Disclosure of Invention
The invention aims to provide a method for starting a current mutation quantity for transformer protection and a transformer protection device, which are used for solving the problem that when a current sensor on one side of a transformer has a disconnection fault, the judgment of the starting of the current mutation quantity is invalid, and the judgment reliability cannot be ensured.
Based on the purpose, the technical scheme of the current sudden change starting method for transformer protection is as follows:
when a current sensor on one side of the transformer has a line break fault, judging the current break variable of any phase on any side of the transformer, and judging the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable and the negative sequence voltage break variable on the corresponding side of the transformer;
when the current break variable of a certain phase at the high-voltage side or the medium-voltage side of the transformer is larger than a set current break variable threshold value, and when the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable or the negative sequence voltage break variable of the corresponding side of the transformer is larger than the set voltage threshold value, controlling a current break variable starting element protected by the transformer to start;
when the current mutation amount of a certain phase at the low-voltage side of the transformer is larger than a set current mutation amount threshold value and the negative sequence voltage or the negative sequence voltage mutation amount of the corresponding side of the transformer is larger than a set voltage threshold value, a current mutation amount starting element for protecting the transformer is controlled to start.
Based on the purpose, the technical scheme of the transformer protection device is as follows:
the transformer protection circuit comprises a processor and is used for executing instructions to realize the current break variable starting method for transformer protection.
The two technical schemes have the beneficial effects that:
according to the method and the element for starting the sudden current change, when the current sensor on one side of the transformer breaks down, the sudden current change of any phase on any side of the transformer is judged, and any condition of the zero sequence voltage, the sudden zero sequence voltage change, the negative sequence voltage and the sudden negative sequence voltage change is combined for judgment, so that the starting element of the sudden current change can still be reliably started even when the current sensor on one side of the transformer breaks down.
The system on the low-voltage side of the transformer is usually a small-current grounding system, when the single-phase grounding of the low-voltage side of the transformer is carried out, the system has zero-sequence voltage, but the transformer can still continuously run for a period of time, so that the low-voltage side of the transformer cannot adopt the zero-sequence voltage and zero-sequence voltage mutation criterion, and only can adopt negative-sequence voltage and negative-sequence voltage mutation to judge; when the high-voltage side or the medium-voltage side of the transformer is a large-current grounding system, the system does not have the condition of continuous operation when single-phase grounding faults occur, so that zero sequence voltage, zero sequence voltage break variable, negative sequence voltage and negative sequence voltage break variable can be adopted for judgment. According to the actual operation condition of the transformer, the zero sequence voltage break variable, the negative sequence voltage and the negative sequence voltage break variable of the corresponding side of the transformer are comprehensively judged, and the current break variable starting element is prevented from being started by mistake.
Further, the discriminant equation for judging the zero sequence voltage of the corresponding side of the transformer is as follows:
3U0(t)>3U0.SET
3U in the above formula0(t) is zero sequence voltage amplitude value of corresponding side of the transformer at time t, 3U0.SETAnd determining a value for the zero sequence voltage in the set voltage threshold value. Specifically, the 3U0.SETHas a value range of 0.06UN~0.15UNWherein U isNIs the rated voltage value of the transformer.
Further, the discriminant equation for judging the negative sequence voltage of the corresponding side of the transformer is as follows:
U2(t)>U2.SET
in the above formula U2(t) is the negative sequence voltage amplitude at time t of the corresponding side of the transformer, U2.SETAnd setting the negative sequence voltage in the set voltage threshold value. Specifically, the U is2.SETHas a value range of 0.06UN~0.10UNWherein U isNIs the rated voltage value of the transformer.
Further, the discriminant equation for judging the zero sequence voltage break variable of the corresponding side of the transformer is as follows:
|3U0(t)-3U0(t-2T)|>Δ3U0.SET
3U in the above formula0(t) is zero sequence voltage amplitude value of corresponding side of the transformer at time t, 3U0(T-2T) is zero sequence voltage amplitude of the corresponding side of the transformer before 2T in two periods at the time T, and delta 3U0.SETAnd determining a value for the zero sequence voltage mutation in the set voltage threshold value. Specifically, the Δ 3U0.SETIs in the range of 0.015UN~0.04UNWherein U isNIs the rated voltage value of the transformer.
Further, the discriminant equation for judging the negative sequence voltage abrupt change of the corresponding side of the transformer is as follows:
|U2(t)-U2(t-2T)|>ΔU2.SET
in the above formula U2(t) is the negative sequence voltage amplitude at time t of the corresponding side of the transformer, U2(T-2T) is the negative sequence voltage amplitude of the corresponding side of the transformer two periods before 2T at time T, delta U2.SETAnd determining the quantity of the negative sequence voltage mutation in the set voltage threshold value. Specifically, the Δ U2.SETHas a value range of 0.01UN~0.03UNWherein U isNIs the rated voltage value of the transformer.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
The first embodiment of the method comprises the following steps:
the invention relates to a method for starting a current break variable for transformer protection, which is mainly applied to a local transformer protection device of a smart grid. The following further describes embodiments of the present invention with reference to the drawings.
