algorithm. The protection device mainly has two phase correction modes: a trigonometric lateral starburst correction (i.e., Δ → Y) and a starburst lateral trigonometric correction (i.e., Y → ∑ Δ). The star-side-delta side correction (i.e., Y → Δ) is used in this embodiment.
The Y → ∑ Δ phase correction algorithm is as follows:
the correction formula of the secondary current of the excitation transformer primary side current CT3 is as follows:
in the formula:
secondary current of the excitation primary side CT 3;
the corrected secondary currents of the respective phases are obtained for the excitation primary side CT 3.
The correction formula of the secondary current of the phase modulation winding N current CT4 on the secondary side of the excitation transformer is as follows:
in the formula:
secondary current CT4 of phase modulation winding N current for the excitation transformer secondary side;
and correcting each phase of secondary current of the excitation variable secondary side phase modulation winding N current CT 4.
Further, the secondary current after the excitation transformer voltage-regulating winding is connected in an M-angle manner is the secondary current flowing through the excitation transformer secondary side phase-regulating winding N current CT4
The triangular side of the transformer is used as a phase correction reference side, and phase correction is not needed.
The purpose of the correction of the steps through a software algorithm is as follows: the phases of the currents on the two sides of the transformer differential loop are consistent. The root sign is divided into three in the formula, because the amplitude is changed into three times of the original root sign except the change of the phase after the two vectors are subtracted, and the amplitude is the same as the original current after the two vectors are divided into three, thereby achieving the purpose of keeping the amplitude unchanged after the phase deviation.
Step two: acquiring equipment parameter data and tap real-time gear data of a device, and carrying out turn ratio intelligent following calculation according to the acquired data to obtain balance coefficients Kpn and Kpm of each secondary current;
further, in this embodiment, the device parameters include: the phase modulation winding N, the voltage regulation winding M tap intermediate gear and the corresponding turn ratio; the turn percentage of each gear of the phase modulation winding N and the voltage regulating winding M; the nameplate capacity and the rated voltage of the transformer; the transformation ratio of the primary side current CT3 of the excitation transformer and the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer are obtained.
Further, in this embodiment, the current gear of the tap is the current gear of the phase winding N and the tap of the voltage regulating winding M.
Factors affecting differential current calculation of transformer differential protection: the transformer mainly comprises unbalance caused by mismatching of current transformers on high and low voltage sides of the transformer, and the current transformers are selected without considering the influence of the transformer on differential current because the transformation ratio of the current transformers is a standard numerical value, and the rated current of the transformer is an irregular number although the capacity of the transformer is a standard value. In the embodiment, unbalance caused by different amplitudes of currents on the high-voltage side and the low-voltage side and mismatching of current transformers is eliminated by introducing the balance coefficient.
The concept of the balance coefficient is: the scaling factor used when two different units or the same unit but different amounts of the reference are reduced to the same unit or the same reference is the balance factor.
Further, in this embodiment, the calculation formula of the real-time balance coefficient Kpn of the secondary current of the excitation variable secondary side phase modulation N winding CT4 is as follows:
Kpn＝Pn*(1+Rn*(Dn-On))*K4/K3
in the formula: pn is the turn ratio corresponding to the middle gear of the phase modulation winding N tap; rn is the turn percentage of each gear of the phase modulation winding N; dn, the current gear of the phase modulation N winding tap, and On, the middle gear of the phase modulation N winding tap; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
Further, in this embodiment, the calculation formula of the real-time balance coefficient Kpm of the secondary current after the M-angle connection of the excitation transformer secondary side voltage regulating winding is as follows:
Kpm＝Pm*(1+Rm*(Dm-Om))*K4/K3
in the formula: pm is the turn ratio corresponding to the middle gear of the M tap of the voltage regulating winding; rm is the turn percentage of each gear of the voltage regulating winding M; the current gear of a Dm voltage regulating winding M winding tap, and the middle gear of the M voltage regulating winding tap Om; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
Further, as a reference side of the balance coefficient calculation, the excitation transformer primary side current CT3 secondary current is not subjected to amplitude compensation, that is, the balance coefficient is 1.
