HIGH VOLTAGE SPARK TESTER
These are designed for checking the quality of PVC or rubber or XLPE or teflon coated wires during manufacturing at shop floor. The coated wire is passed through brass ball chains which carry high voltage.
If any pin hole comes in coating, a spark develops and electro magnetic counter counts the fault. The spark tester is necessary for every cable manufacturing unit. The High Voltage Test Equipment uses a high frequency oscillator circuit for rising frequency to search the fault at low leakage current and signifies that as a fault, the fault is displayed to the operator by means of a visual indicator and audible.
The High Frequency Spark Tester Set can test a variety of cable at various voltages for which KV setting & sensitivity setting is provided. They have High Speed operation upto (1000 m/min). Are Much smaller unit. Have Computer Interface facility available. Efficiency of operation up to 95%. Suitable for extruder and recoiling Short Circuit Protected.
AC HV spark tester
Costly raw material, more demanding end users faster production speeds are forcing Wire & Cable manufacturers to pay more attention to insulation of cable. Emphasis on quality control in wire industry has definitely increased in recent years. One of the latest techniques of Spark Testing is “AC HV Spark Testing". The method surrounds the insulated wire with a concentrated corona discharge which can pick up not only faults in the insulation such as pin holes but also marginal tears. The feature of an instrument, a electromechanical counter, keeps track of the "Number of faults" per cable & helps with quality control statistical studies.
More & more people are going for the AC spark testing because of it's equivalence to water immersion test. "Tank test" has been considered the ultimate wire insulation tool for years. Unfortunately it leaves much to be desired & is not quite as positive as it may appear. Often water does not completely penetrate the layers of the spool, or the copper resistance & wire capacitance reduce the voltage applied to a long length or failure in the tank test damages to the product make the water tank test costly. Studies have shown that the AC spark testing give results equivalent to those of water tank test-tube looking at more feasible proposition.
1.2 General Doubt’s About AC HV spark tester
Q.1 How much should be the test voltage for AC HV spark tester?
Ans. The test voltage for the cable should be decided at site & it cannot tabulate as a standard.
Q.2. How do I trip my machine in case of fault?
Ans. Isolated relay contacts are provided for tripping in case of fault.
Q.3. Can I pass wet wire (with water) through the electrode?
Ans. No. Wet wire should not be passed through the electrode as it is increases the load on H.V. Transformer unnecessarily. Also the moisture on the cable spoils the bead chains of the electrode. Hence the use of pneumatic wiper before Spark Tester is recommended.
Q.4. Can I use this unit as a 'Break down Voltage Tester'?
Ans. No. This unit cannot be used as a 'Break down Voltage Tester' because the voltage, applied to the cable, increases the load on spark tester. Basically, the unit is meant for finding out pinholes & faults in the cable & not to find out the Max.voltage that the cable can with stand.
Q.5. What will happen if we do not move the cable & apply H.V. at one place?
Ans. If the cable is stationary & H.V. is applied, due to continuous application of high voltage, losses in the cable increases & insulating material gets heated up. As a result, the voltage level that the cable can withstand lowers down & the cable insulation may get punctured finally.
Q.6. What happens if a very poor or high quality insulated cable is passed through spark tester?
Ans. For a very poor insulated cable, the cable insulation will break down at a low level of test voltage. For very high quality insulated cable; test voltage with standing capacity is much greater. Hence the cable insulation will not break down even upto high test voltages. For the same voltage level applied, the quality of cable affects load on the H.V.Transformer. Better the insulation quality lesser will be the % load.
Q.7. Is there any effect of physical vibration of wire? How to avoid
Ans . Wire vibration can occur due the wire tension, running speed, wire gauge etc. The moving & vibrating wire causes the beads to loose speed, wire gauge etc. The moving & vibrating wire causes the beads to loose contact with the surface of the insulated wire creating a random & sometimes unnoticeable condition that causes partial or total extinction of the ionization in the immediate area of lost contact. This becomes very noticeable when the test voltages are low. The results of these phenomena cannot be compensated for, by ckt.design, & the only way to eliminate this condition is to damp the vibration of the wire mechanically, by methods like using rollers before & after H.V.unit.
Q.8. Is it necessary to earth the conductor? How to do it?
Ans. Yes, If the conductor is not earthed, then two capacitance's in series come into picture as follows-
1. Electrode to conductor Capacitance.
2. Conductor to earth capacitance.
These two capacitance form a voltage divider & hence full value of high voltage is not applied across the Insulation of the cable. If the conductor is not earthed & incidentally the operator touches the bare wire, he may get a shock. Hence the conductor must be earthed. Normally, on extrusion lines, the input to the extruder is a bare wire, which is wound on a metal bobbin or drum. This drum kept on a metallic. Unwired /let off. The let off stand should be connected to earth in the same manner as that of earthling procedure for electrical appliances. In case of rewinding lines, the start of the cable or let off should be connected to earth.
• Online Extrusion Insulation Testing.
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• For Power Cable , Control Cable , Telephone Cable, LAN Cable,
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