Setting strategy of instantaneous current quick-breaking protection for mine power grid
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摘要: 矿山电网作业环境较差，当井下供电系统发生短路故障时，使用复杂的防越级跳闸保护装置会使整个电网的可靠性降低、成本提高，并且矿山电网需要保证电流速断保护能够瞬时动作以切除短路故障，尤其是线路出口处的短路故障。目前矿山电网防越级跳闸保护方案不能兼顾保护速动性、供电可靠性和设备经济性。针对上述问题，根据矿山电网井下发生短路事故不能越级到井上的最低原则，提出了一种基于整体最优原则的矿山电网瞬时电流速断保护整定策略。分析了矿山电网短路电流与短路点位置的关系及线路首末端短路电流的分布特征，对比研究了传统单一整定方法存在的缺陷。定义了最小−最大系统阻抗比、最大系统阻抗与线路阻抗比、相邻线路阻抗比3个指标，用来表示不同短路电流分布场景的特征关系式和各整定方法满足要求的条件，从而判定不同短路电流分布场景下瞬时电流速断保护所适用的整定方法，并给出相应的最优整定策略流程。以典型矿山供电线路为例，根据所提整定策略对其各级保护开关进行整定计算，结果表明：采用该整定策略对矿山电网模型中5个存在越级跳闸风险的保护开关进行整定，可将其中4个保护开关的保护范围控制在2级线路之内，减少了越多级跳闸事故的次数，降低了矿山电网井下短路故障延伸到井上的概率。Abstract: The mine power grid operating environment is poor. When a short circuit fault occurs in the underground power supply system, the use of complex anti-skip trip protection device will reduce the reliability of the entire power grid and increase the cost. The mine power grid needs to ensure that the current quick-break protection can act instantaneously to remove the short circuit fault, especially at the line outlet. The current mine power grid protection scheme of the anti-skip trip can not take into account the protection quick-action, power supply reliability and equipment economy. In order to solve the above problems, according to the minimum principle that short-circuit accident in the mine power grid can not skip to the ground, a setting strategy of instantaneous current quick-breaking protection for mine power grid based on the overall optimal principle is proposed. The relationship between the short-circuit current value and the location of short-circuit point and the distribution characteristics of short-circuit current at the beginning and end of the line are analyzed. The shortcomings of the traditional single-setting method are compared and studied. Three indexes are defined, which are minimum-maximum system impedance ratio, maximum system impedance and line impedance ratio, and adjacent line impedance ratio. The indexes are used to represent characteristic relational expressions of different short-circuit current distribution scenarios and conditions for each setting method to meet the requirements. The setting methods applicable to instantaneous current quick-breaking protection under different short-circuit current distribution scenarios are determined. The corresponding optimal setting strategy flow is proposed. Taking a typical mine power supply line as an example, according to the proposed setting strategy, the setting calculation of the protection switch at all levels is carried out. The results show that the setting strategy is used to set five protection switches with the risk of the skip trip in the mine power grid model. The protection range of four protection switches can be controlled within the two-level line. The times of skip trip accidents are reduced. The probability of underground short-circuit faults extending to the surface of the mine power grid is reduced.