In the main connection mode of the 220kV transformer shown in fig. 1, the transformer protection device collects the high-voltage side current TA1 and voltage TV1, the medium-voltage side current TA2 and voltage TV2, and the low-voltage side current TA3 and voltage TV3 of the transformer, and sets up the starting criterion of the sudden change amount of the high-voltage side, medium-voltage side and low-voltage side currents of the transformer respectively according to the corresponding side currents and voltages. The starting logic of the method for starting the sudden change of the current for realizing the protection of the transformer is shown in figure 2, and the method comprises the following specific steps:
judging whether the current mutation amount of any phase on any side of the transformer is larger than a set current mutation amount threshold value or not; and judging whether the phase current of the corresponding side of the transformer is larger than a set current threshold value or not.
Specifically, the judgment process includes two criteria:
(1) the phase current sudden change starting criterion (criterion one for short) is that in the criterion, a discrimination equation (namely a current sudden change discrimination condition) that any phase current sudden change of a high-voltage side or a medium-voltage side or a low-voltage side of a transformer meets is as follows:
|IΦ1(t)-IΦ1(t-T)|>1.25|IΦ1(t-T)-IΦ1(t-2T)|+ΔISET
in the above formula IΦ1(t) is the current amplitude of a certain phase at the time t on the high-voltage side or the medium-voltage side or the low-voltage side of the transformer, IΦ1(T-T) is the phase current amplitude of the corresponding phase of the transformer before a period T at the time T, 1.25| IΦ1(t-T)-IΦ1(t-2T)|+ΔISETFor a set current break variable threshold value, where IΦ1(T-2T) is the phase current amplitude of the corresponding phase of the transformer before 2T in two periods at the time T; delta ISETFor setting the starting current to an abrupt magnitude, Δ ISETTake max {0.2Ie,0.1INIn which IeFor secondary rated load current of the corresponding side of the transformer, INThe secondary rating of the current sensor on the corresponding side of the transformer.
(2) Phase current starting criterion (criterion two for short), in the criterion, a discrimination equation which is satisfied by phase current starting at the corresponding side of the transformer is as follows:
in the above formula IΦ1.MAX(t) is the maximum phase current amplitude in the three-phase current of the corresponding side of the transformer, IΦ1.SETFor phase current setting, take 1.2Ie。
When the current mutation amount of a certain phase at one side of the transformer is larger than a set current mutation amount threshold value and the phase current of the corresponding side of the transformer is larger than a corresponding current threshold value, the current mutation amount starting element protected by the transformer is controlled to be started, a current mutation amount starting message is generated to the transformer protection device, and a starting power supply of a related outlet relay is opened.
In order to prevent the failure of the judgment of the phase current when the CT (current sensor) of the transformer is disconnected, the phase current starting criterion (namely the judgment of the phase current locked) is locked when the CT is disconnected, and the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable and the negative sequence voltage break variable criterion (the criterion three for short) which are automatically put into the corresponding side of the transformer are judged, wherein in the criterion, the judgment equation for judging the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable or the negative sequence voltage break variable of the corresponding side of the transformer is as follows:
the above formulas are sequentially corresponding to zero sequence voltage judgment condition and negative sequence voltage judgmentDistinguishing condition, zero sequence voltage break variable distinguishing condition, negative sequence voltage break variable condition, 3U in the above formula0(t) is zero sequence voltage amplitude value of corresponding side of the transformer at time t, U2(t) is the negative sequence voltage amplitude of the corresponding side of the transformer at the time t, 3U0(T-2T) is zero sequence voltage amplitude value of the corresponding side of the transformer before 2T in two periods at time T, U2And (T-2T) is the negative sequence voltage amplitude of the corresponding side of the transformer two periods 2T before time T.
The set voltage threshold value comprises 3U0.SET、U2.SET、Δ3U0.SET、ΔU2.SETWherein is 3U0.SETFor zero sequence voltage constant, 3U0.SETHas a value range of 0.06UN~0.15UNWherein U isNFor the rated voltage value of the transformer, 0.1U is preferably adoptedN;U2.SETFor setting negative sequence voltage, U2.SETHas a value range of 0.06UN~0.10UNPreferably 0.08UN;Δ3U0.SETFor zero sequence voltage step-size, Delta 3U0.SETIs in the range of 0.015UN~0.04UNPreferably 0.02UN;ΔU2.SETFor negative sequence voltage step-size determination, Δ U2.SETHas a value range of 0.01UN~0.03UNPreferably 0.02UN。
It should be noted that, when setting the voltage threshold value, the negative sequence voltage constant value is smaller than the zero sequence voltage constant value because the negative sequence voltage constant value is smaller than the zero sequence voltage constant value under normal conditions; in order to improve the reliability of protection, the zero sequence voltage transient fixed value and the negative sequence voltage transient fixed value are preferably set to be relatively small.