Step three: calculating differential current and brake current of the excitation transformer differential protection according to the corrected secondary current data obtained by calculation and balance coefficients Kpn and Kpm of each secondary current, and if the coordinates of the differential current and the brake current are in a differential proportional action area and other locking conditions do not exist, performing differential protection action;
further, in this embodiment, the differential current and the braking current are calculated according to the following formulas:
in the formula:
the primary side current CT3 of the excitation transformer is the secondary current of each phase after phase correction;
each phase of secondary current after phase correction is carried out on the excitation transformer secondary side phase modulation winding N current CT 4;
each phase of secondary current after the excitation variable voltage regulating winding is connected in an M-angle mode, namely each phase of secondary current flowing through the excitation variable secondary side phase regulating N winding CT 4; i isdzIs the differential current; i iszdIs the braking current.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
Claims (8)
1. An excitation variable differential protection method for a twin-core asymmetric phase-shifting transformer comprises the following steps:
collecting secondary current data as current excitation quantity of differential protection, performing phase correction on secondary current of star-shaped or angle-shaped wiring according to the collected secondary current data, and calculating corrected secondary current data;
acquiring equipment parameter data and tap real-time gear data of a device, and carrying out turn ratio intelligent following calculation according to the acquired data to obtain balance coefficients Kpn and Kpm of each secondary current;
calculating differential current and brake current of the excitation transformer differential protection according to the corrected secondary current data obtained by calculation and balance coefficients Kpn and Kpm of each secondary current, and if the coordinates of the differential current and the brake current are in a differential proportional action area and other locking conditions do not exist, performing differential protection action;
the phase correction is: changing the star connection into an angular connection or changing the angular connection into the star connection;
the excitation variable differential protection method for the double-core asymmetric phase-shifting transformer is adapted to the double-core asymmetric phase-shifting transformer, and the double-core asymmetric phase-shifting transformer is provided with: a series transformer primary system side current CT1, a series transformer primary load side current CT2, an excitation transformer primary side current CT3, an excitation transformer secondary side phase modulation winding N current CT4, a series transformer secondary side winding and an excitation transformer secondary side voltage regulating winding M.
2. The method of claim 1, wherein the secondary current data comprises: the secondary current of the excitation transformer primary side current CT3 and the secondary current of the excitation transformer secondary side phase modulation winding N current CT 4.
3. The method of claim 1, wherein the device parameters include: the phase modulation winding N, the voltage regulation winding M tap intermediate gear and the corresponding turn ratio; the turn percentage of each gear of the phase modulation winding N and the voltage regulating winding M; the nameplate capacity and the rated voltage of the transformer; the transformation ratio of the primary side current CT3 of the excitation transformer and the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer are obtained.
4. The method for protecting the differential excitation transformer of the two-core asymmetric phase-shifting transformer according to claim 1, wherein the current gear positions of the taps are as follows: the current gear of the phase modulation winding N tap and the current gear of the voltage regulating winding M tap.
5. The excitation transformer differential protection method for the two-core asymmetric phase-shifting transformer according to claim 1 or 4,
the calculation formula of the real-time balance coefficient Kpn of the secondary current of the phase modulation winding N current CT4 at the secondary side of the excitation transformer is as follows:
Kpn＝Pn*(1+Rn*(Dn-On))*K4/K3
in the formula: pn is the turn ratio corresponding to the middle gear of the phase modulation winding N tap; rn is the turn percentage of each gear of the phase modulation winding N; dn the current gear of the phase winding N tap; on is a middle gear of the phase modulation winding N tap; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
6. The excitation transformer differential protection method for the two-core asymmetric phase-shifting transformer according to claim 1, 3 or 4,
the calculation formula of the real-time balance coefficient Kpm of the secondary current after the M-angle wiring of the excitation transformer secondary side voltage regulating winding is as follows:
Kpm＝Pm*(1+Rm*(Dm-Om))*K4/K3
in the formula: pm is the turn ratio corresponding to the middle gear of the M tap of the voltage regulating winding; rm is the turn percentage of each gear of the voltage regulating winding M; the current gear of a winding tap of the Dm voltage regulating winding M; om the M tap intermediate gear of the voltage regulating winding; k3 is the transformation ratio of the excitation transformer primary side current CT 3; k4 is the transformation ratio of the secondary side phase modulation winding N current CT4 of the excitation transformer.
7. The method according to claim 1, wherein a secondary current balance coefficient of the excitation transformer primary side current CT3 is 1 as a reference side of balance coefficient calculation.
8. The method according to any one of claims 1 to 7, wherein the differential currents and the braking currents are calculated as follows:
in the formula:
the primary side current CT3 of the excitation transformer is the secondary current of each phase after phase correction;
each phase secondary current after phase correction is carried out on the phase modulation winding N current CT4 on the secondary side of the exciting transformer;
each phase secondary current after the excitation voltage-changing winding is connected in an M-angle mode, namely each phase secondary current flowing through the secondary side phase-changing N winding CT4 of the excitation transformer; i isdzIs the differential current; i iszdIs the braking current.
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| US20110063761A1 (en) * | 2009-09-17 | 2011-03-17 | Kasztenny Bogdan Z | Transformer Differential Protection |
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