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表 1 短路电流分布特征
Table 1. Features of short-circuit current distribution
场景 特征 关系式 1 线路首端最小两相短路电流在本线路首端和末端最大三相短路电流之间 $ 0 ＜ {Z_{{\rm{s}}.\max .{L_i}}} ＜ \dfrac{{0.866}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $或
$0 ＜ {Z_{ {\rm{s} }.\max .{L_{i + 1} } } } ＜ \dfrac{ {0.866{ {Z'} _{ {L_i} } } }}{ {1 - 0.866{Z_{ {\rm{s} }.\min .\max .i} } } }$2 线路首端最小两相短路电流在本线路末端和下级线路末端最大三相短路电流之间 $ \dfrac{{0.866}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} ＜ {Z_{{\rm{s}}.\max .{L_i}}} ＜ \dfrac{{0.866\left( {1 + 1/{{Z'} _{{L_i}}}} \right)}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $或
$ \dfrac{{0.866{{Z'}_{{L_i}}}}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $＜$ {Z_{{\rm{s}}.\max .{L_{i + 1}}}} ＜ \dfrac{{0.866\left( {1 + {{Z'} _{{L_i}}}} \right)}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $3 线路首端最小两相短路电流小于下级线路末端最大三相短路电流 $ {Z_{{\rm{s}}.\max .{L_i}}} ＞ \dfrac{{0.866\left( {1 + {{Z'} _{{L_i}}}} \right)}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $或
$ {Z_{{\rm{s}}.\max .{L_{i + 1}}}} ＞ \dfrac{{0.866\left( {1 + 1/{{Z'} _{{L_i}}}} \right)}}{{1 - 0.866{Z_{{\rm{s}}.\min .\max .i}}}} $
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表 2 线路阻抗参数
Table 2. Line impedance parameters
名称 阻抗 名称 阻抗 L1 0.0938+j0.086 8 L3′ 0.1222+j0.029 1 L2 0.3930+j0.123 6 L4 0.6531+j0.365 0 L3 0.1262+j0.030 1 L5 0.2040+j0.049 1 L2′ 0.4542+j0.142 8 L6 0.3234+j0.134 1
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表 3 短路电流有名值
Table 3. Short-circuit current nominal value
位置 短路点 短路电流有名值/kA 最大三相 最小两相 井上 B1 6.703 4.727 B2 3.920 3.019 B3 3.525 2.757 动力变一次侧 2.936 2.343 井下 B2′ 5.960 4.290 B3′ 4.646 3.500 B3′′ 4.465 3.385 1号电动机母线 4.305 3.286 3号移变一次侧 4.151 3.186
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表 4 指标值
Table 4. Index value
线路 $ {Z_{{\rm{s}}.\min .\max .i}} $ ${Z_{ {\rm{s} }.\max .L_i} }$ ${Z'_{L_i} }$ 所属场景 选择方法 $ {L_1} — {L_2} $ 0.814 7.833 0.310 2 3 $ {L_1} — {L'_2} $ 0.814 7.833 0.268 2 3 $ {L_4} — {L_5} $ 0.814 1.347 3.566 1 1 $ {L_2} — {L_3} $ 0.831 2.690 3.177 3 3 $ {L'_2} — {L'_3} $ 0.831 2.330 3.791 2 3 $ {L_5} — {L_6} $ 0.890 7.512 0.570 3 3
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表 5 保护整定结果及对比
Table 5. Protection setting results and comparison
保护开关 方法1 方法2 方法3 整定值/kA $ {\alpha _{\rm{p}}} $ 整定值/kA $ {\alpha _{\rm{p}}} $ 整定值/kA $ {\alpha _{\rm{p}}} $ 401 5.166 αp＜0 2.333 $ {\alpha _{\rm{p}}} $＞1 3.363 $ {\alpha _{\rm{p}}} $＞1 402 4.981 αp＜0 2.257 $ {\alpha _{\rm{p}}} $＞1 3.652 $ {\alpha _{\rm{p}}} $＞1 201 5.575 αp＜0 2.860 $ {\alpha _{\rm{p}}} $＞2 4.183 $ {\alpha _{\rm{p}}} $＞2 202 5.358 αp＜0 2.860 $ {\alpha _{\rm{p}}} $＞2 4.165 1＜ $ {\alpha _{\rm{p}}} $＜2 101 7.152 αp＜0 3.151 $ {\alpha _{\rm{p}}} $＞2 4.669 1＜ $ {\alpha _{\rm{p}}} $＜2 601 3.871 αp＜0 1.838 $ {\alpha _{\rm{p}}} $＞1 2.735 $ {\alpha _{\rm{p}}} $＞1 501 4.230 αp＜0 2.012 $ {\alpha _{\rm{p}}} $＞2 2.986 1＜ $ {\alpha _{\rm{p}}} $＜2 102 4.704 αp＞0.15 3.151 $ {\alpha _{\rm{p}}} $＞2 4.424 $ {\alpha _{\rm{p}}} $＜1
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