Based on the setting of the voltage threshold value, when the current break variable of a certain phase at the high-voltage side or the medium-voltage side of the transformer is larger than the corresponding current break variable threshold value, and when the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable or the negative sequence voltage break variable of the corresponding side of the transformer is larger than the corresponding voltage threshold value, the current break variable starting element for protecting the transformer is controlled to start.
And when the current break variable of a certain phase at the low-voltage side of the transformer is larger than the corresponding current break variable threshold value and the negative sequence voltage or the negative sequence voltage break variable of the corresponding side of the transformer is larger than the corresponding voltage threshold value, controlling the starting of a current break variable starting element protected by the transformer.
After the transformer current sudden change starting element is started, the fixed time delay returns, and the whole set of resetting time is 7 s.
According to the method and the element for starting the sudden current change, when the current sensor on one side of the transformer has a line break fault, the sudden current change of any phase on any side of the transformer is judged, and any condition of the zero sequence voltage, the sudden zero sequence voltage change, the negative sequence voltage and the sudden negative sequence voltage change is combined for judgment, so that the reliable starting of the sudden current change starting element can be ensured even when the current sensor on one side of the transformer has the line break fault.
In the embodiment, the first criterion and the second criterion can be simultaneously judged, the first criterion and the third criterion can be simultaneously judged when the CT of the transformer is disconnected, as other implementation modes, the first criterion is firstly judged, whether the second criterion or the third criterion is judged according to the result of the first criterion is determined, when the judgment equation of the first criterion is not satisfied, the current mutation starting element is directly judged not to be started, and the second criterion and the third criterion are not judged, so that the calculated amount is saved, and the calculation efficiency is improved.
The second method embodiment:
in order to determine whether a current break variable starting element is started, the current break variable starting method of the embodiment is the same as the first method embodiment, and comprises three criteria, namely, a first criterion, a second criterion and a third criterion, and the starting logic of the method is shown in fig. 3, wherein the first criterion and the third criterion are the same as the description in the first method embodiment, except that the zero-sequence current and negative-sequence current starting criterion is added in the second criterion, so that the judgment equation satisfied by the starting of the phase current or the zero-sequence current or the negative-sequence current on the corresponding side of the transformer is as follows:
the above formulas correspond to phase current discrimination condition, zero sequence current discrimination condition and negative sequence current discrimination condition in sequence, wherein I in the above formulaΦ1.MAX(t) is the maximum phase current amplitude in the three-phase current of the corresponding side of the transformer, 3I0(t) is zero sequence current amplitude of the corresponding side of the transformer, I2(t) is the negative sequence current amplitude of the corresponding side of the transformer, and the set current threshold value comprises IΦ1.SET、3I0.SET、I2.SETIn which IΦ1.SETFor phase current setting, take 1.2Ie;3I0.SETFor zero sequence current constant value, take 0.1IN;I2.SETFor setting the negative sequence current, take 0.2IN。
When the current mutation amount of a certain phase at one side of the transformer is larger than a set current mutation amount threshold value and the phase current or zero sequence current or negative sequence current at the corresponding side of the transformer is larger than a corresponding current threshold value, a current mutation amount starting element protected by the transformer is controlled to start, a current mutation amount starting message is generated to a transformer protection device, and a starting power supply of a related outlet relay is opened.
In order to prevent the phase current, the zero sequence current and the negative sequence current from being judged to be invalid when a Current Transformer (CT) of the transformer is disconnected, the phase current, the zero sequence current and the negative sequence current are locked when the CT is disconnected, a zero sequence voltage, a negative sequence voltage, a zero sequence voltage abrupt change and a negative sequence voltage abrupt change on the corresponding side of the transformer are automatically input, and the judgment is called as the judgment (three) for the short term, because the judgment (three) for the third in the embodiment is the same as the judgment (three) for the first in the embodiment, the description is omitted in the embodiment.
Transformer protection device embodiment:
the embodiment provides a transformer protection device, which includes a processor, configured to execute instructions to implement the following steps:
when a current sensor on one side of the transformer has a line break fault, the current break variable of any phase on any side of the transformer is judged, and the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable and the negative sequence voltage break variable on the corresponding side of the transformer are judged.
When the current break variable of a certain phase at the high-voltage side or the medium-voltage side of the transformer is larger than a set current break variable threshold value, and when the zero sequence voltage, the negative sequence voltage, the zero sequence voltage break variable or the negative sequence voltage break variable of the corresponding side of the transformer is larger than the set voltage threshold value, the current break variable starting element for protecting the transformer is controlled to start.
When the current mutation amount of a certain phase at the low-voltage side of the transformer is larger than a set current mutation amount threshold value and the negative sequence voltage or the negative sequence voltage mutation amount of the corresponding side of the transformer is larger than a set voltage threshold value, a current mutation amount starting element for protecting the transformer is controlled to start.
The method embodiments of the first and second embodiments are described in sufficient detail to avoid unnecessary detail.