Pressure drop comparison method and DC resistance method, etc.; Second, low voltage pulse method, also known as radar method, is the input of low voltage pulse signal to the cable through the instrument at one end of the cable. When encountering a fault point where the impedance is not matched, the pulse signal It will produce reflections and return to the measuring instrument. This method has the advantages of simple operation and high test accuracy. It is mainly used to test the breakage and low resistance faults, but it cannot test high resistance faults and flashover faults; the third is the pulse voltage method, which needs to apply DC high voltage to the faulty cable. Signal; four is the pulse current method, the need to apply DC high-voltage signal to the fault cable; five is the second pulse method.
The main reasons for the failure of low voltage cables in street lamps are as follows: 1. Damage to external lights Due to the non-standard and arbitrary construction of roads and other pipelines, it is often the case that the street light cables are cut off or damaged. Moreover, most of the construction units are digging out the street light cables. , Not to inform the street lamp management department to re-bury it privately, and the resulting cable damage will cause complete damage to the cable after a period of operation.
2. Long-term over-load operation of cables Due to the lack of design, the lack of "double weight" of the cable size, unbalanced three-phase load, and arbitrarily increasing the load, the long-term overloaded operation of some cables causes the temperature of the cable to follow. Increasing, especially during hot summer days, the temperature rise of the cable often leads to weaker cables and the first breakdown at the joints. In summer, the reason for the high rate of cable failure is just this.
3, the construction quality of the cable is not good and brutal construction, illegal dragging the cable, will cause damage to the cable skin, moisture immersed in a few months or even years later, the degree of insulation has led to a complete breakdown of the damage caused by failure. In addition, cable joints are the weakest link in the cable route. During the process of making cable joints, if the joints are not tightly crimped, loosely packed, and poor heat shrinkage quality, etc., the insulation of the cable ends will be reduced, causing The fault occurred.
The common types of street lamp low-voltage cable faults can be divided into open faults with leakage to the soil and closed faults with no leakage to the soil.
2. According to the location of the fault point, it can be divided into failure of the cable body, inside the light pole, under the light pole, in the inspection well, and at the joint.
According to the nature of cable faults are divided into:
(1) Open circuit: It is caused by long-time high-current burnout or excavation due to external force. The phase line and neutral line are disconnected, and normal power transmission can sometimes be performed but some of the streetlights are off. This type of fault is the most common type of street light cable fault and is easier to solve.
(2) Short circuit: often shows a short circuit between the zero line and the phase line or between the phase line and the phase line. It is due to the instantaneous high-current sintering, which cannot be normally transmitted at this time. Short-circuit faults are better resolved if the skin is broken, and failures where the skin is not damaged are more difficult to resolve.
(3) Poor insulation: The power can be transmitted for a short time, but the current in the line is abnormal. After a period of time, the circuit breaker protection action is called “soft failureâ€. The cable is damaged or the insulation is aging. This type of fault is the difficulty of our test.
The main reasons for the failure of low voltage cables in street lamps are as follows: 1. Damage to external lights Due to the non-standard and arbitrary construction of roads and other pipelines, it is often the case that the street light cables are cut off or damaged. Moreover, most of the construction units are digging out the street light cables. , Not to inform the street lamp management department to re-bury it privately, and the resulting cable damage will cause complete damage to the cable after a period of operation.
2. Long-term over-load operation of cables Due to the lack of design, the lack of "double weight" of the cable size, unbalanced three-phase load, and arbitrarily increasing the load, the long-term overloaded operation of some cables causes the temperature of the cable to follow. Increasing, especially during hot summer days, the temperature rise of the cable often leads to weaker cables and the first breakdown at the joints. In summer, the reason for the high rate of cable failure is just this.
3, the construction quality of the cable is not good and brutal construction, illegal dragging the cable, will cause damage to the cable skin, moisture immersed in a few months or even years later, the degree of insulation has led to a complete breakdown of the damage caused by failure. In addition, cable joints are the weakest link in the cable route. During the process of making cable joints, if the joints are not tightly crimped, loosely packed, and poor heat shrinkage quality, etc., the insulation of the cable ends will be reduced, causing The fault occurred.
The common types of street lamp low-voltage cable faults can be divided into open faults with leakage to the soil and closed faults with no leakage to the soil.
2. According to the location of the fault point, it can be divided into failure of the cable body, inside the light pole, under the light pole, in the inspection well, and at the joint.
According to the nature of cable faults are divided into:
(1) Open circuit: It is caused by long-time high-current burnout or excavation due to external force. The phase line and neutral line are disconnected, and normal power transmission can sometimes be performed but some of the streetlights are off. This type of fault is the most common type of street light cable fault and is easier to solve.
(2) Short circuit: often shows a short circuit between the zero line and the phase line or between the phase line and the phase line. It is due to the instantaneous high-current sintering, which cannot be normally transmitted at this time. Short-circuit faults are better resolved if the skin is broken, and failures where the skin is not damaged are more difficult to resolve.
(3) Poor insulation: The power can be transmitted for a short time, but the current in the line is abnormal. After a period of time, the circuit breaker protection action is called “soft failureâ€. The cable is damaged or the insulation is aging. This type of fault is the difficulty of our test.
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