There are many factors influencing the price of box substation in 2019. For example, the material of box substation is steel, wood and ceramic tile. The price of transformers (mainly copper) in box-type substations fluctuates with the market; Cabinet power station inside control components, the price of various brands are different; Transportation costs are high because of its bulk and weight. Therefore, the box substation mainly depends on the model and size configuration to determine its price. Below we will understand the box substation low-voltage main distribution cabinet configuration.
The low-voltage general distribution cabinet of box transformer needs to be equipped with low-voltage disconnecting switch of incoming line, low-voltage general circuit breaker and low-voltage general metering device. The low-voltage disconnecting switch must be installed in order to meet the needs of daily maintenance. The main low-voltage circuit breaker is selected according to the transformer capacity and the short-circuit current at the installation of the circuit breaker.
(1) rated current of circuit breaker. Generally choose the transformer capacity value of 2.0 ~ 2.5 times. The corresponding rated breaking current is larger than the short-circuit current value of the low-voltage side of the transformer, which rarely needs to be verified.
(2) long delay time (i.e. inverse time limit, overload) overcurrent trip setting current Lset, which should meet the requirements of In≤Iset1≤Iz. Where, In is the rated current of low-voltage side of transformer, and Iz is the load capacity of low-voltage bus. In order to make full use of the transformer capacity without affecting its service life, Iset1 should be equal to or close to In.
(3) short delay (i.e., fixed time limit and over current) over current and tripper setting current Iset2, which shall meet the requirements of 1.2Ifj≤Iset2≤Id/1.3. Where, Ifj is the peak current of transformer short-term load, and Id is the single-phase grounding fault current of transformer. This requirement is easy to meet for transformers connected by D and yn11, but not easy to meet for transformers connected by Y and yn0, which is the reason why D and yn11 transformers are often used in boxes.
The setting time of the short-delay over-current trip tripper of the transformer low-voltage main circuit breaker is generally 0.6s, which can ensure that the time difference with the next level circuit breaker is not less than 0.2s.
(4) instantaneous overcurrent trip setting current Iset3. Due to the short delay overcurrent protection, in order to ensure better selectivity, the value of Iset3 can be set larger. Generally, the value of Iset1 is 12 to 15 times.
Because the transformer low-voltage main circuit breaker and the circuit breaker of each outgoing line are installed in the low-voltage distribution panel which is only a few meters apart, according to the operation experience, the probability of short-circuit and grounding fault in this range is very small, so the instantaneous over-current protection can not be set to avoid the non-selective action caused by outgoing fault.
The metering devices in the low-voltage main distribution cabinet include 0.2s class low-voltage current transformer, active power meter, reactive power meter, etc.
At present, power supply enterprises around the measurement device requirements are becoming more and more strict, the parts of the local power supply enterprises must pass the relevant departments of verification before installation. In order to reduce the workload of meter reading, remote reading concentrator can be installed. To facilitate the monitoring and adjustment of three-phase load balance, the active energy meter is changed from one three-phase four-wire energy meter to three single-phase energy meters. Or install a multi-functional electronic watt-hour meter, can monitor three-phase electricity, and can realize reactive energy query.
Based on the above situation, box transformer manufacturers generally reserve only the corresponding installation location according to the metering configuration requirements proposed by power supply enterprises. After the box is put into place, the power supply enterprises install metering devices.
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